Root morphological characteristics of barley (Hordeum vulgare L.) varieties grown in slant-boxes and
pots
by Daniel Mark Roddy
A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE
in Agronomy
Montana State University
© Copyright by Daniel Mark Roddy (1981)
Abstract:
Early maturing isotypes of 'Betzes' and 'Hannchen' barley (Hordeum vulgare L.) grown in slant-boxes
produced smaller root volumes, root weights, and root:shoot ratios than 'normals' due to a reduction in
the elongation rate and number of adventitious root axes. A similar decrease in root volumes, weights,
and root:shoot ratios characterized early isotypes grown in pots.
Twenty-five two-row and 25 six-row barley varieties were grown in germination boxes to determine
differences in mean seminal root numbers. Significant varietal differences in mean seminal root
numbers were observed. Two-row barley varieties generally developed a greater number of seminal
roots than six-row varieties.
Four barley varieties representing a wide range in mean seminal root numbers were evaluated in
slant-boxes and pots to determine if increased branching compensates for low root number. Mean
varietal root numbers were correlated with mean root volumes (r = .96; 2 degrees of freedom) in
slant-boxes. The fresh root volume of 'DeKap' was significantly greater than 'Unitan' (p = .007),
'Briggs' and 'Zephyr' (p = .05) at 25 days from transplanting. Varieties differed in mean elongation rate
of seminal axes in six of eight measurement periods.
Seminal root numbers were more important than elongation rates in determining the total length of
seminal axes at day 12 when grown in pots. STATEMENT QF PERMISSION TQ COPY
In presenting th is thesis in p a rtia l fu lfillm e n t o f the require­
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I fu rth e r
agree th a t permission fo r extensive copying o f th is thesis fo r
scholarly purposes may be granted by my major professor, o r, in his
absence, by the D irecto r o f L ib ra rie s .
I t is understood th a t any
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Signature
Date
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/
ROOT MORPHOLOGICAL CHARACTERISTICS OF BARLEY
( HQRDEUM VULGA.RE L J VARIETIES GROWN IN
SLANT-BOXES AND POTS
by
DANIEL MARK RODDY
A thesis submitted in p a r tia l fu lfillm e n t
o f the requirements fo r the degree
of
MASTER OF SCIENCE
in
Agronomy
Approved:
Head, Major Department
Graduate Dean
MONTANA STATE UNIVERSITY
Bozeman, Montana
June, 1981
TABLE OF CONTENTS
Page
VITA ......................................................................
ii
TABLE OF CONTENTS........................
iii
LIST OF TABLES .................................................. '............................................
v
LIST OF F IG U R E S ..........................................................................................
vi
ABSTRACT .......................................................... ' ..........................
v ii
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . .
I
REVIEW OF LITERATURE................................. ; .............................................
3
MATERIALS AND METHODS. .........................................
Experiment I :
Experiment I I :
Experiment I I I :
Experiment IV:
Experiment V:
Experiment V I:
U
The Relationship Between Heading ‘
Date and Barley Seminal and Adventi­
tious Root Growth
The Relationship of Heading Date
to Barley Fresh Root Volume, Root
Dry Weight, and Root:Shoot.Weight
R a t i o s ....................................................
15
The R ela tio n s h ip .o f Seed Size to
Seminal Root Number o f Barley
. . . . .
The E ffe c t o f Genotype on Seminal
Root Number o f B a rle y .............................. ...........
The Relationship o f Seminal Root
Number to Fresh Root Volume, Root
Dry Weight, and Average Axial
Elongation R a t e .............................
17
Seminal Root Number and Mean Seminal
Root Axial Elongation Rate .. . . . . . .
RESULTS AND DISCUSSION ..................................................................
. . ./
Experiments I and I I
...........................................................................
Experiment I I I
. . . . . . .
.........................
Experiment IV ................................................................
Experiments V and V I ................................... 31
11
16
16
20
21
21
.29
31
iv
Page
SUMMARY AND CONCLUSIONS ..........................................................
LITERATURE CITED
............................. ....
. . . . .
44
47
L IS T OF TABLES
T a b le
1
2
3
4
5
6
7
8
9
Page
C h a ra c te ris tic seed size range, associated seed
weight, and mean seminal root number o f Dekap,
Briggs, Unitan , and Zephyr barley ..................................................
18
Mean fresh root volume, root dry weight, shoot dry
weight, root:shoot r a tio s , and to ta l number o f
root axes o f barley m aturity is o ty p e s ..................................... ....
22
The e ffe c t of seed s ize on the seminal root
number o f Betzes and Compana b a r l e y ................................. .... . .
30
Mean seminal root numbers, seed s ize s , and seed
weights o f 25 two-row barley v a rie tie s
....................................
32
Mean seminal root numbers, seed s ize s , and seed
. weights of 25 six-row barley v a rie tie s . . . . . . . . . .
33
Mean barley seminal root numbers.obtained in
germination tra y s , slant-boxes, and pots .....................
34
Mean root volumes and root dry weights o f barley
grown in slant-boxes ..............................................................
36
Mean elongation rates o f seminal root axes o f
Dekap, Briggs, Unitan , and Zephyr barley . . . . . . . . .
40
Mean elongation rates o f seminal axes and cumulative
root length indexes o f Dekap, Briggs, Unitan
and Zephyr b a r l e y ...........................................
43
LIST OF FIGURES
Figure
. I
2
3
4
Page
The slant-box used fo r measuring root
elongation rates ........................................................................................ 12
Arrangement o f barley m aturity isotypes
in slant-boxes fo r Experiment I .............................
Arrangement o f barley v a rie tie s in
slant-boxes fo r Experiment V ................. . . . . . .
13
. . . .
Elongation rates o f barley seminal foot
axes: Hannchen and Hannchen-early . .. ..................... ....
19
25
5
Elongation rates o f barley seminal root
axes:Betzes and B etzes-early . . . .................. ............................ 26
6
Elongation rates o f barley adventitious
root axes:Betzes and B etzes-early . . ............................. .... .
28
Elongation ra te s o f barley seminal ro o t.
axes:Dekap, Zephyr, Briggsand Unitan .......................................
38
7
ABSTRACT
Early maturing isotypes o f l Betzesl and 'Hannchen1 barley
( Hordeum vulgare L .) grown in slant-boxes produced sm aller root volumes,
root weights, and root:shoot ra tio s than 'normals' due to a reduction
in the elongation ra te and number o f adventitious root axes. A s im ila r
decrease in root volumes, weights, and root:shoot ra tio s characterized
e a rly isotypes grown in pots.
Tw enty-five two-row and 25 six-row barley v a rie tie s were grown in
germination boxes to determine differences in mean seminal root numbers.
S ig n ific a n t v a rie ta l differences in mean seminal root numbers were ob­
served. Two-row barley v a rie tie s generally developed a greater number
o f seminal roots than six-row v a r ie tie s .
Four barley v a rie tie s representing a wide range in mean seminal
root numbers were evaluated in slant-boxes and pots to determine i f
increased branching compensates fo r low root number. Mean v a rie ta l
root numbers were correlated with mean root volumes ( r = .96; 2 degrees
o f freedom) in slant-boxes. The fresh root volume o f 'DeKap' was s ig ­
n ific a n tly greater than 'U nitan ' (p = .0 0 7 ), 'B riggs' and 'Zephyr'
(p = .05) a t 25 days from tran sp lan tin g . V a rie tie s d iffe re d in mean
elongation ra te of seminal axes in six o f eight measurement periods.
Seminal root numbers were more important than elongation rates in
determining the to ta l length o f seminal axes a t day 12 when grown in
pots.
I
INTRODUCTION
The association between root c h a ra c te ris tic s and cereal grain
y ie ld in a rid and sem i-arid climates has been studied extensively
(Troughton, 1962; Hurd, 1976; Jordan, 1980).
These authors generally
agree th a t the value o f any s p e c ific root c h a ra c te ris tic
depends on
the environment in which the crop is produced.
S ig n ific a n t amounts o f plant a v a ila b le water may remain in the
lo w e r,s o il zones (below 60 cm) a t harvest time in many p r a ir ie s o ils .
Plant breeders have sought to increase the e x te n s iv ity o f the root
systems in spring wheat lin e s to use th is moisture (Hurd, 1976).
In many d r ie r areas i t may be desirable fo r wheat grown s o lely on
stored s o il moisture to conserve water during e a rly growth stages.
A ustralian researchers?were able to lim it s o il water use by wheat
during e a rly growth stages by decreasing seminal root numbers
( Passioura, 1972).
Measurements by Brown (1980) in Montana in dicate th a t current
barley v a rie tie s leave a considerable q u an tity of plant a v a ila b le water
in the lower root zone.
A three year study in the G a lla tin V alley
determined th a t l Betzes1 barley rooted to 150 cm each year on a
fallowed loess s o i l .
Soil water use ( i n i t i a l plant a v a ila b le HgO-
harvest plan t a v a ila b le HgO) ranged from 13.2 - 14.2 cm.
r a in f a ll ranged from 5.6 - 16.5 cm.
(6 fe e t) ranged from 14'.2 - 20.1 cm.
Seasonal
Plant a v a ila b le water to 182 cm
A ll a v a ila b le water from the
2
upper .60 cm was used by the crop each year.
g la c ia l t i l l
In a la t e r study on
in Chouteau County, Montana, Brown found th a t lShabetl
barley rooted to 150 - 180 cm.
Most o f the a v a ila b le water was used
in the upper 122.0 cm, but 5.8 cm o f plant a v a ila b le water remained in
the 150 - 180 cm depth.
Brown
e t a l ; (1981) also reported th at
barley y ie ld s increased approximately .148 kg/ha-cm o f HgO (7 bushels/
a c re -in c h ).
Barley y ie ld s could be increased by approximately 1600 kg/
ha (30 bu/acre) i f the root systems o f barley v a rie tie s were modified
to use th is water.
The ob jective o f th is research was to examine the root morpho­
lo g ic a l c h a ra c te ris tic s o f barley which control so il water extraction
patterns.
We postulate th a t the root system o f barley v a rie tie s grown
in Montana may be modified to u t i l i z e the residual s o il moisture
described by Brown (1980).
i
REVIEW OF LITERATURE
B arley, lik e ..other temperate cereals-, develops two root systems:
the seminal, which develops from primordia w ithin the seed, and the
a d v e n titio u s , which in it ia t e s in the basal nodes of the stem (Troughton,
1962).
The seminal roots are important fo r seedling establishment
since they develop f i r s t (F rits c h , 1977).
Adventitious roots develop
anytime a f t e r the 3-4 le a f stage (Briggs, 1978).
Researchers have amputated the adventitious roots o f wheat and
barley to assess the r e la tiv e importance o f the seminal roots beyond
the seedling stage ( Simmonds and S a llan s, 1933; Sal Ians, 1942;
G liemeroth, 1957).
The re su lts o f these amputation studies were gener­
a lly inconclusive.
Hackett (1971) demonstrated th a t the removal of
one part o f the barley root system is generally compensated fo r by
increased growth o f the remainder.
The adventitious roots may dominate the seminal roots due to
greater numbers.
Pavlychenko and Harrington (1935) demonstrated th at
widely spaced barley is capable o f producing 83 adventitious ro o ts/
p la n t.
Eight barley c u ltiv a rs grown in Montana averaged 14.5 adventi­
tious ro o ts /p la n t ( Hockett, 1980).
Briggs (1978) reported th a t barley
seminal roots generally ranged from 5 -7 , over a range o f seeding ra te s .
Troughton (196.2) noted th a t wheat crops may reach m aturity with
only seminal roots when drought prevents the formation o f adventitious
roots.
Ferguson and Boatwright (1968) demonstrated th a t the adventi­
tious roots o f spring wheat w ill not elongate more than a few m i l l i ­
meters when the s o il adjacent to the crown is below a minimum water
content.
F a ilu re o f adventitious root development does not occur
freq uently in Montana.
Most barley production areas have a t le a s t a
70% chance o f re c e iv in g .13 cm or more o f p re c ip ita tio n during the
growing season (C aprio
e t a l . , 1980).
Weaver (1926) and Gliemeroth (1957) observed th a t barley seminal
roots penetrate deeper ,than adventitious roots.
When plants Were
widely spaced, however, both the adventitious and the seminal roots
o f 'Hannchen' barley penetrated to 160 cm ( Pavlychenko and Harrington,
1935).
Barley may be almost e n tir e ly dependent on the seminal roots
to use.moisture stored deep in the s o il p r o file when surface moisture
is depleted (Troughton, 1962).
Although the so il water extraction
patterns o f barley have been studied extensively in Montana, the r e la ­
tiv e depth o f penetration o f the seminal and adventitious roots has
not been determined.
MacKey (1980) described barley seminal roots as thinner and more
branched than adventitious roots.
Goedewaagen (1942) and Krassovsky
(1926) reported th a t seminal roots were able to absorb more HgO/unit
dry weight than adventitious roots.
The number o f adventitious roots/ha is highly v a ria b le w ithin and
between v a r ie tie s , and between years.
In f ie ld studies, l Betzesl
5
barley produced h a lf as many adventitious roots/ha in 1971 as in 1972
(Hockett, 1980).
Seeding ra te was 80.7 kg/ha (72 Ib s /a c re ) both years.
July p re c ip ita tio n was 2.43 cm greater in 1972 than in 1971.
This may
account fo r the large differences in adventitious roots/ha between
years.
A p o sitiv e re la tio n s h ip often exists between the number o f adventi­
tious roots and t i l l e r s per plan t (Brouwer,. 1965).
Adventitious roots
are capable o f developing a t each lower node o f the main culm.
In
a d d itio n , each a x illa r y bud or t i l l e r is capable of developing an inde­
pendent system o f adventitious roots (Troughton, 1962).
The r a tio o f adventitious roots to t i l l e r s
( Brouer, 1965).
is not consistent
Hockett (1980) reported an average o f 4 .3 adventitious
r o o t s / t i l l e r in 1972, but only 1.7 adventitious r o o t s / t i l Ie r in 1971
fo r 'B etzes1.
The average numbers o f t i l l e r s / p l a n t were s im ila r fo r the
two years.
MacKey (1980) described the adventitious root system o f cereals
as "highly fle x ib le " and responsive to d a ily environmental v a ria tio n .
Conversely, he described the seminal root system as "pre-adapted" or
"fixed" because the eventual size is la rg e ly determined by number.
Seminal root number is expressed during germination.
As a re s u lt,
breeders have an opportunity to control the size and d is trib u tio n o f
the seminal root system.
6
The value o f seminal root number as a selection c r ite rio n has
been considered by several researchers.
Fritsch (1977) stressed the
importance o f a high number o f seminal roots fo r seedling e s tab lis h ­
ment.
Pavlychenko and Harrington (1935) and Pavlychenko (1937) sug­
gested th a t cereals with a large number of seminal roots were more
capable o f development under adverse conditions.
Sallans (1942) found
th a t wheat plants which produced the greatest number o f seminal roots
also produced the greatest y ie ld due to an increase in the number o f
kern els/sp ike.
Hurd (1975) reported th a t to ta l seminal root length
a t 5-6 days ranked c u ltiv a rs in a previously determined order of to ta l
root length a t m aturity and y ie ld under moisture stress.
Total root
length a t 5-6 days is la rg e ly a function o f seminal root number.
H istolo gical examinations o f wheat embryos in d icate a th e o re tic a l
maximum o f 10 seminal roots:
the primary axis and 3 whorls with 3 p r i-
mordia each (MacKey, 1980).
Merry (1941 and 1942) found 9 primordia in
'Alpha' b a rle y , each capable o f producing a seminal root.
S ig n ific a n t v a rie ta l differences in barley seminal root numbers
were reported by Pope (1945).
I t was not determined whether these d i f ­
ferences were due to the number o f primordia d iffe re n tia te d in the
embryo or to the number o f primordia a c tu a lly expressed ( i . e . , v is ib ly
elongated).
The v a ria tio n in seminal root numbers commonly observed w ithin
barley lin e s tends to obscure inherent v a rie ta l d iffe re n c e s.
Larger,
7
broader kernels of cereals have been observed to produce a greater
number o f seminal roots w ith in a v a rie ty (Taylor and McCall, 1936;
MacKey, 1980).
Pope (1945) was unable to r e la te v a rie ta l differences in seed
weight to seminal root numbers o f barley.
MacKey (1980), however,
described a good c o rre la tio n ( r = .71.) between seed size and seminal
root number when comparing w ild and c u ltiv a te d wheat.
The p rim itiv e
Aegilops mutica has one seminal root per seed while numbers up to
fiv e or six were recorded fo r some modern v a rie tie s . .
The p rim itiv e b a rle y , Hordeum spontaneum L ., had the smallest
seminal root number (4 .7 roots/seed) o f the Hordeum species tested
by Pope (1945).
The apparent evolutionary trend toward increasing
seminal root number may, in p a rt, re s u lt from selection fo r kernel
plumpness (MacKey, 1980).
Environmental variables during germination, such as s o il tempera
tu re , depth o f planting and s o il m oisture,
o f seminal root number.
influence the expression
The r e la tiv e m aturity of the embryo is also
an important v a riab le (Troughton, 1962).
V a rie ta l comparisons are
v a lid only under c o n tro lled conditions.
The degree o f branching o f the seminal axes w ill determine the
a b il it y of the root system to e ith e r explore a lim ite d s o il volume
exhaustively or a la rg e r volume more exten sively.
The degree of
dominance o f the seminal axes over the branch roots would become an
8
important selection c r ite rio n i f the ob jective is to increase the
depth o f penetration o f the seminal axes (MacKey, 1980).
The seminal root axes show the strongest p o sitiv e geotropic
response, extending v e r t ic a lly downward.
The primary la te r a ls extend
h o riz o n ta lly and then progressively develop p o sitiv e geotropic curva­
ture (R u s se ll,'1 9 7 6 ).
The strong geotropic tendency o f the seminal
axes allow them to extend deeper in the' s o il than the branch roots
(MacKey, 1980).
The degree o f v e rtic a l o rie n ta tio n o f the seminal axes could
also be considered as a selection c r it e r io n , i f genotypic differences
are found to e x is t.
The seminal root axes w ill penetrate deeper than the branch roots
because o f t h e ir higher growth ra te .
prim ary,
The growth rate o f the axes,
and secondary la te ra ls are ty p ic a lly in the r a tio of
4 :1 \ h (M ilthorpe and Moorby, 1974).
The ra te o f extension is often
re la te d to root diameter with the la rg e r men*stems elongating more
ra p id ly (MacKey, 1980; R ussell, 1976; Barley, 1970).
D etailed measurements o f the seminal root system o f barley in d i­
cate th a t the branching pattern is under s t r i c t genetic control
throughout the development o f the p la n t.
For each genotype, as branch
roots progress from lower to higher orders o f magnitude, the character­
is t ic distance between points o f branching decreases and the character­
is t ic o rie n ta tio n becomes more horizontal (Hackett, 1971).
9
The number o f seminal axes, o rie n ta tio n , degree o f branching,
growth ra te , and duration o f the growth period, appear to control the
root d is trib u tio n pattern and thus the a b il it y o f the seminal root
system to e x tra c t a v a ila b le moisture throughout the s o il p r o file .
These morphological c h a ra c te ris tic s are id e n tifia b le a t very e arly
growth stages, thus enhancing th e ir po ten tial value as selection
c r it e r ia (Hurd, 1975; MacKey, 1980).
Montana State U niversity researchers studied the re la tio n s h ip
between heading date and the root growth pattern o f barley v a rie tie s
(SmaiI , 1980; Brown, 1980).
Small (1980) reported a s ig n ific a n t c o rre la tio n (p = .05) between
heading date and s o il water use when comparing 25 m aturity isotypes o f
b arley.
The e a rly maturing isotypes generally used less .s o il moisture
than the •'normals'
Brown (1980) reported th a t differences in to ta l s o il water use
between l Betzes1 and l E rb etl isogenic lin e s (d iffe rin g in heading date
by 8 days) decrease with increasing rates o f nitrogen f e r t i l i z e r .
In
1971, 1Betzes1 used 2.3 cm more s o il water than l E rb etl a t 0 kg N/ha,
1 .5 cm more a t 67.4 kg N/ha^ but only 0 .2 cm more a t 134.7 kg N/ha.
s im ila r trend was exhibited in 1972.
A
l Betzes1 rooted deeper than
l E rb etl and generally used more HgO a t each soil depth a t both 0 and
67.4 kg N/ha.
There was l i t t l e e ffe c t o f heading date on rooting depth
and to ta l s o il water use a t the 134.7 kg N/ha ra te .
10
. In 1971, a very dry growing season, 'E rb e t' produced a greater
number o f adventitious roots/ha than 'B etzes1 a t a ll nitrogen le v e ls .
'B etzes1 used more H2O a t 0 and 67.4 kg N/ha despite having fewer ad­
v e n titio u s roots.
In 1972, a r e la t iv e ly wet y e ar, 'B etzes1 produced a
greater number o f adventitious roots/ha than Erbet a t a ll nitrogen
le v e ls .
MATERIALS AND METHODS
Experiment I: The Relationship Between Heading Date
and Barley Seminal and Adventitious Root Growth
(Slant-Boxes)
Four slant-boxes constructed o f .25 inch plexiglass were used to
measure root growth.
Each box (64.5 cm x 4 .5 cm x 122 cm) was p a r t i­
tioned in to 6 cubicles (10 cm x 4.5 cm x 122 cm) giving a to ta l o f
24 experimental u n its .
The boxes were situ ated a t a 43° angle in a
cabinet in the greenhouse (F ig . I ) .
Opening s lid in g doors in the cabi­
net back allowed observation o f the roots growing along the lower p le x i­
glass face.
The boxes were e a s ily removed from the cabinet fo r washing
ro o ts .
The s o il used in the slant-boxes was from the A^ horizon o f a
ty p ic c a lc ib o ro ll, coarse loamy mixed (Manhattan s e rie s ).
The. so il was
oven dried (IOS0C ), ground, and sieved to a maximum p a r tic le size of
850 microns.
Dry s o il was packed in to the boxes (bulk density =
1.3 g/cm^) and wetted to f ie ld capacity (18% H^O by w eig h t).
The boxes
were covered with polyethylene sheeting to prevent vapor loss and
allowed to e q u ilib ra te fo r one week.
Isogenic pairs o f l Betzes1 and l Hannchenl , each p a ir d iffe r in g -in
heading date by eigh t days, were evaluated in the slant-boxes (F ig . 2 ).
In the Hannchen study, three seeds of uniform size and weight were
planted in each cubicle.
cated 6 times.
The e a rly and the normal isotype were r e p li­
Germination was 100% and emergence r e la t iv e ly uniform.
ThecS la n t- boX used fo r measuring root elongation rates (dimensions are
Figure 2.
Hannchen-early
B
Betzes
BE
Betzes-early
HE1
H2
HE2
H3
HE3
BE2 H4
B3
BE3 HS HE4
uT
B1
HE
CO
BE1
Hannchen
CM
DO
H1
H
H6 HE5 6S BE5 B6
BE6 HE6
Arrangement o f barley m aturity isotypes in slant-boxes fo r
Experiment I (subscripts represent re p lic a tio n s ).
14
The 1Betzes1 isotypes were replanted due to poor germination.
Therefore, the l Betzesl and 'Hannchen' experiments were not run con­
c u rre n tly .
To circumvent the poor germination, seeds o f l Betzesl
(uniform size and weight) were pre-germinated fo r 48 hr.
seedling was transplanted into each cubicle.
One viable
This was a convenient
and r e lia b le method o f s ta rtin g plants in the slant-boxes.
Seminal roots were v is ib le through the p lex i-g la s s w ith in 5 days
o f im b ib itio n , and reached the bottom o f the box in approximately
21-23 days.
Because o f v is ib le w iltin g , the plants o f the Hannchen and Betzes
is o lin e s were ir r ig a te d beginning on the 15th and 17th day, respectively.
Adventitious roots appeared shortly a f t e r ir r ig a t io n .
Approximately
100 ml HgO/cubicle was applied every 5-6 days to f a c i l i t a t e normal
plan t development.
Average elongation rates o f the seminal and adventitious axes were
calculated by the follow ing method:
the lo cation o f each axial root
t ip was marked on the plexiglass a t the end o f each measurement
period (ty p ic a lly 48 h r ).
measured.
The distance between successive marks was
Average a x ia l elongation rates were expressed as cm/root hr.
Plants were harvested a fte r 50 days and the numbers o f t i l l e r s and
heads recorded.
The stems and leaves were dried fo r approximately
48 hr a t GO0C and weighed.
15
The cubicles were saturated fo r several hours to f a c i l i t a t e re ­
moval o f most o f the s o il from the roots.
A fte r soaking, the so il was
washed away using a high pressure nozzle, leaving the root system
v ir t u a lly in ta c t.
The root mass from each cubicle was immersed in
a Calgon solution and gently agitated by hand to disperse the remain­
ing clays.
Root samples were then placed in d is t ille d water to e q u ili­
brate fo r several hours.
The samples were b lo tted dry with paper towel and submerged in a
graduated c ylin d er fo r approximately 2 minutes.
The amount o f water
displaced by the sample was regarded as the fresh root volume.
Total number o f root axes per plant was counted.
The seminal roots
were not distingu ishable from the adventitious roots a f t e r washing.
The root samples were dried a t 60°C fo r 24 hr and ashed ('593°C fo r
two hours) to estim ate the amount o f inorganic so il m aterial l e f t on
the roots a f t e r washing.
The corrected root weights (g dry weight. -
g ash) were used to c a lc u la te the root:shoot weight r a tio s .
Experiment I I : The Relationship o f Heading Date to
Barley Fresh Root Volume, Root Dry Weight, and
Root:Shoot Weight Ratios (Pots)
The two isogenic barley p a irs , 1Betzes1 and l Hannchenl , were
evaluated in 21 cm diameter pots in the greenhouse.
size and weight were pregerminated.
Seeds o f uniform
Three seedlings o f the same
genotype were transplanted into each pot a f t e r 48 hr.
ments were re p lic a te d seven times ( I re p lic a tio n /p o t).
The four tre a ts
The plants were
16
grown in a gravel and sand medium and watered on a lte rn a te days with
1/2 strength Hoagland's solu tio n .
Pots were arranged on the green­
house bench in a randomized block design.
At 48 hr in te rv a ls , the
pots were rotated both w ith in and between blocks.
Plants were harvested a f te r 60 days and the number o f t i l l e r s and
heads, and plant dry weights determined.
Root volumes and root dry
weight were determined using the method described in Experiment I .
Experiment I I I :
The Relationship o f Seed Size to
Seminal Root Number o f Barley
( Germination BoxesT
Two seed lo ts each o f 'B etzes1 and 1Compana1 were separated into
s ix s ize ranges using pairs o f sieves w ith openings 3/4 in long and
widths in 64ths o f an inch o f:
4 .5 and 5 .0 , 5.0 and 5 .5 , 5.5 and 6 .0 ,
6 .0 and 6 .5 , 6.5 and 7 .0 , 7 .0 and 8 .0 .
For each size range, seed
passed through the second (la rg e r) openings and was retained by the
f i r s t (sm aller) sized openings.
F if ty seeds from each size range were
germinated on moist b lo tte r paper in the dark a t 15°C.
The number o f
seminal roots per seedling was counted a f t e r eight days.
Experiment IV: The E ffe c t o f Genotype on Seminal Root
Number o f Barley (Germination BoxeiT
A diverse c o lle c tio n o f 50 barley v a rie tie s consisting o f 25 tworow and 25 six-row types was evaluated fo r differences in seminal root
number.
Seed lo ts produced in one location a t Bozeman, Montana in 1979
were separated in to fiv e size ranges using pairs of sieves whose
17
openings had the follow ing widths, in 64ths o f an inch:
5.0 and 5 .5 ,
5.5 and 6 .0 , 6 .0 and 6 .5 , 6.5 and 7 .0 , 7.0 and 8 .0 (see Experiment
I I I above).
Only the seed size range most c h a ra c te ris tic o f the v a rie ty was
evaluated.
One hundred seed s/variety were germinated on moist b lo tte r
paper a t 15°0 and the number o f seminal roots per seedling counted
a fte r eight days.
Experiment V: The Relationship o f Seminal Root Number
to Fresh Root Volume, Root Dry Weight, and Average
—
Ax ia l Elongation Rate (Slant-Boxes)"
The barley v a rie tie s l DeKap1, 'B rig g s ', ' U nitan' and 'Zephyr' were
selected from the .50 v a rie tie s tested in the previous experiment, fo r
th e ir uniform seed size and weight, and range in mean seminal root
number (Table I ) .
Seeds were treated with Orthocide-Trivax (Vitavax and Captam a t
.007 g/50 seeds) fungicide and pre-germinated on moist b lo tte r paper
fo r 48 hr.
One v iab le seedling was transplanted into each cubicle.
.
The p lo t diagram is given in Fig. 3.
The s o il in the cubicles ^as wet
to f ie ld capacity p rio r to p lan tin g .
Np additional moisture was added
during the course o f the experiment.
Plants emerged uniformly w ith in 48 hr of tran sp lan tin g .
Seminal
roots were v is ib le on the plexiglass face a t the time o f emergence.
Plants were harvested on the 25th day (s ix le a f stage).
A ll other
18
Table I .
C u ltiv a r
C h a ra c te ris tic seed size range, associated seed weight, and
mean seminal root number o f Dekap, Briggs, Unita n , and
Zephyr b arley.
C h a ra c te ris tic
Seed Size
Seed Weight
(sieve open­
ings 64th in )
(g)
Mean Seminal
Root No.
(germ, boxes)
Dekap
(2-row)
6 .5 -7 .0
.049
6.9
Briggs
(6-row)
6 .5 -7 .0
.047
5.9
Unitan
(6-row)
6 .5 -7 .0
.048
5.0
Zephyr
(2-row)
6 .5 -7 .0
.047
. 5.9
D
6T "l
Briggs
U
Unitan
Z
Zephyr
zV
Figure 3.
D2
B2 U2
D3 B3
U3 Z3
-O^.
D1
Dekap
B
U4
Z4
D5 B5
U5 Z5 D6
B6 U6 Z6
Arrangement o f barley v a rie tie s in slant-boxes fo r Experiment V
(subscripts represent re p lic a tio n s ).
20
m aterials and methods were s im ila r to those described for, Experiment I .
Experiment V I: Seminal Root Number and Mean Seminal
Root Axial Elongation Rate (Pots)'
The v a rie tie s evaluated in Experiment V were grown in 21 cm d ia ­
meter pots as described fo r Experiment I I .
Plants were harvested
12 days a f t e r tran s p la n tin g , seminal root axes were counted, and the
length o f each seminal root axis measured.
RESULTS AND DISCUSSION
Experiments I and LI
Fresh root volume
Fresh root volumes o f the e a rly maturing barley isotypes were
s ig n ific a n tly lower than fo r the normal isotypes grown in the s la n tboxes and pots (Table 2 ).
The mean, root volumes o f the 'B e tz e s -e a rly 1
isotype were 59% and 56% o f the 1normal1 in the slant-boxes and pot
experiment, re sp ec tiv e ly .
'Hannchen-early' exhibited a s im ila r ten­
dency, having a root volume 57% o f the normal in the slant-box and 40%
o f the normal in the pot experiment.
Root dry weight
Mean root dry weights (Table 2 ) , which were highly correlated
( r = .94 over both experiments) to root volumes, were greater in
1normal1 is o lin e s .
Root weights of 'B etze s -e arly ' were 65% and 61% of
the normal maturing 'B etzes' in the slant-boxes and pots, respectively
'Hannchen-early' responded s im ila r ly , giving root dry weights of 59%
and 48% o f the 'norm al1 in the slant-boxes and pots, resp ec tiv e ly .
Approximately 50% of the dry sample weight was removed during the
ashing procedure which reduced the w ith in -lin e v a r ia b ilit y o f the
' Hannchen' isotypes.
I t appears th a t in the ' Hannchen' isotypes the
ash correction procedure removed some o f the random e rro r associated
with the inorganic s o il m aterial s t i l l l e f t on the roots a f t e r washing
Table 2.
Mean fresh root volume (m l), root dry weight ( g ) , shoot dry weight (g ), root:
shoot r a tio s , and to ta l number o f root axes o f barley m aturity isotypes (s la n tboxes and pots)
Slant-boxes ( t te s t) Exp. I
Betzes Betzes- Hannchen Hannchene a rly
e a rly
Root
voIumes
(ml)
Root dry
weights
■( g) .
Shoot dry
weights
(g)
.
Rootrshoot
ra tio s
Number of
root axes
23.4
13.8
.002)
Cp S=
25.5
14.5
(p = .004)
Betzes
Pot s (ANOV) Exp. TT
Betzes- Hannchen Hannchene a rly
e a rly
1 1 .5 .
6.5
.001)
(P =
14.3
5.7
.001)
(P =
.89
1.37
.039)
(P =
2.18
1.29
.001)
(P =
2.62
1.60
.004)
(P =
2.85
1.37
.001)
(P =
5.26
NS
5.99
4.76
.010)
.
(P =
8.80
9.34
.402)
(P =
. 9.14
8.09
(p = .010)
5.46
.16
.26
.001)
(p =
.22
.46
.003)
(P =
52
36'
.018)
(P =
39
53
(P = .050)
.30
.17
.001)
(P =
-
-
.
.31
.17
.001)
(P =
-
-
23
P ro b a b ility values were decreased fo r the 1Hannchen1 isotypes from
.0339 to .0001.
However, p ro b a b ility estimates o f 1Betzes1 and
'B e tz e s -e a rly 1 were increased from .0147 to .0394.
The pot experiment allowed comparisons between the l Betzes1 and
l Hannchen1 lin e s .
Differences in mean root weights and volumes be­
tween 'B e tze s -e a rly ' and ' Hannchen' were s ig n ific a n t (.0 1 ) as were
differences between 'Hannchen-early' and 'B etzes1 ( .0 1 ) .
'B etzes' and
' Hannchen' were not d iffe r e n t from each other nor was 'Hannchen-early'
d iffe r e n t from 'B e tz e s -e a rly '.
Root:shoot ra tio s
Since mean shoot dry weights were s im ila r , differences among
root:shoot ra tio s generally re fle c te d the respective differences in
root weights (Table 2 ).
Total number o f root axes
D ifferences among the average number o f root axes roughly p a ra l­
le le d differences in root weight and volume in the slant-box.
The
e a rly isotypes of ' Betzes' and ' Hannchen' had 69% (p = .018) and
74% (p = .049) as many root axes as the 'norm al' , re sp ec tiv e ly .
The
root weights o f 'B etzes1 and 'B e tze s -e a rly ' were highly correlated
( r = .94) to the to ta l number o f root axes (seminal + a d v e n titio u s ).
24
Seminal axes elongation rates
The a x ia l elongation rates o f l Hannchen1 and 'Hannchen-early1
barley generally increased during the f i r s t 15-17 days (F ig . 4 ).
Sharp declines o f axial elongation rates from the 17-19th days were
observed.
The cause o f these declines is unclear.
Low s o il moisture
and/or high temperature may have lim ite d root growth during th at
measurement period.
A d d itio n a lly , a portion o f the photosynthate
previously a v a ila b le fo r seminal root growth may have been p a rtitio n e d
to the adventitious roots which appeared on the 17th day.
Apparent
differences between the 'e a r ly ' and the 'norm al' maturing ' Hannchen' .
on the 21st and 23rd days may have been an a r t if a c t o f the system..
Measurements during these periods are inconclusive because a s ig n if i­
cant number o f seminal axes had reached the bottom of the box.
The elongation rates o f the seminal axes o f 'B etzes1 and 'Betzese a rly ' generally increased u n til the I l t h day (F ig . 5 ).
The rates
s ta b iliz e d during the next four measurement periods and markedly
increased in the fin a l measurement period (1 8 -2 2 ).
Seminal roots may
have responded to surface ir r ig a tio n on the 18th day.
No s ig n ific a n t
differences between the 'e a r ly ' and the 'norm al' maturing Betzes were
observed during the f i r s t 22 days.
A fte r the adventitious roots began to develop, the seminal root
axes o f both isogenic pairs continued to extent v e r t ic a lly a t least
7-10 days (or u n til they reached the bottom o f the box).
This suggests
PO
Ul
5
9
13
17
21
Days from Transplanting
F ig u r e 4 .
E lo n g a t io n
ra te s
o f b a r le y s e m in a l
r o o t a x e s : Hannchen and H a n n c h e n - e a r ly .
ro
5
9
13
17
21
Days from Transplanting
F i g u r e 5.
E lo n g a tio n
r a t e s o f b a r l e y s e m in a l
r o o t a x e s : B e t z e s and B e t z e s - e a r l y .
27
th a t the seminal axes may not cease to elongate during the e a rly
stages o f adventitious root development.
The seminal axes may be
able to penetrate deeper in the s o il p r o f ile than the adventitious
axes because the seminal roots ty p ic a lly have a 2 week head s ta r t.
The a x ia l elongation pattern of seminal roots was not observed during
stem extension, anthesis, and heading because of the lim ite d depth of
the slant-boxes.
Thus, we were not able to study the e ffe c t of
heading date on seminal root elongation ra te s .
Elongation rates o f the adventitious
axes
Q u an tific a tio n
of
adventitious root development was very d i f ­
f i c u l t la rg e ly because of the rapid increase in the number o f axes.
Elongation rates were very e r r a tic (F ig . 6 ) .
Axes often elongated
10-15 cm, ceased elongation and were replaced by new axes in it ia t in g
a t the crown region.
No s ig n ific a n t differences in adventitious root a x ia l elongation
ra te were detected between 'Hannchen' and 'Hannchen-early'.
Three
plants per cubicle produced too many roots on the small viewing sur­
face to allow accurate measurement o f elongation ra te s .
moisture was also d i f f i c u l t to m aintain.
Uniform soil
The large differences in
root volume and weight between 'Hannchen' and 'Hannchen-early' may have
been due to the number o f adventitious axes rath er than elongation
ra te s .
ro
oo
Days from Transplanting
F ig u re 6.
E lo n g a tio n
e a rly .
ra te s o f b a rle y a d v e n titio u s
r o o t a x e s : B e tz e s and B e t z e s -
29
The average adventitious a x ia l elongation rates o f 'B etzes1 and
'B e tze s -e a rly ' roots are plotted in Fig. 6.
1Betzes1 root axes elon­
gated more ra p id ly than 'B e tze s -e a rly ' a f t e r the 34th day.
The heads
o f 'B e tze s -e a rly ' were beginning to appear on the 35th day, while the
plants o f the normal maturing 'B etzes' were s t i l l in the t i l l e r i n g
stage.
'B e tze s -e a rly ' adventitious root axes elongation rates de­
creased a t the onset of heading.
I t is postulated th a t the adventitious roots of e a rly types might
f a i l to reach the lower s o il zones i f the lower elongation rates of
adventitious axes exhibited by ' B etzes-early' are c h a ra c te ris tic o f
e a rly maturing is o lin e s .
Consequently, the e a rly types might depend
almost exclu sively on th e ir seminal roots to e x tra c t HgO from the
lower s o il zones.
Experiment I I I
Mean seminal root numbers of s ix d iffe r e n t seed s ize ranges and
two d iffe r e n t seed lo ts o f 'B etzes' and ' Compana' barley are compared
in Table 3.
S ig n ific a n t co rrelatio n s between seed size and seminal
root number were observed fo r a ll four treatm ents.
The high corre­
la tio n ( r = .9 0 , a ll four seed sources combined) provides additional
evidence o f the w ith in lin e v a r ia b ilit y in root number due to seed
s ize .
30
Table 3.
The e ffe c t o f seed size on the seminal root number o f
Betzes and Compana barley.
Seed Size Range
(sieve openings,
64ths in )
Compana I
Mean Seminal Root Number
Compana I I
Betzes I
Betzes I I
4 .5 - 5.0
5.8
5.7
5.7
5.4
5.0 - 5.5
5.7
6.0
5.9
. 5.9
5.5 - 6.0
6.4
6.4
6.0
6.2
6 .0 - 6.5
6.5
6.6
6.2
6.3
6.5 - 7.0
6.5
7.0
6.5
6.5
7 .0 - 8 .0
6.8
7.0
6.8
6.5
31
Based on th is inform ation, we concluded th at w ithin lin e v a ria ­
b i l i t y in seminal root numbers may be minimized by selecting the seed
size range most c h a ra c te ris tic o f the seed lo t when te s tin g v a rie ta l
d iffe re n c e s.
Experiment IV
The average seminal root numbers o f the 50 barley v a rie tie s are
reported in Tables 4 and 5.
Most (21) o f the 25 two-row v a rie tie s had
average seminal root numbers th a t were greater than any o f the 25 s ix row v a r ie tie s .
The average seminal root number o f the 25 two-row
v a rie tie s (6 .3 ) was s ig n ific a n tly greater (p = .01) than th a t o f the
six-row v a rie tie s ( 5 .2 ) .
Mean root numbers ranged from 5.5 - 6.9
(L.S.D . = .4 ) fo r two-row v a rie tie s and from .4 .3 - 5.9 (L.S .D . = .2 )
fo r six-row v a rie tie s .
Experiments V and VI
Seminal root numbers
Mean seminal root numbers obtained in the various experiments are
compared in Table 6.
tween experiments.
three experiments.
Ranges in mean seminal root numbers varied be­
However, the v a rie ta l rankings were the same in a ll
32
Table 4.
Mean seminal root numbers,. seed s ize s , and seed weights
o f 25 two-row barley v a rie tie s
V a rie ty
Dekap
Erbet
Herta
Compana
P iro lin e
Haisa I I
Horn
Marie
Vanguard
Georgie
Heines Hanna
Freja
Otis
New Moravian
Hannchen
Munsing
Klages
Firlbeck I I I
Spartan
Ingrid
Betzes
Maris Mink
Zephyr
Hector
Vireo
Mean Seminal
Root Number
6.9
6.8
7.8
6.7
6.6
6.6
6.5
6.5
6.5
6.4
6.4
6.4
6.3
6.3
6.2
6.1
6.1
6.1
6.0
6.0
6.0
5.9
5.9
5.9
5.5
Seed Size Range
(sieve openings
64ths in )
6.5
6.5
6.5
7.0
6.5
6.5
6.5
6.5
6.5
. 6.5
6.5
6.5
7.0
6.0
■ 6 .0
7.0
5.5
7.0
7.0
6.5
6.5
6.0
6.5
6.0
6.5
-
7.0
7.0
7.0
8.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
8.0
6.5
6.5
8.0
6.0
8.0
8.0
7.0
7.0
6.5
7.0
6.5
7.0
Mean Seed
Weight (g)
.049
.048
.042
.063
.045
.043
.046
.048
.046
.048
.046
■ .045
.056
.040
.040
.060
.035
.049
.053
.044
.046
.038
.047
.041
.036
33
Table 5.
Mean seminal root numbers, seed s izes, and seed weights
o f 25 six-row barley v a rie tie s
V ariety
Briggs
Beecher
Atlas 46
G lacier
Primus I I
barker
Ga! t
Dickson
Trophy
Harlan
Gem
Hiland
Nordic
Bonneville
Steptoe
Vantage
Montcalm
Steveland
Ca M ariot 67
T r a ill
Titan
Unitan
L iberty
Trebi
F ro n tie r
Mean Seminal
Root Number
5.9
5.8
5.7
5.6
5.6
5.6
5.5
5.4
5.4
5.4
5.4
5.3
5.2
5.2
5.2
5.2
5.1
5.1
5.1
5.0
5.0
5.0
4 .8
4.7
4.4
Seed Size Range
(sieve openings
64ths in )
6.5
7.0
6.5
6 .5
6 .5
6.5
5.5
6.0
6.0
. 6.5
7 .0
6.5
5.5
6.5
6.5
5.5
5.5
6 .0
6.5
5.5
6 .0
6.5
6.0
5.5
6.5
-
7.0
8.0
7.0
7.0
7.0
7.0
6.0
6.5
6.5
7.0
8 .0
7.0
6.0
7.0
7.0
7.0
6.0
6.5
7.0
6.0
6.5
7.0
6.5
6.0
7.0
. Mean .Seed
Weight (g)
.047
.056
.051
.059
.039
.038
.032
.037
.034
.049
.061
.042
.029
.047
.043
.030
.029
.038
.049
.032
.036
.048
.035
.037
.031
-■
34
Table 6.
Mean barley seminal root numbers obtained in germination
tra y s , slant-boxesj and pots.
V a rie ty
Mean Seminal Root Numbers
Slant-Boxes
Germination Trays
Pots
Dekap
6.9
7.2
7.5
Briggs
5.9
5.8
. 5.8
Unitan
5.0
5.6
5.2
Zephyr
5.9
5.8
5.8
6
18
No. of
Replications
100
35
Root volumes
The fresh root volume o f 'Dekap' was s ig n ific a n tly greater than
'U nitan'
(p = .0 0 7 ), 'B riggs' and 'Zephyr' (p - .05) in the slant-box
experiment (Table 7 ).
The root volumes o f 'U n ita n ', 'B riggs' and
'Zephyr' did not d if f e r s ig n ific a n tly .
The c o rre la tio n between root number and volume was not s ig n ific a n t
w ith in lin e s .
This was probably because a discrete v a riab le (root
number) was compared to a continuous v a riab le (root volume) and because
the range in root numbers and root volumes w ithin lin e s was small.
Mean v a rie ta l root numbers, however, are correlated with mean root
volumes ( r = .96; 2 degrees o f freedom).
Using v a rie tie s with a wider
range in mean seminal root numbers may have yielded more conclusive
inform ation.
No inverse re la tio n s h ip between seminal root number and
volume was apparent when v a rie ta l means were compared.
Dekap had the
greatest number o f seminal roots and the la rg e s t root volume a fte r
25 days.
Root dry weight
V a rie tie s had s im ila r rankings fo r root dry weights, seminal root
numbers and root volumes.
Differences among mean root dry weights,
however, were not s ig n ific a n t.
.
Root dry weights were s ig n ific a n tly
correlated to root volumes ( r = .73) when individual values were used
(Table 7 ).
o f freedom.
For comparison o f v a rie ta l means, r = .86 with two degrees
36
Table 7.
V ariety
Mean root volumes and root dry weights o f barley grown in
slant-boxes.
Root Volumes
(ml)
Root Dry Weight
(g)
Dekap
3.48
.2212
Briggs
2.85
.2168
Unitan
2.50
.2039
Zephyr
2.82
.2164
(ANOV)
(p = .007)
(p = .84!
37
Root growth pattern
The seminal axes elongation rates (cm /root-hr) o f a ll barley
v a rie tie s decreased between the 5th and the 8th day (F ig . 7 ).
This
decrease may have been due to the exhaustion o f n u trie n t reserves in
the seed.
Williams (1960) a ttrib u te d a decrease in root growth rates
o f wheat between the 8th and I l t h day from seeding to the depletion of
seed n u trie n t reserves.
Leaf area and net photosynthesis may not have
been s u ffic ie n t to sustain root growth rates attained p rio r to the
8th day.
On the 7th day of our study, mean le a f blade lengths of
l Dekapl , 'B rig g s ', ' Unit a n ', and 'Zephyr' were 9 .6 , 7 .8 , 8 .2 , and .
8.1 cm, re s p e c tiv e ly .
The second le a f t ip was v is ib le on the v a rie tie s
'Dekap' and 'Z e p h yr'.
Root elongation rates o f a ll v a rie tie s increased from day 8
through day 17.
Root elongation rates decreased fo r the two-row types
( 'Dekap' and 'Z e p h y r') and increased fo r the six-row types ('B rig g s '
and 'U n ita n ') between days 17 and 20.
Decreased root growth rates
coincided w ith a period o f high afternoon temperatures and associated
high evap o -tran sp iratio n .
A ll plants showed moisture stress ( i . e . ,
w iltin g ) during the day but regained tu r g id ity a t n ig h t.
Temperatures
moderated a f t e r the 20th day and the a x ia l elongation rates of a ll four
v a rie tie s increased d ram atically during the fin a l measurement period.
Normal shoot growth resumed when daytime temperatures remained below
21°C, in d ic a tin g use o f moisture in the s o il held a t higher tensions.
Axial Elongation Rate (cm /root-hr)
O
DeKAP
•
ZEPHYR
A
BRIGGS
A
UNITAN
VJ
OO
L
5
9
13
17
Days from Transplanting
Figure 7.
Elongation rates o f barley seminal root axes:Dekap, Zephyr, Briggs and
Unitan.
39
V a rie tie s d iffe re d in response to moisture stress.
Axial elon­
gation rates were reduced the most fo r l Dekapl . Since 'Dekap' had a
greater root volume, i t may have conserved less moisture a t e a r lie r
growth stages.
A d d itio n a lly , the elongation o f the branch roots was
not re fle c te d in the ra te determ ination.
'Dekap' may have p a rtitio n e d
a greater proportion o f photosynthate in to la te r a l roots a t the
expense o f a x ia l elongation.
S ig n ific a n t v a rie ta l differences among mean axial elongation rates
were calculated fo r six .of the eight, measurement periods (F ig . 7);
Axial elongation rates, averaged over the 23 day growth period in
slant-boxes, in d icate the penetrating capacity o f the seminal root
system (Table 8 ).
The fin a l depth o f penetration can only be deter­
mined by observing the actual location o f the axial root tip s , a t
p la n t m a tu rity .
The slant-boxes did not have s u ffic ie n t depth to allow
maximum penetration; the m ajority o f the seminal root axes reached the
bottom o f the box w ith in 25 days.
The average axial elongation rates o f 'Dekap' (.166 cm /root-hr)
and 'Zephyr' (.172 cm /root-hr) were not s ig n ific a n tly d iffe r e n t.
'Dekap' (7 .2 axes/p lan t) may be capable of producing a greater root
length a t a given depth (assuming a s im ila r degree o f branching) than
'Zephyr' (5 .8 a xes/p lan t) because o f the greater number o f extended
seminal axes.
40
Table 8.
Mean elongation rates o f seminal root axes o f Dekap1
Briggs, U nitan1 and Zephyr (average ra te during the
2 3 .day growth period in slant-boxes)
V a riety
Mean cm /root.hr
Dekap
.166
Briggs
.190
Unitan
.192
Zephyr
.172
LO
O
Il
CL
(ANOV)
.41
The six-row types, 'B riggs' (.190 cm /root.hr) and 'U nitan'
(.192 c m /ro o t-h r), exhibited higher average axial elongation rates
than 'Zephyr' and ' Dekap' (p = .0 5 ).
Higher elongation rates suggest
a corresponding increase in the depth o f penetration o f the seminal
root system (a t 23 days).
D aily observations o f a x ia l elongation rates f a c i l i t a t e the
id e n tific a tio n o f important genotyperenvirbnment in tera c tio n s ( e . g . ,
the apparent in te ra c tio n between evaporative demand and the axial
elongation rates o f the v a r ie tie s ). . In teractio n s occurring during
la t e r growth stages may preclude e a rly determination o f root growth
patterns o f barley.
Figure 7 shows th at the root axes o f a ll four v a rie tie s were
elongating very ra p id ly near the end o f the slant-box experiment.
This
suggests th a t the major lim ita tio n o f the slant-boxes is the in a b ilit y
to monitor a x ia l elongation rates beyond the six le a f stage o f barley.
D ifferences in seminal a x ia l root elongation rates were greatest
during the fin a l two measurement periods.
Further in ve s tig atio n of the pattern o f axial elongation during
the reproductive phase o f development is warranted.
I t would also be
desirable to observe the ra te of penetration of the seminal axes in a
s itu a tio n where the adventitious roots were allowed to develop normally.
Because of the lim ite d surface m oisture, adventitious roots did.
not elongate more than a few m illim eters in the slant-boxes.
42
S ig n ific a n t v a rie ta l differences (p = .01) in the elongation
rates o f the seminal root axes were also measured in the pots (Table 9)
'U n ita n 1 had the sm allest seminal fo o t number but the highest axial
elongation ra te .
Thus, there may be some tendency fo r root axial
elongation rates to compensate fo r root numbers a t e a rly growth stages.
Root number is more important than elongation ra te in determining the
to ta l length o f axes a t 12 days.
This is illu s tr a te d by comparing the
cumulative root length indexes (mean seminal root number x cm /root-hr)
o f l Dekapl (.5 5 7 ) and l U nitanl (.4 3 8 ).
43
Table 9.
V ariety
Mean elongation rates o f seminal axes and cumulative root
length indexes o f Dekap, Briggs, Unitan, and Zephyr
(average ra te during the 12 day growth period in pots)
Mean cm /root*hr
Cumulative Root
Length Index*
Dekap
.074
.557
Briggs
.076
.440
Unitan
.085
.438
Zephyr
.077
.447
(ANOV)
(p = .01)
(p =
C um ulative root length index = mean seminal root number
x (c m /ro o t*h r).
SUMMARY AND CONCLUSIONS
Seminal and adventitious root morphological c h a ra c te ris tic s o f
barley m aturity isotypes were compared.
Early maturing isotypes of
l Betzesl and 'Hannchen' grown in slant-boxes produced sm aller rpot
volumes, root weights, and rootzshoot ra tio s than 'normals' due to a
reduction in the elongation ra te and number o f adventitious root axes.
A s im ila r decrease in root volumes, weights, and rootzshoot ra tio s
characterized 'e a r ly ' isotypes grown in pots.
Tw enty-five two-row and 25 six-row barley v a rie tie s were grown
in germination boxes to determine differences in mean seminal root
numbers.
S ig n ific a n t v a rie ta l differences in mean seminal root number
were observed.
Two-row barley v a rie tie s generally developed a greater
number of seminal roots than six-row v a r ie tie s .
Within lin e v a r ia b il­
i t y in seminal root number was reduced by te s tin g the seed size range
most c h a ra c te ris tic o f the v a rie ty .
Four v a rie tie s representing a
wide range in mean seminal root number were evaluated in slant-boxes
to determine i f increased branching compensates fo r low root number.
No inverse re la tio n s h ip between mean seminal root number and root
volume 25 days from transplanting was apparent when v a rie tie s were com­
pared.
V a rie tie s d iffe re d
in mean elongation ra te of seminal axes in
six o f eigh t measurement periods.
Seminal axial elongation rates o f
'Dekap' and 'Zephyr' decreased during periods o f high evapotra n s p ira tio n .
The elongation rates o f ' U nitan' and 'Briggs'
45
continued to increase during those periods.
Because o f these
genotype-environment in teractio n s n e ith er the pattern o f seminal
a x ia l elongation nor the fin a l rooting depth is predictable a t early
growth stages.
Seminal axial elongation rates o f v a rie tie s appeared to com­
pensate fo r smaller root numbers when grown in pots.
Seminal root
numbers, however, were more important than elongation rates in deter­
mining the to ta l length o f seminal axes a t 12 days.
The slant-boxes were b e tte r adapted to the study o f seminal than
adventitious roots.
Adventitious root development was e a s ily in h ib ite d
by maintaining a low s o il water content adjacent to the plan t crown. "
Seminal root elongation was observed d a ily u n til the 6 le a f stage o f
bgrley, when seminal root growth was re s tric te d by the bottom o f the
slant-box.
V a rie ta l differences in seminal root number should be demonstrated
fo r other seed sources.
The re la tio n s h ip between seed size and seminal
root number fo r commercial v a rie tie s other than l Betzes1 and 'Compana1
should also be determined.
Breeders may be able to increase the depth o f penetration of the
seminal root system o f barley by combining high seminal root numbers
with long root growth ra te duration, v e rtic a l o rie n ta tio n , and de­
creased branching.
A ll o f these seminal root morphological
46
c h a ra c te ris tic s must be incorporated to s ig n ific a n tly increase u t i l i ­
zation o f residual s o il moisture.
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Roddy, Daniel M
Root morphological
characteristics of "barley
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