AN ABSTRACT OF THE THESIS OF

MAPANGADA CHENGAPPA GANAPATHY for the (Name)

in FARM CROPS (Major)

Ph. D. (Degree)

presented on March 8, 1968

(Date)

Title: INFLUENCE OF POPULATION DENSITY ON LIGHT INTER-

CEPTION AND GRAIN YIELD INVOLVING WHEAT HYBRIDS

Redacted for privacy Abstract approved: Warren E. Kronstad

Six wheat hybrids from two sets of parents and their respective

parents were grown at Hyslop Agronomy Farm near Corvallis, Oregon

in the year 1965 -66. The object of the experiment was to evaluate the

influence of population densities and different planting patterns on

grain yield and factors which determine grain yield. Factors studied

included the leaf area index, percent light interception, plant height,

and the components of grain yield which are tillers per unit area,

kernel per spike and the weight of 1, 000 kernels. The design of the

experiment was first order factorial randomized split plit with 12

phenotypes X two population densities X five patterns of planting.

Leaf area was measured without detaching leaves from the

plant at three stages of growth. These included the jointing stage,

prior to flag leaf and the heading stage. Light interception in the

plant canopy was obtained by exposing ozalid paper which was placed

two inches above the soil surface between the plants for nine hours

during the day, At maturity, data were collected on total dry matter

production, kernels per spike, 1, 000 kernel weight and grain yield.

Leaf area index and tillers per unit area in hybrids and parents

were not significantly different at the jointing stage. However, signi-

ficant differences were observed for both the characteristics in the

later stages of growth due to the reduction in tiller number per unit

area. The lethal effect on tillers was due to shading of upper leaves

on the same plant and from surrounding plants. Significant differences

among parents and hybrids for tolerance to the influence of shading

was observed. Two hybrids derived from the cross Druchamp X

Redmond and Druchamp X Travero were found to be more tolerant

and produced significantly higher grain yield than their respective

parents.

Leaf area index was found to be influenced by plant density,

patterns of planting, tillers per unit area and plant height. Signifi-

cantly higher grain yield was produced with a 12" solid planting than

any other patterns of planting as a result of more tillers per unit

area being present at harvest time.

The percentage light intercepted by the plant canopy was directly

associated with plant height at the jointing stage while in the latter

stages of growth the leaf area index was more important in deter-

mining the amount of light intercepted. Increased population density

per unit area and closer row spacing increased the percentage of

light intercepted. Dry matter production was proportionately higher

with increased light interception. The percentage of light intercepted

at the heading stage was found to have a greater influence on grain

yield than at any other stage of growth. The cross Druchamp X

Travero which produced 33 percent higher grain yield than the better

parent was found to exhibit hybrid vigor for all characteristics in the

later stages of growth.

Influence of Population Density on Light Interception and Grain Yield Involving Wheat Hybrids

by

Mapangada Chengappa Ganapathy

A THESIS

submitted to

Oregon State University

in partial fulfillment of the requirements for the

degree of

Doctor of Philosophy

June 1968

APPROVED:

Redacted for privacy Assistant Professor of Farm Crops

in charge of major

Redacted for privacy Head of he Farm Crops Department

Redacted for privacy Dean of Graduate School ')

Date thesis is presented March 8, 1968

Typed by Gwendolyn Hansen for Mapangada Chengappa Ganapathy

l

ACKNOWLEDGEMENTS

This study was conducted under the guidance of Dr. Warren E.

Kronstad. I take this opportunity to express my sincere thanks to

Dr. Kronstad for his encouragement and helpful suggestions during

the preparation of this manuscript.

Sincere appreciation is extended to Dr, Wilson Foote,

Dr, Ralph Bogart and Dr. William Chilcote for their constructive

criticism and for reviewing the manuscript,

The author is indebted to Dr. D. O. Chilcote for his suggestions

concerning the measurements of light under field conditions.

A special note of gratitude is expressed to my mother,

Mrs. Mapangada Chengappa, for her encouragement and for

sponsoring my studies at Oregon State University.

My appreciation is also extended to Mrs. Gloria M. Foster

for her helpful suggestions in the typing of this manuscript.

TABLE OF CONTENTS

INTRODUCTION

Page

1

LITERATURE REVIEW 3

Leaf Area 3

Light Interception 5

Components of Yield 8

Hybrid Vigor in Wheat 9

MATERIALS AND METHODS 12

EXPERIMENTAL RESULTS 23

DISCUSSION 51

SUMMARY AND CONCLUSIONS 61

BIBLIOGRAPHY 64

APPENDIX 1. Pedigree and description of the six parental winter wheat. 70

APPENDIX 2. Phenotypic appearnace of the six wheat parents and six hybrids. 72

LIST OF TABLES

Table Page 1. Correlation c,e_ficient.=3 involving the percent light

transmission through the Kodak Standard neutral density filters and the number of ozalid papers exposed for nine hours daylight. 21

2. Mean squares for leaf area index and percent light interception in six wheat hybrids and their respec- tive parents at three stages of growth, I- jointing stage, II -prior to flag leaf and III -heading stage.

3. Mean squares for tillers per unit area and plant height in six wheat hybrids and their respective parents at three stages of growth, I- jointing stage, II -prior to flag leaf, III -heading stage.

4. Mean squares for dry matter production per unit area, kernels per spike, weight of 1,000 kernels, and grain yield per unit area in six wheat hybrids and their parents, planted in two plant densities and five patterns of planting.

5. Mean values for leaf area index and percent light interception for six wheat hybrids and their parents at three stages of growth, I- jointing stage, II- prior to flag leaf and III- heading stage.

6. Mean values for tiller number per unit area and plant height in six wheat hybrids and their parents at three stages of growth, I- jointing stage, II- prior to flag leaf, and III- heading stage.

7. Mean values for dry weight per unit area, number of kernels per spike, weight of 1,000 kernels, and grain yield per unit area in six wheat hybrids and their parents grown at Corvallis, Oregon in 1965 -66.

24

25

31

35

36

37

Table Page

8. Mean leaf area index and percent light interception at three stages of growth, I- jointing stage, II- prior to flag leaf, and III -heading stage and mean values for dry matter production per unit area, number of kernels per spike, weight of 1, 000 kernels and grain yield per unit area in six wheat hybrids and their respective parents. 40

9. Mean values for tiller number per unit area and plant height at three stages of growth, I- jointing stage, II -prior to flag leaf, and III -heading stage in five patterns of planting.

10. Mean values for leaf area index, number of tillers, plant height and percent light inerception at three stages of growth, I- jointing stage, II -prior to flag leaf and III- heading stage and mean values for dry matter production per unit area, number of kernels per spike, weight of 1,000 kernels and grain yield per unit area in six wheat hybrids and their respective parents.

11. The mid -parent value (MP) and hybrid performance for leaf area index, number of tillers, plant height, light interception at three stages of growth and mean values for dry matter production, kernels per spike, weight of 1,000 kernels and grain yield per unit area (P1- Brevor, P2 -Sel. 101, P3 -Sel. 172, P4- Druchamp, P5- Redmond, P6- Travero).

12. Correlation coefficients for sixteen variables measured in six wheat hybrids and their respective parents.

41

42

44

45

LIST OF FIGURES

Figure Page

1. Planting patterns of winter wheat varieties for measurements of light interception between rows. 13

2. Ozalid paper exposure to light in wheat field: 18

A, Ozalid book mounted with Kodak neutral density filters.

B. Ozalid book uncovered and arranged to show the depth of light penetrance through the papers under each filter.

C. Ozalid book exposed between four plants. D. Ozalid book uncovered and arranged for

counting the number of pages exposed. E. Ozalid paper exposed to a constant light

for a known period of time which is the index for counting the fractions of exposure.

3. Relationship between the percent light transmittance through the Kodak neutral density filters and the number of Ozalid papers bleached from nine hours exposure to direct sunlight.

4. Relationship of leaf area index and light inter- ception percent in wheat hybrids and their respective parents.

5. A. Influence of the leaf area index on percent of light interception in five patterns of planting.

B. The effect of light interception on the number of tillers per unit area in five patterns of planting.

C. Influence of leaf area index on plant height in five patterns of planting.

20

27

29

Figure

6. A. Relationship of light interception to dry matter production in wheat hybrids and their respective parents.

B. Relationship of light intercepted percent to dry matter production per unit area in six wheat hybrids and their parents involving in two plant densities.

7. A. Path- coefficient analysis showing the direct and indirect relationship of leaf area index (LAI -I), number of tillers per unit area and plant height with the percent light interception at the jointing stage.

B. Path - coefficient analysis showing the direct and indirect relationship between light inter- ception, leaf area index (LAI -II), number of tillers, and plant height prior to flag leaf stage.

C. Path - coefficient analysis showing the direct and indirect relationship between light inter- ception, leaf area index (LAI -III), number of tillers and plant height at heading stage.

8. A. Path - coefficient analysis showing the direct and indirect relationship of the leaf area index on number of kernels per spike at the jointing stage, prior to flag leaf and heading stage.

B. Path - coefficient analysis showing the direct and indirect relationship of the leaf area index, number of tillers and plant height on dry matter production at the heading stage.

9. A. Path - coefficient analysis showing the direct and indirect relationship between leaf area index at three stages of growth on seed yield per unit area.

B. Path - coefficient analysis showing the direct and indirect relationship between spike bearing tillers, kernels per spike and weight of kernels on seed yield per unit area.

Page

33

48

49

50

INFLUENCE OF POPULATION DENSITY ON LIGHT INTERCEPTION AND GRAIN YIELD INVOLVING

WHEAT HYBRIDS

INTRODUCTION

In developing agronomically superior wheat varieties, plant

breeders have been mainly concerned with selecting lines for simply

inherited characters such as disease resistance with little or no atten-

tion being given to developing plants which are more efficient in their

use of light energy. Less emphasis has been given to the vital

process by which a plant synthesizes its products and in developing

techniques for selecting plants which are more efficient in utilizing

light energy and thereby producing more metabolic substrate. Even

though much is known concerning photosynthesis and the importance

of light in crop species, very little is known concerning the amount

of light that is intercepted and the relationship between the total leaf

area and grain yield.

Review papers on the competition for light in crop species by

Donald (1961) and Black (1957) have emphasized the importance of

solar radiation in determining crop production. Data have been

presented which shows that the amount of light intercepted is an

important factor in determining yield in corn (Eik and Hanway, 1966),

orchardgrass (Pearce, et al. , 1965), soybeans (Shaw and Weber,

1967) and cotton (Baker and Meyer, 1966). In addition, the amount

2

of light utilized in photosynthesis is not the same in all species

(Hesketh, 1963). Since there are differences among species in

utilizing light energy, then there could also be differences within

species for more efficient use of light energy. No attempt has been

made to select parents and progeny in wheat which are more efficient

in utilizing light energy under field conditions. Furthermore, wheat

breeders generally evaluate their breeding material under spaced

planted conditions, whereas wheat is grown commercially in solid

planting. This raises the question as to how valued such estimates

and selections are when the materials are not grown under a competi-

tive stress in the early generations.

The objects of this experiment were: (1) to determine the leaf

area of wheat hybrids and their parents which differ in shape and

position of their leaves, (2) to determine the influence of plant

density and patterns of planting on the leaf area and the components

of yield as well as grain yield, (3) to determine the percent light

interception under different plant densities and patterns of planting,

and (4) to determine the possible association of the leaf area, per-

cent light interception, dry matter production and yield components

with grain yield.

LITERATURE REVIEW

Leaf Area

3

Total leaf area is an index of plant growth and as such,

influences the amount of light interception, plant metabolism, dry

matter production, and grain yield. The importance of leaf area in

crop production was first studied by Watson (1947) in wheat, barley,

oats, sugar beets, and other crops. In general, an increase of leaf

area index and net assimilation were associated with grain yield.

The term leaf area index was coined by Watson for measuring the

leaf surface per unit area of land surface. Leaf area index was

found to reach a maximum value at the heading stage in grain crops

with gradual reduction after heading.

Several methods have been described for estimating the total

leaf area in plants (Milthorpe, 1956; Miller, 1938). These include

tracing, blueprinting or photographing leaves, and then measuring

the enclosed area with a planimeter. Also, the ratio between leaf

area and leaf weight has been used to determine the total leaf area.

A simple mathematical relation between leaf area and dimen-

sion of leaves also has been used to measure the total leaf area

without destroying leaves from the experimental plants (Carleton and

Foote, 1965; Stickler, et al. , 1961). In barley, Carleton and Foote

4

estimated leaf area by multiplying length X maximum width X a mean

coefficient (0.75) which was obtained from the ratio of actual leaf area

to measured leaf area from randomly selected tillers. Actual leaf

area was measured by tracing and weighing the enclosed leaf area in

the graph paper. Total leaf area was estimated by multiplying the

total leaf area per tiller with number of tilers per unit area. In

sorghum, Stickler, et al. (1961) used a similar formula, as in barley,

except they used the correlation coefficient value of leaf length and

width (0.747) instead of a mean coefficient value. Estimated leaf

area was found to be very close to the leaf area measurements

obtained from the planimeter method.

Morphological, physiological and environmental factors will

influence the total leaf area in plants. Friend, et al. (1962) listed

several factors which influence total leaf area in wheat: (1) production

of leaf primordia, (2) leaf emergence, (3) expansion of leaf structure,

(4) increase in number of tillers, (5) number of leaves per tiller, (6)

loss of tillers due to plant competition, and (7) environmental factors

such as temperature, light intensity and duration. An increase in

leaf area was observed with a grad- :al increase of temperature

(10° C to 25°C) and with increasing intensities of light from 200-

2500 foot- candle. Gardener, et al. (1964), working with barley,

observed that the total leaf area, leaf size, and leaf orientation were

important factors in determining grain yield. In comparing high and

5

low yielding varieties, they found those which produced the most

grain had narrow upright leaves, while the low yielding varieties had

wide drooping leaves, Other studies in wheat have shown that the

leaf area of the flag leaf was more important in influencing grain

yield than the leaves below flag leaf node (Thorne, 1966; Stoy, 1965).

Light Interception

The distribution of light over the leaves depends on spacial

distribution of incident light, leaf area, leaf orientation and plant

height (Warren, 1959, 1961). Different methods and instruments

were used to estimate light interception by plant communities. An

excellent review on light measurement in relation to plants was made

by Anderson (1964). She suggested that the photosensitive materials

would give a good approximation of light measurements.

Light meters are used in the field where the number of treat-

ments are limited and observations are made for a short duration

(Aubertin and Peters, 1961; Stern and Donald, 1961). The degree of

light intensity on the plant canopy varies according to diurnal fluctua-

tion of sunlight and other environmental factors, such as cloud cover

and wind. Unfortunately, light measurements taken for a short

period in the plant canopy may not tell the total amount of light

intercepted. Friend (1961) developed a technique of measuring

integrated light in oats and red clover using photosensitive ozalid

6

paper. He observed that the ozalid paper readings showed a close

correlation with Western Illumination Meter readings.

Ozalid paper has become useful in place of very complicated

light meters because it is easy to handle under field conditions.

Shibles and Weber (1966, 1965), Sakmaoto and Shaw (1967) have used

ozalid paper successfully in measuring light interception and light

distribution in soybeans. They found a linear relationship between

leaf area index, dry matter production, and percent light intercep-

tion.

Light interception in plant population is governed by many

natural and imposed variables. Davidson and Donald (1958) and

Watson (1958) have observed that percent light interception in crops

and pastures were dependent on planting patterns, plant density, leaf

arrangement, and leaf shape. By increasing plant population per

acre and reducing the row spacing in corn, Yao and Shaw (1964) and

Aubertin and Peters (1961) observed less light energy reached the

ground surface. Studying the light distribution in a corn field,

Denmead et al. (1962) observed that about 73 percent of light was

used by the upper half of the leaves in the corn plant,

Johnson (1953) and Pendleton and Weibel (1965), working with

winter wheat, observed that the top leaves were exposed to maximum

light while the middle and lower leaves were exposed to less and

variable amounts of light due to inter - plant and intra -plant

7

competition. Further investigation by Pendleton et al. (1965) showed

a five percent increase in wheat yield and a nine percent increase in

oat yield when extra light was provided to the lower leaves.

Stoskopf et al. (1963) listed various reasons for selecting plant

types with narrow and erect leaves, and shorter plants with fewer

leaves in wheat. Advantages in selecting such plants were listed as:

(1) angular leaves can receive illumination by sun's rays four times

greater than the horizontal leaves; (2) upright leaves reflect more

light down into the canopy to the lower leaves; (3) narrow leaves

occupy less space, thus the plant population could be increased; and

(4) increased light intensity in the plant canopy favor stronger, non -

lodging tillers. Further investigation showed that narrow and erect

leaves in winter wheat selections produced 9. 3 percent increase in

grain yield over broad and droopy- leaved wheat varieties (Stoskopf,

1967).

Light interception in plants will influence the temperature in

the plant canopy. In wheat, Stoskopf and Klinick (1966) observed

that the day temperature in the plant canopy was less than the

atmospheric temperature and that the night temperature was higher

in the plant canopy as compared to bare ground. In barley, Grafius

(1956a) observed that low night temperatures affect the plant growth

and grain yield, With rice, Takeda and Maruta (1955) studied the

effect of spacing on light utilization. Rice plants spaced 12X12 cms

8

were found to utilize more light energy than the plants spaced

24X24 cms. Efficiency of utilizing light energy was increased from

jointing stage to the boot stage. Foth, et al. (1964) reported that

seven -inch row spacing in oats intercepted more light than 11- or

14 -inch row spacings.

Components of Yield

Yield in cereal crops has been found to be associated with a

number of components, such as tillers per plant, grains per head,

and kernel weight (Hayes and Immer, 1942). Correlation coefficients

have been used to determine the degree of association between the

components and grain yield but they do not show the possible direct

and indirect association of the components with yield. Wright (1921)

developed the method of "path- coefficient" analysis to determine

whether a correlation between two variables is due to a large direct

effect of the independent variable on the dependent variable or

whether the association is due to indirect effects through other

variables.

In analyzing the primary yield components involving a diallel

cross of ten wheat varieties of different genetic origin, Kronstad

(1963) found a high direct association between kernels per spike,

number of spikelets per spike, and weight of kernels with grain

yield. Plant height and number of spikes per plant were found to have

9

an indirect association through the other variables with yield. When

comparing space and solid planted F2 progenies, Sani ( 1968) observed

that spikelet per spike and kernels per spikelet were directly

associated with grain yield.

Comparing the yield components of single plant vs plants per

unit area, Grafius (1956b) found that in oats, environmental factors

were greatly influencing the yield components of a single plant.

Ouisenbery (1928), working with wheat, collected data on a unit area

basis and using path -coefficient analysis, found that the number of

spikes per unit area and the number of kernels per spike were direct-

ly associated. Weight of 1, 000 kernels had a smaller direct rela-

tionship with yield than the other two factors mentioned. Stoskopf and

Reinbergs (1965), utilizing barley and oats, found that kernels per head,

rather than tillers per plant, w as the most reliable component to use

in estimating yield. However, they observed both tiller number and

kernels per spike were found variable among varieties, seeding rate,

seeding date, and soil fertility levels. Thousand kernel weight was

less influenced by these factors and contributed little to the yield.

Hybrid Vigor in Wheat

Hybrid vigor in wheat was reported by Freeman in 1919. Since

that time, the literature pertaining to hybrid vigor in wheat has been

extensively reviewed by Briggle (1963). Most of the experimental

10

results discussed in this review were not conclusive to state the

presence or absence of hybrid vigor in wheat. However, there was

some evidence to show that the F1 hybrid yielded from 33.7 percent

to 84 percent more than the high parent. Briggle, et al. (1964)

reported that the F1 wheat hybrids performed better than their parents

at higher plant densities. Their results indicated that heterosis does

occur in wheat with specific cross combinations.

Kronstad and Foote (1964), in estimating general and specific

combining ability effects in winter wheat varieties, found that most

of the variation in yield and yield components of the F1 hybrids were

associated with high general combining ability effect. Specific com-

bining effects were significant for plant yield and height but not for

yield components. Their studies indicated that the selection of paren-

tal combination is important in producing maximum hybrid vigor in

wheat. McNeal et al. (1965) observed that the grain yield of F1

and F2 spring wheat crosses were either intermediate between the

two parents or equal to one of the parents. None of the yield com-

ponents studied in three crosses showed a significant increase over

the high parent. Crossing non - related wheat varieties involving hard

red winter and soft red winter wheat, Brown, et al. (1966) reported

hybrid vigor up to 131 percent of the high parent. The crosses

between related varieties showed no hybrid vigor. Shebeski (1966)

reported that the F1 hybrids derived from different genetic sources

11

differing in milling and baking quality, produced 26 percent more

grain yield than the high parent without losing milling and baking

quality.

Hybrid vigor in wheat is found to be variable in space and solid

planted trials. Most experiments conducted to measure hybrid vigor

in wheat have been space planted due to the limited population size in

the F1 generation. In a space planted experiment, Fonseca and

Patterson (1964) compared the yields of 21 F1's from a seven - parent

diallel cross with parental yield. Grain yield of the F1's in relation

to the higher parent in cross ranged from 75 percent to 172 percent.

On the other hand, McNeal, et al. (1965) and Rosenquist (1931)

observed no hybrid vigor in solid planted F1 and F2 hybrid wheat.

In reviewing the literature, it was observed that the hybrid

vigor in wheat could be obtained only in selected cross combinations.

To obtain maximum return from the hybrid wheat, breeders should

search for better parents which have greater genetic potentiality to

produce more hybrid vigor.

12

MATERIALS AND METHODS

Primary morphological components of grain yield and percent of

light interception in wheat as influenced by total leaf area, population

density and pattern of planting, were studied under field conditions

during 1965- 66 growing season at Hyslop Agronomy Farm, near

Corvallis, Oregon. Experimental organisms included F1 progenies

from two sets of diallel crosses and the corresponding parents, which

included Brevor, Selection 101 and Selection 172 in the first set, with

Druchamp, Redmond and Travero making up the second set of parents

(Appendix 1). To insure a uniform stand, seeds were germinated in

the greenhouse and transplanted into the field in five spacing patterns.

These patterns included 12 "X12" square, 12" rhombus, 12"X10.39"

rectangular, and two solid plantings with 12" and 10.39" spacing

between rows (Figure 1). The spacing 10.39" was determined as

being the perpendicular distance of a 12" equilateral triangle which

would be the spacing between rows in rhombus planting. It is also

frequently referred to as the equilateral triangle method of planting.

In each pattern of planting, two population densities were maintained,

which involved one seedling and two seedlings per hill in space planted

designs and 6 -10 seedlings per running foot in solid plantings. To

avoid plant competition from weeds, the plots were hand -weeded.

Nitrogen fertilizer was applied at the rate of 60 pounds of N per acre

24

1

20.78 - 2

20.78" 3

1 - 12" x 12" square

2 - 12" rhombus

3 - 12" x 10.39" rectangular

Assigned plant area

Area under competition

Fig. 1. Planting patterns of winter wheat varieties for measurements of light interception between rows,

A A

O

14

on March 2, 1966.

The experimental design was a first order factorial randomized

split plot with a single replication (Cochran and Cox, 1957; Binet et al.,

1955; Cornish, 1936). The experiment consisted of 12 phenotypes X two

population densities X five patterns cf plantings with a total of 120 plots.

The main treatments were varieties with the sub -treatments being

population densities. Performance of each variety was measured

from the means of 10 plots, while the influence of pattern of plantings

was measured from 24 plots and mean population density was obtained

from 60 plots. This design was selected because of the practical

difficulties in producing sufficient F1 hybrid seed in self pollinated

crops, which imposed a limitation on the number of treatments and

replications. Factorial arrangements of treatments provided an

opportunity to obtain more information from the limited population

size. Two guard rows were planted around the main and sub -

treatments to provide a uniform effect of plant competition between

treatments. The semi -dwarf wheat Gaines was used for the guard

rows.

Observations were obtained for total leaf area, tillers per unit

area, plant height, and percent light interception at three stages of

growth. These included (1) the jointing stage (March 23), (2) prior

to flag leaf (April 30), and (3) just after heading (May 21). Total dry

weight, number of spike bearing tillers, number of kernels per spike,

15

weight of 1,000 kernels, and grain yield per unit are were recorded.

In the space planting, leaf area measurements were taken randomly

from five tillers per plant, while 10 tillers were utilized in solid

planted rows. Leaf area was measured without detaching leaves from

the plant, Leaf length was measured on the upper surface from leaf

tip to the point where the leaf was attached to the sheath. Maximum

width of the leaves were measured to the nearest millimeter by

moving the ruler back and forth on the upper surface of the leaf,

Total leaf area per unit area was calculated using the formula:

TLS = XYZ where X is the total leaf area per tiller, Y is the

total number of tillers per unit area, and Z is the mean coefficient

(0.75), obtained from the ratio of actual leaf area to the calculated

leaf area (Carlton and Foote, 1965).

Light interception was measured using the ozalid paper No.

30-- 11251, which contains a diazo compound which is sensitive to

light. Ozalid books were prepared which consisted of 2X2 square

cms of ozalid paper and were 15 layers thick. The books were bound

with a black paper on the dense side of the ozalid paper. The binder

contained three circular exposure holes 0. 6 cms diameter in size.

To prevent water contact, the books were sealed with a fine, clear

'Produced by General Anline and Film Corporation, ANSCO Division, Chicago, Illinois.

16

plastic.

Preliminary experiments indicated there was no advantage in

covering ozalid booklets with a dome- shaped plastic cover, as sug-

gested by Friend (1961). Therefore, all field readings were taken

on plain ozalid books. Light interception was measured in the field

by placing the ozalid books in the center of four plants in the space

planted treatments while in solid plantings, measurements were taken

between rows. The books were attached to wooden clamps two inches

above the ground level. Three readings were taken at the same posi-

tion over a nine -hour period, beginning at 8:30 a. m. and continuing

until 5:30 P. . Ozalid books mounted with the standard Kodak Wartten

neutral density filters, 0. 1, 0. 3, 0. 4, and 0. 6, were exposed to direct

sunlight in the open field (Figure 2 -A, 2 -B). These filters transmit

about 80, 50, 40, and 25 percent of light, respectively, and the

accuracy of filters was ± 5 percent (Eastman Kodak, 1965) . The

booklets were collected in coin envelopes and stored in a black

plastic bag until they were developed. The books were uncovered in

the dark room, labeled and developed in dry ammonia gas for 30

minutes. The unexposed parts of the paper turned brown while the

exposed parts remained white.

The number of pages bleached in each book was counted to one

decimal using a standard exposure of known intensity of light over a

given period of time (Figure 2 -E). The standard exposures were

Fig. 2 . Ozalid paper exposure to light in wheat field:

A. Ozalid book mounted with kodak neutral density filters.

B. Ozalid book uncovered and arranged to show the depth of light peneterence through the papers under each filter : 0- no filter, 1 -0. 1, 2 -0. 3, 3 -0. 4, 4 -0. 6 density filter.

C. Ozalid book exposed between four plants.

D. Ozalid book uncovered and arranged for counting the number of pages exposed.

E. Ozalid paper exposed to a constant light for a known period of time which is the index for counting the fractions of exposure.

3 Z . 5' 9' L. 8' 6' I

J

e

d

tt ti

o

A

2 3 4

411 -`

I .9 .8 .7 .6 .5 .4

B E 3

£ b

b £ Z I p

19

prepared by exposing 6" long strips of ozalid paper to a constant

fluorescent light and recording the time required to bleach one paper.

A second strip of ozalid paper was divided into 10 equal parts and

each division was exposed to less than one -tenth of the original time

it took to bleach one sheet of ozalid paper. Thus, a gradiant of

discoloration could be formed in one strip of paper and developed

immediately in dry ammonia gas. These gradients were mounted on

plain paper and used as a standard to count all the field exposures

(Figure2 -C, 2 -D).

Transmittance of light through the known density filters were

found to be linear and highly correlated with the number of ozalid

papers bleached (Figure3 ). The light interception in the plant

canopy was estimated in percent by drawing a semi - logorithamic

graph of the number of papers bleached under standard density filters

and the number of papers bleached in the plant canopy (Table 1).

A functional analysis of variance was computed for leaf area

index, number of tillers, plant height and the percent light inter-

ception involving the three stages of growth. This analysis was also

conducted for total dry mater production, number of kernels per

spike, 1,000 kernel weight, and grain yield per unit area.

A single replicated factorial experiment provided no degree of

freedom for error. The second order interaction, variety X pattern

for planting X population density was used as a basis for testing the

20

25 W u) o n- 20 x w

w 15

a

10

J

0 ó z

Y=7.97 7.97 + 0.027X

20 40 60 80 100 PERCENT TRANSMITANCE

Fig. 3. Relationship between the percent light transmittance through the Kodak neutral density filters and the num- ber of ozalid papers bleached from nine hours exposure to direct sun light.

N 5

0

Table 1. Correlation coefficient involving the percent light transmission through the Kodak Standard neutral density filters and the number of ozalid papers exposed for nine hours daylight.

transmittance Percent

Number of ozalid papers bleached on each day

Apr, 13 Apr. 16 Apr. 23 Apr. 30 May 28

100 10.5 10.5 10,4 10.9 9.6

80 10.2 10.2 10.2 10.6 9.4

50 9.5 9.5 9.3 3 9. 9.3 8.7

40 9.3 9.3 8.8 8.5 8.4

25 8,3 8.4 7.3 7.8 7.5

Correlation (r) 0.95 0.96 0.93 C. 98 C. 95

22

significant differences between the main effects and the first order

interaction. Non-significant first order i nteractions, variety X

pattern of planting, and variety X population density, were pooled

with the second order interaction to provide the estimate of error

(Cochran and Cox, 1960; Cornish, 1936). The correlation coeffi-

cient was determined for all possible combinations of 16 variables.

A standardized partial regression coefficient method was used to

analyze the correlation coefficient of interrelated variables

(Wright, 1921).

23

EXPERIMENTAL RESULTS

Analysis of variance for four characters involving three stages

of growth and five treatments are presented in Tables 2 and 3.

Differences in the leaf area index at jointing stage was highly signifi-

cant in different patterns of planting, whereas varietal differences

and plant densities had no significant effect. Leaf area index prior

to flag leaf and after heading was highly significant among

varieties and patterns of planting. The interaction of plant density X

patterns of planting was significant before the flag leaf stage and after

heading. The percent light interception was highly significant among

varieties, plant densities, and patterns of planting in all three stages

of growth. A significant plant density X patterns of planting, inter-

action was also noted for the first and third stages but not for inter-

mediate stage.

Differences in tiller number per unit area in the patterns of

planting was highly significant at all three stages of growth. Varietal

differences for tiller number was not significant at the jointing stage;

however, it was highly significant in the later two stages of growth.

The effect of plant density on tiller number per unit area was only

significant at the heading stage. A significant plant density X pattern

of planting, interaction was observed in the first two stages of growth

but not in the third stage.

Table 2. Mean squares for leaf area index and percent light interception in six wheat hybrids and their respective parents at three stages of growth, I- jointing stage, II -prior to flag leaf and III heading stage.

Source of variance DF

Leaf area index % light interception I II III I II III

Phenotypes 11 0.43 5.46** 12.11** 75.20** 294.81** 724.68**

Plant density 1 0.54 3.57** 1.92 357.08** 343.41** 594,08*

Pattern 4 4.06** 14.06** 26.04** 89.02** 656.85**1216.16**

Plant density X pattern 4 0. 41 1.85* 6.45** 44.26** 23.47 202.74*

Error 99 0.23 0, 66 1. 68 12. 49 44.42 68.72

Coefficient variability c'io 33.52 24.03 23.71 10.83 16.54 14.93

* ** Exceeds the 5% and 1% level of significance respectively. '

Table 3. Mean squares for tillers per unit area and plant height in six wheat hybrids and their respective parents at three stages of growth, I- jointing stage, II -prior to flag leaf, III heading stage.

Source of variance DF

Tillers /unit area Mean Square

height crus. Plant I II III I II III

Phenotypes 11 43.97 112.38** 139.18** 53.92** 218.04** 257.55**

Plant density 1 30.50 43. 92 99. 46 ** 3. 33 0. 34 70. 53

Pattern 4 4799.27* 1156.81-, 705.88' 164.89** 279.42 62C. 51-,

Plant density X pattern 4 364.09 ** 227.14** 110. 1 1 1.92 56.14 13.76

Error 99 43.79 42.68 22.94 5.54 33. 69 32.44

Coefficient variability % 16. 69 23. 22 18. 92 9, 9.42 7. 61 5. 62

Exceeds the 5% and 1% level of significance respectively. m

'

26

In all three stages of growth, differences in plant height were

highly significant for all treatments except plant density,

The relationship between leaf area index and light interception

percentage in six wheat hybrids and their respective parents planted

in -five patterns and two plant densities are shown in Figure 4. Per-

cent light interception tended to be linearly associated with the leaf

area index. A positive correlation between leaf area index and light

interception was noted for planting pattern (r = +. 63 and number of

seedlings per hill (r = +. 96). Leaf area index in solid plantings was

not linearly associated with percent light interception at the three

stages of growth. The results obtained for rectangular and solid

plantings were widely scattered from the regression line, as can be

observed in Figure 4.

Influence of the leaf area index on light interception is shown

in Figure 5A. Percent light interception increased in all patterns

of planting until a leaf area index between 4 -5 was obtained, after

which no further significant increase was observed. The rectangular

planting pattern intercepted the maximum light energy with a mini-

mum leaf area index at all stages of growth studied.

In Figure 5B, the association of light interception with number

of tillers per unit area was very conspicuous in all five patterns of

planting. The number of tillers per unit area increased as the light

interception increased until 30 to 40 percent; however, a sharp

INTERCEPTED %

J

100

80

60

40

I PLANTING PATTERN: Y=32.I65t4.278 X r=0.629*`

2 N0. SEEDLING: S>=-41.786 X 2 r=09576"

o

o

o°

o

y o o ° ó a

o 00% o

o o

o= ,.í o n n a

o ,ito

0

12 "x12" SQUARE 12`x12u RHOMBUS

012"x10.39 "RECTANGULAR 12" SOLI D

10.39" SOLID

27

O I 2 3 4 5 6 7 8 9 10

LEAF AREA INDEX

Fig. 4. Relationship of leaf area index and light interception present in wheat hybrids and their respective parents.

6

,. %

c °° '

n C

Fig. 5A. Influence of the leaf area index on percent of light interception in five patterns of planting.

B. The effect of light interception on the number of tillers per unit area in five patterns of planting.

C. Influence of leaf area index on plant height in five patterns of planting.

80 I 12''x12'' SQUARE

a9 2 12"x12" RHOMBUS

p 70 3 12 "x 10 39' RECTANGULAR 412"SOLID

O. 510 39" SOLI D

v 60

W

50

I- =40 J

30

3 4

2

FIG. A

4 W

<60 t`- Z D50 u.t O.

0140 W

30

020 CY W ta IO X z

O

FIG. B

2 3 4 5 6 7 LEAF AREA INDEX

120

;100 E 0

I- 80 _ 0 = 60

10 20 30 40 50 60 70 LIGHT INTERCEPTED %

3 2

20

FIG. C

2 3 4 5 LEAF AREA INDEX

Figure 5

29

i 5

CY

1- Z 40 J O.

4

-

3

0

30

reduction in tiller number was found beyond this point for all patterns

of planting with the largest reduction noted in 12" square planting.

The mean squares for dry matter production per unit area,

kernels per spike, weight of 1,000 kernels and grain yield per unit

area are presented in Table 4. Varietal differences for dry matter

production, kernels per spike, 1,000 kernel weight and grain yield

were highly significant. Plant density had no significant effect on

number of kernels per spike, 1,000 kernel weight, or grain yield,

while differences in dry matter production were significant. Patterns

of planting significantly influenced dry matter production, kernels per

spike, grain yield, but not weight of 1, 000 kernels. A significant

interaction was noted only for plant density X patterns of planting

involving grain yield per unit area.

The relationshp of the light interception to dry matter produc-

tion in the hybrids and their parents are found in Figure 6A, Percent

light interception was closely associated with dry matter production

for both generations. Differences in varietal performances were

very conspicuous, The parents and the hybrids included in the first

group did not intercept as much light energy or produce as much dry

matter as those involved in the second group.

Figure 6B further illustrates the relationship of the light inter-

ception in different densities of planting to dry matter production.

Light interception and dry matter production were closely associated

Table 4. Mean squares for dry matter production per unit area, kernels per spike, weight of 1,000 kernels, and grain yield per unit area in six wheat hybrids and their parents, planted in two plant densities and five patterns of planting.

Source of Variance DF

Mean Square

Dry matter Grms Kernels /s pike

Wt. 1000 kernels Grms

Grain yield Grms

Phenotypes 11 9668. 94** 608.21** 231.89 ** 470.53**

Plant density 1 8526. 78* 170.91 0.43 251.58

Pattern 4 23515.94** 296.67** 14. 62 1691.50**

Plant density X pattern 4 3654. 47 17.89 21.08 343. 99 **

Error 99 1501.97 57.95 12.80 93.32

Coefficient variability % 21.25 16.67 7. 66 18. 62

' Exceeds the 5% and 1% level of significance respectively.

w

Fig. 6A. Relationship of light interception to dry matter production in wheat hybrids and their respective parents.

B. Relationship of light intercepted percent to dry matter production per unit area in six wheat hybrids and their parents involving two plant densities.

250

0

C 3 200

CA

} S 100

=53 771+2 316 X

r=0 7838"

o-

4-

Brevor _ b

Sel 101 o-

Sel 172 -o Brevor x Sel 101

Brevor x Sel 172 -6 Set 101 x Set 172 - -o-

Druchamp Redmond Trovero -* Druchamp x Redmond - - - Dru champs Trovero - - - -4 Redmond x Trovero-.

0 10 20 30 40 50 50 70 BO

LIGHT INTERCEPTED % FIG. A

250

FIG. B

I Number of seeds /j Y=- 24.172-f 3 684 X unit area i r= 09963 **

2 Planting pattern l' =169 124 0 237 X r= 00169

>o<

d

Ya

ä

I Seed per unit ores b

2 Seeds per unit area 2f

Solid planting

VARIETY SYMBOLS SAME AS FIGURE A

10 20 30 40 50 60 LIGHT INTERCEPTED %

Figure 6

33

1

0 - .

- 6-

-.

g

q8

- 2

0 70 60

K Ñ 150

Ld

-.

Y`

_.

-

_____. .__._.e-

3,200 JY

B

34

to the number of seeds planted per unit area. Patterns of plantings

showed a non - linear relationship and a very low correlation with

light interception and dry matter production.

Mean performances of the hybrids and parents are presented

in Tables 5, 6 and 7. Differences in leaf area index at jointing stage

in both parents and hybrids were not significant. Brevor and Sel.

172 produced very few leaves until jointing stage and then rapidly

increased before reaching the flag leaf stage. The hybrids derived

from Brevor, Sel. 101 and Sel. 172 had a smaller leaf area than

their parents in all three stages of development. The parents

Druchamp, Redmond, and Travero produced a higher leaf area

than Brevor, Sel. 101 and Sel. 172. The F1 hybrids, Druchamp X

Redmond, and Druchamp X Travero, produced a significantly higher

leaf area than their parents in the later two stages of growth,

while the hybrids from the cross Redmond X Travero produced a

smaller leaf area than either parent at all stages of growth.

At the jointing stage, tiller number was higher in both parents,

and the F1 hybrids but gradually declined during the later two stages

of growth. The largest reduction in tiller number was found in the

parents Sel. 101 and Sel. 172 and their hybrids just prior to heading

stage. Percent light interception was increased as leaf area

increased until heading. The parents Brevor, Sel. 101 and Sel. 172,

and the resulting hybrids intercepted less light (42. 8% to 53. 0 %)

35

Table 5. Mean values for leaf area index and percent light inter- ception for six wheat hybrids and their parents at three stages of growth, I- jointing stage, II -prior to flag leaf and III -heading stage

Phenotypes

Leaf area index % light interception

I II III I II III

Brevor 1.19 3.30 5.42 32.20 39.50 53.00

Sel. 101 1.27 2.63 5.00 30.90 33.70 51.80

Sel. 172 1.19 2.79 4. 63 33.00 39. 60 50.90

Brevor X

Sel. 101 1.23 2.34 4.10 28.70 34.40 42.80

Brevor X

Sel. 172 1.43 2.86 4.64 28.40 35.00 50.40

Sel. 101 X

Sel. 172 1.41 2.72 3.79 30.30 35.30 43.40

Druchamp 1.57 3.54 5.99 33.40 39.60 55.90

Redmond 1. 69 3.58 6.07 34.10 47.10 60.30

Travero 1.84 3.60 5.69 34.20 43.20 62.90

Druchamp X

Redmond 1.59 4.78 7.45 34.80 43.80 66.50

Druchamp X

Travero 1.47 4.24 7.02 37. 60 51.70 70.20

Redmond X

Travero 1.34 4.07 5.61 35.90 40.30 58.20

L. S. D.* 0. 05 NS** 0. 72 1. 15 3. 13 5. 91 7. 34

L . S. D. 0.01 NS 0. 95 1. 52 4. 14 7. 81 9. 70

: Least significant difference Not significant

36

Table 6. Mean values for tiller number per unit area and plant height in six wheat hybrids and their parents at three stages of growth, I- jointing stage, II prior to flag leaf and III - heading stage.

Phenotypes

Tiller /unit area Plant height cros.

I II III I II III

Brevor 37.80 30.40 29.03 25.45 77.05 101.45

Sel. 101 41.40 31.05 27.30 23.10 69.65 92.00

Sel. 172 37.90 25.20 22.86 22.90 75.30 104.00

Brevor X

Sel. 101 37.95 24.86 21.55 22.55 71.95 97. 35

Brevor X

Sel. 172 38.25 24.10 21.97 23. 60 78.21 103.25

Sel. 101 X

Sel. 172 37.60 22.40 20.75 23.85 76.25 97. 65

Druchamp 40.10 31.50 27. 63 26.75 77. 45 105. 60

Redmond 37.30 27.85 24.93 27.25 75.30 101.80

Travero 43.10 29.55 24.40 24.70 71.40 95.55

Druchamp X

Redmond 42.65 32.40 31.07 28.75 85.25 109.10

Druchamp X

Travero 41.30 32.20 30.72 29.00 83.75 108.25

Redmond X

Travero 40.30 26.06 21.52 23.10 73.80 101.50

L. S. D. 0. 05 NS 5.79 4.25 2.09 6.74 5. 04

L. S. D. 0. 01 NS 7. 65 5. 62 2.77 8.92 6. 67

Table 7. Mean values for dry weight per unit area, number of kernels per spike, weight of 1, 000 kernels, and grain yield per unit area in six wheat hybrids and their parents grown at Corvallis, Oregon in 1965 -66.

Phenotype Dry wt. /unit area

Gms Kernels /spike Wt. 1, 000 kernels Grain yield /unit area

Gms

Brevor 180.19 37.23 46. 75 49, 32

Sel. 101 147.96 41.82 41.79 48.53

Sel. 172 181.13 60.18 39. 20 56. 43

Brevor X Sel. 101 131.07 43. 59 43. 67 40. 43

Brevor X Sel. 172 180.09 55.24 42. 77 53. 91

Sel. 101 X Sel. 172 155. 91 55. 64 42. 43 48. 82

Druchamp 205.82 33.82 52. 51 50. 42

Redmond 198.77 42.00 48. 99 48. 57

Travero 170.88 42. 67 49. 52 49. 62

Druchamp X Redmond 241. 10 43.03 52. 32 60. 12

Druchamp X Travero 222. 40 48.20 54. 00 67. 12

Redmond X Travero 172. 12 44. 62 46. 80 49. 22

L. S. D. 0. 05 34. 32 6.74 3. 17 8.56 i..S.D. 0.01 45. 36 8. 91 4. 18 11.31

38

than Druchamp, Redmond and Travero and their respective hybrids

(55. 9% to 70.2%). The hybrids from the crosses Druchamp X

Redmond and Redmond X Travero, intercepted 66.5 and 70.2 percent

light energy, respectively, which was significantly higher than their

parents.

Mean dry matter production per unit area, number of kernels

per spike, 1, 000 kernel weight, and grain yield per unit area of six

hybrids and parents are presented in Table 7. Differences in dry

matter production among parents and hybrids were significant.

Hybrids which produced the highest dry matter also produced the

highest grain yield per unit area.

In considering the yield components, the number of kernels

per spike was found to be highly variable among all parents and

hybrids. The Sel. 172 and crosses involving Sel. 172, had a

higher number of kernels per spike. The compact spike in Sel. 172

was dominant and the resulting hybrids produced long compact heads

(Appendix 1). The hybrids involving Druchamp X Redmond and

Druchamp X Travero produced more dry matter and grain yield per

unit area than did their respective parents (241.10 and 222.40 grams

dry weight and 60. 12 and 67. 12 grams grain yield per unit area,

respectively). The number of kernels per spike and kernel weight

were also higher than the parents, but were not statistically signifi-

cant. Performance of the cross Redmond X Travero was lower in

39

comparison to the parental values for all characteristics studied,

with the exception of kernels per spike where a significant increase

over the parents was found.

The mean performance of all sixteen variables involving the

five patterns of planting are presented in Tables 8 and 9. Leaf area

index was significantly higher in solid plantings than space planted

patterns. Percent light interception was higher in rectangular

planting at three stages of growth. Number of tillers per unit area

was significantly higher in solid plantings as compared to space

plantings. Dry matter production and grain yield were significantly

higher in 12" solid planting. Among space planted designs, dry

matter production and grain yield were significantly higher in

rhombus pattern of planting. Kernels per spike were significantly

higher in rhombus pattern of planting, while the difference in 1,000

kernel weight was not significant among the patterns of plantings.

The mean results of one seedling and two seedlings per hill in

square, rhombus and rectangular plantings are presented in Table 10.

Differences in light interception and dry matter production were

highly significant where two seedlings per hill were used rather than

single seeding. Leaf area index before flag leaf stage and tiller

number at heading stage were significant with the two seedlings per

hill.

The relative performance of hybrids and mid parent values are

Table 8. Mean leaf area index and percent light interception at three stages of growth, I- jointing stage, II -prior to flag leaf, and III - heading stage and mean values for dry matter production per unit area, number of kernels per spike, weight of 1, 000 kernels and grain yield per unit area in six wheat hybrids and their respective parents.

Pattern Leaf area index % light interception Dry

matter gms

Kernels /spike

1, 000 kernel

wt. Grain yield I II III I II III

Square 0.99 2.66 4.13 31.13 34.50 44.58 148.26 44. 69 46. 67 42.94

Rectan- gular 1.20 3.26 4.78 35.20 48.79 61. 66 165.19 46.15 45.72 47.34

Rhombus 1.31 3.90 5.37 33.50 38.71 52.29 188.82 51.22 45. 64 54.14

12" solid 1.66 3.86 6.56 30.38 39.21 60. 67 231.35 41.60 47.84 65.03

10. 39" solid 2.03 4.39 6.40 39.92 40.33 58.42 177.82 44. 69 46.78 50.04

L. S. D. 0.05 0.28 0.46 0.74 2.02 3.81 4.74 22.16 4.35 NS 5.52

L. S. D. 0.01 0.36 0.61 0.98 2. 67 5.04 6.24 29.29 5.75 NS 7.30

Table 9. Mean values for tiller number per unit area and plant height at three stages of growth, I- jointing stage, II- prior to flag leaf, and III- heading stage in five patterns of planting.

41

Pattern

Tiller /unit area Plant height cros,

I II III I II III

Square 30.42 22.31 20. 64 21.96 70.33 93.58

Rectangular 30.13 22,77 21,75 26.25 77.11 102.10

Rhombus 27.60 25,11 22,52 28.29 79.08 107.73

12" solid 56,79 38.42 33.52 22.83 76.79 101,00

10. 39" solid 53.25 32,04 28.13 26.08 77.83 102, 67

L.S.D. 0.05 3.78 3.74 2.74 1, 35 2.06 3.25

L.S.D. 0.01 5.00 4.94 3. 62 1.79 5.18 4. 30

Table 10. Mean values for leaf area index, number of tillers, plant height and percent light interception at three stages of growth, I- jointing stage, II -prior to flag leaf and III -heading stage and mean values for dry matter production per unit area, number of kernels per spike, weight of 1, 000 kernels and grain 'yicl.d per unit area in six wheat hybrids and their respective parents.

Seedlings

Leaf

I

area index Tamil -

I

/unit a<.a Plant height ems. % light interception Dry matter gms.

Kernel /spike

Weight 1000 kernel

Grain yield /unit

area II III II III I II III I II III

One seed/ hill 1.37 3.20 5.32 39.13 27.53 24.40 24.91 76.28 100.65 30.90 38.62 53.30 173. 85 46.86 46.67 50.45

Two seeds/ hill 1.50 3.55* 5.57 40.14 28.75 26.22* 25.25 76.18 102.18 34.35 *e 42.00 ** 57.75 ** 190.72 ** 44.48 46.79 53.35

L. S.D. 0.05 NS 0.29 NS NS NS 1.73 NS NS NS 1.28 2.41 2.99 14.01 NS NS NS

L. S. D. 0.01 NS 0.39 NS NS NS 2.29 NS NS NS 1.69 3.19 3.96 18.48 NS NS NS

* ** Exceeds the 5% and 1% level of significance respectively.

43

listed in Table 11. Among the six crosses studied, Druchamp X

Travero (P4P6) showed more hybrid vigor than their parents for most

variables with the exception of leaf area index and number of tillers

per unit area at the jointing stage. In the cross Druchamp X Redmond

(P4P5), kernel weight and light interception before heading was higher

than mid parent value with other characters studied being higher than

highest parent.

The correlation coefficient for all possible combinations of the

measured 16 variables are presented in Table 12. At the jointing

stage, leaf area index was highly associated with tiller number per

unit area, dry matter production and grain yield per unit area. The

correlation coefficient between the leaf area index and light inter-

ception increased as the leaf area increased from jointing stage to

heading stage. Highly significant correlations were found between

plant height, leaf area index, number of tillers, dry matter produc-

tion and grain yield. Kernels per spike was negatively correlated

with all the yield components studied, except plant height in all

three stages of growth. Kernel weight was significantly correlated

with leaf area index and light interception at the later two stages of

growth. Light interception in the plant canopy was directly correlated

with leaf area index, number of tillers, and plant height.

The partial regression coefficients with the direct and indirect

influence of the leaf area index, tiller number and plant height on

Table 11. The mid -parent va.ue (MP) and hybrid performance for leaf area index, number of tillers; plant height, light interception at three stages of growth ana mean values for dry matter production, kernels per spike, weight of 1, 000 kernels and grain yield per unit area (Pl- Brevor, P2 -Sel. 101, P3 -Sel. 172, P4- Druchamp. P5- Redmond, P6- Travero).

Components MP P1P2 MP P1P3 MP P2P3 MP P4P5 MP P4P6 MP P5P6

LAI - I 1.23 1.23 1.19 1.43h 1.23 1.41h 1.63 1.59 1.71 1.47 1.77 1.34 - II 2. 97 2. 34 3. 03 2.86 2. 71 2. 72m 3.56 4.78h 3.57 4. 24h 3.59 4.07 - III 5. 21 4.10 5. 02 4. 64 4.82 3. 79 6.03 7. 45h 5.83 7. 02h 5.88 5. 61

Tillers - I 39. 60 37.95 37.85 38. 25m 39.65 37. 60 38. 70 42. 65h 41.60 41.30 40. 20 40. 30m - II 30. 73 24.86 27.80 24.10 28.13 22. 40 34. 68 32.40 30.53 32. 20h 28. 70 26.06 - III 28.16 21.55 25.94 21.98 25.08 20.75 26. 28 31.08h 26.01 30. 73h 24.66 21.52

Plant ht. - I 24. 28 22.55 24. 18 23. 60 23.00 23. 85h 27. 00 28. 75h 25. 78 29. 00h 25. 98 23.00 croc. - II 73. 35 71.95 76. 68 78. 21h 72.48 76. 25h 76. 38 85. 25h 74.43 83. 75h 73. 3S 73.80

- III 96.53 97. 35m 102. 73 103. 25m 98.00 97. 65 103. 40 109.10h 100. 28 108. 25h 98.68 101.50

Light - 1 31.55 28.70 32.60 28.40 31.95 30.30 33.75 38. 80h 33.80 37. 60h 34.15 35. 90h inter( -2p- - II 36. 60 34. 40 39.55 35. 00 36. 65 35. 30 43. 35 43. 80m 41.40 51. 70h 41.14 40. 30

Lion %; - III 52.40 42.80 51.95 50.40 51.35 43.40 58.10 66.50h 59.40 70. 20h 61.60 58.20

Dry matter 164.08 131.07 180.66 180. 09m 164.55 155.91 202.29 241. 10h 188.35 222. 40h 189.82 172. 12

Kernels /spike 39.52 43.59h 48.75 55. 24m 51.00 55. 64m 37.91 43.04h 38.25 48.21h 42.34 44.62h

Wt. /1, 000 kernels grms. 44.27 43.67 42.98 42. 78m 40.50 42. 43h 50.75 52. 32m 51. 02 54. 00h 49. 26 46.80h

Grain yield/ unit area grms. 48. 92 40.43 52.87 53.91 52.43 48.82 49.49 60.12h 50.02 67. 41h 49.10 49.22m

h - hybrid vigor above high parent; m - above mid -parent.

Table 12. Correlation coeffici ..nts for sixteen variables measured in six wheat hybrids and their respective parents.

Variables 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1 LAI - I

2 No. Tillers

3 Plant Height

4 % Light Interception

5 LAI - II

6 No. Tillers

7 Plant Height

8 % Light Interception

9 LAI - III

10 No. Tillers

11 Plant Height

12 % Light Interception

13 Dry Matter Production

14 Kernels /Spike

15 1000 Kernel Weight

16 Grain yield /unit area

0.770 0.310

-0.079

0.242

0.017

0.417

0.442

0.170

0.636

0.467

0.607

0.755

0.146

0.194

0.323

0.387

0.235

0.653

0.280

0.545

0.421

-

0.265

0.055

0.486

0.579

0.435

0.183

0.351

0. 61 9

0.589

0.440

0.377

0.639

0.839

0.620

0.381

-

0.578

0.704

0.246

0.199

0.311

0.863

0.510

0.240

0.792

0.297

0.106

0.610

0.391

0.460

0.299

0.717

0.283

0.536

0.341

0.485

0.363

0.458

0.514

0.442

0.490

0.430

0.712

0.631

0.565

0.362

-

0.511

0.468

0.431

0.326

0. 35 6

0. 65 4

0.648

0.339

0.733

0.803

0.609

0.613

-

-0.186

-0.222

0.038

-0.123

-0.116

-0.333

0.102

-0.144

-0.231

-0.301

0.149

-0.246

-0.080

0.183

0.109

0.325

0.178

0.353

0.214

0.251

0.384

0.375

0.258

0.179

0.372

0.301

0.357

-

0.393

0.473

0.309

0.245

0.252

0.627

0.571

0.293

0.644

0.748

0.517

0.526

0.852

0.196

0.175

The correlation coefficient values which are above 0. 180 significant at 5% level and above 0. 235 significant at 1% level.

-

-

-

-

-

-

-

-

-

46

light interception at each stage of growth are presented in Figures

7A, B and C. Light interception at the jointing stage was directly

influenced by plant height and the leaf area index. Direct effect of

plant height was higher at jointing stage and gradually declined

(0.312 to 0.057) as the plants reached heading stage, while the leaf

area index increased as the plants reached the heading stage.

Indirect effects can be noted for tillers via leaf area index and plant

height. In considering the residual effects, it can be observed that

smaller amounts of the total variation was accounted for as the plant

development.

Tn Figure 8 -A, leaf area index had a small effect on kernels per

spike, with 94.2 percent of the variation due to the residual effect.

Leaf area index, tiller number and plant height have shown a high

correlation with dry matter production. The path -coefficient analysis

indicated that the observed high correlation between leaf area index

and dry matter production was due to indirect effect of tiller number

(Figure 8-B).

Path - coefficient analysis for the leaf area index, tiller number,

kernel per spike and kernel weight are presented in Figures 9 -A and

9-B. The leaf area index at the heading stage had a higher direct

association with the yield as compared to leaf area index in the earlier

stages. The yield components, tiller number, kernel per spike and

kernel weight directly influenced grain yield.

Fig. 7A. Path - coefficient analysis showing the direct and indirect relationship of leaf area index (LA1 -1), number of tillers per unit area and plant height with the percent light interception at the jointing stage.

B. Path - coefficient analysis showing the direct and indirect relationship between light interception, leaf area index (LA1 -II), number of tillers, and plant height prior to flag leaf.

C. Path - coefficient analysis showing the direct and indirect relationship between light interception, leaf area index (LA1 -III), number of tillers and plant height at heading stage.

(2) LAI)

V . \

11 t N

LAI VS LIGHT INTERCEPTION CORR DIRECT EFFECT 0290 INDIRECT VIA TILERS -C.45 INDIRECT VIA PLANT HEIGHT 0.097 TOTAL 0.242

0 T. .LER VS LIGHT INTERCEPTION CORR LIGHT ` r1,3 =011 P13 =- Iee

í M DIRECT EFFECT -0.,88

INTERCEPTION II)' (3) TILLERS = INDIRECT VIA LAI 0.233 9' , Ñ ,NDIRECT VIA PLANT HEIGHT -0,024

A TOTAL 0 0 A O \ 9s

'i,

/ i PLANT HEIGHT VS LIGHT INTERCEPTION _C,RR

pi. / DIRECT EFFECT 0,312 INDIRECT VIA LAI 0.090 INDIRECT VIA TILLERS 0.0,5

(4) PLANT HEIGHT TOTAL

FIG, A RESIDUAL

il21LAI-II

,\ÿ LIGHT II)

rI,3 183 P1.3003 INTERCEPTION

FIG. B

0.242

RESIDUAL EFF EFFECT C8C_

LAI VS LIGHT INTERCEPTION CORR DIRECT EFFECT 0347 INDIRECT VIA TILLERS 04001 INDIRECT VIA PLANT HEIGHT 0.087 TOTAL 0.435

p TILLERS VS LIGHT INTERCEPTON CORR N '

DIRECT EFFECT 0.003 (3) TILLERS a INDIRECT VIA LAI 0I 12

` NDIRECT VIA PLANT HEIGHT 0.068 TOTAL 0.183

I! \(4) PLANT HEIGHT

\ \ RESIDUAL

,(2) LAI -1))

:F,

LIGHT )I) 4 rI,3 ='466 PI,3= 188 (3) TILLERS Ç INTERCEPTION

\

FIG C

(41 PLANT HEIGHT

N N

RESIDUAL

Figure 7

PLANT HEIGHT v5 INTERCEPTION TORR DIRECT EFFECT 0.160 INDIRECT VIA LAI 0189 INDIRECT VIA TILLERS LOU_ TOTAL 0.35,

2.435

O183

0.351

RESIDJA, EFFECT ,7.'9

LAI VS LIGHT INTERCEPTION CORR DIRECT EFFECT 0.45) INDIRECT VIA TILLERS 0.149 INDIRECT VIA PLANT HEIGHT 0.031 IOTA_ 0631

TILLER v5 LIGHT INTERCEPTION CORR DIRECT EFFECT !',168 INDIRECT VIA LAI 0357 INDIRECT VIA PLANT HEIGHT 0.020 TOTA _ !: 56`

V_ANT HEIGHT J$ NTERCEPTION CORR C REGT EFFECT NDIRECT VIA A 0.241 INDIRECT VIA TILLERS 0054 TOTAL 0.362

RESIDUAL EFFECT

0.565

"362

48

¡

r

'

. "4

R \\ ri v

9?""

t

p

41. N

w

\

..

0.05, .

,7 6,r6-'"

ER'

/I

'FF

\

F

Q

KERNELS (I) rL3- 116 PO. 060 PER SPIKE

LAI-II \\9'

I N

\ a \ "

\ Y \ (4) LAI -III

LAI -1 VS KERNELS PER SPIKE CORR. OOPS DIRECT EFFECT -0.074 INDIRECT VIA LAI, 0.027 INDIRECT VIA LAI -Ill -0(39 TOTAL -0 (86

LAI -11 VS KERNELS PER SPIKE CORR -OTIS DIRECT EFFECT 0.060 INDIRECT VIA LAI-I -0.033 INDIRECT VIA LAI -III -0-143 TOTAL -0. 116

LAI -III VS KERNELS PER SPIKE CORR -0.231 DIRECT EFFECT -0-224 INDIRECT VIA LAI -1 INDIRECT VIA LAI -II TOTAL

-0045 -0 038 --0231

RESIDUAL EFFECT 0-942

FIG. A RESIDUAL

PRODUCTION(1) r1.3 803

FIG. B

(4)PLANT HEIGHT

LAI - III VS DRY MATTER PRODUCTION CORR. 0-733 DIRECT EFFECT -0.013 INDIRECT VIA TILLERS 0.540 INDIRECT VIA PLANT HEIGHT 0.206 TOTAL 0 733

TILLERS VS DRY MATTER PRODUCTION CORR DIRECT EFFECT 0.682 INDIRECT VIA LAI -III INDIRECT VIA PLANT HEIGHT O. 131

TOTAL 0 803

0.803

49

PLANT HEIGHT VS DRY MATTER PRODUCTION CORR 0-609 DIRECT EFFECT 0.383 INDIRECT VIA LAI -0.007 INDIRECT VIA TILLERS 0.233 TOTAL 0.609

\ RESIDUAL EFFECT 0.229

\ RESIDUAL

Fig. 8. A. Path - coefficient analysis showing the direct and indirect relationship of the leaf area index on number of kernels per spike at the jointing stage, prior to flag leaf and heading stage.

B. Path - coefficient analysis showing the direct and indirect relationship of the leaf area index, number of tillers and plant height on dry matter production at the heading stage.

aE)LAI-I

.III, j r iv

1 I d 131 " !

\

M 1I

(3)TILLERS á 0.010 0.

-pl

SEED (I) YIELD

FIG. A

(2) LA I- I

\\

Q

r1,3=-252 P1,3'-'27I

ch

Mi

(3)LAI -II Ö cú.

\ \ (4)LAI -III \ \ \ RESIDUAL

SEED (I) r1,3 =I96 P1,3 =504 YIELD

7%.

FIG 8

(2)TILLERS

m N

KERNELS/ SPIKE

N

(4) WT. KERNELS

\ RESIDUAL

50

LAI -1 VS SEE[` YIELD CORP DIRECT EFFECT 0.011 INDIRECT VIA LAI - II -0.120 INDIRECT VIA LAI - I11 0.502_ TOTAL 0.393

0.393

LAI -II VS SEED YIELD CORR 0.252 DIRECT EFFECT -0.271 INDIRECT VIA LAI -1 0.005 INDIRECT VIA LAI -III 0518 TOTAL 0.252

LAI -III VS SEED YIELD CORR 0.644 DIRECT EFFECT 0810 INDIRECT VIA LAI -I -0.173 INDIRECT VIA LAI -11 0,007 TOTAL 0.644

RESIDUAL EFFECT C504

TILLERS VS SEED YIELD CORR DIRECT EFFECT INDIRECT VIA KERNELS /SPIKE INDIRECT VIA WT OF KERNELS TOTAL

0.866 -0-152

0.034 0.748

0.748

KERNELS /SPIKE VS SEED YIELD CORR. 0.196 DIRECT EFFECT 0.504 INDIRECT VIA TILLERS -0.261 INDIRECT VIA WT OF KERNELS -0.047 TOTAL 0.196

WT. OF KERNELS VS SEED YIELD CORR. 0.175 DIRECT EFFECT 0-i31 INDIRECT VIA TILLERS 0223 NDIRECT VIA KERNELS /SPIKE -0.179

TOTAL 0.175

RESIDUAL EFFECT C -231

Fig. 9. A. Path - coefficient analysis showing the direct and indirect relationship between leaf area index at three stages of growth on seed yield per unit area.

B. Path - coefficient analysis showing the direct and indirect relationship between spike bearing tillers, kernels per spike and weight of kernels on seed yield per unit area.

4

ï /

á

I(/ .

\

51

DISCUSSION

Biological reasons for differences in growth and grain yield

among genotypes grown in one location and under similar treatments are

still not well understood. If a plant breeder wants to be effective in

selecting the highest yielding genotypes, it is important that he

recognize and be able to measure those factors which determine the

superiority of one genotype over another. In wheat improvement,

the major effort in developing higher yielding varieties has been to

breed varieties which are resistant to diseases or to select for other

traits which are simply inherited with little or no attention being

given the morphological and physiological differences found between

varieties.

In searching for yield barriers in wheat and corn, Donald (1962)

suggested that a plant with narrow, erect leaves would use more light

energy and produce higher grain yield than plants with broad droopy

leaves. The parents selected for this study differed in the nature of

their leaf shape, with three parents having narrow to intermediate leaves

while the three remaining parents had intermediate to broad leaves. In

addition, the hybrids derived from these parents were grown in dif-

ferent planting patterns and under two different plant densities to

determine how competitive stress for light might influence leaf area,

percent light interception and, in turn total grain yield.

52

Additional information was obtained for the components of

yield; which included tillers per unit area, kernels per spike, and

kernel weight, since they have been found to be very sensitive to

environmental variation. In this study, leaf density, light intercep-

tion and planting patterns also appear to influence these yield compo-

nents, with the exception of kernel weight. Still, these components

can be considered as a reliable estimate of a genotype since they may

not be as complex in their inheritance nor influenced as much by the

environment as total grain yield. This is particularly true, if as

Grafius (1959) suggests, that there are no specific genes for grain

yield per se, but only for the components of yield.

In recent years, more attention has been given to the develop-

ment of plants which are more efficient in utilizing the radiant energy

under field conditions (Stoskopf, 1967; Yao and Shaw, 1964). The

quantity of radiant energy utilized by plants depends upon (1) the

percent of light interception and (2) the efficiency in which the plant

utilizes the intercepted light energy. Although the two factors are

closely related, the latter is more important in crop production, since

the total dry matter production and grain yield in cereal crops appear

to be associated with the amount of light energy utilized in photo-

synthesis (Thorne, 1966; Stoy, 1965). Plant efficiency in utilizing

light energy is dependent on percent light interception and other

environmental factors which regulate plant growth such as water,

53

mineral nutrients, temperature, carbon dioxide and oxygen. In this

study, the leaf area at the heading stage showed a significant positive

correlation (r = +0.73 and r = +0. 64) with dry matter production and

grain yield, respectively. Dry matter production and grain yield were

also highly correlated (r = +0. 85) which suggests that a large per-

centage of the total metabolic activity of wheat plant is associated

with grain yield. Watson, et al. (1963) also observed that the dif-

ferences in total dry matter production between wheat varieties were

due to the differences in leaf area. In corn, Eik and Hanway (1966)

observed that the grain yield was linearly related to the leaf area at

silking time. The results from this study also suggested that the leaf

area is an important factor contributing to grain yield. Therefore,

it appears that the total leaf area could be a very important morpho-

logical feature influencing the grain yield in cereals.

In this study, it was observed that the percent light intercepted

by the plant canopy was directly influenced by leaf area, plant height,

planting patterns and plant density. The leaf area among the parents

and hybrids was significantly different at the boot stage and heading

stage but not at the jointing stage. This difference was due to the

failure of young tillers to develop and produce mature spikes. The

reduction of tillers was found to vary among parents and hybrids

(24. 6% to 46.6%). It appears that the development of younger tillers

was limited by the internal shading of the upper leaves on the same

54

plant and from surrounding plants. The parents, Sel. 101, Sel. 172,

Travero and the hybrids resulting from Sel. 101 and 172, were found

to be very sensitive to this shading effect and lost approximately 34

to 47 percent of their tillers before the heading stage; whereas, the

parents Brevor, Druchamp, Redmond and the hybrids Druchamp X

Travero and Druchamp X Redmond, were found to have a greater

tolerance to shading and produced more tillers and grain yield.

Since leaf density appears to be one of the factors influencing the

tiller number and, in turn light interception, plant breeders should

be careful before selecting only those genotypes that have narrow

erect leaf types.

There is some evidence that plants with narrow leaves produced

higher grain yields than the plants with broad droopy leaves (Stoskopf,

1967; Gardener, et al. 1964). These findings by other workers do not

agree fully with the findings obtained in this study. The genotypes in-

volved in the second group (Druchamp, Redmond and Travero) have

broader leaves than the first group (Brevor, Sel. 101 and Sel. 172) and

produced a significantly higher grain yield, which suggests that the

tolerance of the genotype to a higher leaf area index must also be

considered. Tolerance is then an additional factor besides the leaf

size and orientation in determining the grain yield.

If leaf density influences tiller number per unit area, then

plants seeded in wider rows should produce more tillers and grain

55

yield than plants seeded in narrower row spacings. However, there

are other factors which must also be considered, such as soil

moisture and temperature within the plant canopy, which also affects

tiller number and plant growth (Tanner and Lemon, 1962; Peters and

Russel, 1959). As the size of the plant increases, there is an increase

in transpiration and if the sunlight is not intercepted by the leaves,

evapotranspiration will increase until the water capacity of the soil

reaches a critical point. Therefore, optimum leaf area index and

maximum light interception are necessary for efficient use of light

energy and maximum crop production.

In wider row spacing, the leaf area index will be smaller. As

a result, the temperature in the plant canopy will be higher and the

night temperature will be cooler. In oats and barley, it has been

reported that the cooler night temperature in the plant canopy

influences the total dry matter production and grain yield (Stoskopf

and Klink, 1966; Grafius, 1956a). It was observed in this study that

in the 12'' square planting, the leaf area index and percent light inter-

ception were significantly less than with the other patterns of planting,

and as a result, the plant height and tiller number per unit area at the

heading stage were significantly reduced. Therefore, it would appear

that the percent light interception in the plant canopy is dependent on

plant spacing and the resulting leaf area index, and if the light is not

intercepted, the microclimate in the plant canopy may influence plant

56

growth.

In crops such as corn, rice and soybeans, it has been observed

that there is an increase in grain yield as the percent light intercep-

tion increases (Shaw and Weber, 1967; Eik and Hanway, 1966; Takeda

and Maruta, 1955). The path coefficient analysis in this experiment

indicated that the leaf area index and percent light interception at the

heading stage had a large direct effect on grain yield. Voldeng and

Simpson (1967) have also observed in wheat that the photosynthetic

area at the heading stage was contributing more to the grain yield than

the leaf area in the earlier stages of growth.

The percent light interception in the plant canopy was observed

to be significantly influenced by the plant height at the jointing stage.

During the latter stages of growth, the effect of plant height was

reduced due to an increase in leaf density of the plant canopy. The

taller plants provided more shade to the lower leaves in the earlier

stage of growth than shorter plants resulting in a greater reduction of

spike bearing tillers. Likewise, the taller plants were not as

efficient as short plants in utilizing light energy. However, higher

yields were obtained with the taller plants. This can be attributed

to the higher number of kernels per spike which was directly

associated with plant height and resulted in an increased grain yield.

In considering space planting, it was observed that the angular

position of the plants in the rhombus pattern provided better leaf

57

coverage in the plant canopy than rectangular or square patterns of

planting. The rectangular planting pattern had the same population

size as the rhombus pattern, but differed in the size of the angles

between plants and the adjacent distance between plants. As a result,

the leaf area index was higher at jointing stage and flag leaf stage than

in the rhombus patty -ru of planting. The loss of tillers was much higher

in the rectangular planting than in the rhombus pattern of planting due

to a higher leaf area index in the earlier stage of growth. The diagonal

distance between plants in the square planting was greater than the

adjacent distance, As a result, leaf coverage in the canopy was less

and the percent light interception was significantly less than in any other

patterns of planting. These results indicate that the 60° angular posi-

tion between plants will reduce plant competitor for light and thereby

will increase efficiency of the plant to utilize light energy and grain

yield per unit area. Plant competition for light was greater in the

solid plantings as compared to space plantings, as evidenced by the

greater reduction in tiller number per unit area noted in the solid

plantings, However, total dry matter production and grain yield per

unit area was significantly higher in 12" solid plantings, since the

total number of tillers per unit area was higher than in the space

planting even though more tillers were lost due to the competition

in solid planting.

In recent years, considerable effort has been extended in

58

exploring the possibility of producing hybrid wheat commercially.

Most of the early investigations on the extent of hybrid vigor in

wheat were conducted on space planted material. This raised the

question, if such estimates of hybrid vigor would be the same when

the hybrids are grown in competition. McNeal, et al. (1965) found

that there was no hybrid vigor expressed when hybrids were grown

in solid plantings. This lack of hybrid vigor in solid plantings may

be due to the parental combinations used and their performance under

different environmental conditions. However, in the present study

hybrid vigor was observed for most of the traits studied in two

crosses, irrespective of their patterns of planting.

Results from the present investigation indicated that the effect

of patterns of planting on the expression of hybrid vigor was influ-

enced by the percent light interception and such morphological features

as the leaf area and the tillers per unit area. At the early stage of

growth, there was little or no competition for light and the differences

in leaf area and tiller per unit area among parents and hybrids

were not significant. As the plant growth increased from the jointing

stage to heading stage, competition between plants became greater

and the two hybrids, Druchamp X Travero and Druchamp X Redmond,

were less affected than their parents. These hybrids had a greater

leaf area and more tillers per unit area than their parents. Hybrid

vigor in these two hybrids became prevalent only after the jointing

stage which indicates that the environmental factors are differentiating

between these hybrids and their parents. These hybrids intercepted

more light energy at all three stages of growth with the resulting dry

matter production and grain yield being significantly higher than that of

parents, Among the six hybrids studied, grain yield ranged from 19

percent below to ?" percent above the better parent. It is interesting

to note in the cross Druchamp X Travero which exhibited the largest

amount of hybrid vigor, that hybrid vigor was also noted for all the

components as well as grain yield.

Growth habits of the wheat plant were highly variable between

space and solid plantings. In space plantings the plant growth was

prostrate until jointing stage, then the tillers became erect. In solid

seeded patterns the tillers grew erect throughout the life cycle.

These differences in habit of growth influenced the percent light that

was intercepted in the early stages of growth. It was observed in this

experiment that the leaf area index and tiller number per unit area

were not significant between one and two seedlings per hill; however,

the light interception in the plant canopy was highly significant due to

differences in habit of growth.

These results Would indicate that plant breeders should pay more

attention to the leaf area of a plant, particularly when selecting plants for

which can tolerate a high percentage of intercepted light. Environ-

mental factors, such as light interception and leaf density, will also

5:

60

influence the micro- climate in the plant canopy, which in turn is one

of the factors influencing the yield. Plants selected with narrow and

vertical leaves will allow more light into the plant canopy and will also

provide more favorable micro -climate. However, the plant breeder

must also evaluate the tolerance of genotype to shading if he is to

obtain a maximum number of tillers per unit area and thereby

maximum grain yield. For example, the semi -dwarf wheat selection

101 has narrow and vertical leaves; however, it is quite susceptible

to shading with the result that many tillers did not mature and their

potential contribution to total grain yield was lost. Light distribution

at various heights within the plant canopy, as well as the other factors

which influence the micro -climate, were not investigated thoroughly.

Additional information is needed regarding these factors if plant

breeders are to make progress in developing varieties which will

produce maximum grain yield. Since the expression of genotype is

significantly influenced by planting pattern and by population den-

sity, plant breeders must consider these factors in selecting for

high yielding varieties.

61

SUMMARY AND CONCLUSIONS

Six wheat hybrids and their respective parents were selected

to evaluate the influence of patterns of planting and population density

on grain yield and factors which determine grain yield. The factors

studied included the leaf area, percent light interception, plant

height and the components of grain yield which are considered as the

number of tillers per unit area, kernels per spike and weight of

1,000 kernels. Data were collected at three stages of growth, which

included the jointing stage, prior to flag leaf, and the heading stage.

The experimental design was a first order factorial randomized

split plot with single replication. The experiment consisted of 12

phenotypes X 2 plant densities X 5 patterns of planting.

The following conclusions were made from the results of this

study:

1. Performance of phenotypes were significantly different for all

characteristics studied in space and solid seeded patterns of

planting except for 1,000 kernel weight.

2. Leaf area and tillers per unit area in wheat hybrids and their

parents were not significantly different at jointing stage. How-

ever, they were found to be highly significant at the later stages

of growth. These differences were mainly due to the failure of

young tillers to develop a mature spike.

62

3. Leaf area index was found to be increased by higher plant densi-

ties, more tillers per unit area and increased plant height.

Solid patterns of planting also increased the leaf area as compared

to space planting.

4. Light interception in the plant canopy was measured by means of

ozalid paper which was found to be very sensitive in absorbing

light energy. Standard density filters were found very useful to

estimate the percent light energy absorbed by the ozalid papers.

5. Considerable variation among phenotypes was observed for the

percentage of light intercepted at all three stages of growth.

This variation was due to the differences in leaf area in the later

stages of growth.

6. Rectangular pattern intercepted more light energy than any other

patterns of space planting in the last two stages of growth. How-

ever, there was a greater reduction in tillers per unit area which

resulted in less grain yield.

7. Among the five patterns of planting studied, 6C° angular position

of plants in rhombus pattern of planting favored more uniform

light distribution throughout the plant canopy.

8. Leaf area and percent light interception were found to have

greater effects at the heading stage than at the earlier stages of

growth for grain yield.

9. The components of yield, tillers per unit area, kernels per spike

63

and weight of 1, CCC kernels were significantly different among

the parents and hybrids as the result of the treatments. The

differences in tiller number per unit area was caused by a dif-

ferencial response to the shading effect of upper leaves of the

same plant and of the surrounding plants. Differences in ker-

nels per spike and weight of 1,000 kernels were not influenced

by the leaf area or the percentage of light intercepted.

10. An increase in dry matter production and grain yield was

observed with increases in light interception.

11. Hybrid vigor was observed for all the characteristics studied in

the cross Druchamp X Travero with the exception of the leaf area

and tillers per unit area at the jointing stage. It would appear

that maximum hybrid vigor in wheat can be obtained only in

specific cross combinations where all or <t least most of the com-

ponents exhibited hetrosis.

12. The results of this study indicates that the spacing pattern and

population density are influencing the expression of a genotype.

Plant breeders need to be more concerned when evaluating

breeding material, as to the possible influence that plant spacing

may have on the expression of a character, particularly when the

material will be solid seeded in commercial production.

64

BIBLIOGRAPHY

Anderson, M. C. 1964. Light relation of terrestrial plant com- munities and their measurement. Biological Review 39:425- 48 6.

Aubertin, G. M. and D. B. Peters. 1961. Net radiation deter- mination in a corn field. Agronomy Journal 53:269 -272.

Baker, D. N. and R. E. Meyer. 1966. Influence of stand geometry on light interception and net photosynthesis in cotton. Crop Science 6:15 -19.

Binet, F. G. , R. T. Leslie, S. Weiner and R. L. Anderson. 1955. Analysis of confounded factorial experiments in single replica- tion. Raleigh. 64 p. (North Carolina. Agricultural Experi- ment Station Technical Bulletin 113)

Black, J. N. 1957. The influence of varying light intensity on growth of herbage plants. Herbage Abstract 27:89 -98.

Briggle, L. W. 1963. Heterosis in wheat. Crop Science 3:407- 412.

Briggle, L. W. , R. J. Daum and H. Stevens. 1964. Expression of heterosis in two wheat crosses. Crop Science 4:220 -223.

Brown, C. M. , R. O. Weibel and R. D. Seif. 1966. Heterosis and combining ability in common winter wheat. Crop Science 6:

382 -383.

Carleton, A. E. and W. H. Foote. 1965. A comparison of methods for estimating total leaf area of barley plants. Crop Science 5:602 -603.

Cochran, W. G. and G. M. Cox. 1957. Experimental design. New York, Wiley. 611 p.

Cornish, E. A. 1936. Non - replicated factorial experiments. Journal of Australian Institute of Agricultural Science 2:79- 82.

65

Davidson, J. L. and C. M. Donald. 1958. The growth of swards of subterranean clover with particular reference to leaf area. Australian Journal of Agricultural Research 9:53 -72.

Denmead, O. T. , L. J. Fritchen and R. H. Shaw. 1962. Spatial distribution of net radiation in a corn field. Agronomy Journal 54:505 -510.

Donald, C. M. 1961. Competition for light in crops and pastures. In Mechanisms in Biological Competition, ed. by F. L. Mitthore, Symposium of the Society for Experimental Biology 15:282 -313.

Donald, C. M. 1962. In search of yield. Australian Institute Agricultural Science 28:171 -178.

Eastman Kodak Company. 1965. Kodak wratten filters for scientific and technical use. 22nd ed. Rochester, N. Y. 77 p.

Eik, K. and J. J. Hanway. 1966. Leaf area in relation to yield of corn grain. Agronomy Journal 58:16 -18.

Fonseca, S. and F. L. Patterson. 1964. Heterosis in a diallel cross of seven varieties. American Society of Agronomy, 1964 annual meeting, Agronomy Abstracts, p. 66 -67.

Foth, H. D. , L. S. Robertson, and H. M. Brown. 1964. Effect of row spacing distance on oat performance. Agronomy Journal 56:70 -73.

Freeman, G. F. 1919. Heredity of quantitative characters in wheat. Genetics 4:1 -93.

Friend, D. J. C. 1961. A simple method of measuring integrated light values in field. Ecology 42:577 -580.

Friend, D. J. C. , V. A. Helson and J. E. Fisher. 1962. Leaf growth in Marquis wheat, as regulated by temperature, light intensity and day length. Canadian Journal of Botany 40:1299- 1311.

Gardener, C. J. , J. W. Tanner, N. C. Stoskopf and E. Reinbergs. 1964. A physiological basis for the yield performance of high and low yielding barley varieties. American Society of Agronomy, 1964 annual meeting, Agronomy Abstracts, p. 67.

66

Grafius, J. E. 1956a. The interaction of genotype and night tem- perature in oat and barley varieties. Agronomy Journal 48: 56 -59.

Grafius, J. E. 1956b. The relationship of stand to panicles per plant and per unit area in oats. Agronomy Journal 48:460- 4 62 .

Grafius, J. E. 1959. Hetrosis in barley. Agronomy Journal 51: 551 -554.

Hayes, H. K. and F. R. Immer. 1942. Methods of plant breeding. New York, McGraw -Hill. 432 p.

Hesketh, J. D. 1963. Limitations to photosynthesis responsible for differences among species. Crop Science 3:493 -496.

Johnson, V. A. 1953. Environmental factors affecting plant height in winter wheat. Agronomy Journal 45:505 -508.

Kronstad, W. E. 1963. Combining ability and gene action estimates and association of components of yield in winter wheat crosses. Ph. D. thesis. Corvallis, Oregon. State University. 64 numb. leaves.

Kronstad, W. E. and W. H. Foote. 1964. General and specific combining ability estimates in winter wheat (Triticum aestivum Vill. Host. ). Crop Science 4:616 -619.

McNeal, F. H. , D. E. Baldridge, N. A. Berg and C. A. Watson. 1965. Evaluation of three hard red spring wheat crosses for heterosis. Crop Science 5:399 -400.

Miller, E. C. 1958. Plant physiology. McGraw -Hill, New York. 1201 p.

Milthorpe, F. L. 1956. The growth of leaves. In Proceedings of the third Easter School in Agricultural Science, Nottingham, University of Nottingham. ed. by F. L. Milthorpe. London, Butterworth Scientific Publication. p. 223.

Pearce, R. B. , R. H. Brown and R. E. Blaser. 1965. Relation- ship between leaf area index, light interception and net photo- synthesis in orchardgrass. Crop Science 5:553-55 6.

67

Pendleton, J. W. and R. O. Weibel. 1965. Shading studies on winter wheat. Agronomy Journal 57:292 -293.

Pendleton, J. W. , C. M. Brown and R. O. Weibel. 1965. Effect of reflected light on small grain yield. Crop Science 5:373.

Peters, D. B. and M. B. Rusell, 1959. Relative water losses by evaporation and transpiration in corn fields. Agronomy Journal 23:170 -173.

Quisenbery, K. S. 1928. Some plant characters determining yields in field of winter and spring wheat in 1926. Journal of the American Society of Agronomy 20:492 -499.

Rosenquist, C. E. 1931. Hybrid vigor in wheat (Triticum vulgare). Journal of the American Society of Agronomy 23:81 -105.

Sakamoto, C. M. and R. H. Shaw. 1967. Light distribution in field soybean canopies. Agronomy Journal 59:7 -9.

Sani, S. K. 1968. The influence of plant densities on gene action estimates and associations in seven winter wheat parents and their F2 progeny. Ph. D. thesis. Corvallis, Oregon State University. 69 numb, leaves.

Shaw, R. H. and C. R. Weber. 1967. Effect of canopy arrange- ments on light interception and yield of soybean. Agronomy Journal 59:155 -159.

Shebeski, L. H. 1966. Quality and yield studies in hybrid wheat (Triticum aestivum L. ). Canadian Journal of Genetics and Cytology 8:375 -386.

Shibles, R. M. and C. R. Weber. 1965. Leaf area solar radiation and dry matter production by soybeans. Crop Science 5:575- 577.

Shibles, R. M. and C. R. Weber. 1966. Interception of solar radiation and dry matter production by various soybean planting patterns. Crop Science 6:55 -59.

Stern, W. R. and C. M. Donald. 1961. Relationship of radiation leaf area index and crop growth rate. Nature 189:597 -598.

68

Stickler, F. C. , S. Wearden and A. W. Paule, 1961. Leaf area determination in grain sorghum. Agronomy Journal 53:187- 188.

Stoskopf, N. C. 1967. Yield performance of upright- leaved selections of winter wheat in narrow row spacings. Canadian Journal of Plant Science 7:597 -601.

Stoskopf, N. C. and H. R. Klinck. 1966. Temperature variations in the microclimate of oats. Canadian Journal of Plant Science 46:155 -162.

Stoskopf, N. C. and E. Reinbergs. 1965. Breeding for yield in spring cereals. Canadian Journal of Plant Science 46:513- 519.

Stoskopf, N. C. , J. W. Tanner and E. Reinbergs. 1963. Attack- ing the yield barrier. Cereal News 8:8 -12.

Stoy, V. 1965. Photosynthesis respiration and carbohydrate accumulation in spring wheat in relation to yield. Physiologia Plantarum. Sup. IV. 125 p.

Takeda, T. and H. Maruta. 1955. Studies on CO2 exchange in crop plants. III. The effect of light intensity and spacing on photosynthetic rate of rice seedlings. Proceedings of the Crop Science Society of Japan 24 :34 -40.

Tanner, C. B. and E. R. Lemon. 1962. Radiant energy utilized in evapotranspiration. Agronomy Journal 54 :207 -212.

Thorne, G. N. 1966. Physiological aspects of grain yield in cereals and grasses. In: The growth of cereals and grasses. Proceedings of the twelfth Easter School in Agricultural Science, Nottingham, University of Nottingham, 1965. ed. by F. L. Milthorpe and J. D. Ivins, London, Butterworth.

Voldeng, H. D. and G. M. Simpson. 1967. The relationship between photosynthetic area and grain yield per plant in wheat. Canadian Journal of Plant Science 47:359 -365.

Warren, W. J. 1959. The measurement of grassland productivity. In: The measurement of grassland productivity, ed. by J. D.

Ivins, London, Butterworth. 217 p.

69

Warren, W. J. 1961. Influence of spatial arrangement of foliage area on light interception and pasture growth. In: Proceed- ings of the Eighth International Grassland Congress, Univer- sity of Reading, England, 1961. Berkshire, England, British Grassland Society. p. 274 -279.

Watson, D. J. 1947. Comparative physiological studies on the growth of field crops. I. Variation in net assimilation rate and leaf area between species and varieties within and between years. Annals of Botany 11:41 -76.

Watson, D. J. 1958. The dependence of net assimilation rate on leaf area index. Annals of Botany. New Ser. , 22 :38 -54.

Watson, D. J. , G. M. Thorne and S. A. W. French. 1963. Analysis of growth and yield of winter and spring wheats. Annals of Botany 27:1 -22.

Wright, S. 1921. Correlation and causation. Journal of Agricul- tural Research 20:557 -585.

Yao, A. Y. M. and R. H. Shaw. 1964. The effect of plant popula- tion and planting pattern of corn on net radiation. Agronomy Journal 5 6:165 -1 69.

APPENDICES

APPENDIX 1. Pedigrees and description of the six parental winter wheat

Parent Pedigree Grain Straw Yield Origin

Brevor Selection from White Medium Medium USA Turkey - Florence Moderate X Fortyfold - Federation

Sel. 101 CI 12697 X CI 13253 White Short Medium USA Stiff

Sel. 172 PI 178383 X Omar White Tall Medium USA (Moro) Medium

Druchamp Unknown White Medium High Europe Stiff

Redmond Unknown White Medium Medium Europe Moderate

Travero Unknown White Medium High Europe Stiff

APPENDIX 2. Phenotypic appearance of the six wheat parents and six hybrids used in the experiment showing the difference in height, spike type.

1. Brevor 7. Brevor X Sel. 101 2. Sel. 101 8. Brevor X Sel. 172 3. Sel. 172 9. Sel. 101 X Sel. 172 4. Druchamp 10. Druchamp X Redmond 5. Redmond 11. Druchamp X Travero 6. Travero 12. Redmond X Travero

N n

CO

Je

'41