Initiation of the reproductive stage in wheats varying in winterhardiness
by Sadiq Hussain Chaudhry
A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in
Crop and Soil Science
Montana State University
© Copyright by Sadiq Hussain Chaudhry (1985)
Abstract:
The initiation and duration of the reproductive stage are important factors influencing the yielding
ability of wheat. Lengthening the reproductive stage by delaying maturity increases yield potential if
drought and high temperature stresses during anthesis and grain filling periods can be avoided. In this
study the possibility of increasing yield potential by lengthening the reproductive period through earlier
initiation of the reproductive stage was examined.
Field experiments were conducted over 3 years at western North American locations, differing in
temperature and day length. Five cultivars of winter wheat (Triticum aestivum L.) were grown during
1980-81; during 1981-82 and 1982-83, 13 winter wheat and 1 winter rye (Secale cereale, L.) cultivars
were grown.
Significant differences for days to initiation of the reproductive stage were found among cultivars,
locations, years and environments. Location X cultivar, year X cultivar, and environment X cultivar
interactions were also significant. However, similar rankings of cultivars for reproductive initiation at
all locations suggested that cultivar X environment interactions were due to differential response of
cultivars at several environments. Differences in double ridge formation on the shoot apex of wheat
cultivars (initiation of the reproductive stage) were due mainly to temperature rather than daylength.
Initiation of the reproductive stage in winter wheat cultivars responded linearly to the accumulated
growing degree days.
A consistent negative correlation was found between winterhardiness and early initiation of the
reproductive stage in winter wheat. Lengthening the reproductive period by selecting breeding lines
which initiate this stage earlier in the spring may result in reduced winterhardiness. Seedling erect
growth habit and light green color, which are related to low winterhardiness, were associated with
earlier initiation. Conversely, prostrate growth and dark green color associated with high
winterhardiness were correlated with late reproductive initiation. By selecting plants with the
associated seedling characteristics the breeder can indirectly select for both occurrence of reproductive
initiation and winterhardiness. IN IT IA T IO N OF THE REPRODUCTIVE STAGE IN
WHEATS V A R Y IN G IN W INTERHARDINESS
by
Sadiq Hussain Chaudhry
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Doctor of Philosophy
in
Crop and Soil Science
M O NTANA STATE U N IV E R S ITY
Bozeman, Montana
May 1985
D3? k
C3?3
dop.Z
ii
APPROVAL
of a thesis submitted by
Sadiq Hussain Chaudhry
This thesis has been read by each member of the thesis committee and has been found
to be satisfactory regarding content, English usage, format, citation, bibliographic style,
and consistency, and is ready for submission to the College of Graduate Studies.
Date
0
'
Chairperson, Graduate Committee
Approved for the Major Department
9 / ^ 7 / 4 , / 9£i5~~
Date
Head, Major Department
Approved for the College of Graduate Studies
JT " 2 y Date
Graduate Dean
iii
STATEM ENT OF PERMISSION TO USE
In presenting this thesis in partial fulfillment of the requirements for a doctoral degree
at Montana State University, I agree that the Library shall make it available to borrowers
under rules of the Library. I further agree that copying of this thesis is allowable only for
scholarly purposes, consistent with "fair use" as prescribed in the U.S. Copyright Law.
Requests for extensive copying or reproduction of this thesis should be referred to Uni­
versity Microfilms International, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to
whom I have granted "the exclusive right to reproduce and distribute copies of the disser­
tation in and from microfilm and the right to reproduce and distribute by abstract in any
format."
Signature
iv
Dedicated to my mother, grandmother and eldest sister whose wishes are fulfilled but
who no longer live to share their happiness with me.
V
V IT A
The author, Sadiq Hussain Chaudhry, is the son of Ch. Sher Mohammad and the late
Nawab Begum. He was born on June 17, 1942, in Faisalabad (Lyallpur), Pakistan. He
received his elementary and secondary education in his hometown and got a Bachelor of
Science degree in Agriculture from West Pakistan Agricultural University, Faisalabad. In
1972, he obtained his Master of Science degree in Plant Breeding and Genetics from the
University of Agriculture, Faisalabad. Mr. Chaudhry has been associated with the breeding
program of Wheat Research Institute, A .A .R .I. Faisalabad since 1964.
In January of 1980, he joined Montana State University as a Ph.D. candidate. He is
married to Rashida Begum and they have three children.
ACKNOWLEDGMENTS
I wish to express my sincere appreciation to the following: Dr. G. Allan Taylor, my
major advisor, for valuable advice, friendship, constructive criticism, and encouragement
throughout the course of this study. He was always available for consultation and direction;
the othermembers of my committee Dr. Jarvis H. Brown, Dr. Ray L. Ditterline, Dr. Eugene
L. Sharp and Dr. John M. Martin for sharing their time, efforts and enthusiasms; Dr. Mark
Grant (retired). Agriculture Canada, Lethbridge, AB; Dr. Charles Rhode, Oregon State
University, Pendleton, OR; Mr. Jerry Ellis, Colorado State University, Ft. Collins, CO, who
helped take plant samples to make this study possible; the Montana State University
Research Centers for growing plots; USAID and Montana State University for financial
help that made this program successful.
I would also like to express my appreciation to my parents, relatives and friends for
being my well wishers whose blessings brought me up to this level; my wife, Rashida and
children, Nabila, Ghulam Ghaus and Jamila for their love, sacrifice and great understanding
during this entire program;and Mrs. Jean Julian for typing this manuscript.
vii
TABLE OF CONTENTS
Page
A P P R O V A L .........................................................
ii
STATEM ENT OF PERMISSION TO USE....................
iii
D E D IC A TIO N .............................................................................................................................
iv
V IT A .....................................................................................................
v
vi
TABLE OF C O N TE N TS ..........................................................................................................
vii
L IS T O F TABLES......................................................................................................................
ix
L IS T O F FIG URES....................................................................................................................
xi
A B S T R A C T ...............................................................................................................................
xii
IN T R O D U C T IO N ......................................................................................................................
I
LITE R A TU R E REVIEW ..........................................................................................................
2
Cultivar and Initiation of the Reproductive Stage.....................
Shoot Apex Development.......................................................
Cultivar Variation for Initiation of Reproductive Stage. . .
Environment and Initiation of the Reproductive Stage...........
Effect of Environment on In itiatio n .....................................
Effect of Daylength and Temperatures on Initiation.........
Initiation of the Reproductive Stage and Other Characteristics
Winterhardiness..........................................................................
Seedling Characteristics................................ ...........................
M ATERIALS AND METHODS................................................................................... ...........
Cultivars.............................................................................................................................
Locations..........................................................................................................................
1980- 8 1 ....................................................................................................................
1981- 8 2 ........................................................................................................
1982- 83 .....................................................................................................................
Experimental Design.............. .................................................................................. .. ■.
COCOODCJI-t^-P^OurOM
ACK NO W LEDG M ENTS..........................................................................................................
11
11
11
11
13
13
14
viii
TABLE OF C O N T E N T S -Continued
Page
Characteristics S tu d ied ...................................................................................................
Initiation of Reproductive Stage............................................................................
Plant Sampling ...................i ...........................................................................
Dissection and Data Collection........................................................................
Estimation of Reproductive Initiation............................................................
Winterhardiness..........................................................................................................
Seedling Characteristics............................................................................................
Growing Degree Days ( G D D ) .................................................................................
Estimation of Soil Temperatures. ...................................................................
Estimation of Growing Degree Days..............................................................
Statistical A nalysis..........................................................................................................
RESULTS AND D IS C U S S IO N ..........................................................................................
14
14
15
15
15
16
16
17
17
18
18
.
20
Initiation of the Reproductive Stage, Genotypes and Environments.....................
Cultivars, Locations and Their Interactions for Initiation .................................
1980- 8 1 ..............................................................................................................
1981- 82 .............................................................................................................
1982- 83 .............................................................................................
Comparative Influence of Daylength or Temperatureon Initiation.................
Initiation Response of Cultivars to Temperature.................................................
Relationship of Reproductive Initiation With Other Characteristics.....................
Winterhardiness..........................................................................................................
Seedling Characteristics. ..........................................................................................
20
20
20
22
23
27
28
30
30
34
SUM M A RY AN D CONCLUSIO NS........................................................................................
36
LITER A TU R E C IT E D .............................................................................................................
39
APPENDIX
44
ix
LIST OF TABLES
Tables
Page
1. Cultivars (includedJn three years study). Their Parentage/Pedigree,
Class, Origin and Winterhardiness Level.....................................................
2.
12
Experimental Locations for Three Years, Their Latitudes, Altitudes
and Average Temperatures........................................................................................
13
3.
Planting Dates of Field Experiments Over Three Years.......................................
14
4.
Mean Square Values from the Analysis of Variance of Days from
January I to Reproductive Initiation in 5 Cultivars at 4 Locations
During 1980-81.....................................................................
20
Means and Rankings of 5 Cultivars for Days from January I to
Reproductive Initiation at 4 Western North American Locations
(1 9 8 0 -8 1 )......................................................................................................................
21
Mean Square Values from the Analysis of Variance of Days from
January I to Reproductive Initiation in 14 Cultivars at 2 and
5 Locations During 1981-82 and 1982-83, Respectively.....................................
22
Means and Rankings of 14 Cultivars for Days from January I to
Reproductive Initiation at 2 Locations (1981-82)................................................
22
Means and Rankings of 14 Cultivars for Days from January I to
Reproductive Initiation at 5 Montana Locations (1 9 8 2 -8 3 )..............................
24
Spearman Rank Correlation of 14 Cultivars for Days to Initiation of
the Reproductive Stage from January I at 2 Locations (1981-82)
and 5 Locations (1 9 8 2 -8 3 )...........................................
25
Mean Square Values from the Analysis of Variance of Days from
January I to Reproductive Initiation in 5 Cuitivars Combined
over 11 Locations in 3 Years (11 environments)...................................................
26
11. Mean Square Values from the Analysis of Variance of Days from
January I to Reproductive Initiation in 14 Cultivars Combined
over 7 Locations in 2 Years (7 environments).......................................................
26
5.
6.
7.
8.
9.
TO.
12.
Mean Square Values from the Analysis of Variance of Days from
January I to Reproductive Initiation at Bozeman, MT in 5
Cultivars over 3 Years and 14 Cultivars over 2 Years............................................
26
X
Tables
13.
14.
15.
16.
Page
Initiation of Reproductive Stage at Two Locations Having
Similar Daylengths and Different Growing Degree Days (G D D ).......................
27
Correlation of Days to Reproductive Initiation and Growing Degree
Days to Reproductive Initiation from January I , in 14 Cultivars at
2 Locations (1981-82) and 4 Locations (1 9 8 2 -8 3 )..............................................
28
Days to Reproductive Initiation and Growing Degree Days to
Reproductive Initiation from January I , in 14 Cultivars Averaged
over 6 Locations (1981-82 and 1 9 8 2 -8 3 )................................................................
30
Correlation of Days to Reproductive Initiation and Winterhardiness
of 13 Winter Wheats, at 2 Locations in 1981-82 and 5 Locations in
1982-83..........................................................................................................................
31
Appendix Table
17.
Range of Coefficient of Determination (r2 ) Values for the Estimates of
Days from January I to Reproductive Initiation in 5 Cultivars at 4
Locations. During 1980-81, and in 14 Cultivars at 2 and 5 Locations
During 1981-82 and 1982-83,Respectively.............................
45
xi
L IS T O F FIGURES
Figures
Page
1. Correlation of days to reproductive initiation and growing degree
days to reproductive initiation after January I in 14 cuItivars at
Bozeman, MT averaged over 2 years....................... b...................... .......................
2.
29 2
4
3
Correlation of earliness of reproductive initiation and winterhardiness
scores in 13 winter wheat cuItivars....................................... ..................................
32
3.
I nitiation dates and winterhardiness scores of 13 winter wheats.......................
33
4.
Correlation of days to reproductive initiation and seedling
characteristics of 13 winter wheat cuItivars.....................
35
xii
ABSTRACT
The initiation and duration of the reproductive stage are important factors influencing
the yielding ability of wheat. Lengthening the reproductive stage by delaying maturity
increases yield potential if drought and high temperature stresses during anthesis and grain
filling periods can be avoided. In this study the possibility of increasing yield potential by
lengthening the reproductive period through earlier initiation of the reproductive stage was
examined.
Field experiments were conducted over 3 years at western North American locations,
differing in temperature and day length. Five cultivars of winter wheat (Triticum aestivum
L.) were grown during 1980-81; during 1981-82 and 1982-83, 13 winter wheat and I winter
rye (Seca/e cereale L.) cultivars were grown.
Significant differences for days to initiation of the reproductive stage were found
among cultivars, locations, years and environments. Location X cultivar, year X cultivar,
and environment X cultivar interactions were also significant. However, similar rankings of
cultivars for reproductive initiation at all locations suggested that cultivar X environment
interactions were due to differential response of cultivars at several environments. Differ­
ences in double ridge formation on the shoot apex of wheat cultivars (initiation of the
reproductive stage) were due mainly to temperature rather than daylength. Initiation of
the reproductive stage in winter wheat cultivars responded linearly to the accumulated
growing degree days.
A consistent negative correlation was found between winterhardiness and early initia­
tion of the reproductive stage in winter wheat. Lengthening the reproductive period by
selecting breeding lines which initiate this stage earlier in the spring may result in reduced
winterhardiness. Seedling erect growth habit and light green color, which are related to
low winterhardiness, were associated with earlier initiation. Conversely, prostrate growth
and dark green color associated with high winterhardiness were correlated with late repro­
ductive initiation. By selecting plants with the associated seedling characteristics the
breeder can indirectly select for both occurrence of reproductive initiation and winter­
hardiness.
I
INTRO DUC TIO N
Winter wheat (Triticum aestivum L.) cultivars with high yield potential but low or
moderate winterhardiness may produce a bumper crop under favorable conditions includ­
ing no winter injury. Morrison and Vogel (1962) and Briggle and Vogel (1968) suggested
that high production capability of cultivars is, in part, due to their ability to resume
growth rather than maintain dormancy during winter or early spring periods of above
freezing temperatures. However, at northern latitudes where temperatures of -3 0 C occur,
only cultivars with adequate winterhardiness can survive.
Another factor influencing grain yield is the length of the reproductive stage. Grain
yield potential could be increased by lengthening the duration of the reproductive phase
(Jakolev, 1973). Lengthening the reproductive phase in cultivars by delaying maturity is
associated with problems of high temperatures and water stress prevailing during anthesis
and grain filling periods. Selection of genotypes with early initiation of the reproductive
phase, however, could overcome these problems. The study of initiation of the reproductive
stage included five winter wheats grown in 1980-81 at four locations, and 13 winter wheat
and I winter rye cultivars grown in 1981-82 and 1982-83 at two and five locations, respec­
tively. The objectives of this research were:
1. to examine cultivar variation, cuItivar X location, and cultivar X year interactions
for initiation of the reproductive stage, and
2.
to investigate the relationship between reproductive initiation and adaptive char­
acteristics, including winterhardiness and its related seedling characteristics.
LITE R A TU R E REVIEW
fcultivarand Initiation of the Reproductive Stage
Shoot Apex Development
Methods of describing shoot apex development have evolved to the point where phenological events can be described quantitatively in terms of the onset of a particular stage.
Using these methods, it should be possible to differentiate between shoot apex develop­
ment and initiation of reproductive stage in different genotypes with respect to their
adaptive behavior in a given environment.
Bonnett (1935) divided stem elongation in barley into two phases, i.e., phase of pro­
ducing only leaf initials and phase of internode elongation and appearance of double ridges
on the growing point. A year later, in 1936, he described and illustrated the developmental
phases and grouped them into vegetative, transitional and reproductive stages. In explain­
ing the double ridge formation as indication of initiation of the reproductive stage, he
regarded the upper member of double ridge as spikelet initial. Furthermore, in 1966 he
summarized the information in this area more thoroughly for maize, wheat, rye and oats.
The stages of development, initiation and shape of apices were generally found similar in
these crops. Other investigators, including Andersen (1954), Briggle (1967), Aitken (1967)
and Lucas (.1972), described the development stages of apical meristem in wheat and
cereals.
Nerson et al. (1980) suggested a scale for assessment of the development of wheat
spike consisting of 10 stages beginning with vegetative shoot apex and ending with differ­
entiation of the terminal spikelet. Moncur (1981) described sequential development of
3
shoot apices in a large number of field crops. In wheat, he regarded double ridge formation
as the onset of floral initiation.
George (1982) devised and illustrated a refined scale of head development of winter
wheats consisting of 12 stages. Using this scale, he identified cuItivars vulnerable to winterkill in fall and found his scale a useful measure to discard the lines which were likely to
complete early developmental stages.
Another numerical staging scheme for measuring progression of inflorescence develop­
ment in wheat was presented by Klepper et a I'. (1983). The system clearly measured two
factors of importance in predicting yield: ( I ) the occurrence of the double ridge stage and
(2) the termination of spikelet development.
Cultivar Variation for Initiation of Reproductive Stage
The amount of time required to begin floral initiation and the amount of time required
to reach anthesis following initiation varies according to species and cultivar.
Sharman (1947) reported that the length of the shoot apex varied from species to
species in Graminae, even within a single genus. For any particular species it was constant;
provided shoots of the same maturity and of equivalent vigor were compared. In Triticum
the length of the apex was short during vegetative phase, elongating rapidly only at inflor­
escence initiation.
Cooper (1956) found that the general pattern of inflorescence in cereals was similar
but differences occurred among cultivars in the time at which spikelets were initiated.
Ashraf (1973) determined the relationship of development of external leaf morpho­
logical stages and apical meristem of shoot apex in five diverse winter wheats. According to
his study the general pattern of inflorescence development was similar in all cultivars, but
differences occurred among cultivars for the time of spikelet initiation.
4
Fisher (1973) reported a different pattern of development of apical meristem in
Japanese short statu red wheat, 'IMorin 10' and its derivatives. The single ridges on the
elongating shoot apex were considerably larger and double ridge formation was markedly
delayed, resulting in a long apex with many single ridges which consequently gave rise to
longer heads with more spikelets than in standard wheats.
Environment and Initiation of the Reproductive Stage
Effect of Environment on Initiation
Although genotype controls relative maturity, the control over the actual time of
initiation of reproductive stage and subsequent development of inflorescence involves
interaction of genotype with environmental components.
George (1972) examined the spike primordia of several winter wheat cuItivars period­
ically after early sowing. In some cuItivars the primordia remained near the crown and
were protected from frost, while in others, early culm elongation exposed the primordia to
winterkill. Cisar and Shands (1978), in a study of floral initiation and development in oats,
concluded that late maturing cultivars had longer vegetative periods. They further con­
cluded that a cuItivar earlier in initiation combined with a longer time of panicle develop­
ment is capable of utilizing longer season and gives higher grain yield per unit area provided
the environmental factors are not adverse.
Increase in the rate of spikelet initiation and decrease in duration of spikelet initiation
caused by late sowing in spring wheat varieties were reported by Stern and Kirby (1979).
They found significant variety X time of sowing interaction for rate and duration of spike­
let initiation. A significant effect due to planting date and variety on the number of days
and accumulated growing degree days to reach different stages of development in nine oat
cultivars was reported by Colville and Frey (1983). In general, the genotype X environmen­
tal interaction was not significant.
5
Water stress and seeding rates had no significant effect on the rate of development
of apical meristem of winter wheat even though differences in morphological development
were observed (Dunbar and Simka, 1981). Water stress during the late vegetative phase,
just before spike initiation, adversely affected the number of fertile florets per spike in a
semidwarf spring wheat (Oosterhuis and Cartwright, 1983).
Reproductive initiation differed greatly in six spring wheat cuItivars of diverse cli­
matic origin studied in growth chamber and field experiments (Halloran and Pennell,
1982). Rates of reproductive initiation and stem elongation for the cuItivars within and
between the two environments appeared to be largely independent. Development in hard
red spring wheats was affected more by cultivar than by soil water content or fertilizer N
level (Frank and Bauer, 1984).
Effect of Daylength and Temperatures on Initiation
Flowering in higher plants involves an initial differentiation reaction or floral induc­
tion, followed by initiation of reproductive stage and development. In winter wheat and
other winter cereals, low temperatures are required for the initial reaction of floral induc­
tion. This low temperature induction is generally referred to as vernalization. Daylength
and temperature have been reported by several investigators as the main regulating factory
of reproductive initiation in winter and spring type cereals.
Adams (1924) was probably the first to point out the importance of temperature in
relation to the daily photoperiod in wheat in influencing the time of sexual reproduction.
He claimed that these two factors are interchangeable. Kiesselbach and Sprague (1926)
reported that differentiation of the spike in winter wheat was not evident in the fall
season, and the plants remained essentially dormant during December, January and Febru­
ary due to low temperatures. Brief data on temperature and photoperiod were presented
by Mckinney and Sando (1930). Their results indicated that earliness in winter wheat was
6
influenced both by low temperatures and by short days during early stages of development.
In another study the impbrtarice of temperature and photoperiod in determining the
duration of each growth phase of wheat plants was stressed by Mckinney and Sando
(1933). They indicated the optimum requirement for earliness in winter wheats was low
temperature and short days during the initial growth phase, whereas spring wheats had
optima at the higher temperatures and the longer photoperiods. In 1935 they suggested
that temperature and photoperiod length must increase with the development of plant in
order to induce early sexual reproduction in winter and spring wheats.
Hamilton (1948) studied the development of apical meristem in four varieties of
Avena sativa grown at two temperatures. He found that differentiation of tissues in the
shoot occurred much earlier in plants grown at 28 C than at 16 C. A t the lower tempera­
ture, growth followed the usual pattern but the higher temperature resulted in rapid
maturation of tissues and inhibited panicle initiation. Time of flower initiation in Austral­
ian oats depended greatly on the varietal response to photoperiod and temperature (Aitken,
1961). Aitken (1966) also studied the differences between spring and winter flowering
characteristics in wheat, rye, barley and oats in several field environments with mean
temperatures ranging from 10-22 C and mean photoperiod from IO1Zz to 16 h. He found
that flowering in spring cereal varieties showed insensitivity to temperature and photo­
period and occurred at a lower leaf number. However, in winter cereals, flower initiation
was at a higher leaf number.
Floral initiation in Marquis wheat was earlier with each increase in light intensity
from 200 to 2500 ft-C, and with each increase in temperature between 10 and 30 C
(Friend et al., 1963). In a study on spring wheat Triple Dirk the time of appearance of
double ridges was progressively delayed with an increase in number of short days (Lucas,
1972). Times of floral initiation, stem elongation and maturity varied by about one week
among seven hard red winter wheat cuItivars studied by Wiegand et al. (1978). When 1800
7
degree days had accumulated, from 12.7 to 16.2 fully expanded leaves were produced by
the cuItivars 'Improved Triumph' and 'T A M -W I01', respectively. Fewer leaves were pro­
duced by early maturing cultivars. In another study in 1981, they reported that winter
wheat cultivars remained vegetative during short days of winter and produced leaves
linearly in response to cumulative heat units. Floral differentiation (double ridge stage),
stem elongation (first node) and anthesis varied about a week among cultivars.
Studies by Ritchie (1980) in wheat and maize indicated more varietal variation for
vegetative than for the reproductive phase, when duration of growth period was expressed
as degree days. Generally, the number of leaves produced was directly proportional to
degree days from emergence to floral initiation. Baker and Gallagher (1983), working with
winter wheat, observed slower production of apical primordia in autumn and winter, then
faster in spring as the weather became warmer. Spikelets were initiated three times as fast
as leaves. Double ridges appeared when about 50% of the final number of spikelets were
present. As a second part of the study, in 1983, they concluded that spikelet initiation
responded in a linear fashion to photoperiod over the range experienced in the field, i.e.,
1 1-16 h for winter wheat and 15.5-17.5 h for spring wheat. Leaf maturation in both types
o f wheats showed a rather weak response to photoperiod. The response of spikelet initia­
tion rate to temperature was linear.
Midmore et al. (1982) reported faster development of most wheat cultivars at the
hotter, lower locations compared with the cooler ones. High temperature delayed flower­
ing in the vernalization-responsive cultivars up to initiation of the terminal spikelet and
resulted in more leaves, spikelets and tillers than other cultivars at the hottest sites.
Colville and Frey (1983) examined nine oat cultivars and noticed a significant effect
due to planting date and variety on the number of days and accumulated growing degree
days to reach different stages of development. Mohapatra et al. (1983) observed delay in
initiation of double ridges on the shoot apex, at high temperature (30 C) compared to low
8
temperature (20 C) from germination onwards in an Australian spring wheat cultivar,
'Warimba'. The change in temperature did not affect the subsequent rate of spikelet
development to stamen initiation. Frank and Bauer (1984) reported significant differences
among cultivars of hard red spring wheat in growing degree days accumulated from plant­
ing to double ridge formation.
Initiation of the Reproductive Stage and Other Characteristics
Winterhardiness
Only a few studies have been reported about the relationship of initiation of repro­
ductive stage with winterhardiness of wheat.
Avetisova (1972) reported slower apical meristem growth in winterhardy and frost
resistant winter wheats compared to non-hardy and frost susceptible cultivars. The growth
was virtually nil in most winterhardy and frost resistant types. The cessation of growth was
accompanied by a restriction in the meiotic activity and a reduction in the nucleic acid
contents in the apical meristems of hardy types. Bendarenke and Mitropolenko (1979)
found a negative correlation between the degree of development of the growing point at
development stage 3 (elongation of the stem apex) and winterhardiness of winter wheats;
the less hardy the variety, the longer the growing point. Kuperman et al. (1979) from
USSR examined the growing points of seven winter wheat cultivars after removal of snowcover in winter. They reported that the hardiest varieties. Caesium 39, Ul Yanovka and
Mironovka 808, had the shortest growing points; while the tender variety, Aurora, had the
longest growing point. The moderately hardy types, such as Odessa 51, were intermediate
in length of growing point. Kuperman and Turkova (1980) studied the growth of apical
meristem in several winter wheat and winter rye varieties differing in winterhardiness. They
reported that more rapid apical growth in autumn and winter was associated with reduced
winterhardiness. Kenefic et al. (1981) reported that, under field conditions of South
9
Dakota, the less hardy winter wheat cuItivars initiated inflorescence about 15 days earlier
than hardy ones, but heading dates showed only about a 6-day difference.
Ashraf and Taylor (1974) concluded that long subcrown internode lengths (or shal­
low crowns) of winter wheat genotypes were associated with higher levels of winter survival
under field conditions. George and Morrison (1975) reported early growth resumption
tendency in winter wheat cultivars rendered them more vulnerable to winterkill or frost
injury. Management practices like seeding directly into standing stubble or deep furrows
which catch snow provide protection to winter wheat against winterkill (Aase and Siddoway, 1979). With these practices they were able to avoid winterkill even when air tempera­
ture occasionally approached -4 0 C, provided the wheat went through a proper hardening
process. Fowler and Gusta (1979) developed a field survival index based on 43 winter
wheat cultivars in 61 trials grown in Saskatchewan, Canada from 1972 to 1977. A wide
range in field survival indices was observed for the cultivars considered. Their rating sug­
gested that most successful winter wheat had only marginally greater winterhardiness than
the minimum required for the area in which they were grown.
Seedling Characteristics
Little information is available in the literature about the relationship of initiation of
the reproductive stage with seedling growth habit and seedling color in winter wheat. How­
ever, some investigators suggested the association of these seedling characteristics with
winterhardiness. .
Martin (1927) reported the association of seedling prostrate growth habit, dark color
and narrow leaves with winterhardiness in wheat, but not in rye. Taylor and Olsen (1976)
found relationship of fall and spring growth habit, spring vigor, and dark spring plant color
with field percent winter survival and suggested the use of these seedling characteristics in
screening of wheat lines for winterhardiness in breeding programs. Fowler et al. (1981)
TO
reported that erect seedling plant growth habit was negatively related to winterhardiness.
They further suggested use of this relationship for winterhardiness screening in wheat.
Taylor et al. (1984) used several morphological seedling characteristics for winterhardiness
evaluation in Montana wheat field trials. They used seedling growth habit, seedling color
and leaf width to calculate winterhardiness index which they considered an effective field
method of identifying w intefhardy wheats.
11
M ATERIALS AND METHODS
Cultivars
Five winter wheats were grown at four locations in I SSOvSI; 13 winter wheat and one
winter rye cuItivars were grown during 1981-82 and 1982-83 at 2 and 5 locations, respec­
tively (Table I ) . Included were hard red winter, soft red winter and soft white winter cultN
vars having a wide range of winterhardiness.
Locations
1980-81
Field experiments were planted (see Experimental Design) at the following four
western North American locations representing a wide range of environments:
1. Bozeman, Montana (MT)
2.
Pendleton, Oregon (OR)
3.
Fort Collins, Colorado (CO)
4.
Lethbridge, Alberta (AB)
For more information about locations, see Table 2.
In order to study the comparative influence of daylength and temperature on the
reproductive initiation of winter wheat, two locations (Bozeman, MT and Pendleton, OR)
were used. Both are at similar latitudes and, thus, have similar daylengths. These locations
differ widely in growing degree days (Table 2).
Table I . Cultivars (included in three years study). Their Parentage/Pedigree, Class, Origin and Winterhardiness Level.
Cultivar Name
Nugaines*
Stephens
Blueboy
TAM -W 105
Crest*
Centurk
Cheyenne
Redwin *
Froid
Winalta*
Yogo
Norstar*
Alabaskaja
Frontier (Rye)
Cl Number
13968
17596
14031
17826
13880
15075
8885
17844
13872
13670
8033
17735
P1326301
Cl 182
Parentage/Pedigree
Classt
Origin
Winterhardiness Score*
Cl 13253/Cl 12692//Burt
Nord Desprez/Pullman Sel 101
NIOB/Anderson/Coker 55-9
Scout Sel
Westmont/2/PI 178383
KS8N/3/Hope/2 TK/4/CNN/Parker
Sel of Crimea
Y G /C N N //N 1 0 B 1 4 /3 /3 * YG
MT 1904-7 Bulk-Winterhardiness
Minter/Wichita
Minturk 1/Belogiina//Buffum
Winalta/Alabaskaja
SWW
SWW
SRW
HRW
HRW
HRW
HRW
HRW
HRW
HRW
HRW
HRW
HRW
WR
WA, USA
OR, USA
NC, USA
T X , USA
MT, USA
NE, USA
NE, USA
MT, USA
' MT, USA
AB, Canada
MT, USA
AB, Canada
USSR
AB, Canada
2
2
2
3
3
4
5
5
7
7
7
8
8
9
Note: A ll cultivars were grown in 1981-82 and 1982-83.
*Grown in 1980-81.
,
, .
^
+
t SWW = soft white winter, SRW = soft red winter, HRW - hard red winter, and WR - winter rye.
$ Based on scale 0 -9 (derived from Taylor et al., 1984). See under Winterhardiness, p. 16.
13
Table 2. Experimental Locations for Three Years, Their Latitudes, Altitudes and Average
Temperatures.
Year
Location
Latitude
Altitude
(meters)
Average Temperature^
(centigrade)
1980-81
Bozeman, MT
Pendleton, OR
Fort Collins, CO
Lethbridge, AB
45
45
40
49
40
43
35
43
1455
453
1525
908
2.24
5.91
5.16
1.50
1981-82
Bozeman, MT
Pendleton, OR
45
45
40
43
1455
453
-0 .3 5
5.20
1982-83
Bozeman, MT
Pony, MT
Bridget, MT .
Huntley, MT
Moccasin, MT
45
45
45
45
47
40
40
18
55
3
1455
1676
1121
911
1311
0.79
0.00
2.98
1.62
1.33
t Averaged over development period from October to April for respective years and loca­
tions.
1981-
82
To confirm the results of previous year's study of comparative influence of daylength
and temperature on the reproductive initiation, the number of cuItivars was increased.
Field experiments consisting of 13 winter wheats and one winter rye were planted at
Bozeman, MT and Pendleton, OR (Table I).
1982- 83
The same set of 14 cultivars used in the previous year's study were grown at the fol­
lowing five Montana locations during 1982-83.
1. Bozeman
2.
Pony
3.
Bridger
4.
Huntley
5.
Moccasin
These locations differed greatly in temperatures (Table 2).
14
Experimental Design
Field experiments were planted with the help and cooperation of Experiment Station
staff during the falls o f 1980, 1981 and 1982; planting dates are given in Table 3. The
experimental design was randomized complete block with three replications, consisting of
5 cultivars during 1980-81 and 14 cultivars during 1981-82 and 1982-83. Plots consisted of
4 rows, 30 cms apart and 3 m long. A planting rate of 8 grams of seed per 3 m row was
used. Experimental design, plot dimensions and planting rates were the same for all loca­
tions and years.
Table 3. Planting Dates of Field Experiments Over Three Years.
Year
Location
Planting Date
1980-81
Bozeman, MT
Pendleton, OR
Fort Collins, CO
Lethbridge, AB
25
24
22
29
1981-82
Bozeman, MT
Pendleton, OR
18 September, 1981
22 October, 1981
1982-83
Bozeman, MT
Pony, MT
Bridget, MT
Huntley, MT
Moccasin, MT
23
24
4
22.
20
September, 1980
October, 1980
September, 1980
September, 1980
September, 1982
September, 1982
October, 1982
September, 1982
September, 1982
Characteristics Studied
Initiation of Reproductive Stage
Initiation of the reproductive stage is marked by apical meristem development when
there is visual indication of transition from vegetative to reproductive development. Mor­
phologically it is a change from leaf primordia formation to spikelet primordia formation
and is characterized by appearance of double ridges on the developing shoot apex. The
upper ridge of a pair becomes prominent and differentiates into individual spikelet while
15
the lower one develops into a leaf initial (Bonnett, 1936; Briggle, 1967; Clepper et al.,
1983; George, 1982).
Plant Sampling. Plant samples were taken during the development of shoot apex at
times and intervals shown below
Year
Period of Sampling
Sampling Interval
1980-81
December to February
March to April
twice a month
once a week
1981-82 and
1982-83
Mid February to
Mid May
once a week
A t each sampling time 5-7 plants were dug from each plot. The plants were washed, roots
and leaves cut off and specimens preserved in FAA (Sass, 1964).
Dissection and Data Collection. Three plant specimens per plot per sampling time
were dissected using 40x magnification and the developmental stages of shoot apices were
recorded. The Bonnett (1966) scale was used for rating the developmental stages of shoot
apex for the 1980-81 study. The apices were later rated according to George (1982). This
scale was more appropriate, having numerical values for each stage. George's scale was used
for subsequent studies in 1981-82 and 1982-83. Developmental stages ranging from early
vegetative to terminal spikelet formation were recorded on a scale of 1-12.
Estimation of Reproductive Initiation. Initiation of the reproductive stage in winter
wheat and winter rye cultivars was indicated by formation of double ridges on the elonga­
ting shoot apex (Bonnett, 1936 and 1966; Briggle, 1967; George, 1982) and was regarded
as stage 6 according to George's scale. Stage 6 was estimated for each replication by using
regression equation from the linear regression of days to samplings from January I on the
observed values of developmental stages of shoot apices at different sampling times.
16
High values of coefficient of determination (r2 ) obtained for estimates of time of
reproductive initiation support the reliability of these estimates. The range of r 2 values for
estimates of days from January I to reproductive initiation in 5 cultivars (1980-81), and,
in 14 cultivars (1981-82 and 1982-83) at different number of locations is given in Table 17
(see Appendix). The r2 values are statistically significant except the lowest range values at
Bridger, Montana and Pony, Montana during 1982-83.
The use of linear regression for estimating time of floral initiation was suggested by
Andersen (1954) and Klepper et al. (1983). They reported linear development of apical
meristem of shoot apex in winter wheat during reproductive initiation.
Winterhardiness
Cultivars were rated for winterhardiness on scale 0 to 9, with 0 being nonhardy (or
very tender) and 9 very hardy. These ratings were extension of scale 0 -5 used by Taylor
et al. (1984), originally based on average percent winter survival data of cultivars from
several locations throughout Montana over several years. The extended scale of 0 -9 was
used to account for small differences among cultivars. Winterhardiness scores o f cultivars
included in the study are listed in Table I . Cultivars have a wide range of winterhardiness
and those with a score of 3 or lower are poorly adapted to Montana locations. The winter­
hardiness scores given in Table I were used to examine relationship between winterhardi­
ness and initiation of reproductive stage.
Seedling Characteristics
Two important seedling characteristics, seedling growth habit and seedling color are
known to be highly associated with levels of winterhardiness of wheat cultivars (Fowler
et al., 1981; Taylor and Olsen, 1976; Taylor et al., 1984). These seedling characteristics
were further examined to establish their relationship with initiation of the reproductive
stage in this study. Seedling growth habit and seedling color were rated on scale 1-5, with
17
I upright to 5 prostrate growth habit, and I yellow green to 5 dark green seedling color.
These scales were adopted by Taylor et al. (1984) based on several years of data at several
Montana locations.
Growing Degree Days (GDD)
To study the response of cultivars for time of initiation of the reproductive stage to
temperatures at various locations, the relationship of reproductive initiation and growing
degree days (defined below) was examined during 1981-82 and 1982-83. Moreover, grow­
ing degree days were used to compare the influence of daylength and temperature on
reproductive initiation at Bozeman, MT and Pendleton, OR during 1980-81 and 1981-82.
Soil temperature has an important influence on biological and biochemical processes
of the developing young winter wheat plant (Smith, 1964). Due to the winter nature of
this study, growing degree days were based on soil temperatures. In winter wheat during
the initiation o f the reproductive stage, the apical meristem of shoot apex remains below
the soil surface. During this period, the plants may be covered by snow. Under these
situations soil temperatures are more appropriate to use than air temperatures.
Estimation of Soil Temperatures. Soil temperatures were estimated from air tempera­*1
3
2
tures using regression equations developed by Aase and Siddoway (1979) for 3 different
snowcover depths:
1.
For bare soil (no snowcover)
y = 2.39 + .826x
2.
For snowcover, trace - 5 inches
y = 1.84 + .383x
3.
For snowcover above 5 inches
y = 1.17 + .279x
18
where
y is the estimate of soil temperature (C)
x is the observed air temperature (C)
The r2 values for the above three equations were significantly higher at P = .01,
. thus giving an indication of reliability of estimates.
Estimation of Growing Degree Days. Accumulated GDD were estimated from Janu­
ary I to the time of initiation of the reproductive phase for each cultivar at each location
and for each year. Growing degree days were calculated from daily maximum and mini­
mum soil temperatures (estimated by using regression equations as explained earlier) by
the following formula
T
GDD
where
max,
+ T
min
2
Tb
GDD is growing degree days accumulated over a period of time
T max is the maximum daily temperature (C)
T mjn is the minimum daily temperature (C)
T b is the base temperature
The base temperature (Tb) was 0 C (Baker and Gallagher, 1983; Bauer etal., 1984; David­
son and Campbell, 1983). When T mjn for the day was less than 0 C, it was considered to
be O C (Bauere t a h ,1984).
Statistical Analysis
Time of initiation of the reproductive stage was estimated from the linear regression
of days from January I to sampling dates on the observed values of development stages of
apical meristems at differing sampling dates (Andersen, 1954; Klepper et al., 1983).
Analyses of variance of days to initiation of the reproductive stage were conducted
separately for all three years over their respective cuItivars and locations. Separation of
19
cultivar means for days to initiation of the reproductive stage was accomplished using the
least significance difference (LSD) method at 0.05 level (Lund, 1983).
The combined analysis of variance of days to reproductive initiation for 5 winter
wheat cultivars was obtained by combining 11 locations in 3 years into 11 environments. A
similar combined analysis of variance for days to reproductive initiation was obtained for
14 cultivars by combining 7 locations in 2 years into 7 environments. Environments were
tested using the block/environment mean square. The pooled error mean square was used
to test the significance for cultivar and environment X cultivar interaction mean squares.
Rankings of 14 cultivars for days to reproductive initiation at locations of 1981-82
and 1982-83 were tested by rank correlations calculated by using Spearman's Rank Corre­
lation Method (Lund, 1983).
The relationship between days to reproductive initiation and winterhardiness, seedling
growth habit and seedling color were examined using linear regression analysis. The days
to reproductive initiation of 13 winter wheats were means at Bozeman location over two
years in one analysis and means over two years at seven locations in the other. Linear
regression analysis was also used to examine relationship of the reproductive initiation and
accumulated growing degree days in 14 cultivars averaged over two locations in 1981-82
and over 4 locations in 1982-83. The same relationship was examined by regression analysis
using 5 cultivars combined over 3 years and 14 cultivars combined over 2 years.
20
RESULTS AN D DISCUSSION
Initiation of the Reproductive Stage, Genotypesand Environments
Environmental factors are known to affect the initiation of the reproductive stage and
hence play an important role in altering the duration of vegetative and reproductive phases
in wheat, and other cereals and grasses (Cisar and Shands, 1978; Evans, 1960; Halloran and
Pennell, 1982).
Cultivars, Locations and Their Interactions for Initiation
In this study initiation of the reproductive stage was examined at several locations for
5 winter wheats during 1980-81; and 13 winter wheat and one winter rye cultivars during
1981-82 and 1982-83.
1980-81. The analysis of variance of days to reproductive initiation for 5 winter
wheat cultivars grown at 4 western North American locations indicates significant differ­
ences among locations, cultivars and locations X cultivars at the .01 level (Table 4).
Table 4. Mean Square Values from the Analysis of Variance of Days from January I to
Reproductive Initiation in 5 Cultivars at 4 Locations During 1980-81.
Source
d.f.
m.s.
Location
Block/Location
Cultivar
Location X Cultivar
Error
3
8
4
12
32
1 39 7 .6 7 **
1.04
3 0 8 .6 0 **
6 .2 5 **
2.15
**Significant at .01 level.
21
Locations included in 1980-81 differ in their latitudes except Bozeman, M T and
Pendleton, OR which are located at similar latitudes and hence have similar daylengths.
Other locations differ in daylengths. The 4 locations differed in average temperature (Table
2). The different daylengths and temperatures at these locations provided different envi­
ronments for studying the initiation of the reproductive stage in winter wheat.
Although location X cultivar interaction was significant, the cultivar rankings for
initiation of the reproductive stage were similar at all locations (Table 5). Norstar, Winalta
and Redwin were late in initiation and occupied top three ranks at all locations; while
Crest and Nugaines were consistently early and ranked the same at all locations. The con­
sistent rankings of cu Itivars for initiation time at different locations suggested that although
the cultivar X location interaction was statistically significant, biologically the rankings
were similar. The statistically significant interaction was due to differential response of cultivars at several locations (Table 5).
Table 5. Means and Rankings of 5 Cultivars for Days from January I to Reproductive
Initiation at 4 Western North American Locations (1980-81).
Pendleton
OR
Norstar
Winalta
Redwin
Nugaines
Crest
LSD .05 =
85.9
85.8
84.0
77.8
72.7
2.5
5*
4
3
2
I
Fort Collins
CO
95.9 4
96.1 5
90.6 3
86.0 2
83.6 I
Lethbridge
AB
105.0
' 103.4
102.0
98.2
93.9
2.1
3.4
5
4
3
2
I
Bozeman
MT
Average
105.2
104.1
106.5
98.9
95.0
98.0
97.3
95.8
90.2
86.3
1.7
4
3
5
2
I
5
4
3
2
I
1.1
•!•Cultivar rankings in initiation, I = early, 5 = late.
Rank correlations among locations were not possible due to the small number of cultivars included in first year study. Fourteen cuItivars were included the following year for a
more reliable estimate.
1981-82. In 1981-82 significant differences were found among locations, cuItivars
and locations X cultivars "(Table 6). The mean comparisons and rankings of reproductive
initiation for 14 cultivars at two locations (Table 7) being very similar. The highly signifi­
cant rank correlation of reproductive initiation of 14 cultivars at Bozeman and Pendleton
(r = .94 in Table 9) suggests this trait may be evaluated in any of several environments.
Table 6. Mean Square Values from the Analysis of Variance of Days from January I to
Reproductive Initiation in 14 Cultivars at 2 and 5 Locations During 1981-82 and
1982-83, Respectively.
1981-82
Source
d.f.
Location
Block/Location
Cultivar
Location X Cultivar
Error
I
4
13
13
52
1982-83
m.s.
1 04 6 0.0 0**
0.53
5 3 9 .1 5 **
49.47
2.40
d.f.
m.s.
4
10
13
52
130
2 51 7 .5 0 **
4.30
9 3 8 .4 6 **
2 4 .9 6 **
2.22
^^Significant at .01 level.
Table 7. Means and Rankings of 14 Cultivars for Days from January I to Reproductive
Initiation at 2 Locations (1981-82).
Pendleton, OR
Alabaskaja
Norstar
Yogo
Winalta
Froid
Redwin
Cheyenne
Nugaines
Blueboy
Stephens
T A M -W I05
Centurk
Crest
Frontier (Rye)
LSD .05 =
109.8
109.2
105.1
107.0
104.5
102.2
100.6
94.6
89.5
88.8
88.4
85.0
86.2
66.8
14$
13
IT
12
10
9
8
7
6
5
4
2
3
I
2.8
$ CuItivar ranking in initiation, I = early, 14 = late.
Bozeman, M T
124.2
123.3
126.1
123.3
122.9
120.4
121.6
118.7
116.1
114.4
112.7
115.3
' 111.4
99.9
2.1
13
12
14
11
10
8
9
7
6
4
3
5
2
I
Average
117.0
116.3
115.6
115.1
113.7
111.3
111.1
106.7
102.8
101.6
100.5
100.1
98.8
83.3
1.7
14
13
12
Tl
10
9
8
7
6
5
4
3
2
I
23
Another aspect of first and second year study, to examine the influence of daylength
or temperature on initiation of the reproductive stage at Bozeman, M T and Pendleton, OR,
will be discussed later in this chapter.
1982-83. In 1982-83 the same 14 cuItivars used in previous year's study were exam­
ined for initiation of reproductive stage at 5 Montana locations. The differences among
cuItivars, locations, and locations X cuItivars were significant (Table 6). However, the
rankings for reproductive initiation were similar at all 5 locations (Table 8). Later initiating
cultivars, Alabaskaja, Norstar, Yogo, Winalta and Froid, were generally top ranking at all
locations; while Cheyenne and Redwin were intermediate, and the other cultivars were
early in initiation at most locations.
In the combined analyses of variance including 5 cultivars over 3 years (Table 10) and
14 cultivars over 2 years (Table 11), highly significant differences among environments,
cultivars, and environment X cuItivar interaction were found. Moreover, significant differ­
ences among years for reproductive initiation were found at Bozeman with 5 cultivars over
3 years and 14 cultivars over 2 years (Table 12).
In similar studies, significant differences in initiation of reproductive stage were
reported by Cooper (1956) between cultivars of cereals and by Ashraf (1973) between
winter wheats. Stern and Kirby (1979) found a significant cuItivar X environment inter­
action in spring wheat.
All sources of variation including cultivars, locations, years and their interactions were
significantly different for initiation of the reproductive stage. However, similar rankings of
cultivars for initiation of reproductive stage over locations and years were correlated (Table
9). The statistically significant interactions were due to differential response of several cul­
tivars at several environments. These results suggest that winter wheat cultivars can be
examined for initiation of the reproductive stage over a wide range of environments.
24
Table 8. Means and Rankings of 14 Cultivars for Days from January I to Reproductive
Initiation at 5 Montana Locations (1982-83).
Cultivar
Huntley
Bridget
Bozeman
Moccasin
Pony
Average
Alabaskaja
109.8
13$
112.8
13
121.4
14
118.5
13
128.4
13
118.2
14
Norstar
107.9
11
111.6
11
119.7
13
119.7
14
128.5
14.
117.3
13
Vogo
110.0
14
112.9
14
116.8
12
117.7
12
128.3
12
117.2
12
Winalta
108.0
12
109.4
7
114.9
10
116.0
9
124.5
10
114.6
11
Froid
106.3
10
112.2
12
112.2
8
116.8
11
122.4
7
114JD
10
Redwin
102.4
7
110.1
8
112.5
9
116.0
10
126.7
11
113.5
9
Cheyenne
102.8
8
110.6
10
115.8
11
114.7
8
123.4
8
113.5
8
Nugaines
104.8
9
110.2
9
112.1
7
114.6
7
123^6
9
113.1
7
Blueboy
99.2
6
109.1
6
110.6
6
114.2
6
120.9
6
110.8
6
Centurk
97.5
5
105.8
4
107.7
5
113.0
5
118.1
5
108.4
5
Stephens
94.7
3
108.2
5
107.5
4
112.7
4
116.8
4
108.0
4
Crest
94.5
2
104.4
3
105.9
2
108.6
3
114.8
3
105.6
3
T A M -W I05'
95.2
4
102.9
2
106.3
3
107.6
2
114,0
2
105.2
2
Frontier (Rye)
64.6
I
84.6
I
95.3
I
85.9
I
104.9
I
87.1
I
LSD .05 =
2.9
1.9
3.0
$ Cultivars ranking for initiation, I = early, 14 = late.
1.1
3.2
1.1
Table 9. Spearman Rank Correlation of 14 Cultivars for Days to Initiation of the Reproductive Stage from January I at 2
Locations (1981-82) and 5 Locations (1982-83).
1982-83
1981-82
Bozeman
1981-82
1982-83
Bozeman
Pendleton
Bozeman
Pony
Bridger
Moccasin
1.00
Pendleton
.9 4 **
Bozeman
.9 6 **
.9 3 **
Pony
.9 3 **
.9 2 **
.9 5 **
Bridger
.9 0 **
.8 6 **
.8 7 **
.8 4 **
Huntley
.9 8 **
.9 2 **
.9 2 **
.8 9 **
.8 8 **
Moccasin
.9 6 **
.9 4 **
.9 5 **
.9 5 **
.9 1 **
**Signifleant at .01 level.
Huntley
1.00
-
1.00
1.00
1.00
1.00
.9 1 **
. 1.00
UL
26
Table 10. Mean Square Values from the Analysis of Variance of Days from January I to
Reproductive Initiation in 5 Cultivars Combined over 11 Locations in 3 Years
(11 environments).
Source
d.f.
m.s.
Environment
Block/Environment
Cultivar
Environment X Cultivar
Error
10
22
4
40
88
2 34 8 .0 0 **
2.51
8 2 7 .2 5 **
1 5 .6 8 **
2.29
^^Significant at .01 level.
Table 11. Mean Square Values from the Analysis of Variance of Days from January I to
Reproductive Initiation in 14 Cultivars Combined over 7 Locations in 2 Years
(7 environments).
Source
d.f.
m.s.
Environment
Block/Environment
Cultivar
Environment X Cultivar
Error
6
14
13
78
182
3 56 3 .3 3 **
3.22
1439.23**
3 1 .2 8 **
2.28
**Significant at .01 level.
Table 12. Mean Square Values from the Analysis of Variance of Days from January I to
Reproductive Initiation at Bozeman, M T in 5 Cultivars over 3 Years and 14 Cuitivars over 2 Years.
Over 3 Years
Over 2 Years.
Source
d.f.
m.s.
d.f.
m.s.
Year
Block/Year
Cultivar
Year X Cultivar
Error
2
6
4
8
24
1 17 4 .0 0 **
1.40
1 9 7 .1 8 **
9 .8 5 **
2.63
I
4
13
13
52
8 9 3 .8 0 **
2.12
2 70 .92 **
7 :1 0 **
1.43
^Significant at .01 level.
27
Comparative Influence of Daylength or Temperature on Initiation
The dates of initiation of the reproductive stage at two locations, Bozeman, MT and
Pendleton, OR/ were examined relative to temperatures and daylengths for two consecu­
tive years, 1980-81 and 1981-82. These locations are similar in daylength due to similar
latitudes but differ greatly in temperature (Tables 2 and 13). The average date of initiation
of the reproductive stage at Pendleton was March 21 in 1980-81 and April 6 in 1981-82;
whereas at Bozeman it was April 11 and April 28 for 1980-81 and 1981-82, respectively
(Table 13). The number of growing degree days accumulated from January I to time of
initiation were 461 and 537 in 1980-81 and 1981-82, respectively, at Pendleton; whereas
growing degree days accumulated at Bozeman were 384 in 1980-81 and 313 in 1981-82
(Table 13). Earlier initiation was associated with higher number of growing degree days
at Pendleton and, conversely, later initiation was related to a lower number of growing
degree days at Bozeman for both years. This suggests that temperature was likely the main
factor influencing initiation of the reproductive stage as opposed to daylength. If daylength had been the main controlling factor, initiation should have occurred at about the
same time at Bozeman and Pendleton due to their similar daylengths.
Table 13. Initiation of Reproductive Stage at Two Locations Having Similar Daylengths
and Different Growing Degree Days (GOD).
Pendleton, OR
Latitude
Elevation (meters)
Time of Initiation
1980-81
1981-82
GDD from January I to Initiation
1980-81
1981-82
45
43
Bozeman, M T
45
40
453
1455
March 2 T
(day 81)
April Tl
(day 102)
April 6
(day 96)
April 28
(day 118)
461
537
384
313
28
Initiation Response of Cultivars to Temperature
Response of cultivar reproductive initiation to temperature was examined relative to
number of days required and accumulated growing degree days required for initiation.
Correlations at 2 locations for year 1981-82 and at 4 locations for 1982-83 were higher
than .96 and significant (Table 14). An overall correlation of number of days and growing
degree days to reproductive initiation in 14 cultivars averaged over 6. locations (1981-82
and 1982-83) was highly significant (r = .988, Table 15). Another correlation between
reproductive initiation and growing degree days in 14 cultivars averaged over two years at
Bozeman, MT,was also highly significant (r = .976, Fig. I ).
Table 14. Correlation of Days to Reproductive Initiation and Growing Degree Days to
Reproductive Initiation from January I , in 14 Cultivarsat 2 Locations (1981-82)
and 4 Locations (1982-83).
Year and Location
Correlation Coefficient (r)
1981-82
Bozeman, MT
Pendleton, OR
.9 7 9 **
.9 9 8 **
1982-83
Bozeman, MT
Bridget, MT
Huntley, MT
Moccasin, MT
.9 6 5 **
.9 6 3 **
.9 9 2 **
.9 8 9 **
'
**Signifleant at .01 level.
These correlations indicate that initiation of the reproductive stage in cultivars
responded linearly to the accumulated growing degree days. These results corroborated
those of Weigand et al. (1981), Colville and Frey (1983), Baker and Gallagher (1983), and
Frank and Bauer (1984). The linear response of initiation to accumulated growing degree
days confirms the earlier observation that the temperature was likely the main factor influ­
encing initiation of the reproductive stage.
500
i
95
'
I
1
105
115
Days to reproductive initiation
I
125
Figure I . Correlation of days to reproductive initiation and growing degree days to repro­
ductive initiation from January I in 14 cuItivars at Bozeman, MT averaged over
2 years.
* ’ Significant at .01 level.
30
Table 15. Days to Reproductive Initiation and Growing Degree Days to Reproductive
Initiation from January.I , in 14 Cultivars Averaged over 6 Locations (1981-82
and 1982-83).
Cultivar
I,
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Alabaskaja
Norstar
Yogo
Winalta
Froid
Cheyenne
Redwin
Nugaines
Blueboy
Stephens
Centurk
TAM -W 105
Crest
Frontier (Rye)
Days to Reproductive
Initiation
Growing Degree Days to
Reproductive Initiation
116.1
115.1
114.8
113.1
112.5
111.0
110.6
109.2
106.4
104.4
104.0
102.2
101.8
82.8
545.3
533.8
537.4
519.5
516.3
507.0
500.0
488.2
465.7
449.6
445.1
426.3
423.4
324.7
r = .9 8 8 **
Relationship of Reproductive Initiation With Other Characteristics
Winterhardiness
Winterhardiness in wheat ensures good stands in wheat growing regions of the northern
hemisphere where winter stress is likely during seedling stages. Cultivars used in this study
of reproductive stage initiation ranged widely in their level of winterhardiness (Table 2).
Lengthening the duration of the reproductive phase could result in increased yield poten­
tial of grain crops (Jakolev, 1973). Selecting for early initiation would lengthen the dura­
tion of the reproductive stage in wheat. The main objective of this study was to examine
relationship of initiation of the reproductive stage with winterhardiness. It should be noted
that increasing the length of reproductive stage by delaying maturity is often associated
with drought and high temperature stresses.
The positive correlations of days to reproductive initiation and winterhardiness in 13
winter wheats at two 1981-82 locations and at five 1982-83 locations (Table 16) suggest
31
that winterhardy cultivars are late initiating and less hardy ones are early initiating. This
relationship is also illustrated in Figures 2 and 3. Early reproductive initiation is associated
with reduced winterhardiness (r = -.82 in Fig. 2). Initiation dates and winterhardiness
scores of 13 winter wheats are shown in Figure 3.
Table 16. Correlation of Days to Reproductive Initiation and Winterhardiness of 13 Winter
Wheats, at 2 Locations in 1981-82 and 5 Locations in 1982-83.
Year and Location
Correlation Coefficient (r)
1982-82
Bozeman, MT
Pendleton, OR
.8 4 7 **
.8 9 4 **
1982-83
Bozeman, MT
Pony, MT
Bridger, MT
Huntley, MT
Moccasin, MT
.8 0 9 **
.617*
.650*
.8 2 3 **
.7 4 4 **
*Significant at .05 level.
**Significant at .01 level.
This relationship suggests that lengthening the reproductive phase by earlier initiation
would result in reduced winterhardiness. Earlier inflorescence initiation in less hardy winter
wheats was also reported by George and Morrison (1975) and Kenefic e ta l. (1981). More­
over, studies of Bendarenke and Mitropolenko (1979), Kuperman et al. (1979), and Kuperman and Turkova (1980) indicated that rapid apical growth was associated with reduced
winterhardiness and less hardy varieties had the longest growing points.
These results further suggest that breeders using early initiating winter wheat cultivars
to increase yield potential should be satisfied with reduced winterhardiness. Further, in
wheat growing regions requiring high level of winterhardiness, early initiating cultivars are
not recommended.
Earliness of initiation
(Dayst before April 30)
Figure 2. Correlation of early reproductive initiation and winterhardiness in 13 winter
wheat cultivars.
t Averaged over 7 locations (1981-82 and 1982-83).
’ ’ Significant at .01 level.
Initiation dates* in April
Figure 3. Initiation dates and winterhardiness scores of 13 winter wheats.
* Averaged over 7 locations (1981-82 and 1982-83).
34
Seedling Characteristics
The relationship of seedling characteristics with winterhardiness was reported by
Martin (1927). Seedling prostrate growth habit and dark green color are associated with
high winterhardiness, while upright growth habit and light green color are associated with
reduced winterhardiness in wheat (Fowler et al., 1981; Taylor and Olsen, 1976; Taylor
e ta l., 1984).
Correlation of seedling characteristics and initiation of the reproductive stage is
shown in Figure 4. Late initiation of the reproductive stage is highly correlated with seed­
ling prostrate growth habit and dark green color (r = .776 and .756, respectively). In other
words, seedling upright or erect growth habit and light green color are associated with
earlier initiation. Earlier initiations are also associated with reduced winterhardiness as
previously explained.
A breeder should be able to identify wheat cultivars with varying reproductive initia­
tion dates by selecting for the associated seedling characteristics. Selecting for prostrate
growth and dark green color associated with high winterhardiness and late reproductive
initiation, or erectness and light green color for lower winterhardiness and early initiation.
(prostrate)
(dark green)
Seedling growth habit
D
Seedling color
2
I
o
o
c'
=05)
C/)
Ol
April 15
April 25
(upright)
(light green)
105
110
115
Days to reproductive initiation after January I
Figure 4. Correlation of days to reproductive initiation^ and seedling characteristics of 13
winter wheat cultivars.
' Averaged over 7 locations (1981-82 and 1982-83).
‘ ^Significant at .01 level.
36
SUM M ARY AND CONCLUSIONS
The reproductive stage and its duration are important factors influencing the yielding
potential of wheat cultivars. Lengthening the reproductive stage by delaying maturity
increases yield potential only if drought and high temperatures during anthesis and grain
filling periods can be avoided. In this study, the possibility of increasing yield potential by
lengthening the seed producing period through earlier initiation of the reproductive stage
was examined. The main objective of this study was to examine relationship of initiation
of the reproductive stage and winterhardiness of winter wheat cultivars.
Field experiments were conducted over three crop.years at western North American
locations, differing in temperature and daylength. Five cultivars of winter wheat [Triticum
aestivum L.) were grown during 1980-81; during 1981-82 and 1982-83, 13 winter wheats
and I winter rye (Secale cerea/e L.) cultivars were grown. The cultivars had differing levels
of winterhardiness.
For the purposes of the study of initiation of the reproductive stage, the plant samples
were taken during late winter and early spring at weekly and biweekly intervals. The plant
specimens, preserved in FAA, were dissected and the development stages of the main shoot
apices were recorded. The initiation of the reproductive stage, indicated by formation of
double ridges on the shoot apex, was estimated from the linear regression of days to sam­
pling dates from January I on the observed values of development stages of apical meristems at different sampling dates.
Highly significant differences for days to initiation of the reproductive stage were
found for cultivars, locations, years and environments. Location X cultivar, year X cuItivar
and environment X cultivar interactions were also significant. However, similar rankings of
37
cultivars for initiation stage at locations, within and between years, suggested that cuItivar
and environment interactions were due to differential response of cultivars at several envi­
ronments. These results indicate that winter wheat cultivars could be examined for initia­
tion of the reproductive stage over a wide range of environments.
Comparative influence of daylength or temperature on initiation of the reproductive
stage in winter wheat was examined at Bozeman, M T an d Pendleton, OR. These locations
are similar in daylength, being situated at similar latitudes, but differ greatly in tempera­
ture. Based on two years of data, early initiation was associated with higher growing degree
days at Pendleton and, conversely, the late initiation was associated with lower growing
degree days at Bozeman. The results suggested that temperature influenced initiation of
the reproductive stage more than daylength. If daylength was the main controlling factor,
initiation would have occurred at about the same time at both locations due to their
similar daylengths,
Date of initiation of the reproductive stage and accumulation of growing degree days
in cultivars were correlated at all locations. This relationship indicated that initiation of the
reproductive stage in cultivars responded linearly to the accumulated growing degree days.
This linear response confirmed the earlier observation that temperature was likely the main
factor influencing initiation of the reproductive stage.
The correlation of initiation of the reproductive stage and winterhardiness in winter
wheat cultivars was significant, suggesting that late initiating cultivars were more winterhardy and early ones, less hardy. This relationship indicated that an increase in the dura­
tion of reproductive phase through early initiation is associated with reduced winterhardi­
ness. Breeders, using early initiating winter wheat cultivars to increase yield potential,
should be satisfied with lower levels of winterhardiness associated with such cultivars.
Early initiating cultivars are not recommended in wheat growing regions requiring high
level of winterhardiness.
38
Late initiation of the reproductive stage was highly correlated with seedling prostrate
growth habit and dark green, color. Conversely, seedling erect (upright) growth habit and
light green color were associated with earlier initiation. Earlier initiations are also associ­
ated with lower level of winterhardiness as discussed earlier. The breeder can indirectly
select for both ocfcurrence of reproductive initiation and winterhardiness by choosing
plants with the associated seedling characteristics.
LITERATUR E CITED
40
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43
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44
APPENDIX
45
Table 17. Range of Coefficient of Determination (r2 ) Values for the Estimates of Days
from January I to Reproductive Initiation in 5 Cultivars at 4 Locations During
1980-81, and in 14 Cultivars at 2 and 5 Locations During 1981-82 and 1982-83,
Respectively.
Range of r 2 Values
Location
Lowest
Highest
.962*
.974xx
.947*
.924*
.9 9 5 **
.994xx
.999 xx
.993 xx
.893*
.905*
.988 xx
.979 xx
.901*
.887
.935*
.899*
.820
.986xx
.955*
.998 xx
.995* *
.995 xx
1980-81
Pendleton, OR
Fort Collins, CO
Lethbridge, AB
Bozeman, MT
1981-82
Pendleton, OR
Bozeman, MT
1982-83
Huntley, MT
Bridger, MT
Bozeman, MT
Moccasin, MT
Pony, MT
xSignificant at .05 level.
xxSignifleant at .01 level.
IN IT IA T IO N OF THE REPRODUCTIVE STAGE IN
WHEATS V A R Y IN G IN W INTERHARDINESS
by
Sadiq Hussain Chaudhry
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Doctor of Philosophy
in
Crop and Soil Science
M O NTA NA STATE U N IV E R S IT Y
Bozeman, Montana
May 1985
IN IT IA T IO N OF THE REPRODUCTIVE STAGE IN
WHEATS V A R Y IN G IN W INTERHARDINESS
Sadiq Hussain Chaudhry
Montana State University
1985
Abstract
The initiation and duration of the reproductive stage are important factors influencing
the yielding ability of wheat. Lengthening the reproductive stage by delaying maturity
' increases yield potential if drought and high temperature stresses during anthesis and grain
filling periods can be avoided. In this study the possibility of increasing yield potential by
lengthening the reproductive period through earlier initiation of the reproductive stage was
examined.
Field experiments were conducted over 3 years at western North American locations,
differing in temperature and daylength. Five cuItivars of winter wheat (Triticum aestivum
L.) were grown during 1980-81; during 1981-82 and 1982-83, 13 winter wheat and I winter
rye (Secale cereals L.) cultivars'weYe grown.
Significant differences for days to initiation of the reproductive stage were found
among cultivars, locations, years and environments. Location X cultivar, year X cultivar,
and environment X cultivar interactions were also significant. However, similar rankings of
cultivars for reproductive initiation at all locations suggested that cultivar X environment
interactions were due to differential response of cultivars at several environments; Differ­
ences in double ridge formation on the shoot apex of wheat cultivars (initiation of the
reproductive stage) were due mainly to temperature rather than daylength. Initiation of
the reproductive stage in winter wheat cuItivars responded linearly to the accumulated
growing degree days.
A consistent negative correlation was found between winterhardiness and early initia­
tion of the reproductive stage in winter wheat. Lengthening the reproductive period by
selecting breeding lines which initiate this stage earlier in the spring may result in reduced
winterhardiness. Seedling erect growth habit and light green color, which are related to
low wihterhardiness, were associated with earlier initiation. Conversely, prostrate growth
and dark green color associated with high winterhardiness were correlated with late repro­
ductive initiation. By selecting plants with the associated seedling characteristics the
breeder can indirectly select for both occurrence of reproductive initiation and winter­
hardiness.
MONTANA STATE UNIVERSITY LIBRARIES
3 17 6 2 1 0 0 0 5 4 3 2 7
D3 7 8
C 393
c o p .2
DATE
Chaudhry,S . H.
I n i t i a t i o n o f t he
r e p r o d u c t i v e s t a g e i n ••«
ia S U E D T O
____________ _____ ______________
D378
C39 3
cop. 2