AN ABSTRACT OF THE THESIS OF
Robert K. Thornton for the degree of Doctor of Philosophy in Crop Science presented on
October 17, 1997. Title: Russet Burbank Response to Nitrogen Fertilization and Planting
Date
Redacted for privacy
Abstract approve d
Alvin R. Mosley
Redacted for privacy
Timot1iy L. Righetti
f
Studies addressed impacts of planting dates and variable N applications on numbers
and size of Russet Burbank stems and stolon nodal position in relation to tuber growth and
levels of hollow heart (HH) and brown center (BC).
Low preplant N regimes produced larger tubers and final yields, and less HH and
BC than the high N regime. Reduced preplant N regimes also lowered tuber grade and
specific gravity. Negative effects of the low preplant N regime were offset by delaying
planting or beginning application of post-BC initiation N earlier.
Stem size influenced plants season-long and affected tuber size and yield, early- and
late-season HHBC development, and HHBC dissipation and severity. These responses
were related more to stem and tuber growth than to weather.
Levels of HHBC increased as similar-sized tubers grew. Tubers expressed less
HHBC, regardless of size or stolon nodal position, when growing at different rates or
times than most other tubers. HHBC development began, declined, and increased at
different times during the season.
Tuber susceptibility to HHIBC increased throughout the season in association with
increased stem size and/or reduced stems per plant. Plants with 3 or more stems produced
higher tuber yields but less HHBC than plants with fewer than 3 stems. Large-stem tubers
from I- and 2-stem plants grew faster and were more susceptible to HHBC than large-stem
tubers on plants with 3 or more stems.
Delayed plantings reduced HHBC and increased stem numbers per plant, thereby
reducing the proportion of high yielding, HHBC susceptible stem-types. Delayed
plantings did not affect the growth stage(s) during which tubers became susceptible.
Preplant N regime did not affect stem numbers per plant, but HHBC was reduced
by low regimes. Low preplant N plants exhibited equal or increased tuber growth rates,
but reduced vine biomass compared to high preplant N plants; consequently, large stems,
especially from single- and double-stem plants, showed more BC dissipation, resulting in
less early-season HHBC compared to high preplant N plants. Late-season HFIBC was less
affected by N treatment.
Russet Burbank Response to
Nitrogen Fertilization and Planting Date
by
Robert K. Thornton
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
Completed October 17, 1997
Commencement June 1998
Doctor of Philosophy thesis of Robert K. Thornton presented on October 17. 1997
r uyj,j
Redacted for privacy
Co-Maj or Professor, 'tepresenting CropSEiiice
Redacted for privacy
Co-Major Prof#or, rpresenting Cio Science
Redacted for privacy
Head of Department of Crop and Soil Science
Redacted for privacy
Dean of Graduate
I understand that my thesis will be part of the permanent collection of Oregon State
University libraries. My signature below authorizes release of my thesis to any reader
upon request.
Redacted for privacy
'kobert K. Thonton, Author
ACKNOWLEDGMENTS
The most important thing I have learned from doing the research and preparing this
thesis is that, like life in general, nothing of any value is accomplished without lots of help.
I had, and needed, lots of help.
I would like to thank Agrinorthwest and president Martin Wistisen for allowing me
the time and freedom to pursue this dream. Co-workers Dave Adolf and especially Martin
Moore deserve my gratitude for all the time and effort they put into helping me.
Drs. Righetti, Mosley, and Powelson have done more than could be expected as
editors. Each one in their own way has contributed greatly to this final version. Tim has
proven to be a very special person. He pushed me when I needed it and had the sense to
tell me when we needed help. Any one else would have given up on this long distance
relationship long ago.
My family has always been there for me, and the encouragement they gave me all
these years has been no exception. Along this journey I met, fell in love, and married my
friend and wife, Alix. She taught me that there is more to life than work or this thesis and
helped me remember that life is a journey that you might as well enjoy.
TABLE OF CONTENTS
Page
CHAPTER 1
IN]RCUJCIION .........................................................
1
HAPTER2
UTERATUREREVIEW ...................................................
6
CropGrowth ......................................................
6
Plant Growth ......................................................
9
Soil and Petiole Nutrient Levels .................................
12
Hollow Heart-Brown Center ....................................
14
CHAPTER3
GROW[H PATIERNS C
RUSSE1' BURBANK TUBERS FR(
SINGLE-, IXJBLE-, TRIPLE-, ANDMULTIPLE.-STEMPLANTS
CHAPTER4
19
Abstract .............................................................
19
Introduction ........................................................
19
Materials and Methods ............................................
21
Results ..............................................................
23
Discussion .........................................................
29
Literature Cited ....................................................
31
IHE DISTRII3UTION OF TUBER NUMBER, YJELD AND HCELOW
HEART-BROWN CENTER ON STEMS CF RUSSET BURBANK
POTATOES ................................................................
34
Abstract .............................................................
34
TABLE OF CONTENTS (Continued)
Page
CHAP1FR5
CHAPTER 6
Introduction ........................................................
35
Materials and Methods ............................................
36
Results ..............................................................
38
Discussion .........................................................
45
Literature Cited ....................................................
48
EFFECTS (1 RUSSET BURBANK STEM SIZE AND STOLON N(I
POSifiON ON ThBER GROWTH AND H(LLOW HEART-BROWN
CENTER .................................................................
51
Abstract .............................................................
51
Introduction ........................................................
51
Materials and Methods ............................................
52
Results ..............................................................
54
Discussion .........................................................
54
Literature Cited ....................................................
60
INFLUENCES (F NiTROGEN FERTILIZATION AND PLANTING
DATh ON RUSSET BURBANK TUBER YIELD AND C!JALITV .......
63
Abstract .............................................................
63
Introduction ........................................................
64
TABLE OF CONTENTS (Continued)
Page
CHAPTER 7
CHAPTER 8
Materials and Methods ............................................
65
Results ..............................................................
69
Discussion .........................................................
78
Literature Cited ....................................................
80
GROWITT PAT1ERN RESPONSES OF RUSSET BURBANK T)
VARTABLE NiTROGEN RATES AND PLANTING DATE ...............
85
Abstract .............................................................
85
Introduction ........................................................
86
Materials and Methods ............................................
87
Results ..............................................................
89
Discussion .........................................................
97
Literature Cited ....................................................
100
INFLUENCES CF NiTROGEN FERTILiZATION AND PLANTING
DATE ON RUSSET BURBANK STEM HIERARCHY TUBER
GROWII1 ANDHLLOWHEART-BROWNCENTER ................
104
Abstract .............................................................
104
Introduction ........................................................
105
Materials and Methods ............................................
106
TABLE OF CONTENTS (Continued)
Page
Results ..............................................................
108
Discussion .........................................................
115
Literature Cited ....................................................
120
SUMMARYAND CONCLUSIONS ......................................
125
BIBLIOGRAPHY ..............................................................................
129
APPENDIX.....................................................................................
148
HAPThR9
LIST OF FIGURES
Page
Figure
3.1.
Tuber data from main-stems of single-, double-, triple-, and
multiple-stem Russet Burbank plants over time: a) tuber number,
b) tuber yield, c) average tuber size, d) tubers with hollow heartbrown center (HHBC), and e) % tubers with HHBC ................
3.2.
25
Tuber data from main-stems of single-, double-, triple-, and
multiple-stem Russet Burbank plants over time: a) % tubers, b) %
tuber yield, c) % hollow heart-brown center (HHBC), and d) %
HHBC severity on main stems ..........................................
3.3.
Tuber data from main-, secondary-, or tertiary-stems of single-,
double-, triple-, and multiple-stem Russet Burbank plants at midseason: a) % tuber number, b) % tuber yield, c) % hollow heartbrown center (HI{BC), and d) HHBC severity value (% HHBC
severity within a plant-type) ..............................................
4.1.
26
28
Effect of stem-type on Russet Burbank tuber number by tuber
weight range in a) Early June, b) Late June, c) Early July, d) Late
July, and e) August .......................................................
4.2.
Effect of stem-type on Russet Burbank tuber yield by tuber weight
range in a) Early June, b) Late June, c) Early July, d) Late July,
ande) August ..............................................................
4.3.
39
42
Effect of stem-type on percent of Russet Burbank tubers with
hollow heart-brown center (HHIBC) in tuber weight ranges in a)
Early June, b) Late June, c) Early July, d) Late July, and e)
August ......................................................................
5.1.
5.2.
5.3.
5.4.
6.1.
6.2.
44
Influence of stem-type and stolon node position on the number of
Russet Burbank tubers over time ........................................
55
Influence of stem-type and stolon node position on Russet
Burbank average tuber yield over time ..................................
56
Influence of stem-type and stolon node position on the incidence
of hollow heart-brown center (HHBC)-affected Russet Burbank
tubers over time ............................................................
57
Influence of stem-type and stolon node position on severity of
hollow heart-brown center (HHBC)-affected Russet Burbank
tubers over time ............................................................
58
Total seasonal nitrogen (N) applications ................................
66
Effects of preplant nitrogen (N) regime [56 (Low) or 224 (High)
kg ha-'] and planting date (Early, Mid, and Late) on a) seasonal
soil N and, b) stem nitrate-N level ......................................
70
LIST OF FIGURES (Continued)
Figure
6.3
Page
Effects of preplant nitrogen (N) regime
[56
(Low) or 224 (High)
kg ha-i] and planting date (Early, Mid, and Late) on Russet
6.4.
6.5.
6.6.
Burbank tuber yield.......................................................
71
Effects of preplant nitrogen (N) regime on yields of Russet
Burbank U.S. No. 1 and No. 2 tubers ................................
72
Interaction effects of preplant nitrogen (N) regime [56 (Low) or
224 (High) kg ha1] and planting date (Early, Mid, and Late) on
specific gravity of Russet Burbank tubers ..............................
73
Effects of preplant nitrogen (N) regime [56 (Low) or 224 (High)
kg ha-i] on the distribution of Russet Burbank tuber grade and
size ..........................................................................
6.7.
75
Effects of nitrogen (N) regime on a) % hollow heart (HH), and b)
% brown center (BC) in U.S. No. 1 Russet Burbank tubers in
various tuber weight ranges ..............................................
6.8.
7.1.
7.2.
7.3.
7.4.
7.5.
Effects of nitrogen (N) regime on a) % hollow heart (HH), and b)
% brown center (BC) of U.S. No. 2 Russet Burbank tubers in
various tuber weight ranges ..............................................
77
Distribution of total Russet Burbank: a) tuber number, b) tuber
yield, and c) hollow heart-brown center (HHBC) over time
90
Effects of Russet Burbank tuber size and sampling date on the
incidence of hollow heart-brown center over time .....................
91
Effects of a) growing seasons (1986 and 1987), and b) planting
dates (Early and Late) on the incidence of hollow heart-brown
center in Russet Burbank potatoes ......................................
93
Effects of planting (Early and Late) and sampling dates (Late July
and August) on Russet Burbank: a) vine biomass, b) tuber yield,
and c) weighted incidence of hollow heart-brown center.............
94
Effects of preplant nitrogen regime [56 (Low) or 224 (High) kg
ha-I] and planting date (Early and Late) on the number of Russet
Burbank stems per plant ..................................................
7.6.
95
Seasonal effects (E early; L = late) of preplant nitrogen (N)
regime [56 (Low) or 224 (High) kg ha-I] on Russet Burbank: a)
vine biomass, b) tuber yield, and c) % hollow heart-brown center
(HHBC) ....................................................................
8.1.
76
96
Effects of planting date (Early and Late) and preplant nitrogen (N)
regime [56 (Low) or 224 (High) kg ha1] on Russet Burbank
single-double and triple-multiple plant-types ...........................
109
LIST OF FIGURES (Continued)
Figure
8.2.
8.3.
8.4.
Page
Effects of a) preplant nitrogen regime [56 (Low) or 224 (High) kg
ha4], b) planting date: Early and Late, or c) weeks after planting,
and stem-hierarchy on the number of Russet Burbank tubers over
time ..........................................................................
111
Effects of a) preplant nitrogen regime [56 (Low) or 224 (High) kg
ha1], b) planting date: Early and Late, or c) weeks after planting,
and stem-hierarchy on Russet Burbank tuber yield over time
112
Effects of a) preplant nitrogen regime [56 (Low) or 224 (High) kg
ha1], b) planting date: Early and Late, or c) weeks after planting,
and stem-hierarchy on hollow heart-brown center (HHBC) in
Russet Burbank tubers (except O-13g tubers) over time..............
114
LIST OF APPENDIX FIGURES
Page
Figure
A. 1.
A.2.
A.3.
A.4.
The a) % of tubers, b) % of tuber yield, c) % of hollow heartbrown center (HHBC) distribution and d) cumulative HHBC
severity value on Russet Burbank stems 4, 5, and 6 ..................
149
Effect of stem-type on the total % of Russet Burbank tubers with
hollow heart-brown center (IIHIBC) for all tuber weight ranges,
except O-13g tubers, in August .........................................
150
Influence of stem-type and stolon node position on the number of
Russet Burbank tubers from three fields over time ....................
151
Influence of stem-type and stolon node position on Russet
Burbank average tuber yield from three fields over time .............
A.5.
A.6.
A.7.
152
Influence of stem-type and stolon node position on the incidence
of hollow heart-brown center (HHIBC)-affected Russet Burbank
tubers from three fields over time .......................................
153
Influence of stem-type and stolon node position on severity of
hollow heart-brown center (HHBC)-affected Russet Burbank
tubers from three fields over time .......................................
154
Effects of stem-hierarchy on the a) number, b) yield, and c) level
of hollow heart-brown center (HHBC) in Russet Burbank tubers
over time for three years ..................................................
155
LIST OF APPENDIX TABLES
Page
Table
A. 1.
A.2.
A.3.
Pre-application average soil readings and preplant fertilizer
nutrient applications (less preplant nitrogen) ........................
156
Nitrogen regime and planting date treatments ........................
156
Statistical analyses (mean square and
% of mean square) for
Chapter 3: a) across years, b) 1985, c) 1986, and d) 1987
157
A.4.
Stem- and plant-type designations ....................................
158
A.5.
Statistical analyses (mean square and % of mean square) for
Chapter 4: a) across years, b) 1985, c) 1986, and d) 1987
159
A. 6.
A.7.
A. 8.
Complete statistical comparision for effects of stem dominance,
tuber weight range and sampling date on a) tuber number, b)
tuber yield, and c) % hollow heart-brown center (HHBC)
160
% of mean square) for
Chapter5 .................................................................
161
Statistical analysis (mean square and
Complete statistical comparision for effects of stem, stolon nodal
position and sampling date on a) tuber number, b) average tuber
yield, c) % hollow heart-brown center (HHBC), and d) severity
ofHHBC .................................................................
A.9.
A. 10.
A. 11.
A.12.
162
Statistical analysis (mean square and % of mean square) for
Chapter6 .................................................................
164
Statistical analyses (mean square and % of mean square) for
Chapter 7: a) for figures 7.1 and 7.2, and b) for figures 7.3 7.6 ........................................................................
165
Complete statistical comparision for effects of tuber weight range
and sampling date on a) % tuber number, b) % tuber yield, c) %
total hollow heart-brown center (HHBC), and d) % HHIBC
166
Statistical analyses (mean square and % of mean square) for
Chapter 8 with planting date expressed on a) calandar date basis,
A. 13 a.
A. 13 b.
A. 13 c.
and b) weeks after planting basis ......................................
167
Complete statistical comparision of a) preplant nitrogen regime
and b) planting date effects on tuber numbers per stem ............
168
Complete statistical comparision of a) preplant nitrogen regime
and b) planting date effects on tuber yield per stem .................
168
Complete statistical comparision of a) preplant nitrogen regime
and b) planting date effects on hollow heart-brown center
distribution by stem .....................................................
169
DEDICATION
This thesis is dedicated to the memory of my grandfather, Sam Thornton, who's memory
lives on in my heart, and to the Lord for giving me the strength and will to persevere these
last 13 years.
ii:
RUSSET BURBANK RESPONSE TO NiTROGEN
FERTILIZATION AND PLANTING DATE
Inlmducfion
Potatoes are grown in more countries than any other crop except maize and rank
fourth in total food production. A significant portion of the world's potatoes are grown in
North America (5). North American production is dominated by the U.S. Pacific
Northwest (5). The Russet Burbank cultivar, a russet-skinned mutant of Burbank
introduced by Luther Burbank in 1872, has been extensively grown in the United States
since it's introduction in the early 1900's (5). This cultivar accounts for over 60% of all
potatoes produced in the Pacific Northwest (5) and 35% of the U.S. crop.
Reasons for Russet Burbank's dominance include high yield potential; suitability
for frozen french fry processing and multiple fresh uses; acceptable tuber dry matter; and
long term storability. Tuber quality is excellent but is easily reduced by stresses related to
soil, climate, and cultural management. These stresses can reduce tuber processing
potential because of small size, low specific gravity, internal defects such as internal brown
spot, heat necrosis, sugar-ends, and hollow heart-brown center, and external defects
including knobs, malformations and growth cracks.
Russet Burbank yields in Washington are the highest in the world (5). High yields
and quality are vital to growers since revenue is based on these two parameters.
Processors will pay more for large, smooth tubers because they favor increased frozen
product recovery (88).
Growth patterns of Russet Burbank vines and tubers are profoundly affected by
planting date and nitrogen fertilization regime because of this cultivar's indeterminate
growth habit (203). Therefore, planting date and nitrogen fertilizer scheduling are valuable
tools for influencing yield and quality.
There is a delicate balance between tuber yield and quality. Cultural practices which
favor increased yields in Russet Burbank are often associated with reduced external and
internal tuber quality (16, 160). Loss of tuber quality is especially evident when rapidly
growing tubers are subjected to environmental stresses. Acceptable tuber size and shape
are critical for both fresh market and processing uses. Tubers with few external defects
may be used by either segment of the industry. Regardless of the intended use, however,
external tuber defects increase waste.
2
Tubers with external defects tend to have more internal disorders
specific gravity
(224).
external disorders
(218),
and lower
Not all tubers with low specific gravity, however, show internal or
(98).
The relationship between tuber yield, size, and specific gravity varies. Meredith
(132) found that specific gravity of tubers is not a function of either the number of tubers
per plant or tuber size. Others (148, 169, 224), however, have reported that large tuber
size favors higher specific gravity and that the variation in specific gravity among tubers
from the same plant may be greater than among tubers from different plants (98).
Several internal tuber disorders are commonly found in Russet Burbank. Russet
Burbank is particularly prone to hollow heart-brown center (HHBC). This disorder can
greatly reduce financial returns (162) because: 1) affected tubers have very low consumer
appeal and; 2) fresh pack and processing tuber grade tolerances allow a very low incidence
of the disorder. The discoloration and internal cavity associated with this disorder also
result in more processing trim loss and shorter french fries.
Hollow heart-brown center is associated with large tubers and high tuber yields
(50, 164). Many researchers (144, 156) believe this association exists because rapidly
growing, high yielding plants are unable to provide an adequate and uniform supply of
nutrients and carbohydrates to the vine and tubers concurrently. Harvest data show an
inverse relationship between numbers of stems per plant and the incidence of HIHIBC (86).
Reasons for this relationship are not known. Increased tuber size associated with low stem
numbers is thought to be the major influence, however, not all large tubers develop the
disorder (154, 155, 159). Tuber growth rate and final tuber size may be similar among
cultivars with different HEIBC expression (30). Hollow heart-brown center may also be
associated with tuber shape since malformed tubers tend to have a higher incidence (218).
Attempts to reduce the initiation and/or expression of HHBC have included closer
within- and between-row plant spacing, delaying planting to avoid cooler soil temperatures,
and using nitrogen fertilizer regimes designed to prevent excessive vine growth (203).
These practices have met with some success, however, little is known about why or how
changes in growth and development of plants and tubers of Russet Burbank affect the
HHBC disorder.
Altering vine and/or tuber growth patterns by cultural management profoundly
affect the final yield and quality of tubers. It is essential that observations on growth
patterns during the season be related to tuber yield and quality at harvest. Without these
seasonal observations, explaining how cultural practices affect yield and quality is difficult
(203).
Growth patterns of a potato crop can be separated into vine and tuber components,
3
and the partitioning of photosynthate and nutrients between them (81). Ivins (81) stated
that, "Dry matter distribution within the potato plant, particularly early in it's life, exercises
the dominant role in determining both total dry matter production and yield. The key to
growth and development in the potato crop and to their relationship with yield, lies in the
balance struck between the conflicting demands of foliage and tuber growth; the key to
successful agronomic management of the crop lies in manipulating this balance to best
advantage."
Data relating the number of stems to the tuber yield and quality often conflict (55,
58, 198). Individual plants produce from one to several stems and large (dominant) stems
may behave differently on single-, double-, triple-, and multiple-stem plants (203).
Therefore, each stem must be evaluated both as an individual unit and as part of the whole
plant. Each stem of a multi-stem plant functions as an individual unit, unless the stems
branch above ground, in which case each branch is subordinated to the whole (4, 137).
The rate of individual stem growth is inversely related to the number of stems per plant and
implies competition between/among stems (145). This inter-stem competition is expressed
in many cultivars including Russet Burbank (65). Tubers on different plant-types (single-,
double-, triple-, or more-stems) or on different stems (dominant, secondary, or tertiary)
may therefore be physiologically different.
A hierarchy, or dominance pattern, among tubers on the same stem may affect the
allocation of plant resources (122). This hierarchy is often associated with stolon nodal
position (165). Controversy surrounds the time course of competition among tubers.
Some reports suggest that one tuber on a stem is always the largest at any given time (57,
105) while others disagree (2, 135, 137). Tubers originating from different below ground
stem nodal positions could have different sink strengths and/or a plant's sink strength may
change with the development of the plant. It is agreed, however, that the largest tubers on
a plant are not all from the same stem (105). Regardless of the cultivar, number of stems
per plant, or tuber position on the stem, there is little doubt that the potato plant influences
tuber development (65).
Potato plants may be source-limited; i.e., either the potato vines or roots limit the
productivity of tubers (46, 139). Because vascular continuity exists between tubers and
leaves (57, 188), changes in the rate of tuber growth may enhance translocation of nutrients
and thus hasten plant maturity (81, 82). The rate of tuber bulking can, however, stimulate
photosynthetic rates suggesting that tubers have some control over the vines and/or roots
(39).
Although the study of HHBC is not new, literature relating the growth of plants and
tubers to the development of HHBC is minimal. Information on effects of cultural
rdj
management on the number of stems, hierarchy of tubers, tuber growth rate, and incidence
of HHJ3C in a variety of single- and multi-stem plant-types is not available, Researchers
have typically evaluated tubers for HHBC at the end of the season, determined the final
tuber yield or the yield of the largest tubers, evaluated treatment effects, and drawn
conclusions. The bulking of tubers before evaluation precludes collection of data to
analyze differences among tubers from an array of plant-types (single- vs. multi-stem),
stem-types (large or small), or below ground stolon nodal position. The development of
HHBC is a very dynamic and complex phenomenon; therefore, this type of tuber data
collection is needed. Initiation of HHBC in tubers may be followed by development, or
dissipation (recovery) of the disorder in an extremely complex and variable plant system
(203).
Seasonal variation makes the study of incidence and severity of HHBC difficult.
Differences in the incidence of HHBC may be more evident among years than among
treatments in a given year. It is not known whether these differences result from changes
in the level of HHBC initiation among tubers or from changes in development or
dissipation stages of the disorder. Lower temperatures during tuber initiation are known to
increase the initiation of HHBC (207, 208, 209). Differences in recovery from HFIBC
after initiation have not been evaluated.
In summary, previous investigations of HHBC have focused on factors that
influence either final tuber yields, or growth and development of tubers. Little information
relating seasonal growth of tubers to the development of HHBC is available.
Obtaining statistical significance in studies addressing HHBC is difficult due to the
sporadic nature of HETEC occurrences. This difficulty is especially evident when factors
related to plant-type (single- vs. multiple-stems), stem dominance, below ground stolon
nodal position on the stem, and weight range distribution of tubers are evaluated
throughout the growth cycle (203). The number of stems, below ground stolon nodes,
total tubers, and tubers within a weight range is small for any one plant; therefore, studies
reported here involved sampling thousands of plants and tens of thousands of tubers over
several years. More than 700,000 tubers were evaluated from potatoes grown in these
Columbia Basin trials.
The objectives of this research were to:
1) Quantify the relationship between the incidence of HHBC and final tuber yield
and tuber growth patterns in the Russet Burbank cultivar.
Quantify effects of nitrogen fertilizer management and planting date on tuber
growth, yield, quality, and HHI3C.
2)
3) Determine the relative contribution of single- and multiple-stem plants to growth
of tubers and the incidence and development of HHBC.
4) Determine effects of below ground stolon nodal position on tuber growth rate,
final size, and the incidence of HHBC.
[p :
IPI
to i
k'4 I 3
Cmp Gmwth
It is important to consider growth and longevity of the canopy and
these parameters as they relate to tuber size and quality and final yield. Bremner and
Radley (15), and Bremner and Taha (14) reported a positive linear relationship between
tuber yields and canopy longevity. Gunasena and Harris (59, 60, 61) supported this
concept. Size of the canopy also influences total tuber yield (4, 81, 82, 91, 92, 155, 157),
although canopy size required for maximum tuber yields may vary. Ivins and Bremner
(82) suggested that maximum yields depended more on the maintenance of a certain rate of
leaf production than on the maintenance of a particular leaf area. They concluded that high
tuber yields require superoptimal growth of the canopy to ensure that the period of tuber
bulking is prolonged. Harper (63), however, reported lower tuber yields associated with a
superoptimal canopy. He explained that the production of excess foliage shades the lower
leaves and that these leaves cannot produce sufficient carbohydrate to meet their own
respiratory requirements. More recently, Allen (4) concluded that tuber yield of potatoes
was independent of light interception, implying that size of the canopy has no influence on
tuber yields. Khurana and McLaren (91), however, reported a positive linear relationship
between yield of tubers and light interception up to full development of the canopy.
Although development of the canopy must be important to growth and yield of
tubers, removal of as much as two-thirds of the canopy early in the growing season had
little effect on the rate of tuber growth (76) and yield (29, 47).
Duration of the canopy is influenced by the rate of tuber bulking and the amount of
leaf growth preceding tuber initiation (82). Dyson and Watson (41) concluded that a high
rate of tuber bulking could cause translocation of nutrients from the vines to tubers,
hastening foliar senescence and causing early vine death. The root system of a potato plant
can decline more rapidly than leaves late in the season (115). This rapid decline of roots
could contribute to the early senescence and vine death reported by Dyson and Watson
(41).
The number of stems per plant also influence canopy size. Plants with fewer stems
have less foliage. This may be related to the earlier initiation of tubers observed on singlestem plants (46). Ivins (82) stated that early initiation of tubers can decrease longevity
and/or size of the canopy.
7
Many researchers have shown that the number of stems per plant is positively
related to tuber yield (26, 58, 103, 114, 181) and specific gravity (78). Iritani and others
(79, 80), however, found a negative correlation between the number of stems and tuber
yield in the Russet Burbank cultivar.
Nitrogen fertility strongly influences canopy size and longevity. Two of the more
important responses of plants to nitrogen nutrition are increased canopy size (4, 14, 15, 97,
162, 215), which can lead to a superoptimal canopy (4, 64) and extended canopy longevity
(59, 61, 120, 224). Several authors (41, 64, 77) point out that although high rates of
nitrogen initially favor increased survival of leaves, the rate of foliar senescence, once
started, is more rapid. Nitrogen-prolonged canopy density at the end of the season, if it
occurs, would do so despite an increase in the rate of leaf senescence. This agrees with the
suggestion of Ivins and Bremner (82) that maintenance of canopy density at the end of the
growing season is favored by earlier attainment of high levels of canopy development.
Research on tuber growth by many authors has produced conflicting conclusions.
In an attempt to explain these results, Struik (198) recently summarized the current
understanding of tuber growth and development. He also attempted to separate growth of
the tuber into those characteristics attributable to development at the crop level discussed
here, and at the individual plant level as discussed in a later section.
Struik (198) concluded from Krijth&s work (105) that the largest tuber at any given
time is also the largest tuber at later stages of growth. Citing supporting work by
Mackerron et. al. (122), he concluded that the largest tuber at a given time also has the
highest rate of growth, thereby causing the tuber size differential to increase proportionally
with the increase in average tuber size. Struik (198) further stated that there is a continuous
and gradual shift of tubers from one size range to the next larger size range and that the
potential of tubers for enlargement depends on the total number of tubers on the plant.
Nitrogen fertility, in addition to influencing growth and development of the canopy,
has been shown to affect tuber growth, yield, and quality. High nitrogen nutrition has
been reported to delay tuber initiation (38, 104, 187, 189) and bulking by 7-10 days (95,
97, 140), and prolong the bulking period (14, 15, 24, 81, 82, 175). These combined
responses can result in high yields of large tubers (10). Application of excessive nitrogen,
however, can lead to regrowth of tubers, causing chain tubers or secondary tuber growth
(104) and other malformations (182). Regrowth is most common in cultivars producing
long tubers (62, 160, 224).
Based on evidence that nitrogen fertilizer application begins to assert positive effects
during later stages of tuber growth, Harris (65) concluded that the length of the growing
season has an influence on crop response to added nitrogen. Harvest date and the form,
rate, and timing of nitrogen applications also impact crop response. Effects of additional
nitrogen on total yield and quality of tubers are often variable. Yungen et. al.
(224)
conducted 17 experiments over four years and concluded that negative responses in yield,
grade, and specific gravity of tubers to added nitrogen were associated with adequate or
excess soil nitrogen levels prior to additional applications of nitrogen.
Increased tuber yields from high nitrogen may be associated with a decrease in yield
of No.1 tubers
tuber specific gravity (1, 21, 38, 106, 108, 109, 130,
148, 149, 161, 168, 178, 183, 186, 204), or increased variation in specific gravity among
tubers (129). Other workers have reported that nitrogen can influence the quality of tubers
independent of tuber yields (22, 23, 42, 69, 129). Recently, Jenkins and Nelson (87)
described effects of nitrogen fertility on tuber specific gravity independent of tuber yields.
They showed that a single positive linear relationship existed between total dry matter of
tubers and mean fresh weight of tubers. A delay in senescence of the canopy from
(168, 169, 180),
additional applications of nitrogen was also important in enhancing this positive
relationship. They contend that when this correlation weakens, elevated nitrogen in tubers
is the main cause.
A delay in planting, much like additional nitrogen, increases canopy density (37,
82, 169).
additive
Effects of delayed planting and high levels of nitrogen on canopy density can be
Unfortunately, the length of growing season or harvest schedule often
prevent late planted potatoes from attaining yields as high as those from crops planted
earlier (3, 12, 37, 74, 79, 107, 108). Joseph et. al. (89) documented an increase in tuber
yield with each delay in harvest. Radley (173, 174) concluded that the longer the growing
(97).
season the higher the tuber yields, implying that the earlier the planting date the higher the
expected yield at any given harvest date. Researchers in Europe have estimated that tuber
yields are decreased by 0.75 t ha1 wlc1 (5-10% reduction per week) as planting is delayed
from mid-April to mid-May (12, 37, 40).
Varying the date of planting can influence tuber quality. A delay in planting may
increase the number of stems per plant (74,
undersized tubers (79,
Hiller et. al.
100)
and result in a high proportion of
and Koller and Hiller (100), however, noted
an increase in percent U.s. No.1 tubers with later plantings. Laferriere (111) observed a
reduction in malformed tubers from shading, a consequence of increased canopy density,
80).
(74)
associated with a delay in planting. Accumulation of tuber dry matter (specific gravity) in
many cultivars decreases as planting is delayed (3, 133). This decrease in tuber dry matter
has been shown to be related to lack of maturity in vines and tubers at harvest (108).
Plant Gmwth
The size of potato stems is thought to be influenced by inter-stem competition
(137). Ivins and Bremner (82) stated that the rate of stem growth is inversely related to the
total number of stems per plant. Further, they showed that single-stem plants grow faster
and initiate tubers earlier than plants with multiple stems. Gill and Waister (55) supported
this finding with data from observations comparing one- and four-stem plants of the Mans
Piper cultivar. Some reports have shown that single-stem plants produce relatively few but
large tubers with reduced exterior quality (103, 181, 195). Others suggest that there is no
relationship between size of the main stem and the number of tubers or size of tubers on
that stem (26, 103, 137, 167, 223). Haverkopt et. al. (66), Lemaga and Caesar (114), and
Svensson (202), however, reported that the number of tubers per stem depends on size of
the stem. This finding directly conflicts with data on the number of stems and tubers
presented by Krijthe (105) and Moorby (137). Krijthe (105) demonstrated that the largest
tubers do not all come from the same stem, but are instead distributed equally among the
stems. Oparka and Davies (167) supported this finding and even concluded that stems on
the same plant are independent of each other.
High levels of nitrogen can increase the size and number of leaves (49) and stems
(145) on a plant. Nitrogen does not, however, reduce inter-stem competition (55).
Moorby (138) reported that nitrogen increases the number of tubers per stem. Research by
others does not support this observation (13, 61).
A main effect of delayed planting is increased numbers of stems per plant (79, 80)
associated with increased numbers of tubers.
Differences in the size and number of tubers are associated with the stolon nodal
position on a potato stem. Struik and co-workers concluded from their data and reports by
others that the final size of tubers and variation in tuber size are regulated by the timing of
stolon initiation (196, 199), stolon position (199, 200, 201), and stolon size (45). They
further concluded that the time of tuber initiation is not crucial to this relationship (196,
199). This conclusion agrees with findings by Clark and Downing (23) who reported that
differences in size of tubers are due to unequal rates of tuber growth, not tuber age. Struik
and co-workers also speculated that the position of tubers on the plant affects the size of
tubers due to exposure of the tubers to different environmental conditions (196, 197, 199).
Others (28, 56, 57, 165, 222) have reported that the rate of tuber growth is determined by
the position of the tubers on a stem and that competition for photosynthates within and
among stolon nodes influences the final size of tubers. Struik et. al. (198) noted that the
more tubers formed on a plant, the stronger the competition among tubers, and
10
consequently, more tubers are affected. This interpretation was used to explain the reduced
rate of tuber growth associated with increased numbers of tubers per stem.
Stolons develop first at the basal stem nodes (nearest the mother tuber) and then at
progressively higher nodes (32, 155, 165, 170). There are more stolons (tubers) on basal
nodes (28, 119, 223), equal numbers at nodes 2-6, and fewer at nodes 7 and 8 (223).
Cother and Cullis (28) found that the growth rate of the basal node stolons may depend on
the total number of stolons. When many stolons are formed, the probability of finding
marketable tubers at the lower nodal positions declines. Gray and Smith (57), and Clark
and Downing (23), however, found evidence that the basal tubers can have the highest
growth rates. In fact, Clark and Downing (23) and Oparka and Davies (167) found the
largest tubers at the basal nodes. Clark and Downing (23) also observed a tendency for
tubers on the upper stolons to be smaller than those lower on the stem. Plaisted (170), and
Cother and Cullis (28) also observed that market-sized tubers are more likely to be formed
on basal node stolons than on upper stolons; however, they concluded that the greatest
probability for marketable tubers may be associated with middle stolon nodes. Krijthe
(105), however, reported that the largest tubers consistently developed at nodes 3-5,
medium-sized tubers at nodes 1 and 2, with the smallest tubers developed from secondary
stolon initials.
Struik et. al. (197) summarized the characteristics of tuber growth at the plant level
based on a review of the literature as follows: 1) at any one time only a few tubers grow
rapidly; 2) when certain tubers approach their final weight, the rate of growth declines and
other tubers start to grow faster (137, 138); 3) all tubers have similar opportunities to grow
at a certain rate; 4) some tubers continue to grow for a longer period, thus reaching a larger
final size (28, 139); and finally, 5) tubers show fluctuating rates of growth so that a large
tuber at one time may not be the largest one at a later stage of plant development (2, 43, 44,
45, 57, 137, 139, 171, 188, 200, 223).
Initial differences in size of tubers may be caused by differences in the onset of
rapid growth followed by differences in the rate of growth such that the relative sizes
among tubers from the same plant or stem changes with time (171, 188, 200). A pattern of
tuber size distribution exists, influenced by the average size of tubers and spread of total
tuber yield across the size grades (122, 124, 185, 205).
Patterns of tuber growth seem to be influenced by competition or hierarchy among
tubers on the same stem and by the sink strengths of those tubers (121, 122). Early
workers reported that this hierarchy did not change once established (105). Recent work,
however, shows that the hierarchy of sink strength is not constant during development of
plants, causing continuous differences among rates of tuber growth (2, 166, 171, 188).
11
Engels and Marschner (45) strengthened the tuber competition theory when they
showed that removal of tubers caused increased rates of growth in the remaining tubers.
Struik et. al. (198) showed that yields of large tubers increased at the expense of smaller
tubers. The number of tubers on a plant is usually negatively related to the average weight
of tubers on that plant (66, 114).
Tuber size has been shown to influence quality. It was previously pointed out that
total tuber yield and grade can be inversely related. Specific gravity can also be influenced
by tuber size. Murphy and Goven (150) measured higher specific gravity in larger tubers.
Kleinkopf et. al. (98) reported similar results and also showed wider variation in specific
gravity among tubers within a hill than among tubers from different hills. Ifenkwe et. al.
(78) maintained that spacing between plants influences specific gravity of tubers. High
plant populations result in an increase in specific gravity of small tubers and decreases
specific gravity of large tubers (11, 78, 99). Meridith and Genet (132) could not verify
these reported relationships between specific gravity of tubers and either numbers or size of
tubers,
In addition to competition among stems and tubers, above and below ground parts
of the plant also compete with each other. This competition is caused by concurrent growth
of different plant parts. After extensive research, Moorby (138, 139) concluded that tubers
compete for limited photosynthate. He believed that the tubers had no control over
photosynthate availability. Engels and Marscbner (46) also maintain that growth of tubers
is limited by the ability of the foliage to supply photosynthate. Sale (184), however,
concluded that assimilation depends on the number of developing tubers which provide a
sink for the photosythate. Since vascular continuity exists between leaf and tuber (23, 57,
198), it is not surprising that removal of certain leaves reduces the growth rate of specific
tubers (46).
Although the ability of leaves to supply photosynthate may limit tuber growth,
tubers influence the rate of photosynthesis (54, 138, 183). Moorby (138) concluded that
tubers can increase a planfs photosynthetic rate. Tubers may also influence transport of
photosynthate from the leaf (54, 131, 135, 183). Supporting these data are observations
that removal of tubers decreased photosynthesis (17, 18, 51, 76) and prolonged leaf
viability (158).
Nutrient status affects parts of the potato plant differentially. A change in plant
nitrogen status affects roots and stolons less than leaves or shoots (119). Sommerfeldt and
Knutson (193) reported that a medium level of nitrogen gave maximum growth of roots.
With increasing levels of soil nitrogen, proportionally more of the nitrogen ends up
in the vines (112, 191, 212, 213), increasing the ratio of vine length to tuber weight (104,
12
193, 194) and thus competition between vines and tubers (137). This competition can
reduce the quality of tubers (103). A delay in planting can also increase the vine length to
tuber weight ratio (37).
Soil and Peliole Nuirient Levels
Nutritional status of both soil and plant tissues are essential components of any
discussion of potato growth.
The literature offers a wide range of soil and petiole nitrogen levels for optimum
yield and/or quality of tubers. Soltanpour (192) explained that the amount of nitrogen
needed was the amount required for optimum leaf, stem and tuber growth. For the Russet
Burbank cultivar, research in the western United States indicates that a range of 25 0-440 kg
nitrogen is optimum for growth of plants and tubers (52, 95, 113, 163, 178). Rates
of nitrogen in this range are considered excessive for Russet Burbank in other production
areas (172) and for other cultivars (134).
ha-1
Research has failed to establish a strong correlation between the overall nutritional
level of the plant and tuber yields (110). Early-season nitrate levels in the petiole,
however, have been correlated with tuber yield (52). This correlation is less pronounced
later in the season (8).
Plant petiole nitrate levels are strongly correlated with the rate of applied nitrogen
(172). Asfary et. al. (7) showed a high rate of plant nitrogen use early in the season which
declined later. Oj ala (163) stated that 58 to 71% of the total nitrogen uptake occurs from
early- to mid-bulking in Russet Burbank. The highest demand for nitrogen in long-season
cultivars occurs 50 to 80 days after planting (41, 68, 83). Carpenter (20) and Hawkins
(67) showed that late-maturing cultivars require less early-season nitrogen and more later in
their growth cycle compared to early-maturing cultivars. Regardless of the cultivar, the
need for nitrogen diminishes with plant maturity (8, 191, 206). This type of research may
have prompted the practice of splitting nitrogen fertilization between preplant and in-season
applications. Ivins and Bremner (82) summarized advantages of in-season or split
applications of nitrogen as follows; "The element of yield reduction that is introduced by
the apparent delay in tuber initiation following application of nitrogenous fertilizers raises
the question of whether or not it is possible, by suitable timing of treatment, to get the best
of both worlds: get the vigorous early tuber growth that is associated with low nitrogen
status and the higher rate and greater longevity of tuber bulking that is associated with
optimal nitrogen levels.
13
Supplying nitrogen exclusively by preplant application has some advantages over
in-season applications. This technique requires less management and can thus produce
more predictable results (95). Nitrogen from this application method, however, is utilized
less efficiently by the potato plant, can result in superoptimal growth of vines and more
undersized tubers, and can cause the crop to respond adversely to environmental stress
(91).
Nitrogen applied during the early growing season increases use-efficiency and can
reduce total plant canopy (9) and petiole nitrate levels (120, 128). Delaying initial nitrogen
applications hastens and prolongs tuber growth (41). The use of a split nitrogen
application program is reported to increase tuber yields (9, 25, 96, 163, 179), decrease
tuberyields (27, 61, 82, 146, 150, 182), orhaveno effectontuberyields (31, 178, 220).
Effects of split nitrogen applications on quality of tubers also vary. Increases in
percent No.1 grade (26, 182, 221) and specific gravity of tubers (98, 99, 163, 178, 221,
222) have been reported. Saffigna et. al. (183), and Kleinkopf and Westermann (95)
demonstrated that frequent, smaller increments of seasonal nitrogen improved potato crop
quality. The establishment of more precise critical levels of nitrogen for soils and plant
tissues may make results from a split nitrogen application program more predictable.
Doll et. al. (36) reported that the level of nitrogen in the soil is a better indicator of
critical levels of nitrogen than is the level of nitrogen in plant parts. He estimated that when
levels of soil NO3 fall below 20 ppm before week 12 after emergence, plant performance
declines. Kleinkopf et. al. (94) demonstrated that when the levels of soil NO3 declined to
10 ppm, adding 16 kg ha1 of nitrogen each week for four weeks in August increased tuber
yields. Westermann and Kleinkopf (220) showed that allowing levels of soil NO3 to reach
8 ppm was acceptable. These values are substantially below the 50 ppm reported by
Kirkham et. al. (92) as necessary for satisfactory growth of plants.
Although some support the view of Doll et. al. (36) on the need to establish critical
levels of soil nitrogen, others believe that the nitrogen status of plant petioles is a more
accurate indicator of the plant's requirements for nitrogen (172, 183, 206, 211). Doll et.
al. (36) also established that when critical nitrogen petiole levels are used, plants of the
Russet Burbank cultivar have a higher critical level than other varieties. Levels of petiole
nitrate have been shown to decrease by as much as 1,000 ppm daily during rapid growth
(190). Because of rapid changes in petiole NO3 content, many believe that critical levels
vary with stage of plant growth and/or time of season (52, 53, 93, 117, 118, 172, 204).
Gardner and Jones (52) demonstrated that a petiole NO3 level of 24,000 ppm at the first
sampling period (when the plant has a mature fourth petiole to sample) is essential to
maximize tuber yields for Russet Burbank. He further recommended that petiole NO3
14
levels be allowed to decline from 22,000 to 14,000 ppm from stolon formation to the 5 cm
tuber size. Porter and Sisson (172) reported that a potato petiole reading of 16-22,000 ppm
NO3 at 50 days after planting (DAP) indicated adequate fertility. Roberts and Cheng (179)
established 9-13,000 ppm as the range of critical petiole NO3 levels for Russet Burbank
potatoes grown in Washington, whereas researchers in Idaho and Canada advocate
maintaining a seasonal petiole NO3 level of 15,000 ppm for best results (95, 123, 147).
Hollow Heart-Bmwn Center
To better understand hollow heart-brown center (HHBC), one must first examine
processes at the cellular level. Mogen and Nelson (136) observed that the damage which
resulted in hollow heart in the Norgold Russet cultivar was physical rather than enzymatic
in nature. Others (116, 176, 208, 210, 217) have provided evidence, from observations of
changes in cells, that enzymatic processes may be involved prior to the visual observation
of HHBC. For this review, emphasis will be placed on the cause and effect relationship
between plant growth and the occurrence of HFIBC.
Three types of hollow heart are described in the literature. Two types are associated
with necrosis and browning in tuber pith tissue (brown center). If the necrosis occurs early
in the growth of tubers and is preceded by a clearly defined phase of brown center, the
resulting hollow heart is predominantly, but not always, in the center or toward the stem
end of the tuber (71). This type of hollow heart and brown center association is referred to
as stem-end hollow heart (71, 116, 142, 176, 218). If the necrosis occurs during a later
stage of tuber growth and the resulting hollow heart is predominantly, but not always, at
the apical end of the tuber, it is referred to as bud-end hollow heart (34, 75, 101, 102, 151,
155, 217, 219). The third type of hollow heart is found in the center or apical end of the
tuber but is not associated with or preceded by a necrotic (brown center) area (136, 151,
217).
Distinct phases occur during development of brown center, If cell death in the pith
region is extensive, hollow heart can develop. The necrotic area, however, may remain or
dissipate without progressing to hollow heart (73, 116).
Two theories have been proposed to explain the occurrence of hollow heart. Moore
(141), Moore and Wheeler (144), and Nelson et. al. (155) suggested that induction of
hollow heart results entirely from rapid enlargement of tubers and that stress is not
necessary to produce the hollow cavity. The second theory, based on work by Dinkel (34)
and Crumbly et. al. (30), suggest that hollow heart is caused by either variable moisture or
15
other stress followed by rapid tuber growth soon after the tubers have begun to develop.
Stress results in plant reabsorption of water, minerals, and/or carbohydrates from the
growing tuber.
Much of the contradictory information resulting from the research on hollow heart
could be explained by the fact that it is based on research using different cultivars which
may behave differently. Much of the research on bud-end hollow heart, associated with
and without a necrotic area (brown center), used the Norgold Russet (136, 151-156) or
Rural Russet cultivars (141-144, 218, 219). In contrast, most of the research on stem-end
hollow heart, which is associated with brown center, used the Irish Cobbler (30, 34, 35,
101, 102, 116, 159) or Russet Burbank cultivars (6, 33, 70-74, 84, 85, 100, 125-128,
162-164, 176, 178, 180, 207-210).
As early as 1925, Hardenburg (62) recognized that differences in susceptibility to
hollow heart existed among cultivars. It was not until much later that susceptibility to
hollow heart was shown to be a heritable trait (86, 213). Differences in the size of tuber
cells among cultivars are not related to hollow heart susceptibility, but within a cultivar the
pith cells of tubers with hollow heart are smaller than pith cells from non-affected tubers
Crumbly et. al.
determined that although the rate of tuber growth may be
similar among susceptible and resistant cultivars, there is a positive relationship between
(136).
(30)
rapid rates of tuber growth and hollow heart in Irish Cobbler. Hiller and Koller
found
a similar association between rate of tuber growth in Russet Burbank and the occurrence of
(71)
the brown center phase of the disorder. They associated the more rapid growth of
individual tubers from the same plant with an increase in the incidence and severity of
hollow heart-brown center.
Hiller and Koller (71) showed that within two weeks of tuber initiation Russet
Burbank is susceptible to changes that cause brown center. Levitt (116) found brown
center in tubers as small as 1.8 g and Hiller and Koller (71) stated that brown center was
initiated most frequently in tubers which weighed less than 58 g. Hiller et. al. (73) also
noted that during the period of brown center initiation (two to three weeks after initiation of
tubers) rapid (exponential) rates of tuber growth reported by Moorby (139), and Moorby
and Milthorpe (140) may be associated with the occurrence of brown center.
Several authors have correlated tuber size with hollow heart heritability (86, 213).
Nelson and Thoresen (154) found that 75% of hollow heart occurred in the largest tubers.
Others have observed this same association (42, 62, 90, 101, 116, 144, 162, 164),
although there are some reports that the largest tubers do not always express the most
hollow heart (216,
(71, 102).
218).
Many small tubers can also show brown center and hollow heart
These smaller tubers are often missed in an assay for hollow heart because
16
many researchers choose to examine only the larger tubers (127, 162, 218).
Efforts to grade out hollow heart tubers by removal of progressively smaller tubers
have met with some success, but this association between size of tubers and hollow heart
has not been sufficiently consistent to allow for mechanical separation (50, 156, 159).
A strong positive correlation between yield of tubers and hollow heart also exists
(86, 214), however, Nelson (151), and Nelson and Thoreson (153, 154) reported an
increase in tuber yield associated with reduced hollow heart due to an increase in the
number of tubers and not size of tubers. Because tuber size is often negatively associated
with the number of tubers per plant, there is a strong negative correlation between the
number of tubers and the occurrence of hollow heart (86).
The number of tubers and stems per plant are strongly associated in many cultivars,
so it is surprising that the number of stems per plant and the incidence of hollow heart do
not show a more definite relationship. Moore (143) found that with Russet Rural the
incidence of hollow heart decreased from 22 to 6% in tubers from one- to four-stem plants,
respectively. Werner (218) also used Russet Rural but observed that the occurrence of
hollow heart peaked in three-stem plants and decreased as the number of stems per plant
varied from this. He noted that the one- and two-stem plants were usually weak plants.
Up to eight stems per plant were common in his experiments.
Other tuber quality factors are also associated with hollow heart. Early research by
Moore (141) and Werner (218) demonstrated that tubers of Russet Rural which were rough
or had secondary tuber growth had a high incidence of hollow heart, compared to smoother
tubers with less secondary growth. Werner demonstrated in 1926 (218) and again in 1927
(219) that 60-70% of the tubers showing growth cracks had hollow heart.
Specific gravity of tubers has also been associated with the occurrence of hollow
heart. Several experiments have shown that specific gravity declines as the frequency of
hollow heart increases. Nylund and Lutz (159) showed that hollow heart was evident in
86.1% of all tubers of Irish Cobbler having a specific gravity of 1.060 or less. Finney and
Norris (50) showed that tubers of Norgold Russet with a specific gravity of 1.050 or less
were hollow 66.6% of the time, by weight. Kleinkopf (98) also was able to demonstrate
this negative relationship between hollow heart and specific gravity in tubers of Russet
Burbank.
Experimental treatments which artificially increase inter-plant competition for
nutrients or carbohydrates have had variable effects on the occurrence of HIHIBC. Krantz
and Lana (102), using Irish Cobbler, observed an increase in the occurrence of hollow
heart in tubers when 50% or more of the uppermost foliage was removed by early June,
but not when leaves were removed at later dates. When Dinkel (34), using the same
17
cultivar, removed 50 to 75% of fully expanded potato leaves at tuber initiation, hollow
heart decreased. He prevented the regrowth of the vines and speculated that perhaps
Krantz and Lana (102) removed the growing points, stimulating regrowth and possibly
increasing hollow heart.
In studies repeated over several years, Nelson and Thoreson (152) working with
Norgold Russet, and Hiller et. al. (74) and Fallah (48) with Russet Burbank, showed
variable effects of root pruning on hollow heart, but generally established a negative
relationship with severity of root pruning and hollow heart. Nelson and Thoreson (152)
were most successful in reducing hollow heart by delaying root pruning although these
results also varied over the four year study. Both Hiller et. al. (74) and Nelson and
Thoreson (152) reported reduced yield and weight of tubers from pruning roots which may
have influenced the occurrence of brown center and sub sequent hollow heart.
Other cultural practices have been shown to affect hollow heart-brown center.
Moore (142), reporting on experiments with Russet Rural in 1925 and 1926 noted, "A
heavier than average amount of manure was almost sure to yield more than the average
amount of hollow heart." More recently, Kallio (90) reported that the occurrence of hollow
heart in tubers of Alaska 114 was positively associated with rates of preplant nitrogen.
Kallio speculated about the relationship between nitrogen and length of the potato vines,
but took no measurements. Others have also listed rapid growth of vines as an influence
on expression of hollow heart-brown center (73, 84, 127, 128, 164) but none took
measurements. In contrast, Button and Hawkins (19) found no relationship between
applications of nitrogen to soil or foliage and hollow heart in tubers of Katandin.
Russet Burbank shows a strong positive relationship between increased or
excessive applications of nitrogen and the occurrence of HHIBC. Jackson (84) found that
of several levels of nitrogen, large applications of nitrogen when the potato tubers were
from 19 to 25 mm in diameter (50 DAP) caused the highest occurrence of hollow heart.
When nitrogen fertilizer was applied at planting or split between planting and tuber
initiation, hollow heart declined. Ojala et. al. (164), and McCann and Stark (128) showed
that 101 kg ha1 nitrogen, applied preplant or as in-season applications in increments
smaller than 34 kg ha1 nitrogen per week, reduced the occurrence of HHIBC. Rex (177),
however, also using Russet Burbank, showed that an application of nitrogen (150 kg ha1)
decreased hollow heart compared to zero nitrogen applied.
Recommendations for controlling hollow heart-brown center by altering planting
dates vary. Early planting of Norgold Russet and Russet Rural, which tend to show budend hollow heart, reduces hollow heart (62, 141, 142, 151, 152). Conversely, planting
later is recommended to reduce hollow heart-brown center in Russet Burbank, a cultivar
EI
susceptible to stem-end hollow heart (72, 74, 164). Hiller and Koller (72) demonstrated
over six years (1976-1981) that a negative relation existed between hollow heart-brown
center and delayed planting.
Seasonal temperature differences also may influence the occurrence of hollow heart-
brown center. Exposure of tubers to cool temperatures during the susceptible period for
initiation of hollow heart-brown center is known to increase the occurrence of the disorder
(163, 207, 208, 209).
19
4
GROWTH PATTERNS OF RUSSET BURBANK TUBERS FROM SINGLE-,
DOUBLE-, TRIPLE-, AND MULTIPLE-STEM PLANTS
Abstract
Field studies were conducted with potato cv. Russet Burbank over three seasons to
characterize patterns of tuber growth from single-, double-, and multiple-stem plants and to
associate these patterns with the incidence of hollow heart-brown center (HHBC). Whole
plant samples were collected bimonthly beginning at tuber initiation and extending to late
bulking. The number of stems and tubers per plant, tuber yield per stem, and the
frequency and severity of HHBC associated with each stem-tuber group were recorded.
Differences in the number and yield of tubers and the incidence of HHBC among
stems were established early and remained constant throughout the season. Single-stem
plants were more susceptible to HHI3C than multiple-stem plants. Main (largest) stems
were the most productive stems (most tuber yield), however, the productivity of main
stems decreased as the number of stems per plant increased. The number of tubers on
single-stem plants was positively associated with the incidence of HHBC. Single-stem
plants had more tubers and yield per stem, but were less productive than double- and
multiple-stem plants. Therefore, tuber yield per stem was more strongly associated with
HI-IBC than tuber yield per plant. Tubers on the main stem became less susceptible to
IHIHBC as the number of stems per plant increased. Thus, a higher proportion of multiplestem plants resulted in less HHBC on the main stems and an overall decrease in the
incidence of FIHBC. Multiple-stem plants initiated HHBC later in the growing season
because of either delayed tuber growth or slower rates of early-season growth.
Introduction
Potato plants are described as having single-, double-, or multiple-stems (13).
Stems compete for light, minerals, and water (1, 24), and as a result differ in productivity.
Tubers originate on stems that differ in vigor and productivity and, in turn, vary in growth
rate and size.
The relationship between stem number and tuber yield is not fully understood. A
negative relationship between the number of stems per plant and tuber size or growth rate
20
(16) and yield
has been demonstrated for Russet Burbank. Moorby (16), and
Bremner and Tana (2) reported a decrease in leaf area per tuber as the number of stems per
hill increase. Collins (3), however, reported a positive association between the number of
stems and tuber yield for Kennebec. In contrast, a constant number of tubers regardless of
the number of stems per plant was reported by Moorby (16) for cultivars Majestic and King
Edward. Finally, Svensson (26) presented data indicating a negative relationship between
the number of tubers per stem and the number of stems in the cultivar Bintje.
The frequency and severity of HHBC are important factors in determining tuber
quality. Although it is obvious why HIEIBC frequency is detrimental to quality, the severity
of HHBC also impacts the grade of fresh and processed potatoes. A high incidence of
hollow heart-brown center (H}IBC) is frequently associated with high-yielding crops of
potatoes. Because increased HHBC is associated with productivity (19, 21), it is likely
(9, 10, 26)
that the number of stems contribute significantly to HHBC susceptibility. Hiller et. al. (8)
found that HIHBC decreased as the number of stems per plant increased. The pooling of
different stem-types before evaluation precludes characterizing groups of tubers that may be
more susceptible to the disorder.
Stem hierarchy could be important in determining hulking rates and susceptibility of
tubers to HHBC. For example, single-stem plants produce larger tubers than multiple-stem
plants (3, 13) and these tubers have more HHBC (17, 18, 30). Even though Oparka (23)
suggested that tubers from individual stems should be evaluated, detailed studies of
multiple-stem systems have not been conducted. Published reports on the growth of tubers
from the largest stems of single-, double-, triple-, and multiple-stem plants are lacking.
Changes in the seasonal growth rates of tubers and the development of HHBC in these
various plant-types are poorly understood.
Although obtaining data on tuber yield and quality for individual stems from field-
grown plants is conceptually simple, it is logistically difficult, because there is a limited
number of tubers per stem. Stem size and tuber yield are extremely variable even among
similar stems of the same plant-type. Further, when the incidence of HHBC is low (less
than 10%), it is difficult to obtain significant differences in HHBC among stem-types.
Therefore, thousands of tubers must be sampled to meaningfully evaluate growth patterns
of tubers on stems from various plant-types.
A major goal of this research was to identify unique associations between patterns
of tuber growth and HHBC across a range of plant-types.
Specifically, these
investigations described: 1) growth of tubers on main stems of plants with one-, two-,
three-, or more stems; 2) the effect of size differences among plant stems on tuber growth
and; 3) the relationship between patterns of tuber growth and the incidence of HHBC. To
21
address these objectives, plant samples were collected throughout the growing season
beginning at tuber initiation and concluding at late bulking.
Mateia1s and Methods
fxperimental Design and Data Collection - A factorial combination of
treatments were arranged in a randomized split-split-split-plot design and replicated
5
times.
Planting dates were main plots, preplant nitrogen (N) regimes were subplots, sample dates
were sub-subplots, and stem-types were sub-sub-subplots. Plots were sampled on 10
dates during the
growing seasons. Planting date, nitrogen regime, and
sampling date were preplanned (fixed) factors. Stem-type was a random factor since it was
determined as plants were sampled. The entire experiment was repeated on adjacent plots
in each of the three years. Therefore, years represent differences in both plot location and
1985-1987
time.
Field Plots - Russet Burbank potatoes were grown near Plymouth, WA in
Quincy sandy loam [Typic Torripsamments (Mixed, mesic)] (see Chapter 6 Materials and
Methods and appendix, Table A. 1 for initial soil nutrient values). Seed tubers, stored at 6
C prior to planting, were cut into pieces ranging from 52-79 g and planted 25 cm apart with
86
cm between rows in early and late April. Plots consisted of 6 rows,
10.7
m long.
Fertilizer was broadcast and disk-incorporated into the top 0.2 m of soil prior to
planting at the following rates (kg ha-'): 56 or 224 N, 168 P, 280 K, 56 S, 2 B, 11 Zn, 11
Mg, 6 Mn and 2 Cu. Nitrogen was applied to all plots at 11 kg N ha-1 wk-1 through a
linear move irrigation system from plant emergence until the first symptoms of brown
center (BC) were observed, at which time N was withheld for 3 weeks (wks). Plots were
considered to have reached emergence when plants from 95% of the planted seed pieces
appeared above the ground. Post-BC initiation N applications (56 kg ha1 wk') were then
continued for a seasonal total of 448 kg N ha1 in accordance with local cultural practices.
Materials and Methods are comprehensively described in Chapter
6.
Growth and Analyses - Five to 10 plants were collected weekly from each plot
beginning in early June and continuing through August (10 dates). The 10 data sets were
grouped by date and reported as 5 bimonthly samplings. The first plant collected in each
plot was randomly selected. Additional plants were collected by selecting every second
plant in the same row. Sampling continued until at least one of each plant-type (single-,
double-, triple-, and multiple-stem) were harvested. Sampling began at tuber initiation
which coincided with the first observed swelling of any stolon tip in a given treatment,
22
regardless of which plot tuber initiation first occurred in. Tuber initiation frequently
occurred approximately 1 wk after 95% plant emergence.
Vines and tubers of harvested plants were weighed and stems per plant were
counted. After weighing, tubers were cut longitudinally, and examined for hollow heart-
brown center (HHBC). When HHBC occurred, severity was rated on a I to 7 scale,
consistent with other studies (27, 28). Tubers exhibiting mild brown center were assigned
a value of 1; moderate and severe brown center tubers were given a value of 3 and 5,
respectively. Tubers with hollow heart, regardless of severity, were scored a 7. The
HHIBC severity value was defined as the sum of severity values for all tubers on individual
stems (Fig. 3.3d) and plants (Fig. 3.3d insert). Levels of HHBC were based on the
number of tubers with symptoms (percent by number) (21, 27) rather than on tuber weight
(percent by weight)
(19,
20).
Plant-types were categorized as single-, double-, triple-, and multiple-stem
according to the number of stems per seed piece. Although any plant with more than one
stem is technically multiple-stemmed, for this study a "multiple" or "multi" stem plant is
defined as any plant with 4 or more stems. Stem hierarchy was based on a visual
observation of size (girth and length of the stem) for each plant. The "main' stem (stem 1)
refers to the largest or dominant stem on a plant, stem 2 to the second largest, etc.
Statistical Analyses - Data were analyzed by analysis of variance (ANOVA).
Differences were determined using Duncan's new multiple range test (5). Percentage data
were transformed {(X+0. 5)0.5] prior to analysis to satisfy the assumptions of normality for
the ANOVA (14) as utilized by Nelson and co-workers (19, 20, 21). Data from each year
was analyzed individually and a combined analysis of all three years was also done. The
three year (pooled) analyses were analyzed two ways. Both a broad and narrow scope of
inference were evaluated. For the broad inference, values for blocks were averaged in each
year, and year then used as replications. For the narrow inference, replications were the
five blocks with years as main plots in a split-split-split-split-plot design. Regardless of
scope of inference, stem-type and sampling date were the major parameters affecting tuber
number, tuber weight, and the incidence of HHBC (Table A.3). Stem-type and sampling
date differences were consistent and significant in all three years when using the broad
scope of inference. Therefore, broad scope of inference statistical comparisons are
presented. In later chapters that emphasize the effects of planting date and nitrogen regime,
the narrow scope of inference with more degrees of freedom and higher significance levels
were used (Chapters 6-8).
Data for stems at different sampling dates are presented. Although planting date
(PD) x stem-type (ST) x sampling date (SD), fertility level (F) x ST x SD, and PD x F x
23
ST x SD interactions were significant, the variability attributed to interactions were of far
less magnitude than variability attributed to either stem-type or sampling date (main effects)
(Table A.3). This is especially true for tuber number and tuber weight. For HHBC the
interactions were more important, but still of far less magnitude than the main effects.
Interactive effects of planting date and fertility on stem characteristics (tuber number, tuber
weight, and HHBC) are discussed in detail elsewhere (Chapter 8). The relative magnitude
of main and interactive affects were consistent for all three years (Table A.3b-d). Mean
square values for the year x stem interaction were 5.03, 3.56, and 3.10% of the stem
means square value for tuber number, tuber weight, and HHBC, respectively. Mean
square values for the year x sampling date interaction were 7.20, 1.40, and 9.14% of the
sample date means square value for tuber number, tuber weight, and HHBC, respectively.
Therefore, data for main stems of single-, double-, triple-, and multiple-stem plants were
pooled across all plantings, preplant N regimes, and years to simplify presentation. A
similar statistical approach was used to evaluate differences among plant-types and stemtypes (main, secondary, and tertiary stems) within plant-types (Fig. 3.3). The percentage
of total tubers on the main stem of single-, double-, triple-, and multiple-stem plants was
also calculated (Fig. 3.2). Since single-stem plant values are always 100%, and without
variance, single-stem data was not included in calculating error terms for mean seperation.
Regression analysis also revealed that intercepts for double-, triple-, and multiple-stem
plant-types are less than a 100%.
Data on the distribution of tubers on different stems from various plant-types (Fig.
3.3) were pooled from late June to August since values for the tuber characteristics were
similar at those sampling dates. Distribution percentage for each group of stems for a given
plant-type total 100 (Fig. 3.2). Differences in growth parameters for stems 4 through 6
were not significant, thus data are shown only in appendix, figure A. 1.
Resuhs
Ninety percent of the plants produced two or more stems. Single-, double-, triple-,
and multiple-stem plants made up 10, 32, 34, and 24% of the plant population. Stem
weight varied with plant-type. Plants with single-, double-, triple-, or multiple-stems in
July averaged 629, 752, 852, and 1031 g of stem per plant, respectively (data not shown).
Main stems weighed 49.8, 31.7, and 26.7% more than secondary stems for two-, three-,
and multiple-stem plants, respectively, in July. Similarly, secondary stems weighed 35.3
and 19.8% more than tertiary stems from triple- and multiple-stem plants.
24
Only a few small tubers were present at the early June sampling, regardless of
plant-type (Fig. 3.1 a). By late June, single-stem plants produced 22 to 28% more tubers
than the main stem of other plant-types. After late June, main stems averaged 9.6, 8.6 and
8.2 tubers on double-, triple- and multiple-stem plants, respectively. The number of tubers
on main stems remained relatively constant regardless of plant-type.
For all sampling dates, tuber yield of main stems was consistently higher than
yields from double- through multiple-stem plants (Fig. 3.lb). Yield of tubers on main
stems of single-stem plants increased over time; percent increase in yield from late June to
mid August was 620%. Yields of single-stem plants were 110 to 241% higher than yields
from main stems of other plant-types throughout the season. The main stems from doublestem plants also produced 20-62% higher tuber yields than main stems of multiple-stem
plants after the June sampling dates.
Average tuber weight from single-stem plants tended to be higher throughout the
season than weight of tubers from main stems of double-stem plants (Fig. 3. ic). The yield
from the main stem of double-stem plants was 24.6% greater than yield of the main stem of
triple-stem plants in late July and 50-60% higher than yield from the main stem of multiplestem plants in late July and August. Growth rates of tubers on main-stem plants was most
rapid between late July and August.
The incidence of HHIBC was more prevalent in main stem tubers from single-stem
plants than from other plant-types in late June (Fig. 3.1 d). Levels of HHBC in main stem
tubers from single-stem plants averaged approximately two tubers throughout the season.
Although the frequency of tubers with HHIBC was lower in tubers from the main stem of
other plant-types (< 1.0 tuber per main stem), the incidence of HHBC increased from 75 to
125% between June and July for double-stem plants, and 75 to 100% during August for
triple- and multiple-stem plants, respectively. The July and August increase in HHBC
resulted in similar levels of the disorder (1 .0-1.1) for main stems of double-, triple-, and
multiple-stem plants by the August sampling.
Frequency of HHBC on main stems of single-stem plants increased to 20% by
early July and remained above 16% throughout the season (Fig. 3.1 e). The percentage of
tubers with HHBC was similar for main stems of double-, triple-, and multiple-stem plants
at the end of the season (Fig. 3.1 d). At the August sampling, tubers from single-stem
plants had 20-35% more HHBC than tubers from main stems of triple- and multiple-stem
plants (Fig. 3.le).
After the initial sampling, the proportion of tuber numbers produced by main stems
remained relatively consistent at 100, 52-53, 34-37, and 26-27% for single-, double-,
triple-, and multiple-stem plants, respectively (Fig. 3.2a). Yield of tubers showed similar
25
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Tuber data from mainstems of single-, double-, triple-,
Fig. 3.1.
--TRIPLE
MUL1OPLE
and multiple-stem Russet Burbank
plants over time: a) tuber number,
80
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b) tuber yield, c) average tuber
z
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size, d) tubers with hollow heartbrown center (HHBC), and e) %
tubers with HHBC. E = early; L =
late. Means with the same letter
from the same sampling date are
not significantly different at P <
0.05 (Duncan).
u
EJIJNE
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26
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Fig. 3.2. Tuber data from main-stems of single-, double-, triple-, and
multiple-stem Russet Burbank plants over time: a) % tubers, b) % tuber
yield, c) % hollow heart-brown center (HHBC), and d) % HHBC severity
on main stems. Means with the same letter from the same sampling date
are not significantly different at P < 0.05 (Duncan).
27
patterns (Fig. 3 .2b). There was a trend toward reduced HHBC (relative to single-stem
plants) in main stem tubers for plants with more than one stem (Fig. 3 .2c). No difference
in HHBC in tubers from main stems of single- and double-stem plants was noted at the
June sampling. Total HHBC for tubers on main stems of double-stem plants declined from
90 to 70% by July and remained above 60% for the rest of the sampling period. Total
H}IBC severity values for main stem tubers declined as stem number increased (Fig.
3.2d).
The percentage of total tubers on individual stems decreased with an increase in the
number of stems per plant (Fig. 3.3a). The number of tubers on stems 1 and 2 of doublestem plants were 54 and 46%, respectively, and 3 8-33-29% and 29-26-25% for stems 1,
2, and 3 of triple- and multiple-stem plants, respectively. The first three stems of multiplestem plants produced 82% of the total number of tubers.
Main stems of double-, triple- and multiple-stem plants accounted for 62, 48, and
32% of the total tuber yields, respectively (Fig. 3.3b). As the number of stems per plant
increased, yield per stem decreased and the percent of tuber yields per stem declined
significantly (Fig. 3.3b). The main and secondary stems of double-stem plants produced
62 and 38% of the total plant yield, respectively; main, secondary and tertiary stems of
triple-stem plants produced 46, 32, and 22% of the total plant yield, respectively; and
main, secondary, and tertiary stems of multiple-stem plants produced 32, 24, and 19% of
the total plant yield, respectively. Seventy-five percent of the total tuber yield and 82% of
the HHBC was produced by the three largest stems of multiple-stem plants (Figs. 3.3b and
c). Patterns of HFIBC severity mirrored FIHBC frequency among stems (Fig. 3 ,3d, see
values in parentheses).
Multiple-stem plants produced an average of 4.4 stems per plant (data not shown).
Stems 4, 5, and 6, however, produced only 39% of the tubers, 29% of the total tuber
weight and 16% of the HHBC (appendix, Fig. A. 1). No significant differences in the
number and yield of tubers, or the incidence of HHBC occurred among these stems,
although trends were similar to those of the larger three stems. Many stems from multiplestem plants are similar in size, making size ranking difficult.
Discussion
Differences in the number and yield of tubers on main stems of plants with different
numbers of stems indicated that competition among stems was established early (by the end
of June) and remained relatively constant throughout the season (Figs. 3.1 a and b). This
-
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29
finding complements work by Moorby (16) and Milthorpe (15), although Moorby used the
term 'sprout" rather than stem to refer to shoots arising directly from the seed tuber.
Without interplant or inter-stem competition, main stems from single-stem plants produced
more and larger tubers than main stems of other plant-types (Fig. 3.1).
Higher tuber yield on single-stem plants relative to main stems (Fig. 3, ib) of other
plant-types was more evident by tuber numbers (Figs. 3.la and b), which varied
considerably, than by average tuber size (Fig. 3. lc), which varied little. Lemaga (13) and
Gray (6) also reported that the number of tubers are more important than average tuber size
in yield determination.
The incidence of HHBC was much higher on single-stem plants than on the main
stem of other plant-types (Figs. 3. lc and d). Also, the main stems of double-stem plants
yielded more than main stems of triple- and multiple-stem plants. Higher yields on singlestem plants were associated with higher levels of HHBC. Therefore, patterns for tuber
number (Fig. 3.la) and HHBC incidence (Fig. 3.lc) are similar. Hollow heart-brown
center is more closely related to tuber yield per stem than average tuber size. Early, rapid
tuber bulking may be associated with the high incidence of HHBC in tubers on main stems,
particularly those from single-stem plants. This supports hypotheses of Crumbly et. al. (4)
and Hiller et. al. (7) in which rapid early-season tuber growth is positively associated with
HHBC. An even distribution of tubers among stems for single-, double-, triple- and
multiple-stem plants would produce 100, 50, 33 and 25% respectively, of the total tubers
on the main stem (Fig. 3 .2a). Actual percentages were always within 2-5% of those
expected (Fig. 3.3 a). This even distribution of tubers happened although stems are of
unequal size, vigor, source, or sink strength (22).
As with tuber number, tuber yield distribution among main stems was established
early and changed little over time (Fig. 3 .2b). After tuber initiation in June, however, the
distribution of tuber yield among stems followed a different distribution pattern than seen
with tuber number. Main stems had a higher proportion of total tuber yield than predicted
by the distribution of tuber numbers (Fig. 3.3b). For example, in late June stem 1 on a
double-stem plant accounted for 52% of the tubers, but 61% of the total yield. Stem 1 on
triple-stem plants accounted for 38% of the tubers and 45% of the tuber yield while stem 1
on multiple-stem accounted for 22 and 33% of the tubers and tuber yield of the entire plant.
Tubers on large main stems appeared to bulk consistently faster than tubers on other stems
(Fig. 3 .3b). The proportion of tuber yield represented by main stems remained constant
over time (Fig. 3.2b) even though the dynamics of tuber growth changed during the season
(Figs. 3.la-c). Struik et. al. (25) also indicated that tubers on the same plant differ in the
timing, rate, and duration of growth.
30
A high percent of HHBC occurred in tubers from main stems (Fig. 3 .2c). Once
HHBC began to occur, the percentage of HHBC in tubers from the main stem, regardless
of plant-type, was always at least equal to the percentage of tuber yield produced by main
stems (Fig. 3 .2b) and usually exceeded it. As the number of stems per plant increased, the
percentage of HHBC in main-stem tubers decreased (Fig. 3 .3c). Inter-stem competition
apparently reduces the incidence of HHBC.
When the number and weight of tubers or the frequency and severity of HHBC
among different plant-types were compared (Fig. 3.3), patterns were similar among stems.
Differences among stems decreased as the number of stems increased. Main stems always
produced higher percentages of tuber numbers, tuber yield and HHBC than secondary
stems. Secondary stems, in turn, produced higher percentages of tuber numbers and tuber
yields than tertiary stems. Differences among stems were smallest for tuber number,
followed by tuber yield, and then percentage of HF1BC. Therefore, increased productivity
among stems on the same plant or among stems (main, secondary, and tertiary) from
different plant-types was positively associated with the frequency and severity of HHIBC.
Competition among tubers on each stem- and plant-type was important in
determining the frequency of HIHBC in tubers. Plants with the most tubers and highest
tuber yield did not necessarily develop more HFTBC (Fig. 3.3 inserts). In fact, single-stem
plants had fewer tubers and less total tuber yield than other plant-types, but a higher
incidence and more severe HHBC. Multiple-stem plants had more tubers but less HHBC
which tended to be less severe. The high HHBC incidence and severity values of singlestem plants (Figs. 3.3c and d) suggest that having a large proportion of these plants in a
field could have detrimental effects on crop quality, even though yields of single-stem
plants were lower than those of multiple-stem plants (Fig. 3.3b insert). Therefore, the
proportion of total plant production (number of tubers and yield) by each stem appears to
be a major factor in the expression of HHBC. The main stem, regardless of plant-type,
was likely to have a major proportion of tubers with HHBC. Tuber number per plant is
usually negatively correlated with FIIIBC (11, 29). This association was confirmed by this
study.
In summary, stem hierarchy was established early and remained constant
throughout the season. Stems of single-stem plants were more productive than main stems
of other plant-types because of higher tuber numbers rather than size. Stem size had a
small effect on the relative distribution of tubers, but a much greater effect on tuber yield
and HHBC among stems.
Main stems were the most productive stems, regardless of plant-type. Further,
main stems from single-stem plants were more productive than main stems from plants
31
with two or more stems. Plants with more than one stem, however, were more productive
on a whole plant basis than single-stem plants.
The number and yield of tubers per stem played a major role in determining
frequency and severity of HHBC among stems. In single-stem plants, a large number of
rapidly growing tubers contributed to HHBC development; this appears to have occurred
primarily during the early part of the growing season. Nevertheless, tubers on the most
productive stem, regardless of plant-type, have the most HHBC.
Iiteratun Cited
1.
2.
Allen, E.J. and D.C.E. Wurr. 1973. A comparison of two methods of recording
stem densities in the potato crop. Potato Res 16:10-20.
Bremner, J.M. and M.A. Taha.
1966. Studies in potato agronomy. I. The
effects of variety, seed size and spacing on growth, development and yield. J Agric
Sci 66:241-252.
3.
4.
5.
6.
7.
Collins, W.B. 1977. Analysis of growth in Kennebec with emphasis on the
relationship between stem number and yield. Am Potato J 54:33-40.
Crumbly, I.J., D.C. Nelson and M.E. Duysen. 1973. Relationships of hollow
heart in Irish potatoes to carbohydrate reabsorption and growth rate of tubers. Am
Potato J 50:266-274.
Duncan, D.B. 1951. A significance test for differences between ranked treatments
in an analysis of variance. VirginiaJ Sci 2:171-189.
Gray, D.
The growth of individual tubers. Potato Res
16:80-84.
Hiller, L.K., D.C. Koller and R.E. Thornton. 1985. Physiological disorders of
potato tubers. In: Potato Physiology (P.H. Li, ed). Academic Press, Orlando,
FL.
8.
1973.
pp 3 89-443.
Hiller, L.K., D.C. Koller and R.W. Van Denburgh.
1979.
Brown center of
potatoes--What we have learned. In: Proc Washington State Potato Conf, Moses
Lake.
9.
pp 21-27.
Relationships between
stem number, tuber set and yield of Russet Burbank potatoes. Am Potato J 60:423-
Iritani, W.M., L.D. Weller and N.R. Knowles.
431.
1983.
32
10.
Iritani, W.M., R. Thornton, L. Weller and G. O'Leary. 1972. Relationships of
seed size, spacing and stem numbers on yield of Russet Burbank potatoes. Am
Potato J 49:463-469.
11.
Jansky, S.H. and D.M. Thompson.
12.
Krijthe, N. 1955. Observations on the formation and growth of tubers on the
potato plants. Netherlands J Agric Sci 3:291-304.
13.
Lemaga, B. and K. Caesar. 1990. Relationships between numbers of main stems
1990. Expression of hollow heart in
segregating tetraploid potato families. Am Potato J 67:695-703.
and yield components of potato (Solanum tuberosum L. cv. Erntestolz) as
influenced by different day lengths. Potato Res 33:257-267.
14.
Little, T.M. and F.J. Hills.
15
Milthorpe, F.L. 1963. Some aspects of plant growth. In: The growth of the
potato (Ivins, J.D. and FL. Milthorpe, eds). Butterworths, London. pp 3-16.
16
Moorby, J. 1967. Inter-stem and inner-tuber competition in potatoes. Eur Potato
J 10:189-205.
17
Moore, H. C. 1926. Hollow heart of potatoes-a report of experiments conducted in
1978, Transformations. In: Agricultural
Experimentation, Design and Analysis. (Little, T.M. and F.J. Hills, eds). John
Wiley and Sons, New York. pp 139-164.
1926. ProcPotatoAssocAm 13:180-182.
Moore, H.C. 1926. Hollow heart of potatoes. A defect often found in some
seasons, which may be reduced by proper cultural methods. Michigan Agric Exp
Stn QBu11 8:114-118.
19
Nelson, D.C. 1970. Effects of planting date, spacing and potassium on hollow
heart in Norgold Russet potatoes. Am Potato J 47:130-135.
20
Nelson, D.C. and M.C. Thoreson. 1974. Effect of root pruning and sub-lethal
rates of dinoseb on hollow heart of potatoes. Am Potato J 51:132-138.
21
Nelson, D.C. and M.C. Thoreson. 1986. Relationships between tuber size and
time of harvest to hollow heart initiation in dryland Norgold Russet potatoes. Am
Potato J 63:155-161.
33
22.
Oparka, K.J. 1985. Changes in partitioning of current assimilate during tuber
bulking in potato (Solanum tuberosum L.) cv. Mans Piper. Ann Bot 55:705-7 13.
23.
Oparka, K.J. 1987. Influence of selective stolon removal and partial stolon
excision on yield and tuber size distribution in field-growth potato cv. Record.
Potato Res 3 0:477-483.
24.
Oparka, K.J. and H.V. Davies.
between potato stems. Ann Bot 5
1985.
Translocation of assimilates within and
6:45-54.
25.
Struik, P.C., A.J. Haverkort, D. Vreugdenhil, B.C. Bus and R. Dankert. 1990.
Manipulation of tuber-size distribution of a potato crop. Potato Res 33:417-432.
26.
Svensson, B. 1962. Some factors affecting stolon and tuber formation in the
Potato. Eur Potato J 5:28-39.
27.
Van Denburgh, R.W. 1979. Cool temperature induction of brown center in
'Russet Burbank" potatoes. HortSci 14:259-260.
28.
Van Denburgh, R.W., L.K. Hitler and D.C. Koller.
1980.
The effect of soil
temperatures on brown center development in potatoes. Am Potato J
57:37 1-375.
29.
Veilleux, R.E. and Fl. Lauer. 1981. Breeding behavior of yield components and
hollow heart in tetraphoid-diphoid vs. conventionally derived potato hybrids.
Euphytica 30:547-56 1.
30.
Werner, HO. 1927. The hollow heart of potatoes; occurrence and test of thiourea
seed treatments for prevention. Potato Assoc Am 14:71-88.
34
.: ri
TIlE DISTRIBUTION OF TUBER NUI'.IBER, YIELD, AND HOLH)W ILEARTBROWN CENTER ON STEMS OF RUS SET BURBANK POTATOES
Abs Iract
Field studies were conducted in the lower Columbia Basin of Washington on
potato, cv. Russet Burbank, to characterize the distribution of number and yield of tubers,
and the incidence and severity of HHBC associated with each stem-tuber group. Samples
of whole plants were collected bimonthly from early June through August. Stems were
counted and then grouped as dominant (two largest stems) or nondominant (remaining
stems) and further grouped by plant-type as single- and double-stem or triple- and multiplestem plants.
Susceptibility of potato tubers to hollow heart-brown center (HHBC) from
dominant and nondominant stems of different plants was positively associated with tuber
weight. Tubers in the weight range which accounted for the largest portion of total tuber
yield (primary weight range) had a higher incidence of HHBC than tubers from any other
weight range. Plant-types susceptible to HHBC had more tubers in the primary weight
range, but both susceptible and nonsusceptible plant-types showed similar peaks in tuber
yield distribution. Regardless of weight, tubers showed more HHBC when produced by
plant-types most sensitive to the disorder.
Tubers from dominant stems were more susceptible to HHBC than those from
nondominant stems. Dominant stems from single- or double-stem plants produced both
more tubers and a higher percentage of large tubers than dominant stems from triple- or
multiple-stem plants.
Rates of tuber growth, and development of HHBC, were delayed beyond midseason for tubers from small, nondominant stems. Nondominant stems produced lower
tuber yields and less HHBC than dominant stems. The yield and incidence of HETBC in
nondominant stems increased late in the season, but at a slower rate than for dominant
stems.
Hollow heart-brown center increased over time in all tuber weight ranges,
suggesting that this disorder was initiated throughout the season. The primary tuber weight
range contained a large percent of the tubers, yield, and HHBC. Primary tuber weight
range(s) at each sampling were of a similar size for the different plant and/or stem-types.
35
Primary tuber weight range(s) were, however, less distinct for nondominant stems.
Nondominant stems and triple- and multiple-stem plants produced fewer tubers and less
I-ffIBC in the most susceptible tuber sizes.
hlmduclion
Growth of potato tubers occurs in linear, exponential, or relatively flat phases (10,
Like stems, tubers compete for nutrients and water (5, 13, 14, 16, 17, 26).
Competition among stems is common (24), but inter-tuber competition is unusual in that
14, 26).
tubers are thought to grow sequentially (15,
Moorby
suggested that tubers do not
compete for photosynthate, rather the supply of photosynthate is limited and switches from
one tuber to another. This may explain, in part, why tubers grow at different rates (1, 15).
16).
(16)
A positive relationship exists between the number of stems per plant and tuber yield
(2, 3). Most studies, however, evaluated productivity on a unit area rather than individual
plant basis (8, 9). Information on individual stem performance (3) and seasonal growth
rates of tubers
is limited and that which is known is general in nature.
Therefore, most reports contain data sets with a limited number of tuber sizes (28).
In Chapter 3, data on productivity of individual stems on single- and multiple-stem
(6, 11, 14, 25, 28)
plants were presented. Single-stem plants produced larger tubers with a higher incidence
of HHBC (18, 27). Tuber distribution patterns for the number, size and percent HEIBC
among main-, secondary-, and tertiary-stems were established early and remained constant
throughout the season. Tuber number per stem is more equally distributed than tuber yield
or the incidence of HHBC. A high proportion of tuber yield and HHBC is found on large
stems.
An understanding of the dynamics of tuber growth from various stem-types may
provide insight into where and when HHBC will most likely occur. Because rate of tuber
growth is associated with the incidence of HIHBC (22), an understanding of stem hierarchy
effects on tuber growth rate and distribution of tuber size is important.
The number of large tubers remains constant over a range of stems per plant
whereas the number of small tubers increases with an increase in the number of stems (15).
Because stem productivity, however, was more strongly associated with HHBC than plant
productivity, data comparing weight distribution on various stem-types may be more
valuable than weight distribution by plant-types when evaluating HHBC.
Our previous results (Chapter 3) demonstrated that the number of stems per plant
and size of stems altered the susceptibility of tubers to HHBC. It is not known if the
36
distribution of tuber sizes on highly HHBC susceptible stems is different than on less
susceptible stems, or if tubers of similar size differ in their susceptibility to HIHBC.
Susceptible stems may produce more large tubers that are especially sensitive to the
disorder, but it is not clear if all large tubers are equally susceptible.
In the present research, patterns of tuber growth on individual stems from different
stem-types of the Russet Burbank cultivar were described. Relationships between the size
distribution and growth rate of tubers, and the incidence of HHIBC for different stem-types
were evaluated.
Mtteiials and Methods
Experimental Design and Data Collection - Treatments were arranged in a
factorial, randomized split-split-split-split-plot design and replicated 5 times. Planting dates
were main plots, preplant nitrogen (N) regimes subplots, sampling dates sub-subplots,
stem-type sub-sub-subplots, and weight range were sub-sub-sub-subplots. Plots were
sampled on 10 dates in the 1985-1987 growing seasons. Planting date, nitrogen regime,
and sampling date were preplanned (fixed) factors. Stem-type and weight range are
random factors since they were determined as plants were sampled. The entire experiment
was repeated on adjacent plots in each of the three years. Therefore, years represent
differences in both plot location and time.
Field Plots - Russet Burbank potatoes were grown near Plymouth, WA in
Quincy sandy loam [Typic Torripsamments (Mixed, mesic)] (see Chapter 6 Materials and
Methods and appendix, Table A. 1 for initial soil test values). Seed tubers, stored at 6 C
prior to planting, were cut into pieces ranging from 52-79 g and planted 25 cm apart with
86
cm between rows in early and late April. Plots consisted of 6 rows, 10.7 m long.
Fertilizer was broadcast and disk-incorporated into the top 0.2 m of soil prior to
planting at the following rates (kg ha1): 56 or 224 N, 168 P, 280 K, 56 5, 2 B, 11 Zn, 11
Mg,
Mn and 2 Cu. Nitrogen was applied to all plots at 11 kg N ha1 wlc1 through a
linear move irrigation system from plant emergence until the first symptoms of brown
center (BC) were observed, at which time N was withheld for 3 wks for all treatments.
Plots were considered to have reached emergence when plants from 95% of the planted
seed pieces appeared above the ground. Post-BC initiation N applications (56 kg ha4 wk
1)
were then continued for a seasonal total of 448 kg N ha1 in accordance with local
6
cultural practices. Materials and Methods are comprehensively described in Chapter
6.
37
Growth and Analyses - Five to 10 plants were collected weekly from each plot
beginning in early June and continuing through August (10 dates). The 10 data sets were
grouped by date and reported as 5 bimonthly samplings. The first plant collected in each
plot was randomly selected. Additional plants were collected by selecting every second
plant in the same row. Sampling continued until at least one of each plant-type (single-,
double-, triple-, and multiple-stem) were harvested. Sampling began at tuber initiation
which coincided with the first observed swelling of any stolon tip in a given treatment,
regardless of which plot tuber initiation first occurred in. Tuber initiation frequently
occurred approximately 1 wk after 95% plant emergence.
Plants were harvested and vines and tubers were weighed. Each tuber was
counted, weighed, and assigned to one of the following weight ranges: 0-13 g, 14-27 g,
28-57 g, 58-1 13 g, 114-170 g and> 170 g. A primary weight range is defined as the
range(s) having the most total tuber weight.
After weighing, tubers were cut longitudinally and examined for hollow heartbrown center (HHBC). Any necrotic area or separation of tissue in the pith region was
scored as BC or HF-I, respectively. The level of HHBC was based on the proportion of
tubers with symptoms (% by number), as reported elsewhere (22, 27), rather than tuber
weight. The number of stems per plant were counted.
Plant-types were categorized by the numbers of stems per seed piece. Single-,
double-, triple-, or multiple-stem plant-types were defined. Although any plant with more
than one stem is technically multiple-stemmed, for this study a 'multiple' stem plant is
defined as any plant with 4 or more stems.
Hierarchy of stems was based on observations of stem girth and length for each
plant. "ominant" or largest stem(s) from a plant were designated as D. "Nondominant"
refers to stem(s) other than a dominant (primary or secondary) stem and were designated as
N. The term S-D denotes a stem from a ingle- or double-stem plant. The term T-M
denotes a stem from a triple- or multiple-stem plant. D, S-D, then, refers to dominant
stem(s) from a single- or double-stem plant. D, T-M refers to the .ominant or largest two
stems from a triple- or multiple-stem plant. N, T-M refers to ondominant stem(s) from a
triple- or multiple-stem plant. Nondominant stems occur only on triple- and multiple-stem
plants. The definitions and designation of stem and plant identification is summarized in
Table A.4.
Statistical Analyses - Data from individual stems were grouped according to 1)
stem dominance characteristics (D or N), and 2) total numbers of stems (S-D or T-M) per
plant. Statistical analyses were performed on all growth parameters by analysis of variance
(ANOVA). Differences in stem-type were determined using Duncan's new multiple range
38
prior to analysis to satisfy the
assumptions of normality for the ANOVA (12) as utilized by Nelson and co-workers (20,
21, 22). Data from each year was analyzed individually and a combined analysis of all
three years was also done. The three year (pooled) analyses were analyzed two ways.
Both a broad and narrow scope of inference were evaluated. For the broad inference,
values for blocks were averaged in each year, and year then used as replications. For the
test (4). Percentage data were transformed
[(X+0.5)05]
narrow inference, replications were the five blocks with years as main plots in a split-split-
split-split-split-plot design. Regardless of scope of inference, stem-type, sampling date,
and weight range were the major parameters affecting tuber number, tuber weight, and the
incidence of HHBC (Table A.5). Stem-type, sampling date, and weight range differences
were consistent and significant in all three years when using the broad scope of inference.
Therefore, broad scope of inference statistical comparisons are presented. In later chapters
that emphasize the effects of planting date and nitrogen regime, the narrow scope of
inference with more degrees of freedom and higher significance levels were used (Chapters
6-8).
Data for weight ranges on different stem-types are presented. Although planting
date (PD) x stem-type (ST) x weight range (WI), fertility level (F) x ST x W, and PD x F
ST x W interactions were significant, the variability attributed to interactions were of far
less magnitude than variability attributed to either stem-type or weight range (main effects)
(Table A. 5). The relative magnitude of main and interactive affects were consistent for all
three years (Table A.5b-d). The consistency of year affects can also be seen in Fig. A.7.
Year x stem-type and year x sampling date interactions were also small when compared to
main effects for the narrow scope ANOVA (Table A. 12). Therefore, data for D, S-D; D,
T-M; and N, T-M plants were pooled across all plantings, preplant N regimes, and years to
simplify presentation. A similar statistical approach was used to evaluate differences
among plant-types, (Figs. 4.1-4.3 inserts).
Res uhs
Dominant stems from either single- or double-stem plants (D, S-D) or triple- or
multiple-stem plants (D, T-M) produced more tubers than nondominant stems from
corresponding plant-types (Figs. 4.lb-e inserts). Differences in the number of tubers
between stem-types persisted from late June through late July. After early June, the
number of tubers per stem remained consistent, ranging from 8-10 for dominant stems
regardless of plant-type, to 6-7 for nondominant stems. The number of tubers per stem for
39
b)
a)
10
b
HHIE
82
82
82
B
011111119
5
z
82
83
4
82
82
3
3
2
0-13
14-27
28-57
58-113
14-170
0-13
>170
9
10
14-27
28-57
58-113
14-170
>170
TUBER WEIGHT RANGE (g)
TUBER WEIGHT RANGE (g)
d)
C)
8
7
82
82
B
5
4\
82
3
0
0-13
14-27
28-57
58-111
1*4-970
>170
0-13
14-27
28-51
50-113
114-170
>170
TUBER WEIGHT RANGE (q
TUBER WEIGHT RANGE ()
Effect of stem-type on
Russet Burbank tuber number by tuber
weight range in a) Early June, b) Late
Fig. 4.!.
e)
L_._9TM
113
5
z
w
4
a
0
D, S-D = (D)
dominant stem(s) from (T-M) triple- or
(N)
multiple-stem plants. N, T-M
from
(T-M)
stem(s)
nondominant
triple- or multiple-stem plants. Insert
is total tuber number per stem. Means
82
82
82
Legend:
dominant stem(s) from (S-D) singleand double-stem plants. B, T-M = (B)
7
B
June, c) Early July, d) Late July, and
1_D5D1 e) August.
8
0-13
14-27
28-57
58-113
TUBER WEIGHT RANGE (g)
114-170
0170
with the same letter within the same
weight range are not significantly
different at P < 0.05 (Duncan).
Complete statistical comparisons that
include sampling dates are presented
in appendix liable A..6.
dominant stems of either single- or double-stem plants (D, S-D) or triple- or multiple-stem
plants (D, T-M) did not differ in August.
Only transient differences in weight ranges were seen between dominant stems
from single- or double-stem plants (D, S-D) and triple- or multiple-stem plants (D, T-M)
(Fig. 4.1). Nondominant stems of triple- or multiple-stem plants (N, T-M) consistently
produced fewer tubers in the primary weight range(s) (those containing the most tubers),
compared to dominant stems of either single-, double-, triple-, or multiple-stem plants.
Only at the August sampling date in the 58-113 g weight range did nondominant stems (N,
T-M) produce more tubers than dominant stems from any plant-type in any weight range.
In June, differences existed in the number of small
(0-13
g) tubers per stem among
all stem and plant combinations (Figs. 4.la and b). Dominant stems from single- or
double-stem plants (D, S-D) produced more tubers than dominant stems from triple- or
multiple-stem plants (D, T-M). Dominant stems from both plant-types (D, S-D and D, TM) produced more tubers per stem than nondominant stems from triple- or multiple-stem
plants (N, T-M). During June, these small tubers (0-13g) represented a majority, often
exceeding 7 tubers, on dominant stems (D, S-D and D, T-M) and 6 tubers on nondominant
stems (N, T-M), but steadily declined over time to 3.3 tubers on dominant stems of both
single- or double- (D, S-D) and triple- or multiple-stem plants (D, T-M), and 3.0 tubers on
nondominant stems from triple- or multiple-stem plants (N, T-M) in August. By late June
(Fig. 4. ib), dominant stems of single- or double- (D, S-D) and triple-or multiple- (D, T-M)
stem plants had more tubers in the 14-27 g range than nondominant stems from triple- or
multiple-stem-types (N, T-M). In early July, differences in the number of tubers between
dominant (D, S-D and D, T-M) and nondominant (N, T-M) stems continued, as fewer
tubers were produced on nondominant stems from triple- or multiple-stem plants (N, T-M)
in all weight ranges from
0-113
g (Fig. 4.lc). By late July, (Fig. 4.ld) dominant stems
from single- or double-stem plants (D, S-D) and triple- or multiple-stem plants (N, T-M)
had more tubers than nondominant stems of triple- or multiple-stem plants (N, T-M) in
tuber sizes ranging from 58-113 and from 114-170 g.
In late July and August, dominant stems from single- or double-stem plants (D, SD) had more tubers in the 0-13 g weight range than dominant and nondominant stems from
triple- and multiple-stem plants (D, T-M and N, T-M) Figs. 4. ld and e). Nondominant
stems from triple- or multiple-stem plants (N, T-M) also had less tubers than dominant
stems from single- or double- and triple- or multiple-stem plants (D, S-D and D, T-M) in
weight ranges above 28-57 g. In August, dominant stems from triple- or multiple-stem
plants (D, T-M) produced fewer tubers in the> 170 g range than dominant stems from
single- or double-stem plants D, S-D).
41
Dominant stems from single- or double-stem plants (D, S-D) and from triple- or
multiple-stem plants (D, T-M) consistently produced higher total yields than nondominant
stems from triple- or multiple-stem plants (N, T-M) during the growing season (Figs.
4.2b-e inserts). To a lesser degree, single- or double-stem plants (S-D) produced larger
tubers than triple- and multiple-stem plants (T-M) (Figs. 4.2b-e). At no time did
nondominant stems from triple- or multiple-stem plants (N, T-M) produce higher tuber
yield (Figs. 4.2b-e inserts) or yield within a weight range (Figs. 4.2b-e) than either
dominant stem/plant-type (D, S-D or D, T-M).
In June, yields of smallest tubers (0-13 g) differed among plant-types (Figs. 4.2a
and b). In early June (Fig. 4.2a), dominant stems (D, S-D and D, T-M) produced higher
yields than nondominant stems from triple- or multiple-stem plants (N, T-M). By late June
(Fig. 4.2b), dominant stems (D, S-D and D, T-M) showed higher yields than nondominant
stems (N, T-M) in the < 57 g weight ranges. Dominant stems from single- or double-stem
plants (D, S-D) also had higher tuber yield (24 g vs. < 15 g) in range 28-57 g than either
dominant or nondominant stems from triple- or multiple-stem plants (D, T-M and N, T-M).
By early July (Fig. 4.2c), yields between dominant stems from different plant-types (D, S-
D and D, T-M) were different only for tubers weighing 28-57 g. There was a trend,
however, for tubers on dominant stems from single- or double-stem plants (D, S-D) to
have higher yields in all sizes (i.e., weight ranges < 113 g). Tuber yield was concentrated
in weight ranges of 14-27 g and 28-57 g. Dominant stems from single- or double-stem
plants (D, S-D) and from triple- or multiple-stem plants (D, T-M) produced higher yield in
ranges 28-113 g than nondominant stems (N, T-M). Dominant stems of single- or doublestem plants (D, S-D) also produced higher yield in range 14-27 g than nondominant stems
from triple- or multiple-stem plants (N, T-M).
By late July (Fig. 4.2d), the 58-113 g size range accounted for nearly half of the
total yield. Dominant stems of single- and double-stem plants (D, S-D) produced higher
yields in the three largest size ranges (58-113 g, 114-170 g and > 170 g) than either
dominant or nondominant stems of triple- or multiple-stem plants (D, T-M and N, T-M).
At this sampling, dominant stems from triple- or multiple-stem plants (D, T-M) also
produced higher yield in both the 58-113 g and 114-170 g ranges than nondominant stems
from triple- or multiple-stem plants (N, T-M). In August (Fig. 4.2e), dominant stems of
single- and double- (D, S-D) and triple- and multiple- (D, T-M) stem plants again showed
higher tuber yield than nondominant stems (N, T-M) in the two largest weight ranges (114170 g and> 170 g). Dominant stems of triple- or multiple-stem plants (D, T-M) produced
higher tuber yields in the 114-170 g range, but less (475 g vs. 275 g) in the> 170 g range,
than dominant stems from single- or double-stem plants (D, S-D). Tubers from dominant
42
b)
a)
8
25
10
1,
10
I
\
\
°l
0-13
20-SI
14-27
50-113
114-170
0-13
>170
20-57
50-118
>170
¶14,170
0-03
0
Fig. 4.2.
28-57
58-013
114-170
>170
Effect of stem-type on
weight range in a) Early June, b)
Late June, c) Early July, d) Late
5o
400
350
July, and e) August.
- 300
oft'
000
05-0
0,1-8
Legend
described in Fig. 4.1. Insert is
total tuber yield per stem. Means
300
200
14-27
Russet Burbank tuber yield by tuber
N,T-M
-
>170
e)
I >D.S-D
700
400
114-110
TUBER WEIGHT RANGE (g)
0
450
58-113
d)
TUBER WEIGHT RANGE (g)
800
I
20-07
410
180
0
14-27
I
14-27
c)
200
0-18
-0--Il, 344
TUBER WEIGHT RANGE g)
TUBER WEIGHT RANGE (g)
70'
0
\ \\__
5
with the same letter within the same
1l,18
200
weight range are not significantly
different at P < 0.05 (Duncan).
Complete statistical comparisons
that include sampling dates are
presented in appendix Table A.6.
150
50
0
0-13
14-27
28-57
58-103
114-178
TUBER WEIGHT RANGE (g)
>170
43
stems of single- or double-stem plants (D, S-D) were concentrated in the> 180 g weight
range at the last sampling date (Fig. 4.2e).
A 2-3 fold increase in total yield occurred between the first and last sampling (the
highest proportional increase was six fold during June) (Fig. 4.2b insert) for all stem- and
plant-types (Figs. 4.2b-e inserts) (see appendix, Table. A.6). Total yield of tubers for each
plant-type remained distinct, with easily identifiable peaks throughout the growing season.
Although tuber yield in each weight range increased throughout the growing season
(Figs. 4.2b-e), yield in the primary weight range(s) for dominant stems (D, S-D) and D, TM) increased by about three fold between sampling dates (from 8 to 25 g, 26 to 70 g, 71 to
180 g, and 181 to 500 g) compared to nondominant stems (N, T-M) in July and August
(Figs. 4.2c-e) where yields only doubled.
Incidence of HHBC was distinctly different in tubers from each stem and plant-type
throughout the growing season (Fig. 4.3). Plant-type had an impact on HHBC early in the
season, but by mid- to late-season, stem size had a greater influence on this disorder than
plant-type.
Incidence of HHBC was clearly associated with the same weight range(s) for each
stem and plant-type after June (Figs. 4.3c-e). Trends were apparent even in June, when
the total amount of HHBC was minimal (< 5%) (Figs. 4.3a and b inserts). Tubers on
dominant stems of single- or double-stem plants (D, S-D) had more HIHBC than tubers
from dominant stems of triple- or multiple-stem plants (D, T-M) (Figs. 4.3b and c).
Nondominant stems (N, T-M) produced tubers with less HHBC (<6%) than dominant
stems throughout the season, but especially in late July and August (Figs. 4.3d and e
inserts). Total HHBC did not differ among tubers from dominant stem(s) and plant-types
(D, S-D and D, T-M) in August (Fig. 4.3e insert). When, however, the 0-13 g tubers
(which produced < 1% HHBC throughout the season) were removed from the calculation
of total HHBC (see appendix, Fig. A.2), incidence of HHBC was higher for tubers on
dominant stems of single- or double-stem plants (D, S-D) compared to tubers from either
dominant or nondominant stems of triple- or multiple-stem plants D, T-M or N, T-M).
Maximum levels of HHBC were well defined within weight range(s) and remained
relatively constant (1 5-20% for D, S-D, 10-15% for D, T-M and < 10% for N, T-M)
during late June and July, but increased in August for each plant-type (Figs. 4.3b-e). The
total amount of HHBC increased most during August (Fig. 4.3d insert). Levels of HHBC
in tubers on dominant stems from single- or double-stem plants (D, S-D) were different in
58-113 g and> 170 g weight ranges, than those from dominant stems of triple- or multiplestem plants (D, T-M) in August.
a)
-08.S-0
30
30
'4
-0-
0, T-M
12
25
25
20
20
U
-.-N,T-M
12
IA
0,50
B
15
D. 0-5
5.0-8
10
0-13
28-57
14-27
58-113
114-170
14-27
0-13
>170
08-57
55-153
214-170
>170
TUBER WEIGHT RANGE (g)
TUBER WEIGHT RANGE (g)
C)
i2
1i..I.1114.IIIIILI
85
/\
20
0.13
I
I
I
9-
?-
14-27
28-57
58-113
114-172
>170
0-13
e)
IS
0
14-27
28-57
55-113
114-170
>170
TUBER WEIGHT RANGE (g)
TUBER WEIGHT RANGE (g)
84
Effect of stem-type on
percent of Russet Burbank tubers
Fig. 4.3.
with hollow heart-brown center
82
(HIIBC) in tuber weight ranges in
a) Early June, b) Late June, c) Early
July, d) Late July, and e) August.
0
51:ftI/
2.0-0
2.0-8
5
0
I
Nj-S
0-0,T-M
NOM
Fig. 4.1.
Insert is total IIHBC for each stemLegend described in
Means with the same letter
within the same weight range are
not significantly different at P <
type.
0.05 (Duncan).
Complete statistical
comparisons that include sampling
dates are presented in appendix
0-13
14-27
28-57
58-113
I
I
814-170
>170
TUBER WEIGHT RANGE (g)
Table A.6.
45
Total HHBC during June was minimal (1.8-3.4%) (Figs. 4.3a and b insert). Very
little HHBC was observed in the tuber weight range of 0-13 g. During June, however,
HHBC in tubers exceeded 10% in weight ranges of 14-27 g and 28-57 g. Tubers on
dominant stems from single- or double-stem plants (D, S-D) had higher incidence of
HHBC in the weight range of 28-5 7 g than either dominant or nondominant stems from
triple- or multiple-stem plants (D, T-M or N, T-M).
During early July, HHBC in tubers on dominant stems from single- or double-stem
plants (D, S-D) and dominant stems from triple- or multiple-stem plants (D, T-M) was
highest in the weight range of 28-57 g (Fig. 4.3c). In early July, dominant stems from
single- or double-stem plants (D, S-D) also had higher incidence of HHBC than
nondominant stems from triple- and multiple-stem plants (N, T-M) in tuber weight ranges
of 14-27 g and 28-57 g. Although trends were similar, tubers on the dominant stems of
single- or double-stem plants (D, S-D) were different from dominant stems of triple- or
multiple-stem plants (D, T-M) in the weight range of 14-27 g. By late July (Fig. 4.3d),
dominant stems of single- and double-stem plants (D, S-D) had higher incidence of HHBC
in the largest tubers (114-170 g), than dominant stems of triple- and multiple-stem plants
(D, T-M), and also more than tubers on nondominant stems of triple- and multiple-stem
plants (D, T-M) in weight ranges of 28-57 g and 58-113g.
In late July, (Fig. 4.3d), levels of HHBC in tubers from dominant stems of tripleor multiple-stem plants (D, T-M) were different than in tubers from nondominant stems (N,
T-M) in weight ranges from 114-170 g and in> 170 g tubers in August (Fig. 4.3e).
At each sampling date, the weight range(s) which exhibited the most HHBC and
tuber yield (primary weight range) was the same range, with similar patterns of HHBC and
tuber yield for all stem- and plant-types (Fig. 4.3). These patterns of HHBC and tuber
yield occurred earlier in the season for dominant stems from single- or double-stem plants
(D, S-D) than for dominant and nondominant stems from triple- or multiple-stem plants (D,
T-M and N, T-M).
Discussion
Differences in the number and yield of tubers within weight ranges from different
plant- or stem-types indicate that competition among stems was established early in the
season and remained relatively constant throughout the season. This relationship is similar
to other stem-type research (Chapter 3) and complements work by Moorby (16, 17).
46
Tubers in the weight range with the largest tuber yield (primary weight range),
regardless of stem-type (Fig. 4.2) had the highest incidence of HIHBC (Fig. 4.3c). The
weight ranges with the most tubers (Fig. 4.1), regardless of their weight, (excluding the 013 g tubers), had the highest incidence of HHBC (Fig. 4.3). Tubers larger than those in
the primary weight range had a low incidence of HHB C, indicating that other factors were
more influential than the weight of individual tubers in determining the incidence of
I
i.i
Tuber productivity on stems and plants in certain weight ranges influenced the
expression of HHBC. Large stems, with more tubers and more rapid season-long growth
rates, also had more FIHBC (Figs. 4.1 and 4.2 inserts), and the symptoms were more
severe for smaller stems (Fig. 4.3 inserts). The association between tuber size and HHBC
has been clearly documented in Russet Burbank (9, 10, 17), but not the association with a
primary weight range.
Differences in weight distribution among tubers from different plant or stem-types
(D, S-D; D, T-M; N, T-M) are less apparent for tuber number than for either size of tubers
or incidence of HIHBC. The number of tubers per stem differed for the three stem-types at
the earliest sampling (Fig. 4.1 a), suggesting that tuber initiation occurred first on dominant
stems from single- or double-stem plants (D, S-D), than on dominant stems from triple- or
multiple-stem plants (D, T-M), and finally on nondominant stems of triple- or multiple-
stem plants (N, T-M). Collins (3) also found that initiation of tubers occurred earliest in
single-stem plants for Kennebec. On later sampling dates (Figs. 4. lb-e), dominant stems
from single- or double- and triple- or multiple-stem plants (D, S-D and D, T-M), had
similar total number of tubers and tuber weight distribution.
A continual increase in incidence of HHBC occurs in Russet Burbank, regardless
of stem-type. Because incidence of HHBC increased with time (Fig. 4.3), even though the
total number of tubers remained constant after June (Fig. 4.1), additional HETEC must have
been initiated later in the season. This suggests that FIHBC in Russet Burbank is initiated
both early in the growing season, as reported by Ojala et. al. (23) and Hiller and Koller (7),
and also later in the season, as described by Nelson and co-workers, for tubers of Norgold
Russet (19, 21).
Small, nondominant stems from triple- or multiple-stem plants (N, T-M) produced
fewer tubers (Figs. 4. lb-e), but tubers from these stems were in weight range(s) similar to
dominant stems.
By August, however, the number of large tubers (> 170 g) on
nondominant stems (N, T-M) had increased, but the number was still much lower than for
large tubers on dominant-stem plants (D, S-D and D, T-M) (Fig. 4.le). Therefore, the
potential for HHBC to occur in rapidly growing, similar size, tubers is reduced.
47
The growth of tubers occurred more rapidly on dominant stems from single- or
double-stem plants (D, S-D) than tubers on nondominant stems from triple- or multiplestem plants (N, T-M). Late in the season, differences in tuber yield are most apparent in
the largest weight range (> 170 g) (Figs. 4.2d and e). This indicated that the growth rate of
tubers on dominant stems from single- or double-stem plants (D, S-D) was rapid,
compared to the growth rate of tubers on dominant stems from triple- or multiple-stem
plants (D, T-M).
Incidence of HHBC was influenced by stem-type (Fig. 4.3). Patterns of HHBC
resembled those for tuber yield and the size distribution for each sampling date (compare
Figs. 4.2 and 4.3). Therefore, a close relationship between rates of tuber growth in the
primary weight range(s) and HHBC exists. Stem dominance (size), however, had less
influence on the total tuber yield per stem than plant-type; hence was less likely to affect the
development of HHBC (Fig. 4.3).
Tubers from the primary weight range(s) were more likely to express HHBC
symptoms. These primary weight range(s) also exhibited more tuber yield (Fig. 4.1) than
other weight ranges. This pattern was consistent throughout the season. The increase in
total tuber yield between sampling dates for the primary weight range was much greater
than for other weight ranges. The relationship between productivity of tubers in the
primary weight range and level of HHBC is similar to the association between tuber
productivity and HHBC among the different stem-types. These similarities support the
hypothesis that productivity of similar growing tubers was the most important criterion for
determining which tubers were the most susceptible to HHBC. The greater the number of
tubers which grow rapidly and are of a similar size (on a stem or plant), the more likely
those tubers will develop HHIBC. Wherever total tuber yield is greater, whether comparing
stem-type or tuber weight range, the incidence of HMBC was higher.
Tubers from nondominant stems (N, T-M) had little HUBC (Fig. 4.3), except in
primary weight ranges (Fig. 4.2). Incidence of HHBC in the primary weight range(s)
increased more slowly in tubers from the nondominant stems of triple- or multiple-stem
plants (N, T-M), because the rate of tuber growth was lower. For example, in early July
(Fig. 4.3c), incidence of HHIBC in the principle tuber weight range for nondominant stems
of triple- or multiple-stem plants (N, T-M) was similar to that of dominant stems from
single- or double-stem plants (D, S-D), in late June (Fig. 4.3b).
Regardless of stem-type, the primary weight range contained the largest amount of
HETBC. Although susceptible plant-types produced more tubers in the primary weight
range, both susceptible and nonsusceptible plant-types had similar peaks of weight
distribution. Primary tuber ranges at each sampling date were similar for the three plant-
types. As size and number of stems per plant increased, HIHBC susceptibility, across all
tuber sizes, also increased.
Susceptible stem-types do not appear to produce a
disproportionate number of large tubers that are especially sensitive to the disorder. Since
we did not divide the> 170 g tubers into larger weight groups, we could not determine
whether the largest tubers were less susceptible than tubers in the primary weight range(s)
for the D, S-D group. The stem data presented, however, suggests that tubers larger or
smaller than tubers in the primary weight range(s), regardless of sampling date, were much
less susceptible to HEIBC. Other work (21, 22) also shows variation in HHBC incidence
related to the individual size of tubers.
Stem hierarchy appears to be the most influential factor in determining the
susceptibility of tubers to HETBC. Tubers of similar size growing at similar rates are
clearly more susceptible to HHIBC than either larger or smaller tubers growing at different
rates than the majority. Determining how to alter management practices, to influence stem
hierarchy, and thus reduce the amount of HHBC, is a high priority.
literature Cited
1.
Ahmed, C.M.S. and G.R. Sagar. 1981. Volume increase in individual tubers of
potatoes grown under field conditions. Potato Res 24:279-288.
2.
Bremner, J.M. and R.W. Radley. 1966. Studies in potato agronomy. II. The
effects of variety and time of planting on growth, development and yield. J Agric
Sci 66:253-262.
3.
Collins, W.B. 1977. Analysis of growth in Kennebec with emphasis on the
relationship between stem number and yield. Am Potato J 54:33-40.
4.
Duncan, D.B. 1951. A significance test for differences between ranked treatments
in an analysis of variance. Virginia J Sci 2:171 - 189.
5.
Engels, Ch. and H. Marschner. 1986. Allocation of photosynthate to individual
tubers of Solanum tuberosum L. III. Relationship between growth rate of
individual tubers, tuber weight and stolon growth prior to tuber initiation. J Expt
Bot 37:18 13-1822.
6.
Gifford, R.M. and J. Moorby. 1967. The effect of CCC on the initiation of potato
tubers. Eur Potato J 10:235-238.
7.
Hiller, L.K. and D.C. Koller. 1981. Brown center/hollow heart of potatoes--What
do we know? In:Proc Wash State Potato Conf, Moses Lake. pp 73-80.
8.
Iritani, W.M., L.D. Weller and N.R. Knowles. 1983. Relationships between
stem number, tuber set and yield of Russet Burbank potatoes. Am Potato J 60:423431.
9.
Iritani, W.M., R. Thornton, L. Weller and G. O'Leary. 1972. Relationships of
seed size, spacing and stem numbers on yield of Russet Burbank potatoes. Am
Potato J 49:463 -469.
10.
Krijthe, N. 1955. Observations on the formation and growth of tubers on the
potato plants. Netherlands J Agric Sci 3:291-304.
11.
Lesczynski, D.B. and C.B. Tanner. 1976. Seasonal variation of root distribution
of irrigated, field-grown Russet Burbank potato. Am Potato J 53:69-78.
12.
Little, T.M. and F.J. Hills.
Transformations. In: Agricultural
(Little,
T.M. and F.J. Hills, eds). John
Experimentation, Design and Analysis.
1978.
Wiley and Sons, New York. pp 139-164.
13.
MacKerron, D.K.L., B. Marshall and R.A. Jefferies. 1986. The influence of
early soil moisture stress on tuber numbers in potato. Potato Res 29:299-312.
14.
MacKerron, D.K.L., B. Marshall and R.A. Jefferies. 1988. The distributions of
tuber sizes in droughted and irrigated crops of potato. II. Relation between size
and weight of tubers and the variability of tuber-size distributions. Potato Res
31:279-288.
15.
Moorby, J. 1967. Inter-stem and inner-tuber competition in potatoes. Eur Potato
J 10:189-205.
16.
Moorby, J. 1968. The influence of carbohydrate and mineral nutrient supply on
the growth of potato tubers. Ann Bot 32:57-68.
17.
Moorby, J. 1970. The production, storage and translocation of carbohydrates in
developing potato plants. Ann Bot 34:297-3 08.
18.
Moore, H.C. 1926. Hollow heart of potatoes fertilizers and spacing of potatoes
affect a percentage of hollow potatoes in crop. A report of experiments conducted
in 1926. Mich Agric Exp Stn Q Bull 9:137-139.
50
19.
Nelson, D.C. 1970. Effects of planting date, spacing and potassium on hollow
heart in Norgold Russet potatoes. Am Potato J 47:130-13 5.
20.
Nelson, D.C. and M.C. Thoreson. 1974. Effect of root pruning and sub-lethal
rates of dinoseb on hollow heart of potatoes. Am Potato J 51:132-138.
21.
Nelson, D.C., M.C. Thoreson and D.A. Jones. 1979. Relationships between
weather, plant spacing and the incidence of hollow heart in Norgold Russet
potatoes. Am Potato J 56:58 1-586.
22.
Nelson, D.C. and M.C. Thoreson. 1986. Relationships between tuber size and
time of harvest to hollow heart initiation in dryland Norgold Russet potatoes. Am
Potato J 63:155-161.
23.
Ojala, J.C., J.C. Stark, G.D. Kleinschmidt, R.G. Beaver and E.V. Musselman.
1989. Brown center and hollow heart in potatoes. Univ of Idaho Ext Bull 691:16.
24.
Sadler, E. 1961. Factors influencing the development of sprouts of the potato.
Ph.D. Thesis. Univ Nottingham, London. pp 32-35.
25.
Struik, P.C, A.J. Haverkort, D. Vreugdenhil, B.C. Bus and R. Dankert. 1991.
Possible mechanisms of size hierarchy among tubers on one stem of a potato
(Solanum tuberosum L.) plant. Potato Res 34:187-203.
26.
Struik, P.C., A.J. Haverkort, D. Vreugdenhil, B.C. Bus and R. Dankert. 1990.
Manipulation of tuber-size distribution of a potato crop. Potato Res 33 :417-432.
27.
Veilleux, R.E. and F.I. Lauer. 1981. Breeding behavior of yield components and
hollow heart in tetraphoid-diphoid vs. conventionally derived potato hybrids.
Euphytica 30:547-561.
28.
Werner, HO. 1927. The hollow heart of potatoes. Occurrence and test of
thiourea seed treatments for prevention. Proc Potato Assoc Am 14:71-88.
29.
Wurr, D.C.E. 1977. Some observations of patterns of tuber formation and growth
in the potato. Potato Res 20:63-75.
51
EFFECTS OF RUSSET BURBANK STEM SIZE AND STOLON NODE POSiTION
ON TUBER GROWITI AND HOLLOW hEART-BROWN CENTER
Abs Iract
Studies were conducted in three fields in the south central portion of the Columbia
Basin during 1991 to characterize patterns of tuber growth from stolon nodes on main,
secondary, or tertiary stems of Russet Burbank potatoes and associate these patterns with
hollow heart-brown center (HHBC). Whole plant samples were collected bimonthly in
June and July. The number of stems and stolon nodes per plant, number and individua1
weight of tubers per stem and stolon node, and incidence and severity of HHBC associated
with each stem-tuber and stolon node-tuber group were recorded.
Middle stolon nodes produced more tuber weight than upper and lower stolon
nodes. Productive nodes (more tuber yield) on small stems, however, were not as
productive as the most productive nodes on larger stems. Nodes from the same stolon
position were the most productive, regardless of stem-type.
Differences in tuber number, average tuber yield, and incidence and severity of
HF{BC among stems and stolon nodes were established shortly after tuber initiation and
remained constant throughout the season. Productive stems and nodes had higher growth
rates and higher incidence and severity of HHBC than less productive stems and nodes.
Stem-type, however, influenced tuber productivity and HHBC more than stolon nodal
position.
Inlmduclion
Considerable variation exists in the way potato tubers grow. During the season,
tubers can exhibit linear, exponential, or fairly flat rates of growth (1, 2, 24). In a
summary paper, Struik et. al. (20) concluded that the position of a tuber on a stem does
influence it's growth rate.
The potato plant is limited by the photosynthetic capacity of the canopy (16) which
may influence the rate at which individual tubers grow. Oparka (18) could not show a
relationship between stolon node of origin and the amount of C14 taken up by the tuber.
This suggests that tubers at different nodes grow similarly. Despite these findings, there is
52
evidence that tubers at different nodes do compete. Some have shown that basal node
tubers grow fastest (5, 19); others believe that middle nodes may produce the largest tubers
(2, 3, 7). Considerable variability in tuber growth exists among and within potato varieties
under different environmental conditions. Cother and Collis (3) explained apparent
inconsistencies by stating that as stolon number increases the probability of marketable
tubers at the lower and upper nodal positions declines. The relationship between hollow
heart-brown center (HHBC) and stolon nodal position or number of nodes per plant has
not been studied. HHBC has been correlated to fast growing and/or large tubers (6, 12).
The tuber weight range containing the most yield also accounts for the most HHBC,
whether comparing stem-type (Chapters 3 and 4) or tuber weight range (Chapters 4 and 7).
Therefore, nodes with rapid rates of tuber growth may have more HHBC than slower
growing tubers.
This study evaluated performance of different stolon nodes from a variety of stemtypes. Tuber number, weight and HHBC for different nodes on different stem-types were
evaluated because productivity and growth of different stem-types is strongly associated
with HHBC (Chapter 3). Individual plant and total crop productivity have not been
consistently associated with HHIBC (Chapter 3). Our hypothesis is that stolon nodes with
tubers having the highest growth rates will also have the most HHBC regardless of stem-
type. This information may be used for a better understanding of the relationship between
tuber growth and HHBC in Russet Burbank potato.
Materials and Methods
Experimental Design and Data Collection
A factorial combination of
treatments were arranged in a randomized split-split-split-plot design and replicated 10
times. Fields were main plots, sampling dates were subplots, stem-types were subsubplots, and nodes were sub-sub-subplots. Plots were sampled on 6 dates during the
1991 growing season. Field, sampling date, and stem-type were preplanned (fixed)
factors. Node was a random factor since it was determined as plants were sampled.
Field Plots- Russet Burbank potatoes were grown in the lower Columbia Basin
of southeastern Washington during 1991 at three locations. Soil textures ranged from a
Quincy sandy loam [Typic Torripsamments (Mixed, mesic)J to a Warden silt loam [Xerollic
Camborthids (Coarse-silty, mixed, mesic)]. Potatoes were planted during April. Preplant
N was applied, and subsequent weekly applications were made in irrigation water
throughout the season to meet the potato crop needs.
53
Stem/nodal Analyses - Single-, double-, and triple-stem plants were evaluated.
Thirty plants (10 from each plant-type) were collected weekly from each field beginning in
early June and continuing through July for 6 weeks. The 6 data sets were grouped into 2
wk intervals, resulting in data being reported as 3 sampling dates. The first 10 plants from
each plant-type that were observed were harvested. Sampling began at tuber initiation
which coincided with the first observed swelling of any stolon tip in a given treatment,
regardless of which plot tuber initiation first occurred in. Tuber initiation frequently
occurred approximately 1 wk after 95% plant emergence.
Plants were harvested, and tubers were immediately grouped by stem and nodal
position, and weighed. Hierarchy of stems was based on the relative size of stems
(diameter at the base and length of the stem) from individual plants. The "maint stem was
defined as the largest stem of any plant, the secondary stem to the second largest, etc. The
correct term for the position of the tubers we examined is underground stem nodes on the
end of the stolon. However, in an effort to be consistent with the term other researchers
have used (5, 7, 24), the term stolon nodal position was used. Stolon nodes were
numbered from 1 to 6 beginning at the seed piece (parent tuber). Stolon nodes above 6
were grouped with node 6 data. After weighing, tubers were cut longitudinally, and
examined for hollow heart-brown center (HIHIBC). Severity of HHBC was rated on a I to
7 scale, similar to other studies (21, 22). Tubers exhibiting mild brown center were
assigned a value of 1; moderate and severe brown center tubers were given a value of 3 and
5, respectively. Tubers with hollow heart, regardless of severity, were scored a 7. The
total HHBC severity value, (sum of tuber score), for each stem was divided by the severity
value for the plant to provide a weighted severity rating for each stem. Levels of HHBC
were based on the proportion of tubers with symptoms rather than tuber weight, as
reported elsewhere (15, 23).
Statistical Analyses
Data for all parameters were analyzed by analysis of
variance (ANOVA). Differences were determined using Duncan's new multiple range test
(4).
Data for HHBC were transformed
[(X+0.5)°.5]
prior to analysis to satisfy the
assumptions of normality for the ANOVA (8), as utilized by Nelson and co-workers (13,
14, 15). A combined analysis of all three fields and each individual field was done. Data
for each stem-type at different node positions was presented. Although field (FD) x stem-
type (ST), FD x node (N), and FD x ST x N interactions were significant, the variability
attributed to interactions were of far less magnitude than variability attributed to either field,
stem-type, or node (main effects) (Table A.7). Therefore, data for nodes on different
stems were pooled across all fields to simplify presentation. Data for each individual field
is presented in appendix, figures A.3-6.
54
Resuhs
In early June, there was a trend for more tubers on nodes at the base compared to
the top of the underground part of the stem, (Fig. 5. la). As the season progressed,
however, stolon node position had little bearing on tuber number. Throughout the season,
larger stems produced more tubers per stolon than did smaller stems. Stolon nodes on
secondary stems averaged one tuber per node over the season whereas tertiary stems
averaged less than one tuber per node (Fig. 5.1), indicating stolon nodes on some plants
failed to produce tubers.
Average tuber weight at each stolon nodal position generally doubled between
samplings, (i.e. 30, 60, and 120 for tubers on node 4 of main stems) (Fig. 5.2). Stolon
nodes on small stems were 20-40% less productive than nodes on larger stems, even
though in both cases the same nodes were the most productive on each stem-type.
Differences in average tuber weight per stolon node were consistently four-fold higher for
the most productive node compared to the least across stem-types.
By the first sampling, the incidence of HHBC differed among stolon nodes and
stems (Fig. 5.3a). Tubers from stolon nodes 1 through 3 generally had less HUBC than
tubers on nodes 4 through 6. Stolon node 4 consistently produced tubers with the most
HHBC over the sampling periods (Figs. 5.3 a-c). Stem size affected HHBC; more HHBC
was consistently found in tubers from stolon nodes on large (main) stems compared to
smaller stems throughout the season. By late July, the incidence of HHBC on tertiary
stems decreased more than 20% across all stolon nodes (Fig. 5.3c).
Regardless of stem-type, the severity of HHIBC increased and peaked at either node
4 or 5 (Figs. 5.4a-c). Hollow heart-brown center severity was 1.0 or less in tubers from
tertiary stems for the sampling periods and severity peaked at 2.8 and 1.5 in main and
secondary stems, respectively. Across stolon nodal position, stem size influenced
incidence of HHBC. Tubers on the main stem consistently had more tubers and HIHBC
than those on secondary stems, which had more tubers and HHBC than tertiary stems.
Discussion
Differences in tuber productivity (numbers and weight) on stolon nodes from
different stem-types were established early (by early June) and remained relatively constant
throughout the season. Relationships between stem size and tuber growth in this study
were similar to the 1984-1987 results described previously (Chapters 3 and 4). There was
55
a)
STEM-TYPE
8 TERTIARY
0 SEDRY
MAIN
ii
TUBER
NUMBER
STOLON NODE
6+
Influence of
stem-type and stolon
node position on the
number of Russet
Burbank tubers over
Sampling dates
time.
Fig. 5.1.
b)
STEM-TYPE
0 TERTLARY 0 SEGJDARY I MAIN
are: a) Early June, b)
Late June, and c) Early
July. Stem designation:
main = largest stem,
ii
TUBER
secondary = next largest,
and tertiary = third
Means
largest stem.
NUMBER
with the same letter are
[a
not
different at
STOLON NODE
6+
STEM-TYPE
c )
8 TERTIARY
0 SEDIY I MAIN
TUBER
NUMBER
C
STOLON NODE
6+
significantly
P
<
0.05
(Duncan).
Complete
statistical comparisons
that include sampling
dates are presented
appendix Table A.8.
in
56
a)
STEM-TYPE
TERTIARY
0
'JDARY
U
MAIN
41
3
AVERAGE
TUBER YIELD 2
(g
STOLON NODE
b)
6+
STEM-TYPE
B TERTIARY
Influence of
stem-type and stolon
node position on Russet
Fig. 5.2.
0 SEONDRY' U MAIN
Burbank average tuber
See
yield over time.
6
5.1 for stem
designation and sampling
Fig.
5
dates. Means with the
same letter are not
AVERAGE
TUBER YIELD
(g)
significantly different at
(Duncan).
statistical
comparisons that include
P
<
0.05
Complete
STOLON NODE
c )
6+
STEM-TYPE
8 TERTIARY 0 SEcGDAR' U MAIN
12
10
AVERAGE
a
TUBER YIELD
(9)
STOLON NODE
6+
sampling dates are
presented in appendix
Table A.8.
57
a)
STEM-TYPE
6 TERTIARY 0 SEDARY I MAIN
7
6
5
I-IHBC (%)
STOLON NODE
b)
6+
Fig. 5.3.
STEM-TYPE
TERTIARY
0 SE'JDARY I MAIN
7
6
j
Influence of
stem-type and stolon
node position on the
incidence of hollow
heart-brown
center
(HHBC)-affected Russet
Burbank tubers over
time.
stem
See Fig. 5.1 for
designation and
sampling dates. Means
with the same letter
HHBC (%)
within
are
not
significantly different at
P
0.05
(Duncan).
statistical
comparisons that include
<
Complete
STOLON NODE
6+
Table A.8.
STEM-TYPE
c)
rDTERTIARY
0 SENDiY I MAIN
7
6
HHBC (%)
STOLON NODE
sampling dates are
presented in appendix
6+
a)
STEM-TYPE
6 TERTIARY
0
PDARY i MAIN
2.
KHBC
SEVERITY
1
VALUE
U
STOLON NODE
6+
STEM-TYPE
b)
TERTIARY
0 SEDAY U MAIN
Russet Burbank tubers
2.
over time. See Fig. 5.1
for stem designation and
sampling dates. Means
HHBC
SEVERITY
Influence of
stem-type and stolon
node position on severity
of hollow heart-brown
center (HHBC)-affected
Fig. 5.4.
1
with the same letter are
VALUE
not
C
different at
STOLON NODE
c )
6+
STEM-TYPE
B TERTIARY 0 SEXDP.RY U MAIN
2.
HHBC
SEVERITY I
VALUE
STOLON NODE
6+
significantly
P<
0.05
Complete
(Duncan).
statistical comparisons
that include sampling
dates are presented
appendix Table A.8.
in
59
a positive association between increased tuber number and size, and stem size throughout
the sampling periods (Figs. 5.1 and 5.2). This demonstrates an early and also long lasting
influence of stem-size on tuber productivity. These data complement work by Moorby (12)
and Milthorpe (11).
Tubers from the middle stolon nodes (positions 3-5), regardless of stem-size, were
the most productive, whereas tubers on upper stolon nodes (position 6 and above), were
more productive than on the lowest two nodes (Figs. 5.1 and 5.2). This agrees with work
by Cother and Collis (3). Their data on numbers of stems per plant for Sebago are very
similar to data collected here. Further, they found that when injury to the middle stolons
occurred, tubers from stolons at the upper and lower nodes were able to compensate by
growing faster and reaching a larger final tuber size. This agrees with observations made
from samples collected in 1995 (unpublished data). These observations give strength to the
theory (20) that competition exists among stolon nodes on individual stems.
Tuber productivity from stems and stolon nodes influenced the expression of
HHBC. Large (main) stems, with more tubers and more rapid season-long growth rates
also had more HEIBC (Fig. 5.3) and symptoms were more severe in tubers from main
stems than in tubers found on smaller stems (Fig. 5.4). This association between tuber
size and HHBC has been clearly documented in Russet Burbank (9, 10, 17).
Tubers from productive stolon nodes (3-5) (Figs. 5.1 and 5.2) were more likely to
express HHBC symptoms (Figs. 5.3 and 5.4). These stolon nodes showed larger average
tuber size (Fig. 5.2) and more tubers per node (Fig. 5.1). This pattern was repeated
throughout the sampling period. The increase in average tuber yield between samplings for
the middle stolon nodes (3-5) was much greater than for either upper or lower nodes (Fig.
5.2) (see appendix, Table. AS). The relationship between stolon node productivity and
level of IEHTIBC appears to be similar to the association between tuber productivity and
HHBC among the different stem-types. These similarities support evidence that tuber
productivity is the most important criterion for determining which tubers were more
susceptible to HHBC. The more rapid that tuber growth was on a stem or stolon node, the
more likely those tubers were to express HIIiBC. Stem-type, however, had more effect on
tuber productivity and hence HHBC than stolon nodal position. Although HHIBC is
associated with large tubers, as tuber size increased over the season incidence of HHBC
remained relatively stable (Fig. 5.3).
Wherever tuber yield was greater, whether comparing nodes, stem-types (Chapters
3 and 4), or tuber weight ranges (Chapters 4 and 7), more HHBC occurred. More HHBC
from stolon nodes with large tubers is likely associated with higher yield from these same
stolon node(s). Tuber yield on middle stolon nodes was generally higher than on either
lower or upper nodes (calculated from Figs.
5.1
and
5.2)
with the exception of the earliest
sampling of tertiary stem-types. Differences in average tuber yield were closely associated
with total tuber yield. Although tuber size, total yield, and tuber growth rates were
obviously related to each other, growth rates were probably a more important factor than
size. Large tubers that grew slower were not as susceptible to HHBC as smaller, more
rapidly growing tubers (see Chapter 4).
The relationship of stem-type and stolon node position to incidence and severity of
HHBC is clear. Tubers from the more productive stems (main and secondary), and stolon
nodes (4 and 5), also had a higher incidence and severity of FIIIBC than other stems and
nodes.
The same nodes may not always be the most productive every season.
Environmental factors may influence which nodes produce the most tubers (3). Regardless
of stem-type, however, the same nodes were the most productive in a given season in these
studies. The dominant nodes were established soon after tuber initiation and differences in
productivity among nodes did not change.
Stolon nodal position had a small influence on the proportion of nodes that either
fail to produce a tuber or produce more than one tuber per node. Tubers on productive
nodes grew rapidly whereas tubers on other nodes did not. Tubers on productive nodes
were more susceptible to HHBC as stem size increased.
Literature on HHBC is derived from studies that relate treatment-induced changes in
individual plants or total crops to the incidence of HHBC. Based on this study, an
interpretation of treatment effects on growth of susceptible tuber groups may be different
than an interpretation based on individual plants or total crop production.
Litemtiin Cited
1.
2.
Ahmed, C.M.S. and G.R. Sagar. 1981. Volume increase in individual tubers of
potatoes grown under field conditions. Potato Res 24:279-28 8.
Clark, C.F. and C. Downing.
Bull 958:1-27.
1921.
Development of tubers on the potato. USDA
3.
Cother, E.J. and B.R. Cullis. 1985. Tuber-size distribution in cv. Sebago and
quantitative effects of Rhizoctonia solani on yield. Potato Res 28:1-14.
4.
Duncan, D. B. 1951. A significance test for differences between ranked treatments
in analysis of variance. Virginia J Sci 2:171-189.
61
5.
Gray, D. and D.J. Smith. 1973. The pattern of assimilate movement in potato
plants. Potato Res 16:293-295.
6.
Jansky, S.H. and D.M. Thompson.
7.
Krijthe, N. 1955. Observations on the formation and growth of tubers on the
potato plants. Netherlands J Agric Sci 3:291-304.
8.
Little, T.M. and F.J. Hills.
9.
McBride, R.L. 1985. Potash fertilizer effects on yield, hollow heart and nutrient
levels in potato tubers and petioles. M.S. Thesis. Oregon State Univ, Corvallis.
pp 22-25.
10.
McCann, I.R. and J.C. Stark. 1989. Irrigation and nitrogen management effects
on potato brown center and hollow heart. HortSci 24:950-952.
11.
Milthorpe, F.L. 1963. Some aspects of plant growth. In: The growth of the
potato (Ivins, J.D. and F.L. Milthorpe, eds). Butterworths, London. pp 3-16.
12.
Moorby, J. 1967. Inter-stem and inner-tuber competition in potatoes. Eur Potato
J 10:189-205.
13.
Nelson, D.C. 1970. Effects of planting date, spacing and potassium on hollow
1990. Expression of hollow heart in
segregating tetraploid potato families. Am Potato J 67:695-703.
Transformations. In: Agricultural
Experimentation, Design and Analysis. (Little, T.M. and F.J. Hills, eds). John
Wiley and Sons, New York. pp 139-164.
1978.
heart in Norgold Russet potatoes. Am Potato J 47:130-135.
14.
Nelson, D.C. and M.C. Thoreson. 1974. Effect of root pruning and sub-lethal
rates of dinoseb on hollow heart of potatoes. Am Potato J 51:132-138.
15.
Nelson, D.C. and M.C. Thoreson. 1986. Relationships between tuber size and
time of harvest to hollow heart initiation in dryland Norgold Russet potatoes. Am
Potato J 63:155-161.
16.
Nosberger, J. and E.C. Humphries. 1965. The influence of removing tubers on
dry-matter production and net assimilation rate of potato plants. Ann Bot 29:579588.
62
17.
Ojala, J.C., J.C. Stark, G.D. Kleinschmidt, R.G. Beaver and E.V. Musselman.
1989. Brown center and hollow heart in potatoes. Univ of Idaho Ext Bull 691:16.
18.
Oparka, K.J. 1987. Influence of selective stolon removal and partial stolon
excision on yield and tuber size distribution in field-growth potato cv. Record.
Potato Res 30:477-483.
19.
Plaisted, P.H.
20.
Struik, PC, A.J. Haverkort, D. Vreugdenhil, B.C. Bus and R. Dankert. 1991.
Possible mechanisms of size hierarchy among tubers on one stem of a potato
1957.
Growth of the potato tuber. Plant Physiol
32:445-453.
(Solanum tuberosum L.) plant. Potato Res 34:187-203.
21.
Van Denburgh, R.W. 1979. Cool temperature induction of brown center in
"Russet Burbank" potatoes. HortSci 14:259-260.
22.
Van Denburgh, R.W., L.K. Hiller and D.C. Koller.
1980.
The effect of soil
temperatures on brown center development in potatoes. Am Potato J
23.
Veilleux, R.E. and FT. Lauer.
1981.
57:37 1-375.
Breeding behavior of yield components and
hollow heart in tetraphoid-diphoid vs. conventionally derived potato hybrids.
Euphytica 30:547-561.
24.
Wurr, D.C.E. 1977. Some observations of patterns of tuber formation and growth
in the potato. Potato Res 20:63-75.
INFLUENCES OF NiTROGEN FERTILIZATION AND PLANTING
DATE ON RUSSET BURBANK TUBER YIELD AND QUALITY
Abs Iract
In the U.S. Pacific Northwest, nitrogen (N) fertilization of potatoes frequently
involves both preplant and post-emergence applications. This study was designed to
determine effects of: 1) preplant N levels; 2) post-brown center (BC) initiation N
applications; and 3) planting date on Russet Burbank tuber yield and quality.
Potatoes were planted into a virgin Quincy sandy loam on three dates representative
of local planting times. Nitrogen treatments included two preplant rates [56 (low) or 224
(high) kg ha-i] and large (56 kg ha-i) seasonal N applications initiated at 1, 2, or 3 wks
after BC initiation for low preplant N regimes or at 3 wks for the high preplant N regime.
Weekly large N applications continued for all treatments until a total seasonal N rate of 448
kg ha-' was reached. Therefore, the low preplant N regime had more N applied later in the
season (by 1, 2, or 3 wks) than the high preplant N regime.
The low preplant N regime produced larger tubers and higher yields than the high
preplant N regime across all planting dates. Most of the increase in yield and size,
however, was limited to the U.S. No. 2 (rougher) tuber grade. The low preplant N regime
also produced tubers with lower and/or more variable tuber specific gravity when large N
applications were withheld until 3 wks after initiation of BC compare to the high preplant N
regime. Later N applications during the growing season may have contributed to the low
preplant N regime's effects on reduced specific gravity. No adverse effects from either the
low preplant N regime or delayed post-emergence N applications occurred when the
potatoes were planted late.
The incidence of hollow heart (HH) and BC in the low preplant N regime was less
than or equal to levels in the high preplant N regime. This trend held true regardless of
tuber size or grade when post emergence N was withheld for 2 or 3 wks after initiation of
BC.
The incidence of HFI in U.S. No. 2 tubers was not affected by N regime.
Differences in FIJI and BC levels among N regimes were most evident in large U.S. No. 1
tubers. Beginning large N applications 1 wk after initiation of BC negated the reduction in
tuber HH and/or BC observed in the other low preplant N regimes.
The low preplant N regime(s) resulted in less HH than the high preplant N regime
in large (>284 g) tubers and less BC in all U.S. No. 1 tubers. The low preplant N regime
also produced less BC in
284-397
g U.S. No. 2 tubers.
Low preplant N regimes reduced HH and BC and increased yield compared to the
high regime. Although a low preplant N regime may reduce tuber specific gravity, this can
be offset by either delaying planting or withholding large N applications for only 2 rather
than 3 wks after the onset of BC.
Introduction
Potato (Solanum tuberosum L.) yield and quality are strongly influenced by
nitrogen (N) fertility. High levels of soil N can delay tuber bulking (14, 32) leading to
decreased tuber yields (12, 27) and increased variability in the size of tubers (28, 51).
High N levels can also increase variation in (20) and reduce dry matter content of tubers (1,
When initial soil N is high, desirable tuber growth patterns will occur using
low preplant N (51), particularly when planting is delayed or the crop is harvested early
(12). Low preplant N rates, however, may not favor maximum tuber growth in regions
with a long growing season (7, 24, 42). Dividing N fertilization into preplant and post
emergence applications is commonly practiced in the longer-season growing areas of the
Pacific Northwest. This practice permits the use of low preplant N rates while still
maintaining adequate plant and tuber growth for maximum yields (9, 27, 49).
Results of studies on split applications of N and tuber quality are inconsistent. Split
N applications have been reported to increase (8, 15), decrease (36, 42) or not affect (43,
49) the external quality of tubers and to have variable effects on tuber specific gravity (40,
42, 44). Several researchers (9, 20, 43, 49), however, have reported high yields and
quality for Russet Burbank with a low preplant rate of 56 kg N ha1.
Effects of split N applications on internal tuber quality have only recently been
investigated. Work by Jackson et. al. (16) and McBride (28) indicate that application of 67
kg N ha1 or more before July 7 (approximately 50 days after planting) increases hollow
heart (HH) and brown center (BC) dramatically in large tubers. McCann and Stark (29)
and Ojala et. al. (38) reported that application of small weekly increments of N (17 kg ha1)
over a long period (more than 3 wks) beginning shortly after the initiation of tubers reduced
the incidence of BHBC.
Nitrogen fertilization and planting date can influence HH and/or BC as well as other
yield and quality components in Russet Burbank (13, 15, 28, 38). Less HH and/or BC are
6, 22, 23).
65
expected from late planting (13). Reduced preplant N improves tuber yield, especially if
planting is delayed (12). Further, large applications of N at BC initiation (38) or as a
preplant application (15) tend to increase the incidence of HIHBC.
Our research obj ectives were to determine effects of high and low preplant N
regimes in combination with post-BC initiation N applications on tuber yield and quality of
Russet Burbank potatoes planted on three dates. Variable N applications were designed to
determine how long after BC initiation N applications would: 1) influence HHBC, and 2)
affect tuber yield and quality. Large (56 kg ha-i) post-BC initiation N rates were chosen in
order to reach accepted total seasonal N requirements.
Matenals and Methods
Treatments and Experimental Design - Treatments were arranged in a
factorial, randomized split-split-plot design and replicated 10 times during the 1984-1987
growing seasons. The entire experiment was repeated on adjacent plots in each of the four
years. Years were designated as main plots, planting dates were subplots, and preplant
nitrogen (N) regimes were sub-subplots. Either two (1984-1987) or four (1986-1987)
variable preplant N regimes were used. These regimes differed in the timing of N
application(s) (Fig. 6.1). Low (56 kg ha-i) and high (224 kg ha4) preplant N regimes
were used in all four seasons (1984-1987). Large (56 kg ha') N applications were begun
3 weeks (wks) after brown center (BC) initiation for both treatments. These weekly N
applications continued longer for the low preplant N regimes so that all treatments reached a
total seasonal N rate of 448 kg ha1 (Fig. 6.1). In 1986 and 1987 two additional low (56
kg ha-') preplant N regimes were added. These two regimes began receiving large (56 kg
ha-i) weekly N applications 1 and 2 wks after initiation of BC rather than 3 wks as for the
previously described treatments. Therefore, the low preplant N regimes had seasonal N
applied 1, 2, or 3 wks later in the season than the high preplant N regime. When
illustrating data from only the low and high preplant N regimes, which began receiving
large N applications 3 wks after BC initiation (data from all four years), the legend refers to
the treatments as Low and High (see figures 6.2, 6.3, 6.6-6.8). In figures illustrating data
from all 3 low preplant N regimes (large N applications begun 1, 2, or 3 wks after BC
initiation) and the high preplant regime (large N applications begun 3 wks after BC
initiation), the legend refers to the treatments as Low-lwk, Low-2wk, Low-3wk, and
High-3wk (see figures 6.4, 6.5, 6.7 and 6.8 inserts).
450
3y3y3
400
57"6 5,/"5
1
.- 350
BC NTIATI0N
300
565/
Ui
-J
0-
Iuu-----.
250
0
56/56/5
z
0
+
/
200
--HIGH-3WK
I-
56/56/56
z
D-----LOW-IWK
150
I-
I
I
LOW-2WK
0
56/56/56
I.-
1 00
0--- LOW-3WK
1
50
[I]
o
N
(f)
LC)
(0
r
(0
0)
0
-
N
-
'-
U)
C')
'-
WEEK AFTER EMERGENCE
Fig. 6.1. Total seasonal nitrogen (N) applications. Total N applied was
448 kg ha- 1 Post-emergence N applications of 11, 34, and 56 kg ha-1 are
shown for the wk applied. Preplant N applications were: 56 (Low) or
224 (High) kg ha- 1 N applications (56 kg ha- 1) began at 1, 2, or 3 wks
after brown center (BC) initiation. Legend describes amount of preplant
N and delay after BC initiation before N applications began (example:
Low-2wk).
67
Field Plots - Russet Burbank potatoes were grown in a Quincy sandy loam
[Typic Torripsamments (Mixed, mesic)] with pH 7.4 at Plymouth, WA. Soil nitrogen
concentrations averaged 4.0 ug/l nitrogen [KCL- extracted N}{4+(1 8) + saturated CaSO4
extracted NO3- (3) determined colorimetrically] in the top 0.2 m. Phosphorus and
potassium averaged 8.0 and 138.0 ugh, respectively, using the Olsen extraction procedure
followed by colorimetric determination for phosphorus
(5)
and flame emission
spectrophotometry for potassium (45) determinations. Sulfur, which averaged 2.0 ugh,
was measured colorimetrically following a water extraction (17). Hot 0.02 M CaCL2
extracted boron (30) averaged 0.3 ugh and was determined colorimetricafly (50). Average
zinc, manganese, copper, and iron values were 0.5, 1.0, 4.0, and 7.0 ughl, respectively,
when extracted with DTPA and analyzed with a flame atomic absorption spectrophotometer
(25).
Calcium, magnesium, and sodium were analyzed by atomic absorption
spectrophotometer after extraction with ammonium acetate solution (41) and averaged
1.2
4.0,
and 0.1 meqhloo g, respectively.
Fertilizer was applied to all plots prior to planting at the following rates (kg ha'):
168 P, 280 K, 56 5, 2 B, 11 Zn, 11 Mg, 6 Mn and 2 Cu. Preplant N treatments of 56 or
224 kg N (NH4-NO3) ha-1 were also applied and disked into the top 0.2 m. Plantings
were scheduled for early, mid, and late April each year to simulate local commercial
practices. Seed tubers, stored at 6 C prior to planting, were cut into pieces ranging from
52-79 g and planted 25 cm apart with 86 cm between rows. Plots were 10.7 m long and 6
rows wide. Two inside rows were used for vine and tuber growth measurements, two
outer rows were used as buffer rows, and the remaining two inside rows were used for
yield determination.
Onset of BC was determined by daily sampling and examination of developing
tubers on several plants from each subplot within each main plot for symptoms of necrotic
tissue in the pith region. Post BC N applications began 1, 2, or 3 wks after the first signs
of BC (Fig. 6.1). Between 95% plant emergence and the first appearance of BC, 11 kg N
ha1 wk4 were applied through the irrigation system. Post-BC initiation N applications
were broadcast as dry ammonium nitrate to individual plots and incorporated with sprinkler
irrigation. Treatment descriptions (ex. Low-2 wk) include both the level of preplant N (kg
ha') applied [high (224) or low (56)], and the delay (1, 2, or 3 wks) after BC initiation
before large (56 kg ha1 wki) N applications were begun.
Potatoes were irrigated by a Nelson model "Spray I" linear move irrigation system
with sprinkler heads spaced 1.5 m apart. Water was delivered at a rate of 15.45 Lbm at 103
kPa. Soil moisture was monitored at a depth of 0.2 m with a neutron probe (Campbell
Pacific Nuclear Neutron meter gauge-model
503 DR)
twice weekly. Soil moisture in the
L!Z
root zone (0.2 m) was maintained at 8 5±5% of available. Metribuzin [4-amino-6-(l, 1dimethylethyl)-3 -methylthio)- 1, 2, 4-triazine-5 (4H) and P endimethalin [N-( 1ethylpropyl)-3, 4-dimethyl-2, 6-dinitro-benzenaminej were each applied at 0.4 kg ha-1 (ai)
for weed control. Aldicarb [2-methyl-2(methylthi o) propionaldehy de 0-(methylcarbamoyl) oxime] was applied at 3.3 kg ha-1 (ai) to control insects.
Beginning in June, the largest mature stem from 10 plants, from each N regime,
were harvested weekly and stripped of petioles. The stem tissue was oven-dried at 70 C,
and ground in a Wiley mill to pass through a 40 mm screen. Samples were analyzed for
nitrate (NO3-N) utilizing the chromotropic acid method described by Barker (3). In
conjunction with the stem samples, composites of five soil cores per treatment per wk,
taken with a 30.5 cm long x 19 mm wide tubular stainless steel soil sample probe, were
ground through a 1 mm screen using a wooden pestle. Soil samples were analyzed for
NO3-N as described above, and for NH4-N by the berthelot reaction method described by
Chaney and Marbach (4).
All plant tops were mechanically removed from the plots in mid-September in
preparation for final harvest. Tubers were mechanically harvested from the middle two
rows of each plot. Tuber specific gravity was determined from 4 kg samples of randomly
selected USDA No. 1 (process grade) tubers (21). Total yield, grade, hollow heart (HH),
and brown center (BC) incidence (2) for tubers in five size ranges (1 14-170 g, 171-227 g,
228-283 g, 284-3 97 g, > 397 g) were determined immediately after harvest and differences
among treatments for each size range were evaluated. Hollow heart and BC were
determined by longitudinally cutting all tubers in each size range. A tuber was scored for
HH when a visible tear in the pith region occurred. As described above, BC was scored
when necrotic tissue in the pith region was apparent. If both HH and BC symptoms
occurred, the tuber was scored for HH only. Hollow heart and BC data were calculated
using tuber weights (33, 34) rather than tuber numbers. Although the incidence of HFIBC
can also be calculated by tuber number, most commercial harvest evaluations and grower
payments are based on the weight of tubers in various grades (2).
Statistical analyses - Data were analyzed by analysis of variance (ANOVA).
Differences were determined using Duncan s new multiple range test (10). Percentage data
were transformed [(X+0. 5)0.5] prior to analysis to satisfy the assumptions of normality for
the ANOVA (26) as utilized by Nelson and co-workers (33, 34, 35). Data from each year
was analyzed individually and a combined analysis of all four years was also done. The
variability attributed to planting date (PD) x fertility (F) interactions were usually of far less
magnitude than variability attributed to either planting date or fertility (main effects) (Table
A.9). Only data from main effects are presented with the exception of total yield (Fig. 6.3)
and specific gravity (Fig. 6.5), where PD x F interactions were of interest. Data on the
effects of planting date and HHBC are not presented since PD x F interactions are of
similar magnitude to planting date effects. For most parameters the magnitude of year (Y)
x PD and Y x F interactions were also relatively small when compared to main effects.
Therefore data were pooled across seasons to simplify the presentation. However, planting
date effects on tuber grade and HIHIBC were inconsistent among years (Table A. 9), so only
the more consistent nitrogen regime effects are discussed (figs. 6.7 and 6.8).
Hollow heart-brown center data were evaluated after weighting values across years
(47). This permitted analysis of data without bias from year-to-year influences due to
differences in magnitude, but not the ranked performance of treatments. The weighted
HHBC values given in figures 6.7 and 6.8 are additive. Percentages add to 100 when
totaled across all weights and grades for brown center or hollow heart.
Resuhs
Levels of soil nitrogen (N) decreased for the high (224 kg ha') preplant N regime
until early July, then leveled off (Fig. 6.2a). In contrast, very little change in the levels of
soil N occurred over time with the low (56 kg ha') preplant N regime.
Elevated plant tissue NO3-N levels (10,000-13,000 ppm) were apparent early with
the high preplant N regime, but declined compared to the low preplant N regime (Fig.
6.2b); by August, tissue levels in the high preplant N regime were similar (6,000-8,000
ppm) to those of the low preplant N regime, which were relatively constant throughout the
season.
Tuber yields from the low preplant N regime were 9, 11, and 15% higher than from
the high preplant N regime for the early, mid and late plantings, respectively (Fig. 6.3).
Late planting decreased yields by 22% compared to early or middle planting dates.
Nevertheless, the late planted, low preplant N regime yielded less than the high preplant N
regime from the beginning or middle of the planting season.
Nitrogen regime had no effect on yield of U.S. No. 1 tubers (Fig. 6.4). Yield of
U.S. No. 2 tubers, however, were 21-40% higher in the low preplant N regime and
accounted for 13-19% higher total yield. The high preplant N regime had a lower (3-8%)
percentage of U.S. No. 2 tubers than any low preplant N regime.
A delay in planting increased tuber specific gravity, regardless of N regime (Fig.
6.5). Planting date strongly influenced effects of post-BC initiation N applications.
Delaying large N applications until 3 wks (vs. 1 wk) after BC initiation for the low preplant
70
a)
SOIL NITROGEN
HIGH-EARLY
OLOW-EARLY
BC initiation
200
1 80
1 60
1 40
120
.
100
z
'
80
0
U)
60
40
20
0
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N-
N-
(0
C
(
(0
N-
N-
N-
N-
N
0)
cJ
(
N-
N-
(0
N
(0
(0
(0
SAMPLE DATE
b)
PLANT NO3
I
HIGH-EARLY
LOW-EARLY
I
1.4
1.2
z
0.8
Iz
0.6
04
0.2
0
C
(0
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N
C
(0
N-
(0
(0
N-
N-
C
(0
N
N-
C
N
(0
N
(0
SAMPLE DATE
Fig. 6.2. Effects of preplant nitrogen (N) regime [56 (Low) or 224
(High) kg ha- J and planting date (Early, Mid, and Late) on a) seasonal
soil N and, b) stem nitrate-N level.
.
IL
o
.
I
a
iiwIOII1iIh.
a
a
a
I
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-
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r////,;:;;_
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73
1.085
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TE
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rruiui i
HIGH-3WK
Fig. 6.5. Interaction effects of preplant nitrogen (N) regime [56 (Low) or
224 (High) kg ha- and planting date (Early, Mid, and Late) on specific
gravity of Russet Burbank tubers. Seasonal N applications (56 kg haw k- 1) began 1, 2, or 3 wks after brown center initiation. Means with the
same letter are not significantly different at P < 0.05 (Duncan).
'1
1
74
N regime reduced specific gravities (1.078 vs. 1.081) for potatoes planted early, but not
for potatoes planted later. Tubers from the middle planting for the high preplant N regime
had specific gravities equal to or higher than any tubers from the low preplant N regime
(1.082 vs. 1.079). The low preplant N-2wk regime also produced tubers with higher
specific gravities (1.079 vs. 1.082) than tubers from the low preplant N-3wk regime for
the middle planting. Additionally, the low preplant N-lwk regime produced tubers with
higher total yield (Fig. 6.3), grade (Fig. 6.4), and specific gravities (1.078-1.08 1) than the
low preplant N-3wk regime for early planted potatoes.
The distribution of tuber yields among weight ranges was affected by nitrogen
regime (Fig. 6.6). The low preplant N regime produced lower (11.4%) yields of small
(114-170 g) U.S. No. 1 tubers and higher (23.8%) yields of large (> 397 g) U.S. No. 1
and U.S No. 2 tubers than the high preplant N regime. The low prepiant N regime
produced similar amounts of U.S. No. 2 tubers in the smallest size tubers and 18.5% more
large (> 397 g) U.S. No. 2 tubers than the high preplant N regime.
Total HHBC was significantly greater for the Low-iwk and High-3wk treatments
at 8.01 and 13.50%, respectively, compared to the Low-3wk and Low-2wk treatment
values of 5.54 and 4.2 1%, respectively (original values added across all tuber grades and
weights). A detailed discussion of tubers with HH and BC in U.S. No. 1 and No. 2
grades and tuber weight ranges follows.
U.S. No. 1 tubers > 397 g from the high preplant N regime were more susceptible
to hollow heart (HH) than those from the low preplant N regime (3.4 vs. 9.1%) (Fig.
6.7a). Tubers from the low preplant N regime, regardless of size, tended to have less HH
than those from the high preplant N regime. Tubers from the low N-2 wk and 3wk
regimes tended to have less 1*1, especially in the largest tubers, than the low N-i wk and
high preplant N regime (1.6 and 3.4 vs. 13.8 and 9.1%) (Fig. 6.7a insert).
Tuber size had little affect on brown center (BC) in U.S. No. 1 tubers from the low
preplant N regime (Fig. 6.7b). Brown center occurred less often (2-3% vs. 5-10%),
regardless of size, in the low preplant N regime than in tubers from the high preplant N
regime. The high preplant N regime, however, showed a negative association between
tuber size and BC frequency. Beginning N applications 1 wk after BC initiation resulted in
as much BC in tubers > 397 g from the low preplant N regime as beginning N applications
3 wks after BC initiation for the high preplant N regime (Fig. 6.7b insert).
Neither preplant N nor post-BC initiation N applications affected the incidence of
HH in U.S. No. 2 tubers (Fig. 6.8a insert). Hollow heart accounted for less than 6% of
internals in U.S. No. 2 tubers, except for tubers > 397 g (Fig. 6.8a). Hollow heart
affected 16.8 and 19.4% of large tubers (> 397 g) from the low and high preplant N
II.
Vf
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p
-
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-
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25
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I-
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z
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.5
4
a
10
z
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-------
114-170
171-227
228-283
U
U
284-397
>397
TUBER WEIGHT RANGE (g)
20
b
16
18
LOW-25P(
12
16
o
8
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o---Low.lw(
fl----HIGH-3W1(
14
to
-- LOW-3WK
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0
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a
a
a
8
6
z
0
b
b
b
b
b
2
0
114-170
I
171-227
I
I
228-283
284-397
I
>397
TUBER WEIGHT RANGE (g)
Fig. 6.7. Effects of nitrogen (N) regime on a) % hollow heart (HH), and
b) % brown center (BC) in U.S. No. 1 Russet Burbank tubers in various
tuber weight ranges. N regimes were: 56 (Low) or 224 (High) kg ha 1
preplant N. N applications (56 kg ha- wk 1) began 1, 2, or 3 wks after
BC initiation. Means with the same letter within the same tuber weight
range are not significantly different at P < 0.05 (Duncan). HHBC was
evaluated after weighting values across years. Weighted values add to
1
100 when totaled across all weights for both U.S. No. I and No. 2
tubers.
77
a)
30
25
25
-.-10V4-3W1<
25
15
(0
-.-O-----LOW1WK
10
a
-.-O----HIGH-3W(
20
5
a
I
0
o
2
15
4
4
4
(I;
10
2
I
I
'LOW-3WK
0----- HGH-3WK
5
a
0
U
114-170
171-227
284-397
228-283
>397
TUBER WEIGHT RANGE (g)
20
b)
20
-U-----LOW.>Y41(
16
18
$
LOW-2iN1(
12
16
8
-0----- HI GH-3W1(
(I)
w
14
4
12
I-
10
Lri
a
4
a
z
8
D
(1
-'--- LOW-3WK
-HIGH-3\M<
6
2
a
I
a
a
b
a
0
114-170
171-227
228-283
>397
284-397
TUBER WEIGHT RANGE (g)
Fig. 6.8. Effects of nitrogen (N) regime on a) % hollow heart (IIH), and
b) % brown center (BC) in U.S. No. 2 Russet Burbank tubers in various
tuber weight ranges. N regimes were: 56 (Low) or 224 (High) kg hapreplant N. N applications (56 kg ha-1 wk 1) began 1, 2, or 3 wks after
BC initiation. Means with the same letter within the same tuber weight
range are not significantly different at P < 0.05 (Duncan). HHBC was
evaluated after weighting values across years. Weighted values add to
1
100 when totaled across all weights for both U.S. No.
tubers.
1.
and No. 2
regime, respectively. Tubers from the low preplant N regime showed more HIT in the 284397 g weight range than in smaller (< 283 g) sizes.
Brown center was much more frequent in the largest (> 397 g) U.S. No. 2 tubers
from both N regimes (Fig. 6.8b). The high preplant N regime also had a higher level of
BC (6.64 vs. 1.74) in tubers weighing 284-397 g than in the low preplant N regime.
Brown center in the low preplant N regime was consistently low (1.0 to 2.8%) except in
tubers > 397 g (9.3%).
The low preplant N regimes showed less BC (1.74 vs. 6.64%) than the high
preplant N regime in tubers weighing between 284 and 397 g (Fig. 6.8b). In the> 397 g
weight range BC was lower than any other N treatment at 5.2 1% in response to large N
applications begun 2 wks after BC initiation; beginning large N applications 3 wks after BC
initiation produced similar results to the high preplant N-3wk regime, and beginning large
N applications 1 wk after BC initiation increased BC to 13.49% vs. 9.71 for the high
preplant N-3wk regime.
Discuss ion
A number of reports indicate that low rates of preplant nitrogen combined with
additional post-emergence application(s) consistently produce higher Russet Burbank tuber
yields than high preplant nitrogen (16, 19, 24, 42, 43, 49).
The low preplant nitrogen regime positively influenced tuber size and yield,
compared to the high preplant N regime, and the effect increased with delayed planting
compared to the high preplant N regime (Fig. 6.3). The increase in yield associated with
the low preplant nitrogen regime (Fig. 6.3) was accompanied by a higher proportion of
large U.S. No. 2 tubers (Figs. 6.4 and 6.6). Painter and Augustin (39) reported a negative
relationship between yield and percent U.S. No. 1 tubers. In this research, total yield of
U.S. No. 1 tubers did not decrease, but the percent of total yield composed of U.S. No. 1
tubers declined with increasing total yield from all grades of tubers. Ohms (36) reported an
increase in the percent of rough tubers associated with an increase in total yield. These data
indicate an increase in size for both U.S. No. 1 and No. 2 tubers with a low preplant
nitrogen regime. Yields of large U.S. No. 1 tubers tended to be lower than U.S. No. 2
yields, regardless of nitrogen regime (Fig. 6.6).
Tuber specific gravity increased with delayed planting (Fig. 6.5). Negative effects
of a low preplant nitrogen regime on specific gravity were offset by either planting later or
applying nitrogen 1 or 2 wks after initiation of brown center (BC). Early planting and the
79
associated differences in maturity of both tubers and vines may cause tubers to be more
sensitive to timing of post-BC nitrogen applications. Withholding nitrogen for 2 rather
than 3 wks after BC initiation ended seasonal nitrogen applications sooner, and retained
tuber yield benefits without severely reducing specific gravity. Reduced specific gravities
with the low preplant nitrogen regime could be caused by either less early-season nitrogen
or more late-seasonal nitrogen applications (Fig. 6.1). Because late-season nitrogen
applications could delay maturity, it is likely that the late-season nitrogen applications were
more important than reduced early-season nitrogen applications. These finding support
research by Westermann and Kleinkopf (49), who showed that low preplant nitrogen
coupled with additional nitrogen applied post-emergence either decreased or had no affect
on specific gravity. Metzger et. al. (31), however, showed a decrease in tuber specific
gravity with delayed planting. A much longer delay in post-emergence nitrogen application
(3 wks after BC initiation) and/or subsequent nitrogen applications later in the season in
these studies may account for the apparent conflict between this study and that of Metzger
et al. The Metzger study allowed soil nitrogen to decline in a timely manner, probably
allowing tubers to "mature" relatively early. In this research, levels of soil nitrogen for the
low preplant nitrogen regime were supplemented throughout the growing season (Fig.
6.1). As a consequence, soil and stem tissue nitrogen levels declined slowly or even
increased near the end of the season, especially with the early planting date (Figs. 6.2a and
b). These late season nitrogen levels may have contributed to tuber shape and specific
gravity problems resulting from the early-planted, low preplant nitrogen regime.
Regardless of tuber yield or grade, the low preplant nitrogen regime never had
more, and sometimes less, HR and BC than the high preplant nitrogen regime across all
tuber sizes. Beginning large nitrogen applications 1 wk after initiation of BC negated
favorable effects of low preplant nitrogen regime on the incidence of HH and BC.
Withholding nitrogen for only 1 wk after BC initiation may not have allowed enough time
for dissipation of BC (see Chapter 8) or may have initiated additional BC. Low rates of
post-BC nitrogen spread over a longer period, as suggested by McCann (29) and Ojala
(37), may have discouraged the formation of additional BC and/or reduced the amount of
HR. Jackson et. al. (15) speculated that when Russet Burbank received only 5 kg N ha1
at planting, available soil nitrogen "ran out" by July 7 resulting in plant stress which, unlike
the data reported here, increased the frequency of HH.
The percent of U.S. No. 1 tubers declined and No. 2 tubers increased with
increasing tuber size, irrespective of nitrogen regime (Fig. 6.6). This relationship is not
unusual in Russet Burbank (11, 46). The positive association between tuber size and the
incidence of RH and BC has also been reported (11, 13, 29, 38, 48). Clearly, in this
study much of the HH and BC occurred in large tubers, especially in U.S. No. 2's,
regardless of nitrogen rate (Figs. 6.8a and b). The increase in HH and BC in U.S. No. 2
tubers was not due simply to an increase in tuber size. A four-fold increase in the incidence
of HH occurred between the largest (> 397 g) and second largest U.S. No. 2 weight
ranges (284-397 g) (Fig. 6. 8a) even though the percent of tuber yield in these sizes differed
by less than 50% (Fig. 6.6). The two largest U.S. No. 1 sizes had a similar proportion of
total tubers, by size (Fig. 6.6) but showed a two-fold increase in HH (5% vs. 10%)
between the largest size (> 397) and second largest size (284-3 97) in the high preplant
nitrogen regime (Fig. 6.7a).
The high preplant nitrogen regime decreased the incidence of BC in U.S. No. 1
tubers as tuber size increased, while the percent of BC increased in U.S. No. 2 tubers as
tuber size increased (Figs. 6.7b and 6. 8b). Ojala and co-workers reported similar results
(37, 38). It appears that the expression of BC in potatoes under a high preplant nitrogen
regime (Figs. 6.7b and 6.8b) is closely associated with tuber size distribution (Fig. 6.6).
A low preplant nitrogen regime (with nitrogen applications beginning 2 or 3 wks after BC
initiation) increased tuber size and yields without an associated increase in BC, except in
the largest U.S. No. 2 tubers (Fig. 6.8b). The low preplant nitrogen regime also reduced
the incidence of HH in large U.S. No. 1 tubers (Fig. 6.7a) while increasing yield and size
(Figs 6.3 and 6.6), but these nitrogen regimes had no affect on the incidence of RH in
U.S. No. 2 tubers (Fig. 6.8a).
In summary, low preplant nitrogen regimes positively influenced tuber yield and
size. Many larger tubers, however, were graded U.S. No. 2. Regardless of tuber grade,
low preplant nitrogen regimes at no time had more and sometimes had less HH and BC,
across all tuber weight ranges, than the high preplant nitrogen regime. Beginning large
nitrogen applications 3 wks after BC initiation reduced the incidence of RH and BC less in
high than in the low preplant nitrogen regime. Negative effects of low preplant nitrogen
regimes on tuber specific gravity were offset by either planting later or starting large
nitrogen applications 2, rather than 3 wks after initiation of BC.
Litemture Cited
1.
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E;II
2.
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19
AS
21
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Roberts, S., W.H. Weaver and J.P. Phelps. 1982. Effect of rate and time of
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44.
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Schoenau, J.J. and RE. Karamanos. 1993. Sodium Bicarbonate-extractable P,
K, and N. In: Soil Sampling and Methods of Analysis (Carter, M.R., ed) Lewis
Publishers, Boca Raton, FL. pp 53-5 5.
46.
Sparks, W.C.
1958.
Abnormalities in the potato due to water uptake and
translocation. Am Potato J 35:430-436.
47.
Steel, R.G.D. and J.H. Torrie. 1960. Analysis of variance III: Factorial
experiments. In: Principles and procedures of statistics (Steel, R.G.D. and J.H.
Torrie, eds). McGraw-Hill, New York. pp 180-193.
48.
Werner, HO. 1926. The hollow heart situation in the Russet Rural potato. Potato
AssocAm 1:45-51.
49.
Westermann, D.T. and G.E. Kleinkopf. 1985. Nitrogen requirements of potatoes.
Agron J 77:616-621.
50.
Wolf, B. 1974. Improvements in the azomethin-H method for the determination of
Boron. Comm Soil Sci Plant Anal 5:39-44.
51.
Wurr, D.C.E. 1977. Some observations of patterns of tuber formation and growth
in the potato. Potato Res 20:63-75.
85
ChAPTER 7
GROWFH PATFERN RESPON SES OF RUS SET BURBANK
TO VARIABLE NiTROGEN RATES AND PLANTING DATE
Abs tract
Effects of planting date and variable nitrogen fertilization on seasonal tuber and vine
growth and the incidence of hollow heart-brown center (HHBC) in Russet Burbank were
studied over four seasons.
Potatoes were planted into a Quincy sandy loam near Plymouth, WA on two dates
representative of early and late local planting times. All plots received 448 kg ha-1 of
nitrogen (N) during the season; however, levels of preplant N [224 (high) or 56 (low) kg
ha-i] and the number of subsequent weekly N applications (56 kg ha4 wk1) beginning 1,
2, or 3 wks after initiation of brown center (BC), were varied. Plants were collected
bimonthly from early June to mid-August. Weights of vines, numbers of tubers,
individual tuber weights, and levels of HHBC were determined.
A high preplant N regime increased vine biomass and the incidence of HIHIBC
compared to a low regime. Planting late also increased vine mass but reduced HHBC.
Potatoes planted late had more stems per plant, but lower tuber yields and less HHBC.
Even with the low preplant N regime, the incidence of HHBC was high when seasonal
applications of N began 1 wk after initiation of BC. Hollow heart-brown center was not
increased when applications of N for the low preplant N regime began 2 or 3 wks after
initiation of BC.
Large tubers may not necessarily be more susceptible to HHBC. Tubers in weight
range(s) containing the most tuber yield [termed the primary weight range(s)] were most
prone to HHIBC. Tubers either larger or smaller than those in the primary weight range for
a given sample date were less affected. Early in the growing season, small tubers (14-27
g) accounted for 50 to 80% of the HHIBC. However, the tuber size range with the highest
level of both HHBC (about 50% of the total) and tuber weight represented progressively
larger tubers over time.
The incidence of HHBC and tuber growth rate increased as the season progressed.
Enlargement of tubers with HHBC could not entirely account for high levels of HHBC in
large tubers late in the season. Therefore, some HHBC must have been initiated after midseason.
Russet Burbank tubers develop both early- and late-season HHBC. Less HHBC
with delayed planting was most apparent among large tubers suggesting that potatoes
planted late have slow tuber growth rates, resulting in reduced late-season HHBC. In
comparison, the low preplant N regime reduced vine biomass and consequently both earlyand seasonal amounts of HHBC, but had no effect on the incidence of late-season HHBC.
Iniroduclion
Potato crop development has been divided into four distinct stages: 1) vegetative
growth, 2) tuber initiation, 3) tuber growth, and 4) plant maturation (20, 40). Although it
seems logical that physiological events associated with plant growth initiate development of
some internal tuber disorders, relationships between plant growth and hollow heart-brown
center (HHBC) are not clear. Rapid growth of vines reportedly favors the development of
HHBC symptoms in tubers (17, 19) during early growth (15, 35, 36). Regrowth of vines
during early tuber development can also increase the incidence of IIHBC (5, 19), while
timely removal of fully expanded leaves at tuber initiation can reduce levels
(5, 17).
Rapid growth of Russet Burbank tubers has been linked to an increase in HHIBC
(15). Although large tubers have been associated with increased HHIBC, Crumbly et. al.
(4) and Hiller and Koller (15) found similar tuber growth rates among HHB C-susceptible
and resistant cultivars.
Because tubers on the same plant vary in size and growth rate (1, 22, 26), it is not
clear whether HH or BC is initiated early in crop development with no increase during
various stages of tuber growth, or initiated throughout the season. It is possible that BC
could decline over time, but the fate of mildly affected young tubers is not known. In
young tubers, BC could either dissipate (14, 16) as tubers grow, or affected tubers could
be reabsorbed and replaced by new tubers (3). A nondestructive evaluation of tubers for
HHBC throughout the growing season is clearly not possible. However, to progress in
our understanding of HHBC, we need to determine how tuber size or growth rate at
specific times are associated with HFIBC levels.
Both planting date and soil nitrogen (N) status can influence potato crop growth
stages. Differences in plant or stem size may affect tuber susceptibility to HHBC. A delay
in planting or additional N fertilizer can delay tuber initiation (15, 28), promote canopy
growth (27) and delay plant senescence (10, 12). Although a delayed planting and
increased availability of soil N have similar effects on potato growth patterns, late planting
has been shown to reduce the incidence of HIIBC (13, 16, 17, 21) whereas elevated N
levels promote JHIHBC (24, 25, 32).
This study evaluated effects of planting date and N regimes on Russet Burbank vine
and tuber growth patterns. Tuber distribution was evaluated throughout the season to
establish relationships with HHBC.
Materials and Methods
Experimental Design and Data Collection
A factorial combination of
treatments were arranged in a randomized split-split-split-split-plot design and replicated 5
times. Years were main plots, planting dates were subplots, preplant nitrogen (N) regimes
were sub-subplots, sample dates were sub-sub-subplots, and weight ranges were sub-sub-
sub-subplots. Plots were sampled on 10 dates during the 1985-1987 growing seasons for
tuber number, tuber weight, and hollow heart-brown center (F1IHBC) by weight range.
Weight range was a random factor since it was determined as plants were sampled
(Figs. 7.1 and 7.2). All other factors were fixed. The number of stems per plant, vine
biomass, total yield, and total HHBC were also measured. For these parameters the design
was a split-split-split-plot with years as main plots, planting dates were subplots, preplant
nitrogen (N) regimes were sub-subplots, and sample dates were sub-sub-subplots (Figs.
7.3-7.6). The entire experiment was repeated on adjacent plots in each of the three years.
Therefore, years represent differences in both plot location and time.
Low (56 kg ha-i) and high (224 kg ha-i) preplant N regimes were used in all three
seasons. Nitrogen regimes differed in the timing of N application(s) (Fig. 6.1). Large (56
kg ha-i) N applications were begun 3 weeks (wks) after brown center (BC) initiation.
These weekly N applications continued longer for the low preplant N regimes so that all
treatments reached a total seasonal N rate of 448 kg ha1 (Fig. 6.1). In 1986 and 1987 two
additional low (56 kg ha-i) preplant N regimes were added. These two regimes began
receiving large (56 kg ha-i) weekly N applications 1 and 2 wks after initiation of BC rather
than 3 wks as for the previously described treatments. Therefore, the low preplant N
regimes had seasonal N applied 1, 2, or 3 wks later in the season than the high preplant N
regime. When illustrating data from only the low and high preplant N regimes, which
began receiving large N applications 3 wks after BC initiation (data from all four years), the
legend refers to the treatments as Low and High. In figures illustrating data from all three
low preplant N regimes (large N applications begun 1, 2, or 3 wks after BC initiation) and
the high preplant regime (large N applications begun 3 wks after BC initiation), the legend
refers to the treatments as Low-lwk, Low-2wk, Low-3wk, and High-3wk.
Field Plots - Russet Burbank potatoes were grown near Plymouth, WA in
Quincy sandy loam [Typic Torripsamments (Mixed, mesic)} (see Chapter 6 Materials and
Methods and appendix, Table A. 1 for initial soil test values). Seed tubers, stored at 6 C
prior to planting, were cut into pieces ranging from 52-79 g and planted 25 cm apart with
86 cm between rows in early and late April. Plots consisted of 6 rows, 10.7 m long.
Fertilizer was broadcast and disk-incorporated into the top 0.2 m of soil prior to
planting at the following rates (kg ha4): 56 or 224 N, 168 P, 280 K, 56 S, 2 B, 11 Zn, 11
Mg, 6 Mn and 2 Cu. Nitrogen was applied to all plots at 11 kg N ha1 wk through a
linear move irrigation system from plant emergence until the first symptoms of brown
center (BC) were observed, at which time N was withheld for 1, 2, or 3 wks (see Fig. 6.1
and appendix, Table A.2). Plots were considered to have reached emergence when plants
from 95% of the planted seed pieces appeared above the ground. Post-BC initiation N
applications (56 kg ha-1 wkl) were then continued for a seasonal total of 448 kg N ha4 in
accordance with local cultural practices. Materials and Methods are comprehensively
described in Chapter 6.
Growth and Analyses - Five to 10 plants were collected weekly from each plot
beginning in early June and continuing through August (10 dates). The 10 data sets were
grouped by date and reported as 5 bimonthly samplings. The first plant collected in each
plot was randomly selected. Additional plants were collected by selecting every second
plant in the same row. Sampling continued until at least one of each plant-type (single-,
double-, triple-, and multiple-stem) were harvested. Sampling began at tuber initiation
which coincided with the first observed swelling of any stolon tip in a given treatment,
regardless of which plot tuber initiation first occurred in. Tuber initiation frequently
occurred approximately 1 wk after 95% plant emergence.
Plants were harvested and vines and tubers were weighed. Stems per plant were
counted after the vines were weighed. Tubers were counted, weighed, and assigned to one
of the following weight ranges: 0-13 g, 14-27 g, 28-57 g, 58-113 g, 114-170 g and> 170
g. A primary weight range is defined as the range(s) containing the most tuber weight.
After weighing, tubers were cut longitudinally, examined for HHIBC, and recorded.
Any necrotic area or separation of tissue in the pith region was scored as BC or HH,
respectively. The level of HHBC was based on the proportion of tubers with symptoms
rather than tuber weight, as reported elsewhere (31, 37).
Statistical Analyses - Data were analyzed by analysis of variance (ANOVA).
Differences were determined using Duncan's new multiple range test (8). Percentage data
were transformed [(X+0. 5)0.5] prior to analysis to satisfy the assumptions of normality for
the ANOVA (23) as utilized by Nelson and co-workers (29, 30, 31). Data from each year
was analyzed individually and a combined analysis of all three years was also done. The
variability attributed to year interactions were of a far less magnitude than variability
attributed to either fertility or planting date (main effects) (Table A. 10). Planting date and
fertility interactions are much smaller in magnitude than main effects. Therefore, only main
effects are presented.
HFIBC data were evaluated after weighting values across years (34) for figure 7.4.
This permitted analysis of data without bias from year-to-year influences due to differences
in magnitude, but not in the ranked performance of treatments. Percentages add to 100 for
the treatment with the highest number of HHBC tubers in a given year.
Resulls
In early June, 100% of the tubers (Figs. 7. la and b), weighed 13 g or less. As
expected, tuber yield and size increased as the season progressed. The incidence of HIHIBC
was influenced by tuber size (Fig. 7.2 compared to Fig. 7.lb). Forty to 50% of the total
yield (Fig. 7.lb) and HHBC (Fig. 7.lc) were found in a specific tuber weight range (see
arrows, Figs. 7.la-c) which increased in average tuber size as the season progressed. We
termed this category the 'primary weight range."
Small tubers (0-13 g) were relatively free of HHBC at any sampling date (Fig.
7.2). Only 15-20% of the HHBC occurred in the smallest tuber size range in June (Fig.
7.lc) even though most tubers weighed 0-13 g (Fig. 7.lb). No appreciable HELBC was
found in small tubers (<27 g) in late July and August (Fig. 7.2).
By late June, about 50% of the total HHBC occurred in tubers weighing 14-27 g
(Fig. 7.lc), even though only 10% of tubers were in this weight range (Fig. 7.la).
Approximately 50% of the HHBC occurred in the primary weight range during the season
(Fig. 7. ic), even though < 25% of the total tubers were represented (Fig. 7. la).
The percent of tubers with HHBC in each weight range is presented in figure 7.2.
Small tubers (0-13 g) showed a low incidence of HFTBC (< 3.0%) on all dates. The
incidence of HHBC was highest in the primary tuber weight range, which increased in
average tuber size as the season progressed. Tubers larger and smaller than those in the
primary weight range were less susceptible to HHBC. For example, in early July, 28-113
g tubers (the primary weight range) had the highest incidence of HF{BC with approximately
15% of the tubers affected. Larger (> 113 g) and smaller (<28 g) tubers had less HF]BC.
b)
a)
100
a
90
EL0'JE
80
80
'0JL8.Y
EJULY
----O--- L JULY
70
70
00
AU0UST
AUUUST
a
00
_.1
w
z
00
50
e
w
S
55
40
-J
b
b
b
20
I:
d
b
0-03
:
14-27
29-57
58-113
114-170
>170
:
0-13
14-27
TUBERS WEIGHT RANGE (g)
25-57
58-113
114-170
>170
TUBER WEIGHT RANGES (g)
C)
k
50
10
00
50
U
S
40
I-
20
10
O
0-13
14-20
21-51
58-Ill
114-110
>110
TUBER WEIGHT RANGE (g)
Fig. 7.1. Distribution of total Russet Burbank:
a) tuber number, b) tuber
yield, and c) hollow heart-brown center (HHBC) over time. E = early; L
= late. Means with the same letter within the same sampling date are not
significantly different at P < 0.05 (Duncan). Arrows indicate the tuber
weight range with the highest total % of tuber numbers, yield, or HHBC
at the various sampling dates.
Complete statistical comparisons that
include sampling dates are presented in appendix Table A.!!.
91
30
25
20
0
to
I
I
I
F
15
Cl)
w
to
I
a
b
b
C
0-13
1427
2857
58113
114170
>170
TUBER WEIGHT RANGE (g)
Fig. 7.2. Effects of Russet Burbank tuber size and sampling date on the
incidence of hollow heart-brown center over time. E = early; L late.
Means with the same letter within the same sampling date are not
significantly different at P < 0.05 (Duncan). Complete statistical
comparisons that include sampling dates are presented in appendix Table
A.!!.
92
Although there was little HIHBC in the 14-27 g and 114-170 g weight ranges in early July,
a large number of tubers was represented in these weight ranges because data were pooled
across treatments and years.
While susceptibility to HIHBC shifted to larger tubers over time, HFIBC increased
most rapidly (from 6.1 to 27%) in the largest (> 170 g) tubers between late July and
August (Fig. 7.2). At this same time, the overall incidence of HHBC also increased in the
largest tubers (Fig. 7.lc).
When results were pooled across sampling dates, a positive relationship between
hollow heart-brown center (HHBC) and tuber size (up to 58-113 g tubers) was evident,
regardless of year (Fig. 7.3a) or planting date (Fig. 7.3b). Levels of HHBC peaked at 8.6
and 9.3% for 1986 and 1987, respectively (Fig. 7.3a). Relative to 58-113 g tubers, 16.8
and 42.3% less HHBC occurred in the two largest tuber size ranges (114-170 and> 170 g)
for late-planted potatoes (Fig. 7.3b). No significant tuber size x year interaction effects on
HFTIBC incidence were evident.
Vine weight in early-planted potatoes peaked at 1174-1202 g per plant in late July
(Fig. 7.4a). In late July, vines of potatoes planted late were 18.7% heavier than those
planted earlier. This difference increased to 31.5% at the August sampling. Potatoes
planted early also produced 15.5% fewer stems per plant than those planted late (Fig. 7.5).
Compared to the late planting, potatoes planted early produced tuber yields 28.6
and 17.9% higher at the late July and August samplings (Fig. 7.4b). Tuber yield per plant
increased by 100%, regardless of planting date, during the 2 wks between late July and
mid-August (Fig. 7.4b). During the same period, the incidence of HHBC in potatoes
planted early and late increased 28.6 and 37.5%, respectively (Fig. 7.4c). Late-planted
potatoes showed 28-30% less HHBC at each sampling date than those planted early.
Stem numbers were unaffected by preplant nitrogen (N) regime (Fig. 7.5). Vine
biomass was 19% less in the low preplant N regime compared to the high preplant N
regime during late June (Fig. 7.6a). Fresh weights of vines for both preplant N regimes
increased with each sampling. By August, high preplant N plants had 71% more vine
biomass than low regime plants (1802 vs. 1056 g). The low preplant N regime with large
(56 kg ha') applications of N started 1 or 2 wks after BC initiation had 23.6 to 32.7% less
vine biomass, respectively, than the high preplant N regime by late July (Fig. 7.6a insert).
The low N-3 wk regime produced 12% less vine biomass than the low preplant N-i wk
and 2 wk regimes in late July. Vine weights for all the low preplant N regimes were 34.8
to 4 1.2% lower than for the high regime in August.
Tuber yields increased rapidly after early June (Fig. 7.6b).
Yields were
approximately equal for the low and high preplant N regimes through early July. The low
93
a)
10
9
8
7
0
I
I
6
5
3
2
0
0-13
14-27
28-57
58-113
114-170
>170
TUBER WEIGHT RANGE (g)
-- EARLY
b)
anting
ter in
same
UI
"iiiiIiiiOiiiiiiiiii
uiiiiiiniiiiiiiiiiiiiiiiiii
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3.
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2.
I-
0,
2.
2.
2.
EARLY
LATE
PLANTING DATE
LOW
HIGH
PREPLANT NITROGEN
Fig. 7.5. Effects of preplant nitrogen regime 156 (Low) or 224 (High) kg
ha- '1 and planting date (Early and Late) on the number of Russet Burbank
stems per plant. Means with the same letter are not significantly different
at P < 0.05 (Duncan).
b)
2000
AU0000
L JULY
a
b
;::4
FERTILITY
1200
-I.
Co
I
_J
0
I
LU
I
>-
I
LU
LU
600
600 .
z
I
I
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LOW-OW K
I
400
400
--LOW-OWK
---HlGH-2WK
0--- HIGR-OWK
EJUNE
LJUNE
EJULY
LJULY
AUGJSI
EJUNE
LJUNE
DATE
I
I
LJULY
PLJG.JST
DATE
ab
1 0
a
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I
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8-II
:
2
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0
EJUNE
LJUNE
EJJLY
LJULY
AUGJSr
DATE
Fig. 7.6.
Seasonal effects (E = early; L late) of preplant nitrogen (N)
regime [56 (Low) or 224 (High) kg ha- on Russet Burbank: a) vine
biomass, b) tuber yield, and c) % hollow heart-brown center (HIEIBC).
Insert shows effects of N regime for the two latest sampling dates (late
July and August) for two years (1986 and 1987). N regimes include N
applications (56 kg ha- wk- began 1, 2, or 3 wks after brown center
(BC) initiation. Legend describes amount of preplant N and delay after
1J
1
1)
BC initiation before N applications began (example:
Low-2wk).
Means
with the same letter from the same sampling date are not significantly
different at P < 0.05 (Duncan).
97
preplant N- lwk regime showed tuber yields similar to those of the high regime in late July
(Fig. 7.6b insert). By August, all three low preplant N regimes showed 15.9 to 17.9%
higher yields per plant than the high regime. Yields were similar for the low preplant N
regimes in late July and August.
Less than 0.5% of the tubers had HHBC in early June (Fig. 7.6c), but the
incidence of HHBC increased thereafter. In late June, the low preplant N-3 wk regime
showed 3 times as much HHBC (4.6 vs. 1.5%) as the high N regime. Hollow heartbrown center in the low preplant N regime plateaued during July and peaked, at 8%, in
August. Hollow heart-brown center was higher in tubers from the high N regime than in
the low preplant N regime after late June. The incidence of HTHI1BC increased in the high
preplant N regime from 1.5% in early June to 13.9% at season's end.
The low preplant N regimes showed low levels of HHIBC (3.9 to 7.9%) in late July
(Fig. 7.6c insert). However, seasonal applications of N begun 1 wk after BC initiation for
the low preplant N regime or the high preplant regime resulted in similar incidences of
HHBC, approximately 8% in late July and> 13% in August. Low preplant N-2 wk and 3
wk regimes had only 6.8 and 8.1% HHBC, respectively, through August.
Discussion
Tuber size is less influential than tuber growth rate on the incidence, of HHBC.
More tubers of similar size (i.e. primary weight range) growing at the same rate, would
increase competition for photosynthates, water, and mineral elements possibly leading to an
increased incidence of HHBC. Large tubers are not necessarily more susceptible to HHBC
than small tubers. This relationship can be seen by examining tubers which had exceeded
170 g by late July (Figs. 7.la and b). Less than 6% of these large tubers were affected by
HHBC (Fig. 7.2). Although these tubers were large, they were few, and grew with less
inter-tuber competition than most tubers which enlarged later and faster.
The incidence of HEIBC in larger tubers, however, increased over time (Table
A. 11) suggesting that small tubers with HHBC grew larger or that new initiation of HHBC
occurs in large tubers (Fig. 7.2). The total number of tubers per plant is relatively constant
late in the season (see Chapter 3). Since the total incidence of HFIBC increases with time,
it appears that large tubers develop additional HHBC late in the season. Growth of tubers
previously affected with HHBC can not fully account for the increased incidence of HIHBC
in large tubers in late summer.
One type of HHIBC (late-season) in Russet Burbank tubers may resemble that
expressed by Norgold Russet and Russet Rural (31, 39). This form (17, 38) increases
during the latter part of the season (late July and August, Fig. 7. ic), as tubers enlarge, and
causes a physical tearing of internal tissues. Late-season hollow heart may differ from
HHBC expressed early in the season. This difference between the two types could help
explain these data which suggest that differences in HHIBC levels between planting dates
are due to a lower incidence of HHBC in late-developing, large tubers (Fig. 7.3b).
Differences in HIIBC with planting date are only apparent in tubers weighing at least 114 g
(Fig. 7. ib). Tubers greater than 114 g did not exist until late July (Fig. 7.3a).
Several explanations for reduced H}IIBC in late-planted potatoes have been
proposed: 1) warmer weather conditions later in the season may be less favorable for
development of HHIBC (11, 13, 16, 21); and/or 2) potatoes planted later have a low rate of
tuber growth (2, 6, 9) resulting in either less initiation (Fig. 7.4b) or more dissipation (13,
14) of brown center (BC). Although the above explanations may be important, the
increased number of stems associated with delayed planting probably strongly influenced
the incidence of HHIBC and vine biomass in this study. Planting date altered the number of
stems per plant (Fig. 7.5) and consequently vine biomass per plant (Fig. 7.4a). Multiplestem plants were less susceptible to HJ-IBC than single-stem plants (37). Potatoes planted
late would emerge from physiologically older seed tubers than those planted earlier. This
would increase both the number of stems (and vine biomass) and tubers per plant, and
reduce the incidence of HHBC due to slower individual tuber growth in multiple-stem
plants and reduced tuber size. Iritani (18) showed a relationship between increasing
numbers of stems and reduced tuber size.
The high preplant nitrogen regime increased vine biomass (Fig. 7.6a) and the
incidence of hollow heart-brown center (HHBC) (Fig. 7.6c). Late planting also increased
vine biomass (Fig. 7.4a) but actually reduced the incidence of HHBC (Fig. 7.4c).
Nitrogen regime and planting date may affect the expression of HHBC and vine biomass
through different mechanisms. Nitrogen management did not alter stem number (Fig. 7.5);
therefore, the high nitrogen regime probably caused a general increase in size of all vines.
Differences in vine biomass induced by nitrogen regime (Fig. 7 .6a) are most likely caused
by assimilate partitioning differences between tubers and shoots. Total fresh weight of
vines and tubers differed by less than 10% between the two nitrogen regimes (add data
from Figs. 7,6a and b).
Early season levels of HHBC were higher with low preplant nitrogen regimes than
with the high nitrogen regime (late June, Fig. 7.6c), probably because low initial soil
nitrogen levels favored early tuber formation and development of large tubers which were
more susceptible to HHBC (7, 34). Vine biomass differences were not large at this stage
of growth. Slowing vine growth may help reduce early-season HHI3C (before late July),
but it had little effect in this and other (17, 31) studies on late-season HHBC. Large
difference in both vine biomass and HHBC levels between the nitrogen regimes occurred
after late June (Figs. 7.6a and c). This supports speculation that slowing vine biomass
strongly influences the incidence of HHBC (17, 19). The stable period of HI{BC
incidence in the low preplant nitrogen regime (Fig. 7.6c) could be due either to lack of
initiation of new HHBC or to the dissipation of HHBC which may be replaced by new
HHBC. These mechanisms could not be differentiated here.
A delay in large applications of nitrogen for more than 1 wk after BC initiation was
required in the low preplant nitrogen regime to obtain both increased tuber growth and
reduced HHBC (Figs. 7.6b and c inserts); when applications were delayed for only 1 wk
vine biomass and the incidence of HHBC were similar to those of the high preplant
nitrogen regime. Although the low preplant nitrogen regime reduced HF]BC incidence, it is
not clear whether lower preplant nitrogen, or longer applications of late-season nitrogen
were responsible for decreased HHIBC levels.
In summary, HHBC increased as the season progressed and tuber growth rates
increased. Growth of small tubers with HHBC cannot entirely account for high levels of
HFIBC in large tubers late in the season. These results suggest that Russet Burbank tubers
may be susceptible to both early and late forms of HHBC. The initiation of both types of
HI-lB C and possible dissipation of early-season HHBC will determine the level of HHBC
at harvest. Although planting date and nitrogen regime effect HFJBC, it is important to
determine to what extent early HFEBC initiation, HHBC dissipation and late HHBC
initiation are altered. Planting late reduced late-season HHBC. Total seasonal expression
of HIHIBC was also reduced by a low preplant nitrogen regime even though the late-season
incidence of HHBC was not affected.
Tuber size was less important than tuber growth rates in causing HHBC within the
primary weight range. Tubers outside the primary weight range were less susceptible to
HHIBC throughout the season.
Variations in planting date and nitrogen management altered both plant and tuber
growth patterns and the incidence of HHBC, apparently through different mechanisms.
Delayed planting increased the number of stems per plant which, in turn, reduced the
number of rapidly growing tubers; this was evident because the increase in stem numbers
per plant still produced less tuber yield. A reduction in tuber growth rates also decreased
late-season HI-lB C.
100
Delaying applications of nitrogen for more than 1 wk past BC initiation with a low
preplant nitrogen regime increased tuber growth, reduced vine biomass, and lowered the
incidence of HHBC during the early growing season.
Uteratun Cited
1.
Ahmed, C.M.S. and G.R. Sagar. 1981. Volume increase in individual tubers of
potatoes grown under field conditions. Potato Res 24:279-288.
2.
Boyd, D.A. and G.V. Dyke. 1950. Maincrop Potato growing in England and
Wales. NAAS Q Review 10:47-57.
3.
Cho, J.L., D.C. Nelson and M.E. Duysen. 1973. Comparison of growth and
yield parameters of Russet Burbank for a two year period. Am Potato J 60:569575.
4.
Crumbly, I.J., D.C. Nelson and M.E. Duysen. 1973. Relationships of hollow
heart in Irish potatoes to carbohydrate reabsorption and growth rate of tubers. Am
Potato J 50:266-274.
5.
Dinkel, D.H. 1960. A study of factors influencing the development of hollow
heart in Irish Cobbler potatoes. Ph.D. Thesis. Univ of Minn, St. Paul. pp 28-36.
6.
Doncaster, J.P. and P.H. Gregory. l948. The spread of virus diseases in the
potato crop. In: Agric Res Comm Rpt Series 7 HMSO, London. pp 1-7.
7.
Dubetz, S. and J.B. Bole. 1975. Effect of nitrogen, phosphorus and potassium
fertilizers on yield and components and specific gravity of potatoes. Am Potato J
52 :399-405.
8.
Duncan, D .B. 1951. A significance test for differences between ranked treatments
in an analysis of variance. VirginiaJ Sci 2:171-189.
9.
Dyke, G.V. 1956. The effect of date of planting on the yield of potatoes. J Agric
Sci, 47:122-138.
10.
Dyson, P.W. and D.J. Watson. 197l. An analysis of the effects of nutrient
supply on the growth of potato crops. Ann AppI Biol 69:47-63.
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11.
Fallah, A.S. 1979. The effect of temperature, nitrogen, foliage removal and root
pruning on growth and brown center development in the potato. M.S. Thesis.
Washington State University, Pullman. pp 4 1-49.
12.
Harris, P.M. 1978. Mineral nutrition. In: The Potato Crop (P.M. Harris, ed).
Chapman and Hall, London. pp 195-243.
13.
Hiller, L.K. and D.C. Koller. 1977. First year results on hollow heart research.
Spud Topics, 21:23-24.
14.
Hiller, L.K., D.K. Koller and R.W. Van Denburgh. 1979. Brown center of
potaotes--What we have learned. In: Proc Wash State Potato Conf, Moses Lake.
pp 21-27.
15.
Hiller, L.K. and D.C. Koller. 1981. Brown center/hollow heart of potatoes--What
do we know? In: Proc Wash State Potato Conf, Moses Lake. pp 73-80.
16.
Hiller, L.K. and D.C. Koller. 1982. Brown center and hollow heart as a quality
factor. In: Proc Wash State Conf, Moses Lake. pp 10 1-108.
17.
Hiller, L.K., D.C. Koller and R.E. Thornton. 1985. Physiological disorders of
potato tubers. In: Potato Physiology (P.H. Li, ed). Academic Press, Orlando,
FL. pp 389-443.
18.
Iritani, W.M., L.D. Weller and N.R. Knowles. 1983. Relationships between
stem number, tuber set and yield of Russet Burbank potatoes. Am Potato J 60:423431.
19.
Kallio, A. 1960. Effect of fertility level on the incidence of hollow heart. Am
Potato J 37:338-343.
20.
Kleinkopf, G.E., and D.T. Westermann and R.B. Dwelle. 1981. Dry matter
production and nitrogen utilization by six potato cultivars. Agron J 73:799-802.
21.
Koller, D.C. and L.K. Hiller.
1982.
The effect of planting date and soil
temperature on brown center and hollow heart in Russet Burbank potatoes. Am
Potato J (abstr) 59:475.
22.
Krijthe, N. 1955. Observations on the formation and growth of tubers on the
potato plants. Netherlands J Agric Sci 3:291-304.
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23.
Little, T.M. and F.J. Hills.
24.
McBride, R.L. 1985. Potash fertilizer effects on yield, hollow heart, and nutrient
levels in potato tubers and petioles. M.S. Thesis. Oregon State Univ, Corvallis.
pp 22-25.
25.
McCann, I.R. and J.C. Stark. 1989. Irrigation and nitrogen management effects
on potato brown center and hollow heart. HortSci 24:950-952.
26.
Moorby, J. 1967. Inter-stem and inner-tuber competition in potatoes. Eur Potato
J 10:189-205.
27.
Moorby, J. 1968. The influence of carbohydrate and mineral nutrient supply on
the growth of potato tubers. Ann Bot 32:57-68.
28.
Moorby, J. and F.L. Milthorpe. 1975. Potato. In: Crop Physiology--Some Case
Histories (L.T. Evans, ed). Camb Univ Press, London. pp 225-257.
29.
Nelson, D.C. 1970. Effects of planting date, spacing and potassium on hollow
1978. Transformations. In: Agricultural
Experimentation, Design and Analysis. (Little, T.M. and F.J. Hills, eds). John
Wiley and Sons, New York. pp 139-164.
heart in Norgold Russet potatoes. Am Potato J 47:130-135.
30.
Nelson, D.C. and M.C. Thoreson. 1974. Effect of root pruning and sub-lethal
rates of dinoseb on hollowheart of potatoes. Am Potato J 51:132-138.
31.
Nelson, D.C. and M.C. Thoreson. 1986. Relationships between tuber size and
time of harvest to hollow heart initiation in dryland Norgold Russet potatoes. Am
Potato J 63:155-161.
32.
Ojala, J.C., JC. Stark, G.D. Kleinschmidt, R.G. Beaver and E.V. Musselman.
1989. Brown center and hollow heart in potatoes. Univ of Idaho Ext Bull 691:1 -
6.
33.
Sattelmacher, B. and H. Marschner. 1979. Tuberization in potato plants as
affected by application of nitrogen to the roots and leaves. Potato Res 22:49-57.
34.
Steel, R.G.D. and J.H. Torrie. 1960. Analysis of variance III: Factorial
experiments. In: Principles and procedures of statistics (Steel, R.G.D. and J.H.
Torrie, eds). McGraw-Hill, New York. pp 180-193.
103
35.
Van Denburgh, R.W. 1979. Physiological changes during the development of
brown center in 'Russet Burbank" potatoes. Ph.D.Thesis. Washington State
Univ, Pullman. pp 43-45.
36.
Van Denburgh, R.W., L.K. Hiller and D.C. Koller. 1980. The effect of soil
temperatures on brown center development in potatoes. Am Potato J 57:37 1-375.
37.
Veilleux, R.E. and F.I. Lauer. 1981. Breeding behavior of yield components and
hollow heart in tetraphoid-diphoid vs. conventionally derived potato hybrids.
Euphytica 30:547-561.
38.
Wenzl, V.H. 1965. Die histologische unterscheidung dreier typen von
hohlerzigkeit b ei kartoffelknoll en. Z. Pflanzenkr. (Pfanzenp athol.) und
Pflanzenschutz 72:411-417.
39.
Werner, HO. 1926. The hollow heart situation in the Russet Rural potato. Potato
AssocAm 1:45-51.
40.
Westermann, D.T. and G.E. Kleinkopf. 1985. Nitrogen requirements of potatoes.
Agron J 77:616-621.
104
[IiTLi I
iNFLUENCES OF NITROGEN FERTILIZATION AND PLANTING DATE ON
RUS SET BURBANK S TEM HIERARCHY, TUBER GROWifI, AND
HOLLOW HEART-BROWN CENTER
Abs Iract
Manipulation of plant nitrogen levels and planting schedules greatly influence the
productivity of potato plants The objective of this study was to quantify relationships
between these practices and tuber growth and hollow heart-brown center (HHBC) from
large (dominant) and small (nondominant) stems on single-, double-, triple- and multiplestem plants.
Russet Burbank potatoes were evaluated over 4 years on a virgin Quincy sandy
loam in a split plot design using low and high preplant nitrogen (N) regimes and 2 planting
dates. Total N applications were similar for all treatments, but the seasonal distribution
varied. Plants were collected bimonthly from early June through mid-August. The number
of stems per plant, tuber number and yield on each stem, and the incidence of HHBC were
recorded.
Influences of stem hierarchy on tuber growth and HHBC were predictable and
consistent over time. Dominant (large) stems produced more tubers, yield, and HHBC
than nondominant (small) stems.
Regardless of cultural practice or plant-type, there was evidence for 2 distinct stages
of HHBC development (early- and late-season) and a period during which early-season
HHBC may dissipate.
These stages of HHBC development and dissipation were
associated more with plant growth stage than chronological date.
Delayed planting increased the number of stems per plant, resulting in more
nondominant stems and triple- and multiple-stem plants. Tubers from early plantings had
more HHBC because there were more HHBC-susceptible plant-types and these plants had
more time for late-season HHBC to develop. Although late plantings reduced the number
of susceptible plant-types, tubers on large (dominant) susceptible stems grew faster and
had more early-season HHIBC than tubers on similar stems from early-planted potatoes.
Preplant N regime did not alter the number of stems. Neither N nor planting dates
changed relative stem productivity (tuber number and yield). However, dominant stems
for single- and double-stem plants were more productive from the early-planted and low
preplant N regime potatoes than from the opposing treatments.
105
Although tubers on dominant stems of the low preplant regime were fast growing,
they had less HHBC than tubers from the high regime. The low regime showed more
dissipation of early-season HHBC, especially on dominant stems from single- and doublestem plants, than the high preplant N regime.
Iniroduclion
Researchers and growers have traditionally modified nitrogen (N) fertilizer regimes
and/or planting schedules to enhance yield and quality of potatoes. However, results of
these modifications are not always predictable and strongly depend on the growing season.
Potatoes often respond similarly to increased preplant N and delayed planting.
Effects of these two practices may also be additive (22). Both can delay tuber initiation (5,
27, 42, 44, 45) and growth (22, 23, 31). Increased preplant N or delayed planting can
also lead to excessive canopy growth (7, 12, 19) and increased tuber numbers (31),
accompanied by reduced tuber size and yield (15, 18, 19, 26). High N and delayed
planting are not always undesirable. Researchers have documented increased tuber yield
and quality with optimum N timing (4, 8, 21, 41, 51) and delayed planting (14, 24).
Effects of high N and delayed planting on the internal tuber disorder hollow heart-
brown center (HHBC) vary. Nelson's work on Norgold (34) documented increased
hollow heart with later planting. However, Hiller and co-worker's (14) six-year study on
Russet Burbank indicated reduced HHBC with delayed planting. High N effects on the
disorder are also variable, having shown increased (20, 38), decreased (40), or unchanged
levels of HBBC (2).
Our previous research (Chapter 7) indicated two distinct stages of HHBC,
occurring early and late in the growing season. It is possible that dissipation of earlyseason HHBC is affected by early cultural practices (13). Season-long monitoring is
required to determine the relative contributions of early-season HHBC development, earlyseason dissipation, and late-season development to final HHBC levels and the degree to
which each is altered by cultural practices. Differences in expression of these three factors
for a given season may explain varied results reported by others.
Influences of preplant N regime and planting date on stem hierarchy and tuber
growth may also help explain discrepancies. Patterns of HHBC development that are
apparent in individual stem-types may not be obscured when similar stem-types are
arranged together. However, little is known about how tuber distribution and growth
among stems respond to cultural management. Most researchers agree that increased N
106
and delayed planting
can increase the number of stems per plant and/or
the ratio of stem length to tuber weight (26, 45, 46, 47, 48). Stems on the same plant are
(33)
(10, 16, 17)
thought to perform independently of each other (39), yet N applications do not reduce inter-
plant competition
(9, 30).
No data were found on the effect of planting date on stem
hierarchy.
Tuber susceptibility to HHBC in different plant-types has been inconsistent. In this
study, single-stem Russet Burbank plants were more susceptible to HHBC than multistemmed plants (Chapter 3). As stems per plant increase, HHBC may also increase (32,
50). Werner's (50) work, however, specified that 2-3 stems per plant favored maximum
levels of HHBC. It is not known whether increased HHBC associated with early
plantings, and sometimes with changes in N management, is due to increased numbers of
susceptible stem-types, higher tuber growth rates on all stem-types, changes in the
distribution of tubers and their growth among stems, and/or differences in either early- or
late-season HHIBC development or early-season HHBC dissipation; all may be important.
This research included season-long monitoring of HHIBC associated with effects of
N regime and planting date on stem number, tuber growth, and tuber distribution among
various stem-types.
Stem hierarchy was evaluated by quantifying effects of stem number and size on
tuber number and yield, and HHBC levels on dominant (large) and nondominant (small)
stems from single-, double-, triple- and multiple-stem plants.
Matetials and Methods
Experimental Design and Data Collection - A factorial combination of
treatments were arranged in a randomized split-split-split-split-plot design and replicated 5
times. Years were main plots, planting dates were subplots, preplant nitrogen (N) regimes
were sub-subplots, sample dates were sub-sub-subplots, and stem-types were sub-subsub-subplots. Plots were sampled on 10 dates during the 1985-1987 growing seasons.
Planting date, nitrogen regime, and sampling date were preplanned (fixed) factors. Stemtype was a random factor since it was determined as plants were sampled. The entire
experiment was repeated on adjacent plots in each of the three years. Therefore, years
represent differences in both plot location and time.
Low (56
kg ha1) and high
(224
kg ha4) preplant N regimes were used in all three
seasons. Nitrogen regimes differed in the timing of seasonal (post-emergence) N
applications. Large (56 kg ha-') N applications were begun 3 weeks (wks) after brown
107
center (BC) initiation. These weekly N applications continued longer for the low preplant
N regime so that both treatments reached a total seasonal N rate of 448 kg ha-1. Therefore,
the low preplant N regime had seasonal N applied 3 wks later in the season than the high
preplant N regime.
Field Plots
Russet Burbank potatoes were grown near Plymouth, WA in
Quincy sandy loam [Typic Torripsamments (Mixed, mesic)] (see Chapter 6 Materials and
Methods and appendix, Table A. 1 for initial soil nutrient values). Seed tubers, stored at 6
C prior to planting, were cut into pieces ranging from 52-79 g and planted 25 cm apart with
86 cm between rows in early and late April. Plots consisted of 6 rows, 10.7 m long.
Fertilizer was broadcast and disk-incorporated into the top 0.2 m of soil prior to
planting at the following rates (kg ha'-1): 56 or 224 N, 168 P, 280 K, 56 S, 2 B, 11 Zn, 11
Mg, 6 Mn and 2 Cu. Nitrogen was applied to all plots at 11 kg N ha4 wk4 through a
linear move irrigation system from plant emergence until the first symptoms of brown
center (BC) were observed, at which time N was withheld for 3 wks. Plots were
considered to have reached emergence when plants from 95% of the planted seed pieces
appeared above the ground. Post-BC initiation N applications (56 kg ha1 wk"1) were then
continued for a seasonal total of 448 kg N ha1 in accordance with local cultural practices.
Materials and Methods are comprehensively described in Chapter 6.
Growth and Analyses - Five to 10 plants were collected weekly from each plot
beginning in early June and continuing through August (10 dates). The 10 data sets were
grouped by date and reported as 5 bimonthly samplings. The first plant collected in each
plot was randomly selected. Additional plants were collected by selecting every second
plant in the same row. Sampling continued until at least one of each plant-type (single-,
double-, triple-, and multiple-stem) were harvested. Sampling began at tuber initiation
which coincided with the first observed swelling of any stolon tip in a given treatment,
regardless of which plot tuber initiation first occurred in. Tuber initiation frequently
occurred approximately 1 wk after 95% plant emergence.
Plants were harvested and vines and tubers were weighed. Stems per plant were
counted after the vines were weighed. Levels of HHBC were reported by tuber count
rather than tuber weight, as reported elsewhere (36, 49).
Plant-types were categorized according to the number of stems arising from the
seed piece. Single-, double-, triple-, and multiple-stem plants were identified. Although
any plant with more than one stem is technically multiple-stemmed, for convenience we
define "multiple" as any plant with four or more stems.
Stem hierarchy was based on observations of size (girth and length of the stem) for
stems from each plant.
"ominant" or largest stem(s) were designated as D.
'Nondominant" refers to stem(s) other than a dominant (primary or secondary) stem and
were designated as N. The term S-D denotes a stem from a .ingle- or double-stem plant.
The term T-M refers to a stem from a triple- or multiple-stem plant. D, S-D, then, refers to
dominant stem(s) from a .ingle- or double-stem plant. D, T-M refers to the dominant or
largest two stems from a Iriple- or multiple-stem plant. N, T-M refers to ondominant
stem(s) from a Iriple- or multiple-stem plant. Nondominant stems occur only on triple- and
multiple-stem plants. The definitions and designations of stem and plant identification are
summarized in Table A.4.
Statistical Analyses Data from individual stems were grouped according to:
1) stem dominance characteristics (D or N), and 2) numbers of stems (S-D or T-M) per
plant. Statistical analyses were performed on all growth parameters by analysis of variance
(ANOVA). Significant differences were determined using Duncan's new multiple range
test (6). Percentage data were transformed
prior to analysis to satisfy the
assumptions of normality for the ANOVA (28) as utilized by Nelson and co-workers (34,
35, 37).
[(X+O.5)05]
Both a broad (see Table A. 5) and narrow scope of inference (presented here) were
evaluated. Two ANOVA were calculated, with sample date expressed on both a calendar
date and weeks after planting basis (Table A.12). Sampling date (SD) x stem (ST)
response was the largest interactive effect. This interaction is discussed in detail with
special emphasis on how the response was altered by planting date and fertility. The
consistency of year effects is also shown in figure A.7. Year (Y) x planting date (PD), Y x
fertility (F), and PD x F interactions were small when compared to main effects (Table
A. 12). Therefore, treatments were pooled across years because the interactions with years
were less meaningful than the main effects presented. Statistical evaluation of HHBC
levels revealed N regime x stem-type interactions which are discussed in detail. Because of
this interaction, only HHBC data from the high preplant N regime were presented when
illustrating I{HBC differences between planting dates. Complete seasonal statistical
evaluations can be seen in table A.13.
Resulls
Delaying planting of Russet Burbank from early to late April increased the number
of stems per plant from 2.6 to 3.05 (Fig. 8.1 insert), indicating more triple- and multiple-
stem plants (72.1 vs. 55.5%) and fewer single- and double-stem plants (27.8 vs. 44.5%)
109
14
12
10
w
0.
>II..
z
8
4:
-J
0.
LL
0
6
>C.)
z
w
D
a
w
U-
EARLY
LATE
LOW
PLANTING DATE
HIGH
PREPLANT N
PLANT-TYPES
SINGLE-DOUBLE
TRIPLE-MULTIPLE
Fig. 8.1. Effects of planting date (Early and Late) and preplant nitrogen
(N) regime [56 (Low) or 224 (High) kg ha- on Russet Burbank singledouble and triple-multiple plant-types. Frequency of plant-types are
calculated within planting date and N regime. Insert shows the number of
stems produced per plant. Means with the same letter are not significantly
different at P < 0.05 (Duncan).
'1
110
from planting late (Fig. 8.1). However, preplant nitrogen (N) regime did not affect the
number of stems per plant (Fig. 8.1 insert) or the frequency of plant-types (Fig. 8.1).
Tuber number increased between early and late June, across all planting dates and
fertility regimes, and remained constant throughout the remainder of the season (Figs. 8.2a
and b). Dominant stems of single- or double-stem plants (D, S-D) produced 8-10 tubers
per stem, while dominant and nondominant stems from triple- and multiple-stem plants (D,
T-M and N, T-M) produced 7-8 tubers and 6-7 tubers per stem; respectively.
In early June, the low (56 kg ha-i) preplant N regime (Fig. 8.2a) and early planting
(Fig. 8.2b) showed more tubers per stem, regardless of stem- or plant-type, than the high
(224 kg ha-') preplant N regime and late plantings. After the initial sampling, neither N
regime nor planting date influenced the stem hierarchy-tuber number relationship, although
the high preplant N regime and late plantings tended to have slightly more tubers per stem
than the low regime and early plantings.
At 8 weeks after planting, late plantings showed more tubers than early plantings
(Fig. 8.2c), but by 10 wks, planting date had no effect on the number of tubers from
various stem- and plant-types.
Tuber yields were consistent among stem- and plant-types throughout the season,
regardless of N regime or planting date (Fig. 8.3). Stem hierarchy influenced tuber yield
early (by July) and consistently throughout the rest of the season. Dominant stems of
single- or double-stem plants (D, S-D) produced higher tuber yields than dominant stems
from triple- or multiple-stem plants (D, T-M), which, in turn, showed higher yields than
nondominant stems (N, T-M).
After early July, the low preplant N regime showed higher tuber yields on dominant
stems of single- or double-stem plants (D, S-D), while stems from triple- or multiple-stem
plants (D, T-M and N, T-M) showed similar seasonal tuber growth patterns, regardless of
preplant N regime (Fig. 8.3 a). In comparison, higher tuber yields were found in early- vs.
late-planted potatoes, especially on dominant stems of single- or double-stem plants (D, SD), but also on dominant and nondominant stems from triple- or multiple-stem plants (D,
T-M and N, T-M), even in June, although differences were not always statistically
significant (Fig. 8.3b). Therefore, differences in yield associated with planting date
became more obvious as the season progressed and were first apparent between dominant
stems of single- or double-stem plants (D, S-D), next between dominant stems from tripleor multiple-stem plants (D, T-M) and finally by August, between nondominant stems from
triple- or multiple-stem plants (N, T-M).
Based on physiological age (Fig. 8.3c), planting date effects on tuber yield indicate
that during the same physiological time frame, late-planted potatoes produced 38 to 94%
111
LOW,
a )
LOW, 0, 04.1
EANLY, D, ED
b)
'6
12
LOW. 8. 1.6
000
FE
In
IJJ
In
In
Z
10
HIOH.D.1-M
LII
Z
6
In
LII
to
DO
I..
I-
6
In
to
4
E liNE
L .IJNE
E JULY
L JULY
EJNE
AIGIJUT
LJNE
EJULY
DATE
LJULY
ftLJGUST
DATE
C)
12
EA#LY, 0,8.0
EANLY.D.T-M
EARLY,N,T-M
10
LATE.D,S.D
0LATE, D,T.M
LATUNT-M
In
In
III
Z
6
DO
In
In
I-
0
I
WK U
WK 10
W1112
WE 14
WK 16
WEEKS AFTER PLANTING
Fig. 8.2. Effects of a) preplant nitrogen regime [56 (Low) or 224 (High)
kg ha- 1j, b) planting date: Early and Late, or c) weeks after planting, and
stem-hierarchy on the number of Russet Burbank tubers over time.
Legend: D, S-D
(D) dominant stem(s) from (S-D) single- and doublestem plants. D, T-M = (0) dominant stem(s) from (T-M) three- or morestem plants. N, T-M
(N) nondominant stem(s) from (T-M) three- or
more-stem plants. Means with the same letter within the same sampling
dates are not significantly different at P < 0.05 (Duncan). Complete
statistical comparisons that include sampling dates are presented in
appendix Table A.13a.
112
800
LOW,0$.D
LOW. O,T-M
700
0,5.0
600
0H104,0,T'M
HIGH N, TM
500
80
-J
Si
;: 400
I
UI
Si
300
Ji11fl
0 'r5
EJNE
LJIJNE
EJULY
LJULY
UU8015T
DATE
C)
905
EOSLY. 8.5.0
SOOtY 0, TM
800
..:.'---J SOOtY. N.T-M
LATE,D,S-0
700
-G-- LOTS, D,T-M
600
LOTO,N,T-M
555
Si
>-
400
305
5000
50010
WKI2
WE 04
WE 06
WEEKS AFTER PLANTING
Fig. 8.3. Effects of a) preplant nitrogen regime [56 (Low) or 224 (High)
kg ha 1, b) planting date: Early and Late, or c) weeks after planting,
and stem-hierarchy on Russet Burbank tuber yield over time. 0, S-B =
(0) dominant stem(s) from (S-D) single- and double-stem plants. B, T-M
(D) dominant stem(s) from (T-M) three- or more-stem plants. N, T-M =
(N) nondominant stem(s) from (T-M) three- or more-stem plants. Means
with the same letter within the same sampling period are not significantly
different at P < 0.05 (Duncan). Complete statistical comparisons that
include sampling dates are presented in appendix Table A.13b.
113
higher yields, across all stem- and plant-types and samplings, than early-planted potatoes.
Trends showed more HHIBC in tubers on dominant stems of single- and doublestem plants (D, S-D) than in tubers from triple- or multiple-stem plants (D, T-M or N, T-
M) and more HHBC in tubers from dominant than nondominant stems from triple- or
multiple-stem plants (D, T-M vs. N, T-M) (Fig. 8.4). In general, HIHBC tended to
increase early, decline during mid-season, and increase to highest levels late in the season,
regardless of stem- or plant-type.
Through early July, HHBC increased in tubers from the high preplant N regime,
regardless of stem- or plant-type (Fig. 8.4a). However, the increase in HHBC was slower
in smaller stems and/or as the number of stems per plant increased.
In late June, the incidence of HFIBC increased in plants from the low preplant N
regime (Fig. 8.4a). However, tubers on dominant stems of triple- and multiple-stem plants
(D, T-M) had as much HHBC as dominant stems from single- and double-stem plants (D,
S-D). In early July, the incidence of HHBC in tubers on either dominant or nondominant
stems of triple- or multiple-stem plants (D, T-M or N, T-M) declined; conversely, tubers
with HHBC on dominant stems of single- and double-stem plants (D, S-D) increased
through early July. In late July, HHBC declined in tubers on dominant stems of single- or
double-stem plants (D, S-D), but increased in tubers from both stem-types of triple- or
multiple-stem plants (D, T-M and N, T-M). In August, HHBC increased by 100% and
70% in tubers on dominant stems of single- or double-, and triple- or multiple-stem plants
(D, S-D and D, T-M), respectively, but HHBC remained below 10% on nondominant
stems (N, T-M).
From late June through early July, HHBC increased in tubers on dominant stems of
single- or double-stem plants (D, S-D) under both N regimes. In early July, HHIBC was 2
to 3 times higher in tubers on dominant and nondominant stems of triple- or multiple-stem
plants (D, T-M or N, T-M) in the high compared to the low preplant N regime. From late
June through early July, HIHBC declined in tubers on triple- or multiple-stem plants (D, T-
M or N, T-M) from the low preplant N regime. The decline occurred 2 wks later for all
stem- and plant-types under the high preplant N regime and also for dominant stems of
single- or double-stem plants (D, S-D) under the low preplant N regime.
The incidence of HHBC in tubers on dominant stems of single- or double-stem
plants (D, S-D) in early-planted potatoes increased from 0 to 17% between early to late
June, declined to < 10% in early July, returned to about 17% in late July, and then doubled
to approximately 35% in August (Fig. 8.4b). During August, the incidence of HTHIBC
increased on nondominant stems (N, T-M). In late-planted potatoes, the same pattern of
increase, then decrease, and final rapid increase in the incidence of HHBC was observed.
114
b)
I
35
35
LOW, 5, 0.5
EARLY. 5 0.5
a
LOW, 3, TM
30
EMRLY. D.T-M
''''LOWNT-M
E---
o
EAMLY.N.T-M
OHI0H.D.T-M
a aa
ab
ace
EIONE
LJJNE
EJULY
bcbc
LJULY
a
Mab
0HNb
NIOftOS-D
LATEOT-M
cc e
a
abc
ccc
b be
abc
EJJNE
LOJNE
SAlLY
LJMLY
.SJ005T
b
OIJGUST
a
DATE
DATE
C)
35
EARIY.O&D
EAWY. OEM
JEANLyNr-M
30
LATE,O,S-D
Q
LATE. U. TM
25
LATE, MOM
(8
20
II
Ma
I
WE 8
I
WE 10
I
WKI2
WOO 04
I
WE 06
WEEKS AFTER PLANTING
Fig. 8.4. Effects of a) preplant nitrogen regime 156 (Low) or 224 (High)
kg hab) planting date: Early and Late, or c) weeks after planting, and
stem-hierarchy on hollow heart-brown center (HHBC) in Russet Burbank
tubers (except 0-1.3g tubers) over time. D, S-B = (B) dominant stem(s)
from (S-D) single- and double-stem plants. D, T-M = (B) dominant
1],
stem(s) from (T-M) three- or more-stem plants. N, T-M = (N)
nondominant stem(s) from (T-M) three- or more-stem plants. Means with
the same letter within the same sampling period are not significantly
different at P < 0.05 (Duncan).
Complete statistical comparisons that
include sampling dates are presented in appendix Table A.13c.
115
These changes in HHBC levels, however, occurred 2 wks later in the season for late
plantings (Fig. 8.4b), but at the same physiological age as for early plantings (Fig. 8.4c).
The incidence of HHBC was two-fold higher in tubers from late-planted potatoes than in
early planted potatoes during wks 8-14 after planting.
Discussion
The size and number of stems per plant (stem hierarchy) influenced tuber growth
and HHBC incidence more than either changes in planting date or preplant nitrogen regime;
although these treatments did influence overall tuber growth and HHBC incidence, they
only had minor influences on effects of stem hierarchy. Dominant stems of single- and
double-stem plants (D, S-D) showed more tubers which grew faster and had more HHBC
than dominant stems of triple- and multiple-stem plants (D, T-M), which in turn showed
more tubers which grew faster and had more HHBC than nondominant stems from the
same plant-types.
As was apparent for entire plants (Chapter 7), and regardless of imposed treatment
or plant-type, there was evidence for two distinct stages of HIHBC development--a period
when initiation or dissipation of early HHBC may occur (by late July, see Figs. 8.4a and
b), as speculated by Ojala (37) and Hiller et. al. (13), followed by late-developing HIHBC
(during late July and August, see figures 8.4a and b). Dissipation of HF{BC generally
occurred between 10 and 12 weeks after planting (Fig. 8.4c), for all stem-types, regardless
of planting date.
This suggests that plant growth stage is more important than
chronologically-related factors such as day/night temperatures and day-length.
Tubers susceptible to HHIBC may be predestined to form both types of HHBC.
Although the incidence and dissipation of HHIBC may be influenced by climatic conditions;
nitrogen regime, planting date, and stem-type alter the incidence of both types of HHBC
and the dissipation of early-season HIIBC.
Tuber growth rates are a major factor in determining the incidence of HHBC.
Susceptible dominant stems (D) had more rapid tuber enlargement than nondominant stems
(N). Fast, early-season tuber growth rates from the low preplant nitrogen regime (Fig.
8.3 a) and physiologically earlier tuber growth in late plantings (Fig. 8.3c) were associated
with higher early-season HHBC (Figs. 8.4a and c).
Comparison of the low (bars) and high (lines) preplant nitrogen regimes (Figs. 8.2a
and 8.3a) with early (bars) and late (lines) plantings (Figs. 8.2b and 8.3b) shows
remarkably similar seasonal patterns, thus figures 8.2a and b, and 8.3a and b are almost
116
interchangeable. By calendar date, both late plantings and the high preplant nitrogen
regime delayed tuber initiation and reduced yield. These differences were most apparent
for tubers on dominant stems of single- and double-stem plants (D, S-D) and least apparent
on nondominant stems of triple- and multiple-stem plants (N, T-M).
The number of tubers per stem showed no response to planting date after June
(Figs. 8.2b and c), suggesting that tuber initiation for late-planted potatoes occurred at an
earlier physiological age than for early plantings. When tuber numbers were plotted by
weeks after planting (Fig. 8.2c), rather than calendar date (Fig. 8.2b), earlier initiation for
late-planted potatoes was apparent. Associations between the physiological timing of tuber
initiation and growth, and the incidence of early-season HHBC are also apparent. Earlier
initiation of tubers (Fig. 8.2c) and faster, physiologically early tuber growth (Fig. 8.3c) in
late- vs. early-planted potatoes, resulted in higher levels of early-season HHIBC in all stemand plant-types.
Later plantings produced a lower proportion of dominant stems (Fig. 8.1), and
these stems, when present, showed smaller tuber size and yield than early plantings (Fig.
8.3b). However, the remaining HHB C-susceptible plant-types in late-planted potatoes had
a higher incidence of early-season HHBC. Early and late plantings showed similar tuber
growth patterns on nondominant stems. The more stems per plant, and therefore more
triple- and multiple-stem plants, the higher the yield potential (Chapter 3). Late plantings
had both more stems per plant, and triple- and multiple-stem plants (Fig. 8.1 and insert).
However, tubers from these stem- and plant-types required more time to reach a given size
than tubers from other stem- and plant-types (Chapters 3 and 4). Therefore, late-planted
potatoes apparently require extended, favorable growing conditions to obtain tuber sizes
equal to those of early-planted potatoes. A common final harvest date did not give the late-
planted potatoes an equally long growing season. However, reduced day-length and
day/night temperatures late in the growing season may either create less favorable growing
conditions or shorten the effective growing season for late-planted potatoes, even when
given the same amount of time to mature. This may explain the association between
reduced tuber yield, tuber size, and delayed planting (11, 40, 73, 78).
Although the high preplant nitrogen regime and delayed planting had similar effects
on vine (Chapter 7) and tuber growth (Figs. 8.3a and b), these treatments showed opposite
effects on HHIBC at harvest (Chapter 6). The high preplant nitrogen regime was associated
with increased HHBC, while delayed planting reduced HHBC (Chapters 6 and 7). Less
HHBC from delayed planting was also apparent in the final (August) sampling (Fig. 8.4b).
Reduced HHBC with delayed planting at the August sampling was largely
explained by less HHBC in tubers on dominant stems of single- and double-stem plants
117
(Fig. 8 .4b). The incidence of HHBC in tubers from triple- and multiple-stem plants were
similar for early and late plantings.
Reductions in both final HHBC incidence
(approximately 25%) in tubers on single- and double-stem plants (Fig. 8.4b) and HHIBCsusceptible single- and double-stem plants (approximately 33% less) (Fig. 8.1) explain the
decreased incidence of HHIBC.
Reduced levels of HHBC with late plantings have been attributed to warmer
weather during BC initiation (13, 38) and slower seasonal tuber growth rates (7, 13, 14).
A reduction in the number of highly susceptible stem-types and a shorter or less favorable
growing season are more likely explanations. Late planted potatoes have less opportunity
to develop late-season HHBC.
Based on days from planting, at any given age, tubers from late-planted potatoes
actually grew faster (Fig. 8.3c) and were more susceptible to HHBC (Fig. 8.4c), than
tubers from early plantings. In these studies, final incidence of HHBC from late plantings
was low compared to early-planted potatoes (Chapter 6) because late plantings produced
fewer highly susceptible stem- and plant-types (less dominant stems and less single- and
double-stem plants) and a shorter growing season (less time to develop late-season
HHBC). As mentioned above, at the end of the season, less favorable climactic conditions
exist for late-season tuber growth and HHBC development.
The high preplant nitrogen regime did not increase tuber number, as reported by
others (41, 46). Plants from the low preplant nitrogen regime showed increased tuber yield
(and size) mainly on dominant stems of single- and double-stem plants (D, S-D), after midJuly (Fig. 8.3a).
Tubers from dominant stems of single- and double-stem plants (D, S-D) are
generally more susceptible to HHBC than tubers from other stem-types (Chapter 4). This
occurred for both planting dates and the high nitrogen regime (Fig. 8.4). The low preplant
nitrogen regime was the exception to this generalization. Greater HHIBC dissipation in
tubers on dominant stems of single- and double-stem plants (D, S-D) reduced the HHBC
incidence (Fig. 8 .4a). Other researchers have shown a positive relationship between earlyseason nitrogen level and HHBC (13, 20, 38), in agreement with data presented here.
If reduced vine biomass is the controlling mechanism for lowering early-season
HHBC in potatoes under a low preplant nitrogen regime, as proposed previously (Chapter
7), stems and plants most likely affected by this reduced vine biomass would be singlestem plants. These plants normally produce more vine per stem than other plant-types (3,
18). Under the low preplant nitrogen regime, less early-season HHBC occurred even
though tuber growth was not affected (Fig. 8.3b).
118
Both late planting and the high preplant nitrogen regime produced more vine
biomass than the opposing treatments (Chapter 7). However, the observed increases in
vine biomass occurred through different mechanisms. The high preplant nitrogen regime
increase in overall vine biomass (Chapter 7) occurred across all plant-types (data not
shown), and nitrogen regime did not alter the frequency of stem- or plant-types (Fig. 8.1
and insert). Increased vine biomass from with delayed planting was associated with more
multiple-stem plants which had greater vine mass per plant (18). The greater vine biomass
with multiple-stem plants was not detrimental to these plant-types because tubers from
multiple-stem plants are less susceptible to HHBC (Chapter 3). Therefore, vine mass per
stem may be more important than total vine biomass in controlling HHBC.
increased dissipation of HIIBC under low preplant nitrogen conditions occurred,
(Fig. 8 .4a, early to late July) despite similar nitrogen applications and tuber growth rates
during dissipation (Chapter 7, Fig. 7.4). Although the low preplant N regime has more
nitrogen applied late in the season, at the time dissipation occurs (12 wks after planting) the
low and high preplant N regime differ only in the amount of nitrogen applied before
planting. Therefore, less nitrogen early in the season was associated with more HHBC
dissipation. Low preplant N regime plants may have been predisposed to increased
dissipation when vine biomass was decreased early in the season (Chapter 7). Vines from
the low preplant N regime remained smaller than those from the high preplant N regime
(Chapter 7) even though both treatments received identical amounts of total nitrogen during
the season.
Even though the low preplant N regime received more nitrogen during the period of
late-season HHBC initiation, HHBC incidence between late July and August was never
higher than for the high preplant N regime (Fig. 8.4a). Increases of 100% occurred in
HHBC between late July and August sampling dates for D, S-D stems for both N regimes.
Respective increases in FIFIBC incidence for high and low preplant N regimes were 92%
vs. 54% for D,T-M stems and 120% vs. -22% for N, T-M stems. Late-season nitrogen
applications in the low preplant N regime appeared to reduce specific gravity (Chapter 6).
Stem-type x treatment interactions, although subtle, are still important. Averaging
values for the three stem-types make HHBC dissipation and the onset of late-season
HHBC patterns less distinct. When average values for all stem-types are used in an
analysis of HHBC (Chapter 7), the dissipation pattern apparent for individual stem-types
completely disappears. Treatment effects are also more apparent when evaluating
individual stem-types than when presenting average values pooled across all stem-types.
In summary, tuber growth rates were the most important factor associated with
HHBC. Stem-type, planting date, and preplant nitrogen regime affected tuber growth rate
119
and thereby influenced HHBC incidence. Tubers on dominant stems of single- and
double-stem plants grew larger and faster than those from dominant stems of triple- and
multiple-stem plants, which in turn grew larger and faster than tubers on smaller,
nondominant stems on the same triple- and multiple-stem plants.
HHBC was initiated throughout the season. Regardless of cultural practice, the
incidence of HHBC increased, declined, and then rapidly increased.
Late plantings increased the number of stems per plant, which reduced the
proportion of stems with fast-growing, more HHIBC-susceptible tubers. Preplant nitrogen
regime did not alter stem number. Neither nitrogen nor planting date changed relative stem
productivity (dominant vs. nondominant). Dominant stems of single- and double-stem
plants, however, were more productive from early-planted and/or low preplant nitrogen
regime potatoes than from the opposing treatments.
Patterns of tuber growth and HHBC development were similar for all treatments.
The more tuber growth on a stem, the more HHBC was associated with it. Dominant
stems from the low preplant nitrogen regime were the exception. Tubers from these stems,
although fast growing, had less HHBC than tubers from dominant stems from the high
preplant nitrogen regime.
The low preplant nitrogen regime showed more HHBC dissipation in all stem- and
plant-types early in the season than the high preplant nitrogen regime. Increased tuber and
stem competition from additional vine biomass in the high preplant nitrogen regime delayed
tuber initiation and decreased dissipation. Late-season tuber growth rates were high for
both preplant nitrogen regimes, but total HHBC at final harvest was lower with the low
preplant nitrogen regime even though the rate of increase in new HHBC late in the season
was less affected.
The late-planted potatoes showed more early-season HHBC and more dissipation.
Planting later in the season reduced HHBC at seasonts end only in tubers from dominant
stems of single- and double-stem plants (D, S-D). Although susceptible plant-types for
late-planted potatoes had a much greater incidence of early-season HHBC, planting later in
the season radically reduced the number of susceptible plant-types. The higher overall
HHBC incidence for early-planted tubers is likely due to more HHIBC-susceptible planttypes and a longer period of favorable growing conditions. Climactic conditions are better
during late-season tuber growth and HI-IEC development periods for early-planted than for
late-planted potatoes.
120
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125
CHAPTER 9
SUMMARY AND CONCLUSIONS
Results of this study substantiate and expand on previous observations. Potatoes
from the low (56 kg ha-i) preplant nitrogen (N) regime produced larger tubers with
increased yield and less hollow heart (HH) and brown center (BC) than tubers from the
high (224 kg ha-i) regime. The low preplant N regime, however, also produced more
U.S. No. 2 tubers and reduced tuber specific gravity. These negative effects were offset
by planting later or reducing from 3 to 2 wks the interval between BC initiation and the
beginning of large N applications. Beginning N applications 2 wks after BC initiation
appeared to have little adverse effect on tuber yield, size, or specific gravity. Planting late
reduced HFIBC but also reduced yield in all N regimes. This reduction in yield was less
with low preplant N regimes. A delay in planting and a high preplant N regime produced
similar growth patterns. Both increased vine biomass and decreased yield. Their effects
on HHBC, however, were different. The high preplant N regime increased HHBC while
delayed planting reduced it. Delayed planting and low preplant N regimes likely reduced
HHBC through different mechanisms.
Past explanations for decreased HHBC in later-planted potatoes include: 1) warmer
conditions may be less favorable for development of HFTBC late in the planting season, and
2) potatoes planted late have slow late-season tuber growth rates, resulting in either less
initiation and/or more dissipation of BC. Rapid tuber growth rates induced by more vine
growth for the high preplant N regime is generally accepted as a causal factor for increased
HHBC under high N conditions. Although the above explanations may be important, most
studies have been based on final harvest evaluation which combines possible tuber data
groups at harvest. A hypothesis of this study was that season-long evaluation of a wide
variety of tuber categories would better explain fertility and planting date effects on the
incidence of HHBC.
This study focused on the possibility that HHBC can develop in tubers either early
or late in the season. Without monitoring plants throughout the season, treatment effects
on the initiation of early or late types of HHBC and possible dissipation of early-season
HHBC could not be observed. Tubers can vary in size and stolon nodal origin. Single-,
double-, triple-, and multiple-stem plants form a variable population of plant-types.
Furthermore, individual stems differ in relative size. The possibility that different
categories of tubers differ in susceptibility to HHIBC was evaluated. It was important to
126
determine if cultural practices can change the amount or susceptibility of various tubers to
HHBC.
Differences in the number and yield of tubers and the incidence of HHBC per stem
were established early in the season and remained constant. Stem-type strongly influenced
tuber number and yield and the incidence of HFTBC. The level of HIHIBC was related to
stem productivity (tuber yield), but not to plant productivity. Single-stem plants were more
susceptible to HHBC than multiple-stem plants. Main (largest) stems produced highest
yields; however, productivity of main stems decreased as the number of stems per plant
increased. The number of tubers on single-stem plants was positively associated with the
incidence of HHBC. Single-stem plants had more tubers and yield per stem, but were less
productive than double-and multiple-stem plants. Therefore, HFIBC was associated with
stem productivity, and not plant productivity. Tubers in the weight range with the largest
proportion of tuber yield (termed the primary weight range) had a higher incidence of
HHBC than any other tuber weight range. Throughout the season, tubers which were
either larger or smaller than tubers in the primary weight range had less HHIBC. Although
susceptible plant-types produce more tubers in the primary weight range, both susceptible
and nonsusceptible plant-types have similar peaks in distribution of tuber weight.
Regardless of weight, tubers are more susceptible to HHIBC when produced by plant-types
most sensitive to the disorder.
Middle stolon nodes produced more tuber yield than upper and lower nodes,
regardless of stem-type. Productive nodes on a small stem, however, were not as
productive as corresponding nodes on a larger stem. Productive nodes had higher average
tuber yield with greater weight gain between samplings dates. Stem-type and stolon nodal
position influenced tuber number and yield, and the incidence and severity of HHBC.
High yielding stolon nodes had both higher tuber growth rates and more HHBC than lower
yielding nodes.
Season-long evaluations of stem hierarchy and HHBC in susceptible tubers
revealed important facts that are obscured when whole plants are evaluated at harvest.
Delaying the date of planting, which can physiologically age the seed tuber, increased the
number of stems per plant, reducing the proportion of more productive, and therefore more
susceptible stem-types. Changes in planting date altered the number of rapidly growing
tubers, but did not affect the stage of growth when tubers became susceptible. Tubers on
late-planted, HHBC-susceptible plant-types actually grow faster and are more susceptible
than similar tubers on early-planted potatoes. Hollow heart-brown center was reduced
because there were fewer susceptible plant-types and less time for late-season HBBC to
127
develop. If the growing season was extended, late planted potatoes may be as, or more
productive than potatoes planted earlier and therefore, as or more susceptible to HHBC.
Altering the preplant N regime does not affect the number of stems per plant.
Overall expression of HHBC, however, was reduced by using a low preplant N regime.
Potato plants grown under a low preplant N regime showed equal or increased rates of
tuber growth, but reduced rates of vine biomass compared to those from a high N regime.
Consequently, especially in vines from large stems of single- and double-stem plants,
which would be slowed most by the low preplant N, there was more dissipation of BC,
resulting in less early-season HHBC compared to the high preplant regime. The low
preplant regime resulted in less total HHBC even though late-season HHBC was
unaffected by N treatments. Stems from single- and double-stem plants were more likely
affected by the low preplant N regime because they emerged first and had longer exposure
to low N conditions.
An observation not explained by these data was the failure of plants under a low
preplant N regime to have less HHBC in U.S. No. 2 tubers, as was observed for U.S.
No. l's. The No. 2 tubers may have been mis-shapen due to stress caused in part by the
low preplant N regime. It is possible that these two tuber groups had different growth rates
at the time of HHIBC initiation or expression, thus allowing symptoms of HH and/or BC to
show up in rapidly growing tubers and not be expressed in slow growing tubers. Higher
U.S. No. 2 yields in the low preplant N regime may also have influenced the positive
association between tuber shape and internal quality (HHBC).
Reduced tuber specific gravity associated with a low preplant N regime may
preclude commercial implementation. Processors are demanding increasingly high, less
variable specific gravity in order to maximize processing efficiency. Low specific gravities
can be partially offset by planting later and resuming N application soon (2 wks) after
initiation of BC. Specific gravities were probably reduced considerably by late season N
applications associated with the low preplant N regime. Stopping these late-season
applications sooner may allow potatoes under a low preplant N regime to mature more fully
than was possible in these experiments. With full maturation, specific gravities may not be
reduced.
Some potatoes, for a variety of reasons, must be planted early. Planting date
effects the proportion of plant-types most susceptible to HHBC that occur in the
population. More mature seed pieces produce more multiple-stem, less HHBCsusceptible, plants. However, these plant-types need more time to reach maximum yield
potential. It may be advantageous to use more physiologically mature seed for early
plantings and the youngest seed possible for potatoes planted late. This approach would
128
minimize the possibility of getting HELBC, while at the same time maximize yield potential,
regardless of planting date.
Commercially, the low preplant N regime has some inherent risks. A virgin soil
has little crop residue to tie up N. Because most soils have crop residue, more preplant N
is likely to be tied up than in these experiments which were conducted on virgin soil. A
prudent approach would be to increase the amount of preplant N to compensate for
microbial tie-up early in the season. The seasonal N requirement probably would not
change due to N release from the decomposing previous crop residue.
Due to the required narrow focus of this research, low preplant N treatments were
varied in an effort to improve the performance of plants under this N regime. Similar
efforts focused on high preplant N treatments may lead to improved performance under this
regime.
Possible variations should include reducing or increasing the delay in N
application following the initiation of BC. The 56 kg-1 N ha1 seasonal applications were
high by industry standards. Lower rates may reduce the overall level of HHIBC. The total
seasonal application of N under both N regimes should also be reviewed so that regardless
of preplant N rate, soil N is allowed to decline late in the season.
129
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149
b)
a)
-J
w
U)
a:
>-
w
a:
w
I-
I-
STEM 4
STEM 5
STEMS
STEM 4
STEM NUMBER
STEM 5
STEM 6
STEM NUMBER
d)
C)
0
C-)
I
x
0
STEM 4
STEM 4
STEM 5
STEM 6
STEM 5
STEM 6
STEM NUMBER
STEM NUMBER
Fig. A.i. The a) % of tubers, b) % of tuber yield, c) % of hollow heartbrown center (HHBC) distribution and d) cumulative HHBC severity
value on Russet Burbank stems 4, 5, and 6. Stems 4, 5, and 6 are the
fourth, fifth, and sixth largest stems, respectively.
150
35
25
-
20
C-)
m
I
I 15
10
n
D, S-D
D, T-M
N, T-M
STEM-TYPE
Effect of stem-type on the total % of Russet Burbank tubers
with hollow heart-brown center (IEIHBC) for all tuber weight ranges,
Fig. A.2.
except
O-13g tubers, in August.
I
I
I
I'I
S.
:
ill
I!
I
1
:ii'i
:Ii
I
I
: in L
1 I) I
I
I
:
HlIIII[
:
S.
I
I
I.
I
S
I
i
S
l
l
I
II
II
1 I'
SI
I H ri
I
I
I
I
I ___________
I
1:
i!!IF
.,.
.
S
.1
.1
:
airi!ii
IIIIIi'I..L
II ______________
.:
n
11"111
I,
I
I! I
I
-
I
I
S
I I
I
5
5
I
S
I"
.
i
I
SI
S
ii
s
'I
is
ii
,
s
I
I I
153
FIELD I
FIELD 2
FIELD 3
a)
80
80
IMAIN
Dx'j
60
60
60
HHBC 40
40
40
20
20
%
:
20
0
0
1
2
3
4
56+
0
1
2
3
4
5
6
1
2
34 56+
b)
C)
HHBC
1'
0
STOLON NODE
Fig. A.5. Influence of stem-type and stolon node position on the
incidence of hollow heart-brown center (HHBC)-affected Russet
Burbank tubers from three fields over tinie. See Fig. A.3 for stem
designation and sampling dates.
154
FIELD I
FIELD 2
FIELD 3
a)
3.5
3.5
2.5
2.5
2
2
HHBC
1.5
SEVERITY
0.5
0
1
2
3
4
5
6+
b)
3.5
3
1
I__
2.5
2
HHBC
I
1 5
SEVERITY
_
-
Ii!
0.5
i'i
0
1
2
3
4
5
6+
I.I
1-ill
i
:i
i
I
II!:
I
I
1
1
U"!'!
C)
3.5
2.5
2
HHBC
1 5
SEVERITY
u_I I.
0.5
0
1
2
3
4
5
6+
Fig. A.6. Influence of stem-type and stolon node position on severity of
hollow heart-brown center (HHBC)-affected Russet Burbank tubers from
three fields over time. See Fig. A.3 for stem designation and sampling
dates.
155
1985
1986
1987
a)
A/USE
LOUSE
EOULV
LOULU
AUjST
F/USE
U/TIE
EUULE
C/UI?
AUTI
U/USE
c/USE
EUUCU
C/UI?
Ui/TIE
LI/lIE
EJULU
C/U/I'
NisT
3]
1000
1000
EJUIIE
LOUSE
UIr'_
EJULU
C/GUY
AUGUST
EJUIIE
100
LJUNE
5 JULY
LJULY
AUGUST
-----------------------------------------------------------------------------
25
ALISITIT
----------------------------------------------
c)
HHBC
(%)
I
[JUNE
C/USE
I
[JULY
I
I
UGLY
AUGUST
01
[JUNE
I
I
CJUNE
[JULY
IJULY
AUG/Sr
EJUNE
U/UT/S
I
I
I
F/ACE
LJULU
OUST/TI
DATE
Fig. A.7.
Effects of stem-hierarchy on the a) number, b) yield, and c)
level of hollow heart-brown center (HHBC) in Russet Burbank tubers
over time for three years. Legend: D, S-D = (0) dominant stem(s) from
(S-D) single- and double-stem plants. 0, T-M
(0) dominant stem(s)
from (T-M) three- or more-stem plants. N, T-M = (N) nondominant
stem(s) from (T-M) three- or more-stem plants.
156
Table A.1. Pre-application average soil readings and preplant fertilizer
nutrient applications (less preplant nitrogen).
Element
Average soil level
Preplant Apolication Rate (ko ha-i)
N
4.0 ppm
(see Table 2)
P
8.0 ppm
168
K
138 ppm
S
2ppm
280
56
4.0 meq/iOOg
-
Mg
12 meq/iOOg
2
B
0.3 ppm
Zn
0.5ppm
ii
ii
Mn
1.0 ppm
5.6
Cu
0.4 ppm
2
Fe
7.0 ppm
-
Na
0.1 meq/lOOg
-
Table 4.2. Nitrogen regime and planting date treatments.
nt
a-i)
Treatments
Post-BC initiated N (kg ha-i)
i
2
3
56
56
0
0
56
56
56
56
0
0
56
56
weeks following B.C.
157
Table A.3. Statistical analyses (mean square and % of mean square) for
Chapter 3: a) across years, b) 1985, c) 1986, and d) 1987.
a
cuber
)
MS
Factors
Date
Fertility
(F)
Sampling
Date (SD)
(PD)
1ST)
PD X SD X ST
F X SD X ST
PD X F X SD X ST
b
247.2
5.7
337.1
7.7
2613.6
880.7
147.4
95.3
50.8
MS
Factors
Planting Date
Fertility
(F)
Sampling
Date
(PD)
(SD)
(ST)
F X SD X ST
PD X F X SD X ST
lanting
Date (PD)
(F)
Sampling Date (SD)
1ST)
PD X SD X ST
F X SD X ST
PD X F X SD X ST
d
20.3
74.6
39.2
3252298
368101
82385
117167
5.9
56.1
0.7
5.4
29.5
2.8
89.4
24.3
0.1
11.1
5.8
22.5
0.2
3.4
1.8
8.6
20.1
3.4
2.2
1.2
% of
Total
51.9
14.0
4.1
2.6
2.9
Numbei
% of
3.6
0.1
368.4
10.9
2330.3
MS
868410
17844
20064098
2566467
177109
39701
45809
Date (PD)
(F)
Sampling
Date
(SD)
(ST)
MS
0.1
36.4
8.5
1.6
235.1
54.9
7.9
20.9
5.7
5.3
2.0
4.0
0.8
48.8
24.7
4.9
0.9
0.9
5.6
5.6
Trans. HHBC
MS
% of
0.6
9.9
HHBC Sev.
MS
Total
%of
Total
3.7
2.5
2.9
16.9
7.3
4.0
4.7
12.1
5.2
2.3
0.6
23.5
0.1
84.4
50.0
58.3
3.4
13.9
16.2
135.5
25.3
58.5
10.8
10.9
1.0
34.7
9.8
0.7
6.8
7.9
19.3
8.3
0.7
7.0
0.2
3.3
3.9
9.7
0.9
9.3
0.2
5.2
6.1
12.8
4.2
5.5
0.9
9.2
% of
MS
Total
% of
Total
Trans. HHBC
MS
% of
6.5
-HHBC Sev.
MS
Total
%of
Total
0.2
9.7
3.3
2.1
14.6
8.1
40.0
22.1
44.4
15.0
2.9
20.2
68.7 14887993
81.8
77.5
54.3
39.1
7.9
37.8
43.0
21.0
161.0
1441894
190866
139889
52162
8.1
50.8
1.5
132.6
3.9
61.2
1.8
% of
165.1
25.5
27.9
159.4
4.3
145.0
% of
2.6
12.1
Total
Tuber Yield (g) HHBC Number
24.6
PD X SD X ST
82.2
22.4
12.7
F X SD X ST
45.6
7.0
PD X F X SD X ST
22.2
3.4
1.0
3.6
2.0
24.0
5.4
1.8
5.6
0.6
0.8
0.8
10.6
5.9
19.7
6.6
1.0
7.0
0.3
10.6
5.9
32.5
11.0
1.3
9.1
Tuber Yield (g) HHBC Number
MS
Total
Fertility
MS
%of
Total
0.3
13.2
MS
% of
Total
MS
0.1
447.3
Factors
Planting
Tuber Yield (g) HHBC Number
% of
Total
HHBC Sev.
5023
1479737
Tuber Numbe
)
Stem
38.5
Total
Fertility
Stem
1.0
90.9
1308.7
MS
MS
59.8 50154546
4.3
Factors
% of
Total
0.5
20.3
Tuber
)
MS
1.0
108.9
72.3
% of
Total
1.2
511.1
353.6
103.5
65.0
PD X SD X ST
c
MS
Trans. HHBC
647177
544854
cuber Numbe
)
Stem
% of
Tuber Yield (g) HHBG Number
Total
Planting
Stem
Numbe'
% of
MS
MS
Total
Total
534278
26018
13668940
666230
276419
34922
85850
% of
Trans. I*IBG
% of
4.5
5.6
-HI-IBC Sev.
MS
Total
% of
Total
3.5
23.5
27.6
90.2
27.2
4.0
29.2
0.2
3.3
4.9
24.3
7.3
0.5
3.6
89.4
15.8
18.6
62.0
18.7
2.3
16.8
4.4
26.3
30.9
81.9
3.1
22.6
1.8
8.5
10.0
1.9
13.9
0.2
5.7
6.7
37.3
26.4
24.7
11.2
8.0
1.0
7.3
0.6
2.0
2.4
9.5
2.9
0.9
6.6
158
Table A.4. Stem- and plant-type designations.
Stem-types
Plant-types
Designation
Dominant [largest 1-2 stem(s)]
1 Stem
D S-D
Single
2 Stems = Double
D S.D
3 Stems = Triple
D T-M
4 or more Stems
Multiple D T-M
Nondominant (other than Dominant stems) 3 Stems = Triple
N T-M
4 or more Stems
Multiple N T-M
159
Table A.5. Statistical analyses (mean square and % of mean square) for
Chapter 4: a) across years, b) 1985, c) 1986, and d) 1987.
a)
Tuber Number
MS
Planting Date (PD)
(F)
Sampling Date (SD)
Stem (SI)
!Veight Range (W)
PD X ST X W
F X SIX W
PD X F X SIX W
b
Total
MS
0.2
161
< 0.1
12812
270655
96832
91430
2069
3441
3798
6.6
3.1
89.9
< 0.1
< 0.1
< 0.1
Tuber Number
)
MS
Planting Date (PD)
(F)
Sampling Date (SD)
Stem (SI)
'Veight Range (W)
PD X ST X W
F X ST X W
PD X F X ST X W
9.89
0.03
70.31
30.25
686.61
3.45
2.27
1.47
Total
< 0.1
8.7
3.8
85.4
0.4
0.3
0.2
422904
115319
111059
408
5032
574
Tuber Number
))
D)
0.2
1.0
118.9
44.2
1156.7
1.9
1.3
4.5
Total
< 0.1
0.1
8.9
3.3
87.1
0.1
0.1
0.3
Tuber Number
6.4
D)
1.2
16.8
9.6
188.2
0.6
0.7
0.7
Total
0.9
0.2
2.3
1.3
95.0
0.1
0.1
0.1
0.9
64.0
17.4
16.8
0.1
0.8
0.1
1.2
4.0
16.7
11.6
6.0
0.3
0.2
0.4
9735
138444
701973
250432
170184
29509
10514
55937
1.7
0.2
27.6
13.4
7.5
0.8
1.5
3.2
2.5
51.4
18.3
12.5
2.2
0.8
64.9
26.3
14.1
3.5
1.8
2.6
0.8
0.6
60.8
15.5
21.8
0.3
49.4
24.0
13.3
1.4
2.7
5.7
Total
1.9
12.2
49.3
19.9
10.7
2.6
1.3
2.0
Trans. HHBC
%of
4600
3333
365743
93221
131022
716
3.1
%of
MS
16.1
Total
MS
Total
Trans. HHBC
0.7
Tuber Yield (g)
3.0
9.9
41.2
28.8
14.7
0.8
0.5
1.0
%of
MS
10.1
4.1
Total
Trans. HHBC
%of
Total
MS
%of
MS
< 0.1
Tuber Yield (g)
%of
MS
%of
MS
%of
Total
MS
76
5734
1.2
<0.1
2.7
56.2
20.1
19.0
0.4
0.7
0.8
Tuber Yield (g)
%of
Factors
Fertility
1.2
0.3
35.3
16.5
478.5
0.3
0.2
0.3
Total
Trans. HHBC
%of
%of
Factors
Fertility
Tuber Yield (g)
%of
MS
Total
10.4
22.8
11.0
21.2
26.5
14.4
1.1
1.5
0.8
1.1
16.4
7.8
15.3
19.1
721
0.1
0.1
2022
0.3
1.1
1.5
160
Complete statistical comparision for effects of stem
dominance, tuber weight range and sampling date on a) tuber number, b)
tuber yield, and c) % hollow heart-brown center (HHBC).
Table A.6.
a)
Stem
Dominance
Weight
Range (g)
D,
D,
D,
D,
D,
D,
S-D
S-D
S-D
S-D
S-D
S-D
0-13
14-27
28-57
58-113
114-170
D,
D,
D,
D,
D,
D,
T-M
T-M
T-M
T-M
T-M
T-M
0-13
14-27
28-57
58-113
114-170
> 170
N,
N,
N,
N,
N,
N,
T-M
T-M
T-M
T-M
T-M
T-M
0-13
14-27
28-57
58-113
114-170
> 170
Sample Date
E JUNE
ef
y
L JUNE
a
nopqr
stuvw
y
E JULY
L JULY
AUGUST
c
de
tuvwx
mnopq
lii
vwxy
tuvwxy
j
opqrst
uvwxy
opqrst
nopqrs
jkl
fg
tuvwxy
mnopq
vwxy
tuvwxy
klmn
jklm
opqrst
y
> 170
- --
y
nopqrs
uvwxy
y
---
mriopq
linn
pqrstu
y
-
jk
luvwxy
y
c_________
y
tuvwxy
wxy
opqrst
nopqr
-
gh
tuvwxy
y
nopq
nopq
xy
-- -
---
vwxy
rnnopq
imno
mnopq
uvwxy
qrstuv
mnop
rstuv
tuvwxy
b)
Stem
Dominance
Weight
Range (g)
Sample Date
E JUNE
D,
D,
D,
D,
D,
D,
S-D
S-D
S-D
S-D
S-D
S-D
0-13
14-27
28-57
58-113
114-170
> 170
pqr
D,
D,
D,
D,
D,
D,
T-M
T-M
T-M
T-M
T-M
T-M
0-13
14-27
28-57
58-113
114-170
qr
> 170
S
L JUNE
opqr
nopqr
mnopqr
pqr
E JULY
pqr
imnop
hijk
hijk
L JULY AUGUST
qr
pqr
jklm
cd
pqr
ghij
S
pqr
nopqr
pqr
r
pqr
pqr
qr
pqr
nopqr
ghij
e
a
pqr
mnopqr
hijk
jklm
ijkl
de
pqr
hijk
c
pqr
b
qr
pqr
opqr
fg
161
N, T-M
N,
N,
N,
N,
N,
T-M
T-M
T-M
T-M
T-M
0-13
14-27
28-57
58-113
114-170
> 170
pqr
pqr
pqr
S
S
pqr
opqr
kimno
opqr
pqr
pqr
qr
pqr
klmn
gh
s
pqr
lmnopq
fg
gh
ghi
c)
Stem
Dominance
D,
D,
D,
D,
D,
D,
S-D
S-D
S-D
S-D
S-D
S-D
D, T-M
D,
D,
D,
D,
D,
T-M
T-M
T-M
T-M
T-M
T-M
T-M
T-M
T-M
IN, T-M
N, T-M
N,
N,
N,
N,
Weight
Range (g)
E JUNE
Sample Date
L JUNE
E JULY
0-13
14-27
28-57
58-113
114-170
AUGUST
St
ijk
efg
cd
fgh
kimno
kimno
st
-- -
fghi
ghij
de
cd
a
imnop
St
St
def
pqrs
jklm
de
pqrs
jkl
nopq
b
St
C
jkl
> 170
0-13
14-27
28-57
58-113
114-170
L JULY
t
St
t
hijk
pqrs
pqrs
rst
> 170
0-13
14-27
28-57
58-113
114-170
> 170
St
St
t
klmn
qrs
hij
st
- --
---
-
--
rst
St
mnop
opqr
St
---
ijk
hijk
kimno
Table A.7. Statistical analysis (mean square and % of mean square) for
Chapter 5.
Tuber Number Ave Tuber Yield Trans. % HHBC
Factors
Field
(FD)
Sampling Date (SD)
Stem
(ST)
Node (N)
FD X ST
ED X N
FD X ST X N
MS
%of
MS
Total
3.6
4.5
13.9
4.0
0.1
1.5
0.4
12.8
16.1
49.7
14.3
0.4
5.4
1.3
%of
Total
173542
520466
94655
113610
6454
7932
1915
MS
18.9 1211.7
56.7
77.1
10.3 366.4
12.4 713.1
0.7
33.7
0.9
95.7
0.1
17.7
%of
Total
48.4
3.1
14.5
28.2
1.3
3.8
0.7
162
Table A.8.
Complete statistical comparision for effects of stem, stolon
nodal position and sampling date on a) tuber number, b) average tuber
yield,
c) % hollow heart-brown center (HIIBC), and d) severity of
HHBC.
a)
STEM NODE
E JUNE
efghij
jklmn
ghijklmn
bcde
bcdefg
bed
1
1
1
2
1
3
1
4
1
5
1
6
2
1
p
2
2
flop
2
3
2
4
2
5
2
6
ghijk
fghijklm
defghijk
ghijklm
3
3
1
q
2
p
3
3
3
3
4
5
3
6
jkfmnop
jklmnop
hijklmno
cdefghi
Sample Date
L JIJNE
bedef
jklmn
bcdef
be
E JULY
cdefghij
hijklmn
defghijk
efghijkl
bcdefgh
a
bedef
cdefghij
jklrnnop
efghijk
defghijk
efghijkl
cdefghij
ijklmnop
ijklmnop
ghijk
fghijklm
cdefgli
defghijk
ab
imnop
imnop
kimnop
jklmnop
kimnop
op
p
mnop
flop
jklmnop
cdefghi
cdefgh
b)
1
1
1
1
2
3
1
4
1
1
5
6
mnop
nopq
opqrstuv
Sample Date
L JuNE
opqrstu
kimn
fgh
fgh
efghi
ghijk
2
1
xy
rstuvwxy
pqrstuvw
2
2
2
2
2
3
4
rstuvwxy
qrstuvw
opqrs
nopq
hijk
Iuj
5
opqr
2
6
qrstuvwx
STEM NODE
F JUNE
uvwxy
pqrstuvwx
opqrstuv
efghij
ijkl
jklm
E JITLY
1mb
ef
a
ab
de
ed
be
ed
hijk
163
3
3
1
y
2
3
3
3
4
3
5
wxy
stuvwxy
rstuvwxy
qrstuvwx
3
6
opqrstuv
tuvwxy
opqrstuv
imno
jkl
mnop
opqrs
vwxy
opqrst
efghij
efg
efghij
jkl
c)
STEM NODE
1
I
1
2
1
3
1
I
4
5
1
6
2
1
2
2
2
3
2
E JUNE
mno
hijklmn
defgh
abc
abc
defgh
Sample Date
L JUNE
jklmnop
defghi
abc
a
ab
bede
E JULY
imnop
ghijklmn
bcde
a
a
cdef
op
kimnop
mnop
jklmnop
bcdef
bcdef
abc
abcd
2
4
5
6
nop
hijklmn
fghijk
defg
abc
defg
abc
abed
bed
3
1
mnop
3
2
p
3
3
imnop
kimnop
jklmnop
ghijklmn
3
4
bcdef
3
5
efghi
3
6
fghijkll
2
def
bcdef
defgh
defgh
p
mnop
ghijklm
defghi
ghijklmn
ijklmno
U)
STEM NODE
E JUNE
Sample Date
L JUNE
pq
klrnn
cd
a
E JITLY
pqrs
on
ghij
be
ab
fghij
1
1
rs
1
2
pqr
1
3
1
4
1
1
5
6
mno
cd
cd
efgh
2
1
S
S
S
2
2
3
qrs
ijkl
opq
2
pqr
nop
2
ijkl
de
ef
2
4
5
2
6
jklm
ab
efgh
efg
efghi
hij
de
de
lrnn
164
qrs
qrs
3
3
1
3
3
s
opq
flop
3
4
flop
hijk
jklm
3
5
3
6
pq
n
s
2
rs
fiO
flop
flop
imfi
Table A.9. Statistical analysis (mean square and % of mean square) for
Chapter 6.
Total
Specific
Yield
Gravity
% of
Factors
Total
MS
% US No. I
HH (>397g)
% of
Total
MS
Trans. HHBC
% of
Total
MS
% of
Total
MS
Planting Date (PD)
405665
55.4 0.00100
39.1
0.49
15.4
0.63
9.7
Fertility (F)
258387
35.3 0.00100
39.1
0.99
31.1
1.47
22.5
35.0
(ear (Y) X PD
13394
1.8
0.00019
7.3
0.31
9.7
2.28
XF
F X PD
26801
3.7 0.00003
1.1
0.39
12.3
0.32
4.9
1987
0.3 0.00032
12.3
0.04
1.3
0.92
14.1
Y X PD X F
26184
3.6 0.00003
1.1
0.96
30.2
0.90
13.8
(
% US No. I Yield % US No. 2 Yield
(114-1 70g)
Factors
Planting Date (PD)
Fertility (F)
Year (Y) X PD
YXF
F X PD
Y X PD X F
Total
732
% US No. 2 Yield
(>397g)
(>397g)
(114-1 7Og)
% of
MS
% US No. I Yield
% of
Total
MS
% of
% of
MS
Total
MS
Total
30.7
280
25.9
1732
52.5
32165
93.5
169
7.1
551
51.0
688
20.9
1585
4.6
1318
55.2
112
10.4
675
20.5
362
1.1
44
1.8
3.5
0.3
50.4
1.5
26.2
<0.1
46
1.9
37
46.5
1.4
148
78
3.3
3.4
9.0
107
3.2
130
0.4
0.4
97
165
Table A.1O.
Statistical analyses (mean square and % of mean square) for
Chapter 7: a) for figures 7.1 and 7.2, and b) for figures 7.3 - 7.6.
a
Total Tuber
Number (%)
)
%of
Factors
Neight (W)
Year X W
Planting Date X W
Fertility X W
b
714.5
98.4
7.3
1.0
4.5
0.6
3.4
0.5
Vine Biomass
(g/plant)
)
MS
(Y)
Planting Date (PD)
Fertility
(F)
Sampling Date (SD)
YXPD
YXF
YXSD
PDXF
Y X PD X F
YXPDXSD
(X F X SD
PD X F X SD
1917410
15744831
6273445
16052661
805458
1289645
126838
2682605
27664
1592564
75928
122003
Total
4.1
HHBC (%)
%of
%of
MS
150630
8526
14068
2252
Total
Total
MS
87.0
11.5
4.9
0.8
5.2
8.1
1.5
10.3
1.3
0.9
6.2
Tuber Yield
(g/plant)
MS
635928
33.7 16843622
13.4
394782
34.4 44189649
751375
1.7
272805
2.8
0.3
404541
131
5.7
0.1
28987
3.4
29685
0.2
79422
0.3
43571
Total
78.3
HHBC
(%)
%of
%of
Factors
Year
Total
MS
Tubers with
Total Tuber
Yield (%)
%of
MS
1.0 260.6
26.5 1987.0
0.6
16.6
69.4 1030.3
1.2 137.9
0.4
0.2
0.6 138.4
<0.1
2.7
< 0.1
355.9
<0.1 317.4
0.1
42.0
0.1
39.6
Total
6.0
45.9
0.4
23.8
3.2
< 0.1
3.2
0.1
8.2
7.3
1.0
0.9
166
Table A.!!. Complete statistical comparision for effects of tuber weight
range and sampling date on a) % tuber number, b) % tuber yield, c) %
total hollow heart-brown center (HHBC), and d) % HHBC.
a)
Weight Range (g)
Sample Date
E JULY
L JULY
AUGUST
c
d
e
jkl
gh
ijk
E JUNE
L JUNE
0-13
a
14-27
1
b
hij
28-57
1
jkl
ghi
fg
58-113
1
kI
hij
1
1
ki
1
1
1
114-170
> 170
b)
gh
gh
ijkl
ki
fg
Sample Date
Weight Range (g)
E JUNE
L JUNE
£ JULY
0-13
14-27
I
58-113
AUGUST
I
I
I[
-;Jj_
28-57
L JULY
'I
I
I
'I
I
-sF
114-170
> 170
I
I
I
II
Sample Date
c)
Weight Range (g)
E JUNE
L JUNE
0-13
E JULY
I
14-27
I
28-57
Sri
58-113
I
114-170
L JULY
III
I
I
AUGUST
'I
-
'I
I
I
> 170
S
d)
Sample Date
Weight Range (g)
E JUNE
0-13
14-27
28-57
58-113
114-170
> 170
ghi
L JUNE
hi
cde
efg
ghi
E JULY
L JULY
AUGUST
i
i
i
gh
bc
hi
gh
cd
hi
ghi
i
i
def
b
fg
a
cd
cd
167
Table A.12. Statistical analyses (mean square and % of mean square) for
Chapter 8 with planting date expressed on a) calandar date basis, and b)
weeks after planting basis.
a)
Tuber Number Tuber Yield (g)
MS
Planting Date (PD)
X PD
FertiUty
(F)
0.04
Sampling Date (SD)
Y X SD
PD X SD
F X SD
Stem (ST)
Y X ST
PD X ST
F X ST
SD X ST
Y X SD X ST
PD X SD X ST
FXSDXST
PDXFXSDXST
YXPDXFXSDXST
0.01
29.50
2.13
3.68
0.72
12.70
0.64
0.14
0.04
0.56
0.24
0.19
0.13
0.15
0.25
Total
10.73
2.15
0.30
0.35
0.06
0.02
49.91
3.60
6.22
1.22
21.49
1.08
0.23
0.06
0.94
0.41
0.31
0.22
0.25
0.43
Total
MS
5204
1145
464
1.39
0.31
0.12
10351
2.76
2.06
0.48
61.23
0.86
0.55
7714
1809
229231
3229
2054
3407
76959
2729
1120
2093
22200
1796
323
1306
447
816
0.91
20.56
0.73
0.30
0.56
5.93
0.48
0.09
0.35
0.12
0.22
Tuber Number Tuber Yield (g)
)
MS
(Y)
Planting
Date
(PD)
Y X PD
Fertility
(F)
YXP
PXF
Sampling Date (SD)
Y X SD
PD X SD
F X SD
Stem (ST)
Y X ST
PD X ST
F X ST
SDXST
V X SD X ST
PDXSDXST
F X SD X ST
PD X F X SD X ST
YX PDX F X SD X ST
8.06
4.28
0.89
Total
19.95
10.60
2.21
0.61
1.51
0.12
0.08
4.45
0.65
3.73
0.62
14.27
0.89
0.69
0.04
0.06
0.14
0.12
0.08
0.27
0.33
0.30
0.21
11.02
1.60
9.24
1.55
35.34
2.21
1.72
0.09
0.14
0.35
0.30
0.20
0.66
0.81
%of
MS
7.75
4.96
3.45
2.77
0.84
0.33
51.80
4.74
4.54
1.75
37.83
1.17
0.51
1.49
5.44
0.85
0.64
2.06
1.89
1.71
Total
MS
7261
61020
1980
14360
10468
18
183964
3644
13049
3958
97882
4149
3543
3336
18673
2648
716
1544
35
408
1.68
14.10
0.46
3.32
2.42
0.00
42.52
0.84
3.02
0.91
22.62
0.96
0.82
0.77
4.32
0.61
0.17
0.36
Total
5.68
3.63
2.52
2.03
0.62
0.24
37.94
3.47
3.33
1.28
27.71
0.86
0.37
1.09
3.98
0.63
0.47
1.51
1.38
1.25
Trans. HHBC
%of
%of
%of
Factors
Year
6.34
1.27
0.18
0.21
YXP
PXF
b
%of
%of
Factors
rear (Y)
Trans. HHBC
MS
2.71
12.16
0.23
4.12
0.20
0.11
8.70
1.99
0.80
1.26
Total
5.64
25.31
0.47
8.58
0.43
0.22
18.11
10.71
4.14
1.67
2.62
22.30
0.48
1.01
0.31
0.65
1.74
2.95
0.82
0.29
1.47
0.44
1.13
0.84
1.42
0.39
0.14
0.01
0.71
0.21
0.09
0.54
Table A.13a.
Complete statistical comparision of a) preplant nitrogen
regime and b) planting date effects on tuber numbers per stem. For
legend see figure 8.2.
a)
Preplant N/Dominance
LOW D S-D
LOW D T-M
LOW N T-M
HIGH D S-D
HIGH D T-M
HIGH N T-M
EJUNE
LJUNE
Sample Date_______________________
EJULY
LJULY
AUGUST
kl
a
abc
abc
efgh
Im
cde
def
efghi
m
fghij
hijk
jk
ghijk
n
ab
a
ab
defg
n
def
bcd
bcd
efgh
n
ijk
efghi
ghijk
hijk
LJUNE
Sample Date
E JULY
LJULY
AUGUST
a
abc
ab
bcde
cdef
efgh
fghi
hij
hij
b)
Planting/Dominance
EJUNE
EARLY D S-D
EARLY D T-M
EARLY N T-M
LATE D S-D
LATE D T-M
LATE N T-M
jk
kI
ij
m
ab
a
ab
h ij
fghi
fghi
m
cdef
bcd
bcd
efgh
m
hij
efgh
ghij
defg
kI
Table A.13b.
Complete statistical comparision of a) preplant nitrogen
regime and b) planting date effects on tuber yield per stem. For legend
see figure 8.3.
a)
Preplant N/Dominance
EJUNE
LOW D S-D
LOW D T-M
LOW N T-M
HIGH D S.D
HIGH D T-M
HIGH N T-M
LJUNE
EARLY D S-D
EARLY D T-M
EARLY N T-M
LATE D S-D
LATE D T-M
NT-M
LJULY
AUGUST
'II
b)
Planting/Dominance
Sample Date
EJULY
EJUNE
LJUNE
Samp'e Date_______________________
EJULY
[JULY
AUGU
!:1iii
_
I!
1fflu1s
iiiii.I
it. _
li
169
Table A.13c.
Complete statistical comparision of a) preplant nitrogen
regime and b) planting date effects on hollow heart-brown center
distribution by stem. For legend see figure 8.4.
a)
Prepiant N/Dominance
LOW D S-D
LOW D T-M
LOW N T-M
HIGH D S-D
HIGH 0 T-M
HIGH N T-M
E JUNE
pqr
LJUNE
efghi
Sample Date________________________
F JULY
LJULY
AUGUST
bc
jkImno
defgh
ghijkl
ijkImn
cdef
lmnopq
mnopq
cd
cdefg
a
opqr
ghijk
fghij
fghij
defgh
fghij
b
qr
ijklm
hijkl
nopqr
fghij
EJLJNF
FJULY
LJULY
AUGUST
m
I JUNP
def
fg
a
ghijkl
fghi
fghijk
cde
Im
fghi
Cd
bc
r
r
r
b)
cde
kimnop
Sample Date
Planting/Dominance
EARLY D S-D
EARLY D T-M
EARLY N T-M
LATE D S-D
LATE D T-M
LATE N T-M
kim
rn
ghijkl
jklm
ijklrn
m
m
ab
m
fghij
bc
fghi
Cd
rn
ef
fgh
hijkIm
fghi