Physiological aspects of maize (Zea mays L.) yield

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Physiological aspects of maize (Zea mays L.) yield
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PHYSIOLOGICAL ASPECTS OF MAIZE (Zea mays L.) YIELD


By

RAUL RENE VALLE MELENDEZ


















A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORIDA


1981















ACKNOWLEDGMENTS

I wish to express my sincere appreciation to Dr. D. E. McCloud

for being chairman of my supervisory committee during most of my

program; his guidance and assistance were invaluable throughout my

graduate work. I also would like to thank Dr. K. J. Boote, Dr. W. G.

Duncan, Dr. E. S. Horner, and Dr. W. G. Blue for being members of my

committee and for their support during my graduate studies.

Thanks are also in order to Dr. F. P. Gardner for assuming respon-

sibility as chairman of my supervisory committee and for helping me

edit this dissertation and to Dr. E. G. Rodgers for his help in getting

me started into Graduate School.

Words of gratitude are given to the Ministry of Natural Resources

in Honduras for the permission to continue my graduate work and to the

Organization of American States for financial support without which my

work would hardly have been accomplished.

Special words of thanks go to all graduate students of the physi-

ology group; to Mr. R. A. Hill for his help in the conduction of the

field experiments; to Mrs. Carolyn Meyer for typing this manuscript;

to Mrs. Beth Chandler for drawing the figures; and also to all those

persons who directly or indirectly helped me in this endeavor.

I gratefully acknowledge my wife, Ivete, for her understanding,

patience, and encouragement. Thanks and excuses are presented to Raul

Rene and Marco Antonio, children sometimes neglected.










I am grateful for the moral support of my mother, family, and

friends throughout our stay in Gainesville. I want to recognize the

great value of the teachings of my late father, to whom education was

a primary sign of progress.

To God I humbly give thanks.















TABLE OF CONTENTS
Pag(

ACKNOWLEDGMENTS............................................ .....i

LIST OF TABLES................................................... vi

LIST OF FIGURES................................................. vii

ABSTRACT ......................................................... ix

INTRODUCTION..................................................... 1

LITERATURE REVIEW................................................ 3

MATERIALS AND METHODS........................................... 19

RESULTS AND DISCUSSION.......................................... 28

1978 Experiment ............................................ 28
Vegetative Yields ....................................... 28
Crop Growth and Ear Growth Rates....................... 30
Brix Readings ........................................... 31

1979 Experiment............................................ 31
Cultivar Characteristics............................... 31
Total Dry Weight........................................ 34
Root Dry Weight......................................... 37
Stalk Dry Weight ........................................ 37
Leaf Dry Weight ......................................... 39
Ear Dry Weight .......................................... 41
Dry Matter Distribution................................ 41
Crop Growth Rates...................................... 44
Ear Growth Rates ........................................ 50
Ear Effective Filling Periods.......................... 51
Kernel Growth Components............................... 53
Total Available Carbohydrates.......................... 56
Brix Readings ........................................... 64
Partitioning Coefficient............................... 70
Yield Dynamics.......................................... 73

SUMMARY AND CONCLUSIONS......................................... 76

LITERATURE CITED................................................ 78









Page
APPENDICES

A AMYLOGLUCOSIDASE-INVERTASE PROCEDURE FOR HYDROLYZING TOTAL
AVAILABLE CARBOHYDRATES (STARCH, SUCROSE) TO REDUCING
SUGARS ......................................................... 87

B TABLES: SOIL FERTILITY ANALYSIS, DRY WEIGHT OF PLANT
COMPONENTS FOR THE 1978 AND 1979 GROWING SEASONS, TOTAL
AVAILABLE CARBOHYDRATES, AND PERCENT BRIX READINGS.............90

BIOGRAPHICAL SKETCH................................................ 97















LIST OF TABLES


Table Page

1 Fertilizer and pesticides used in the maize
growth analysis experiments of 1978 and 1979 ............ 22

2 Mean Brix readings per internode and per plot for
the hybrid corn Pioneer Brand 3369A and the inbred
Iowa B37 studied in 1978 ................................ 32

3 Characteristics of the cultivars studied in 1979........ 33

4 Dry matter distribution in percent of the total
dry weight .............................................. 43

5 Crop growth rates, EGR, and distribution index for
the maize cultivars grown in 1979...................... 46

6 Estimation of glucose required for the vegetative,
seed, and cob components of a maize plant ............... 48

7 Summary of related yield parameters for the maize
cultivars grown in 1979................................. 52

8 Percentages of total available carbohydrates (TAC)
for the stalks, leaves, cobs, and grain of the
maize cultivars studied in 1979........................ 57

Appendix B Tables

B-1 The pH, nitrogen, and double-acid extractable
nutrients in the soil used in the 1979 experiment....... 90

B-2 Dry weight of plant components and LAI for the
hybrid corn Pioneer Brand 3369A and the inbred
line Iowa B37 investigated in 1978..................... 91

B-3 Dry weight of plant components for the maize culti-
vars investigated in 1979.............................. 92

B-4 Total available carbohydrates (TAC) in the different
plant components of the maize cultivars grown in 1979... 93

B-5 Average percent Brix readings per plot and for the
maize cultivers grown in 1979.......................... 94

B-6 Average percentage Brix readings per internode for the
maize cultivars studied in 1979........................ 95















LIST OF FIGURES


Figures Page

1 Climatological data for the 1978 experimental
period. Averages of 10-day periods coinciding
with harvest dates..................................... 20

2 Climatological data for the 1979 experimental
period. Averages of 10-day periods coinciding
with harvest dates.................................... 21

3 Total, stalk, leaves, roots, and ear dry weight
accumulation for the hybrid (H) Pioneer Brand
3369A and the inbred line (I) Iowa B37 studied
in 1978 ................................................ 29

4 Leaf area index for the maize cultivars grown in
1979. CH + Chapalote; CO = Coker 77; MC = Maiz
Criollo; NT = Nal-Tel. Arrows indicate anthesis
dates .................................................. 35

5 Total dry matter accumulation for the maize culti-
vars grown in 1979. CH = Chapalote; CO = Coker 77;
MC = Maiz Criollo; NT = Nal-Tel. Arrows indicate
anthesis dates....................... .................. 36

6 Stalk dry matter accumulation for the maize culti-
vars grown in 1979. CH = Chapalote; CO = Coker 77;
MC = Maiz Criollo; NT = Nal-Tel. Arrows indicate
anthesis dates ......................................... 38

7 Leaf dry matter accumulation for the maize cultivars
grown in 1979. CH = Chapalote; CO = Coker 77; MC =
Maiz Criollo; NT = Nal-Tel. Arrows indicate
anthesis dates ......................................... 40

8 Ear dry matter accumulation for the maize cultivars
grown in 1979. CH = Chapalote; CO = Coker 77;
MC = Maiz Criollo; NT = Nal-Tel...................... 42

9 Kernel dry matter accumulation for the maize culti-
vars grown in 1979. CH = Chapalote; CO = Coker 77;
Mc = Maiz Criollo; NT = Nal-Tel...................... 54












10 Stalk TAC weight in the maize cultivars grown in
1979. CH = Chapalote; CO = Coker 77; MC =
Maiz Criollo; NT = Nal-Tel. Arrows indicate
anthesis dates ......................................... 59

11 Leaf TAC weight in the maize cultivars grown in
1979. CH = Chapalote; CO = Coker 77; MC = Maiz
Criollo; NT = Nal-Tel. Arrows indicate anthesis
dates ........................................ .......... 60

12 Cob TAC weight in the maize cultivars grown in 1979.
CH = Chapalote; CO = Coker 77; MC = Maiz Criollo;
NT = Nal-Tel .................... ................... 61

13 Grain TAC weight in the maize cultivars grown in
the 1979 growing season. CH = Chapalote; CO =
Coker 77; MC = Maiz Criollo; NT = Nal-Tel ............. 63

14 Average percent Brix readings per plot in the
cultivars grown in 1979. CH = Chapalote; CO =
Coker 77; MC = Maiz Criollo; NT = Nal-Tel ............. 65

15 Average percent Brix readings per internode in
Coker 77. Smaller numbers indicate lower inter-
nodes. Arrow marks anthesis date..................... 66

16 Average percent Brix readings per internode in
Nal-Tel. Smaller numbers indicate lower inter-
nodes. Arrow marks anthesis date..................... 67

17 Average percent Brix readings per internode in
Chapalote. Smaller numbers indicate lower inter-
nodes. Arrow marks anthesis date..................... 68

18 Average percent Brix readings per internode in
Maiz Criollo. Smaller numbers indicate lower
internodes. Arrow marks anthesis date................ 69


viii


Page


Figures















Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

PHYSIOLOGICAL ASPECTS OF MAIZE (Zea mays L.) YIELD


By

RAUL RENE VALLE MELENDEZ

March 1981

Chairman: F. P. Gardner
Major Department: Agronomy

Two experiments were conducted to study physiological reasons

for yield differences among diverse maize (Zea mays L.) cultivars.

Growth analysis techniques were used to test the hypothesis that

high yields of commercial maize hybrids are due to: (1) high rates

of dry matter accumulation, (2) a proportionally larger distribution

of assimilates to reproductive growth, and/or (3) longer filling

period. Attention was also given to storage of assimilates.

In 1978 the single-cross hybrid Pioneer Brand '3369A' was com-

pared with the inbred line Iowa B37, and in 1979 the hybrid 'Coker 77'

was compared with two ancient Mexican races, 'Chapalote' and 'Nal-Tel',

and a Cuban accession, 'Maiz Criollo'. These experiments were planted

at the University of Florida Agronomy Farm in Gainesville at population

densities expected to give approximately equal leaf area indices (LAI).

Refractometric readings per internode and per unit area were determined

in both experiments. Also, in 1979 total available carbohydrate (TAC)

ix










in plant components (stalk, leaf, cob, and grain) were measured.

Rates of dry matter accumulation (crop growth rates), computed during

the vegetative (CGRv) and reproductive (CGRr) phases, were examined as

estimates of canopy capacity to produce assimilates. Ear growth rates

(EGR) were also determined. The partitioning coefficient (PC) was used

as an estimate of assimilate distributed to ear growth as opposed to

vegetative growth, and effective ear filling period (EEFP) and

effective seed filling period (ESFP) were estimates of filling periods.

In 1978, the hybrid and inbred ear yields were drastically reduced

by poor environmental conditions; however, the hybrid yield was signif-

icantly greater than that of the inbred. Stalk refractometric readings

per unit land area were higher in the inbred than in the hybrid. This

suggested a higher accumulation of soluble solids in the inbred line,

probably because of its lower sink capacity.

Except for Nal-Tel, the cultivars compared in 1979 did not signif-

icantly differ in CGRv and LAI. However, Coker 77 maintained its high

LAI for a longer period than the other cultivars. During reproductive

growth, all cultivars showed a decrease in canopy assimilate production.

Although CGRr values of Chapalote and Coker 77 were not significantly

different, the CGRr of Coker 77 was sustained for a longer period.

Maiz Criollo and Nal-Tel had the lowest CGRr values. Partitioning

coefficient varied among cultivars. Nal-Tel had the highest PC followed

by Coker 77, Maiz Criollo, and Chapalote. Final ear yields for Coker

77, Maiz Criollo, Nal-Tel and Chapalote were 1023, 776, 607, and

578 g m-2, respectively. Total available carbohydrates were higher in

the plant components of Coker 77 than in the other cultivars. Contri-

butions of remobilized TAC from vegetative components to final ear










yield were estimated to be 9, 13, 21, and 26% in Coker 77, Maiz

Criollo, Nal-Tel, and Chapalote, respectively.

Similar CGRv values in Chapalote, Coker 77, and Maiz Criollo

indicated similar potential to produce high yields. Chapalote, however,

produced many barren tillers in addition to ear-bearing stalks. This

tillering habit of Chapalote explains its lower PC and yield. Nal-Tel

had the highest PC, but its ear yield was low probably because of its

low LAI. Length of filling period, either as EEFP or ESFP, was not a

significant factor in yield differences. Coker 77 had the highest

EGR; differences in EGR accounted for most of the yield differences

among cultivars.

The results of these experiments suggested that under conditions

of similar LAI, the physiological characteristics of a high-yielding

maize cultivar are high PC, high EGR, and a longer duration of CGRr.















INTRODUCTION
While it is generally recognized that commercial hybrid maize

(Zea mays L.) cultivars outyield their inbred parents, or ancient races

(Duncan and Hesketh, 1968), the physiological and ecological bases for

their increased yield have not yet been adequately explained.

A basic step toward increasing the yield of any crop is to under-

stand its pattern of dry matter accumulation. When only final economic

yields are determined, little knowledge can be gained on how high

yields are achieved. However, growth analysis is an effective way to

study the dynamics of dry matter accumulation and yield physiology.

The experiments discussed in the following pages permitted observa-

tion and recording of physiological responses of hybrid maize when

compared with an inbred line, and with ancient races of Central and

North America. However, the main objective was to investigate which

of three major hypotheses for differences in yield among cultivars best

explained the higher yield of hybrid maize. These hypotheses are:

i) Higher yielding cultivars have higher crop canopy photosynthetic

efficiency. Cultivars with more efficient canopy photosynthesis would

produce more assimilates with a given amount of solar radiation and

should produce higher yields. The crop growth rate (CGRv) after the

canopy has reached 97% ground cover (light interception) and prior to

ear development, reflects canopy assimilate production which can go to

grain fill. ii) High yielding cultivars have longer duration of the

effective grain filling period. The longer the grain filling period a








2

cultivar has the more solar radiation it can intercept to produce

photosynthate for ear growth, iii) High yielding cultivars have

different distribution of assimilates between reproductive and vegeta-

tive growth during the period of ear establishment. A cultivar

with greater distribution of assimilates to the reproductive sink

during the grain setting period should have greater yield.

It was hoped that this study would help elucidate differences in

yield among hybrid, inbred, and ancient races in terms of physiological

parameters.















LITERATURE REVIEW

Increase in dry weight is a useful definition of growth for

scientists interested in crop productivity. Crop growth is usually

more accurately characterized by measurement of dry weight than

measurements of fresh weight, which can be strongly influenced by

prevailing moisture conditions. However, dry weight increase is not a

completely satisfactory definition of growth; because growth also

includes germination during which dry weight is lost, cell multiplica-

tion and increase in volume both may represent little change in dry

weight (Salisbury and Ross, 1969).

Dry weight increase has been described mathematically as a

function of physiological, phenological, and environmental factors.

Increase in dry weight with time is usually characterized by a sigmoidal

curve (Leopold and Kriedemann, 1975), in which three primary phases are

recognized: expansion, linear, and senescence (Richards, 1969). In

the expansion phase, the growth rate (increase in dry weight per unit

of time) is initially slow but the rate increases continuously as more

dry weight is added. Growth of a higher plant during its exponential

phase is analogous to the accumulation of capital at a continuous com-

pound interest and can be described by the equation Wi = Wo (1 + r)t,

where Wo is the initial weight, r is the rate of growth or capacity to

add dry weight (Blackman, 1919), and Wi is the total dry weight after

a certain time t. Accumulation of dry weight is exponential until

self-shading or other conditions prevent the increasing leaf area from








4

producing a proportionate increase in the weight of the plant (Watson,

1958; Leopold and Kriedemann, 1975; Duncan et al., 1967).

The end of the expansion phase marks the beginning of the linear

phase in which the increase in dry matter continues at a constant

rate. The final, senescence phase is characterized by a decrease in

growth rate as the crop approaches maturity and begins to senesce

(Salisbury and Ross, 1978).

Growth analysis, by periodic harvest, is a useful tool to charac-

terize and describe these growth phases of single plants or plant

communities (McKinion et al., 1974). The use of relative growth rate

(RGR, g g-1 time), net assimilation rate (NAR, g dm-2 time-1), and

leaf area ratio (LAR, dm2 g-1) to quantitatively analyze plant growth

has become known as "growth analysis." The measurement of the total

dry weight of plant material per unit land area and the measurement

of the assimilatory system are the two parameters needed to conduct

a growth analysis of a plant community (Radford, 1967). The assimila-

tory system of a plant community is generally computed as the total

leaf area (one side) per unit land area and is known as the leaf

area index (LAI) of a canopy (Watson, 1947a and 1947b).

The introduction of the crop growth rate (CGR) function (Watson,

1958), to the traditional "growth analysis," has been recognized

(Williams et al., 1965b) as the most meaningful growth function, since

it represents the net results of photosynthesis, respiration, and

canopy area interactions. As noted by Williams et al., CGR is also
representative of the most common agronomic measurement, i.e., yield

of dry matter per unit of land area.









The CGR is defined as the increase in plant material per unit land

area per unit time. The mean CGR over a time period tI to t2 is given

by CGR = W2 Wl / t2 tl, where Wl and W2 designate the total dry

weights at periods tl and t2, respectively (Watson, 1958). Thus, CGR

represents total dry matter productivity of a plant community and,

except for a small mineral component, it can be equated as an estimation

of net carbon fixed for a crop canopy (Duncan et al., 1978).

Crop growth rate shows a close relationship to LAI in all plant

communities, especially below LAI of four (Duncan, 1975). For certain

crops such as kale (Brassica oleracea L.), subterranean clover

(Trifolium subterraneum L.), sunflower (Helianthus annuus L.), and rice

(Oryza sativa L.) optimum LAI values have been shown to exist (Watson,

1958; Black, 1963; Takeda, 1961; Hiroi and Monsi, 1966; Yoshida, 1972).

According to these authors increasing LAI beyond the optimum caused a

decline in CGR, which was attributed to mutual shading of leaves, such

that further increase in leaf area did not compensate for the reduction

in net photosynthesis because of less effective illumination. The

community still gained dry weight at high LAI, but the rate diminished

(Leopold and Kriedemann, 1975). However, experiments with mixed

pastures by Brougham (1956), sugar beet (Beta vulgaris L.) by Watson

(1958), maize (Zea mays L.) by Williams et al. (1965b), soybeans

(Glycine max L., Merr.) by Shibles and Weber (1966), and rape (Brassica
napus L.) by Clarke and Simpson (1978) have not displayed an optimum

LAI. The CGR response to LAI for corn does not indicate a peak in CGR

at some optimum LAI (Williams et al., 1965b; Duncan, 1975); rather,

the trend of the curve, after the initial rise at the low end of the LAI

range, is toward an asymptotic plateau. Decline in CGR at later stages









of the growth cycle of corn has been associated partly to the decline

in radiation received as the season advances (Duncan et al., 1967;

Williams et al., 1968). The asymptotic relationship between CGR and

LAI has also been demonstrated for wheat (Triticum aestivum L. em Thell.)

by Puckridge and Donald (1967), soybean by Shibles and Weber (1965),

and rape by Clarke and Simpson (1978). One explanation for the plateau

at high LAI values has been elucidated by experiments in cotton

(Gossypium hirsutum L.) by Ludwig et al. (1965), and white clover

(Trifolium repens L.) by McCree and Troughton (1966a, 1966b). These

authors demonstrated that respiration in shade-adapted leaves of the

basal strata in dense canopies of these crops is lower than in leaves

exposed to more intense illumination. Thus, CGR may attain a plateau

rather than decline beyond an optimal value of LAI. Watson (1958)

stated and Williams et al. (1965a, 1965b, 1968) confirmed that the

form of the curve relating CGR to LAI and the maximum value of CGR

are determined by the way in which the spatial distribution of leaves

effectsthe utilization of incident radiation. Furthermore, at high

LAI vertical leaves allow more uniform light incidence, enhancing CGR

(Williams et al., 1968). This depends upon light intensity (Kriedemann

and Smart, 1971) and adaptation in respiration rates, since lower

leaves are not parasitic as was once thought (Ludwig et al., 1965;

McCree and Troughton, 1966a, 1966b).

Computer simulations by Duncan (1971) suggested that leaf angle

in maize has small effects on photosynthetic rates of a crop canopy

per unit land area at LAI values lower than four. Williams et al.

(1965a, 1965b, 1968) have shown, however, that the difference in light

interception in the range of LAI of 2.7 to 4.5 can be as high as 30%










and that CGR varied proportionally. Their research was conducted with

a single-cross hybrid, Dekalb Brand 805, over a wide range of population

densities varying from 1.15 to 12.5 plants per m2. These experiments

point to the conclusion that the amount of irradiance intercepted by

the canopy is a major determinant of the CGR during the vegetative

phase of maize growth where nutrients and soil moisture are not limiting.

Grain yield correlates well with CGR up to an optimum density.

Decline in yield at high populations is mainly due to barren plants

(Prine, 1971; Yoshida, 1972; Duncan, 1975). However, an increase in

grain yield with increase in planting rate normally ceases before

significant number of barren stalks are found. This yield plateau

occurs when light interception by the canopy is essentially complete

so that little increase in photosynthesis per unit land area is

possible (Prine, 1971; Duncan, 1975).

The grain yield of a crop is the product of the average rate of

grain dry matter accumulation per unit area and the effective duration

of grain filling. The effective period of grain filling (EFP) is

defined as the quotient of final reproductive dry weight and the average

rate of grain dry matter accumulation per unit area (Daynard et al.,

1971). The average reproductive dry-weight accumulation rate can be

estimated from the slope of a plot of reproductive dry weight against

time during the linear phase (Johnson and Tanner, 1972b; Duncan, 1973).

An alternative method of measuring relative differences in the

duration of the grain filling period involves the use of black-layer

development and silking date. Black-layer at the base of the nucellus

of maize kernels coincides with maximum kernel dry weight (physiological

maturity) and marks the end of the filling period (Daynard and Duncan,










1969; Daynard et al., 1971; Daynard, 1972). Thus, total filling period

can be estimated on a phenological basis as days from pollination to

black-layer formation.

A linear relationship has been found among corn cultivars between

grain yield and duration of the phenologically estimated total filling

period (Funnah, 1971), and between grain yield and duration of the EFP

(Daynard et al., 1971; Daynard, 1972). In Daynard's experiments, yield

was more highly correlated with EFP than with the rate of filling. In

a comparison between inbreds and hybrids, Johnson and Tanner (1972a,

1972b) found the EFP to be much longer in the hybrids, but their rates

of growth per unit area were also higher. Several authors (Daynard

et al., 1971; Peaslee et al., 1971; Egli and Leggett, 1976) have

suggested that an extension of the filling period will result in higher

yields, provided that the rate of dry matter accumulation does not

change, the grain has larger potential size, and environmental and

nutritional conditions do not limit yield.

Estimation of maize grain yield as the product of mean ear growth

rate multiplied by EFP is convenient, since it evades the assessment

of the lag phases either at the beginning or at the end of ear growth

(Duncan, 1975). The initial lag period, from pollination to the

beginning of EFP, may be important in relation to the number of kernels

in each inflorescence. Among wheat cultivars, the longer the initial

lag phase the more kernels there were in each ear (Rawson and Evans,

1971), especially at low temperatures (Sofield et al., 1974). However,

the length of the lag phase in wheat is only a few days, whereas in

maize it is between 15 to 18 days (Evans, 1975), comprising from 47 to

84% as long as the effective duration of grain filling (Johnson and








9

Tanner, 1972a, 1972b). This much longer duration of the lag period may

be associated with the presence of 10 to 100 times as many grains per

inflorescence in maize compared with wheat, and may be necessary to

allow the later florets in the maize inflorescence to set grains (Evans

and Wardlaw, 1976).

Recently, investigations have been reported that give insight into

which of the parameters, rate or duration, can be most easily modified

to increase the final yield. Gay et al. (1980) investigated the

physiological basis for the difference in yield between old, low-yielding,

and new, high-yielding soybean cultivars in two maturity groups. They

concluded that the increase in yield between new and old varieties

has been the result of increased length of the filling period. However,

Duncan et al. (1978), in a similar study with peanut (Arachis hypogaea

L.), assessed equal importance to duration of the filling period and

growth rates.

Daynard and Kannenberg (1976) provided results supporting the

suggestion that selection for a longer EFP represents a feasible means

of increasing yields of corn; in their experiments, however, dif-

ferences in filling period accounted for only a limited portion of

the total variation in yield among 30 hybrids in one experiment and

35 in another. They also noted that some of the high-yielding hybrids

had shorter than average filling periods in both experiments. Con-

trastingly, some of the hybrids had long filling periods and below

average yields. They speculated that length of filling period and

yield are set primarily by the size of the ear sink capacity, i.e.,

kernel number, established soon after flowering, and kernel size,

which is to a large extent genetically controlled.








10

With a given rate of grain dry-matter accumulation, larger kernel

weight may allow a longer filling period and higher yield, assuming

that supply of assimilates is adequate to satisfy ear demands.

Duncan et al. (1978) proposed the concept of partitioning,

defined as the division of daily assimilate between reproductive and

vegetative plant components, and concluded that the yield increase

in newly developed peanut cultivars has been the result of higher

partitioning to reproductive sink. However, the possibility of yield

improvement from an increase in the partitioning of the photosynthate

to seed would be reduced when partitioning approaches the maximum

(Gay et al., 1980). In the study reported by Duncan et al. (1978)

the old peanut cultivars partitioned poorly whereas new peanut culti-

vars were approaching a maximum. In maize, partitioning and daily

photosynthate supply determine kernel number set during or shortly

after silking. A relatively large kernel set would be beneficial

since the sink demand (kernel number times growth per seed) would

determine the rate of utilization of assimilate, whether from photo-

synthesis and/or from labile storage (W. G. Duncan, Professor of

Agronomy, University of Florida, personal communication). However,

another possibility for establishment of the sink may be by setting

the kernel size soon after flowering, as Wilson and Allison (1978a)

suggested; perhaps this occurs once the number of endosperm cells

has been determined (Wardlaw, 1970). Wilson and Allison (1978b)

found that the removal of alternate plants in the field had little

effect on the average weight per kernel of the remaining plants when

it was done more than two to three weeks after silking, but increased

final average kernel weight when removal of plants was done close to







11

the time of silking. Very similar results have been reported by Prine

(1971) who worked with semi-prolific maize hybrids.

The assimilate used for ear growth may come from current photo-

synthate produced by the canopy or from labile assimilate stored

earlier in the vegetative component, particularly in the basal inter-

nodes (Duncan, 1975). Normally, the high rate of photosynthate

utilization by the growing plant does not permit a substantial accumula-

tion of assimilates (Duncan, 1975; McPherson and Boyer, 1977); however,

many studies (Singh and Nair, 1975; Campbell, 1964; Jurgens et al.,

1978; Hume and Campbell, 1972) have revealed that previously stored

assimilate can be mobilized and utilized for grain filling, even when

all leaves were removed and the entire plant was wrapped in foil

(Duncan et al., 1965). The results of these experiments have clearly

demonstrated that assimilates can be translocated from other plant

components to the ears; however, it is also likely that storage of

soluble materials occurs when photosynthate exceeds utilization, and

depletion when the demand is greater than the amount of assimilates

produced by photosynthesis. Incomplete utilization of photosynthate

for grain would also occur in cultivars in which the grain matures

before leaf senesce (Duncan, 1975). In such cases, an assessment of

the soluble materials accumulated in the stem sap could provide

useful information about yield-limiting factors. That is, if sink is

limiting, soluble materials should accumulate during the period of

active ear filling since assimilate production exceeds utilization.

On the other hand, if photosynthesis is limiting, soluble materials

should decline as utilization exceeds supply. Indeed, the decrease

in stalk weight before and shortly after anthesis and its subsequent








12

decrease during ear filling show the storage and utilization of soluble

solids (Hume and Campbell, 1972; Vietor et al., 1977; Major et al.,

1972; Johnson and Tanner, 1972a).

Normally, in a maize field, there is considerable variation

among plants in Brix readings of stalk-sap. The Brix reading is an

expression of the refractometric index using the correspondent percent

of dissolved sucrose which would give a similar index. Willaman et

al.(1924), in an intensive study of the possibilities of using corn-

stalk juice as a source of syrup, found that the stalk-sap of sweet

corn at the canning stage had a density of 9 to 10 Brix. After

standing 10 to 20 days following removal of the ears, the stalk-sap

density was reported to increase up to 13 to 17 Brix, with sucrose

in some plants reaching as high as 15%. Clark (1913) and Bodea (1934)

have shown that the expressed juice of maize stalks contains from

10 to 12% sugar at the time of ear formation and as high as 17% sugar

if pollination is prevented. Duncan (1975) reported that from corn

plants selected at random, stalk-sap Brix readings from lower inter-

nodes ran from 3 to 11%. He suggested that this variation probably

reflected differences in sink capacity and/or inadequate photosynthetic

rates, and that stalk Brix readings could furnish diagnostic indica-

tions, pointing to causes for yield limitations of varieties and

locations. Van Reen and Singleton (1952) showed that reliable com-

parisons between varieties can be made using Brix readings. However,

they also pointed out that caution should be taken, since some

varieties could store much of the sugars as hexoses rather than

sucrose, or the concentration of salts and non-sugars components

may be high. They recommended that in order to apply the hand








13

refractometer to other varieties with some assurance as to the meaning

of the results, sucrose should be determined chemically with at least

a few samples over the range of Brix values encountered.

Assimilate remaining in maize stalks at the end of the growing

cycle represents energy fixed by photosynthesis that was not converted

into grain, and hence a loss of potential yield. A complication is

the fact that lodging is negatively correlated with sugar content in

the stalks (Mortimer and Ward, 1964; Campbell, 1964). Campbell (1964)

studied three single-cross corn hybrids and showed that structural

tissues and vascular systems, the insoluble fraction, from unpollinated

and pollinated plants did not differ significantly. Unpollinated

plants accumulated more total dry matter in stalks and leaves than

pollinated plants. The difference in stalk dry matter was readily

accounted for as soluble solids. His results showed an inverse

relationship between ear dry matter and soluble solids in the sap just

before maturation. The prolific, high-yielding, lodging-susceptible

hybrid maintained a soluble solids level in the stalk juice between

8 to 10% Brix. Non-prolific, low-yielding, but lodging-resistant hybrids

gradually attained concentrations of 12 to 14%. Non-lodging unpol-

linated plants of all hybrids accumulated soluble solids from 15 to

17% Brix. Campbell concluded that since pollinated and unpollinated

plants differed primarily in stalk soluble-solids content, this stalk

component influenced final stalk strength and, therefore, lodging

resistance. Thus, selection of varieties for resistance to lodging

operates against complete utilization of assimilates for grain.

Photosynthesis provides essentially all the increase in crop

weight and all of the metabolic energy required for crop development.








14

The course of photosynthesis is thus a major determinant of crop yield.

In maize the leaf blades are the main photosynthetic organs. Allison

(1964) found leaf blades to comprise more than 80% of the total green

surface at both anthesis and maturity. Crop growth rate depends on

both the rate of leaf area expansion and the rate of photosynthesis

per unit leaf area. During early growth, the rate of leaf area

expansion is of greatest importance; however, once the leaf canopy

has closed, canopy photosynthetic rate becomes the most important

determinant of CGR depending on climatic conditions and canopy archi-

tecture (Duncan, 1971).

A vertical leaf arrangement is usually desirable in dense crops.

Maize cultivars generally have a leaf arrangement intermediate between

horizontal and vertical (Allison and Thomas, 1974). McCree and

Kenner (1974) felt that the degree of change in leaf angle which is

likely to be practicable probably would not have a marked effect on

crop assimilation. Furthermore, optimum leaf arrangement for various

conditions is far from clear because of the possible influence of

factors other than the light relations to which attention is usually

confined (Evans, 1975). Differences in leaf arrangement are probably

of little importance in maize stands with an LAI of 3 to 4 (Loomis

and Williams, 1969; Duncan, 1971).

From a survey of 22 races of maize, ranging from ancient varieties

to a modern hybrid, Duncan and Hesketh (1968) found no evidence that

improvement of maize over the centuries has been associated with

increase in leaf photosynthetic rate. There were, however, differences

among races in the way their photosynthetic rates responded to

temperature, which appeared to be adaptive. High-altitude races, for








15

example, had relatively lower rates at high temperature, but did not

differ from low-altitude races at low temperatures. The ancient

races had net photosynthetic rates near the average for all races. In

their experiment, only the modern single-cross hybrid ranked con-

sistently high in photosynthetic rates at all temperatures. Differences

among maize cultivars in photosynthetic rates have been reported, but

rate differences appear to be dependent on environmental conditions.

Rate differences found by Heichel and Musgrave (1969) in the Philippines

were not always apparent at Cornell University at Ithaca, New York

(Gifford, 1970). Similarly, although heterosis in photosynthetic rates

was reported by Heichel and Musgrave (1969) and Derieux et al. (1973),

there are other studies where it was not found (Duncan and Hesketh,

1968).

Apparent photosynthesis (Shibles, 1976) has been shown to decrease

as leaves age. Vietor et al. (1977) studying the effect of leaf age

on photosynthetic rates in maize showed decreases in apparent photo-

synthesis of individual leaves at different positions in the stalk.

The study was done in greenhouse and field cultured open pollinated

varieties, inbred lines, and single-cross hybrids. Mean apparent

photosynthetic rates across leaf position at pre-tassel, silking, and

dough stages for one inbred line were 52.8, 39.1, and 20.0 mg COz

dm-2 h-1, respectively. These measurements were done under greenhouse

conditions. In an open-pollinated, field grown cultivar, mean apparent

photosynthetic rate at the same stages as above and across leaf posi-

tions were 58.1, 45.0, and 28.7 mg COz dm-2 h-1. Pre-tassel, silking,

and dough stages were at 44, 71, and 88 days after emergence, respec-

tively. Their measurements of apparent photosynthesis in eight










single-cross hybrids at the silking stage ranged from 68.7 to 55.2

mg CO2 dm-2 h-1. The silking stage was recorded 71 days after

emergence; the measurements were done on the leaf immediately above

the ear. At the dent stage, 110 days after emergence, the range was

48.7 to 36.9 mg C02 dm-2 h-1. Leaf area index at the silking stage

ranged from 4.31 to 4.12, and at the dent stage from 4.08 to 3.99.

Thus, their study showed a reduction in mean apparent photosynthesis

of more than 62% in inbred lines, 50% in open pollinated varieties,

and 32% in single-cross hybrids from the early stages to the latest

one. They attributed the decrease in mean apparent canopy photosynthesis

to the decrease in mean leaf photosynthesis as caused by leaf aging.

Crosbie et al. (1977) also have shown a decrease in leaf photo-

synthetic rate from the vegetative to the reproductive stage. They

studied photosynthetic rate variability in 64 inbred lines, which were

selected randomly from a set of 247 inbred lines developed from Iowa Stiff

Stalk Synthetic (BSSS) population. They showed decreases of 30% in

the mean CO2 exchange rate (Shibles, 1976) from measurements performed

at stage 3.5 (twelfth leaf completely visible) to measurements taken

at stage 6.0 [12 days after silking or "blister" stage (Hanway, 1971)].

At stage 3.5 they measured 36.6 mg CO2 dm-2 h-1 from the most recently

expanded leaf. At stage 6.0 they measured 25.7 mg CO2 dm-2 h-1 from

the second leaf below the tassel.

Wilhelm and Nelson (1978b) studied leaf growth, leaf aging, and

photosynthetic rates in tall fescue (Festuca arundinacea Schreb)

genotypes. The genotypes were selected (Wilhelm and Nelson, 1978a)

to represent four carbon-exchange rate-yield categories: high CER-high

yield, high CER-low yield, low CER-high yield, and low CER-low yield.








17

Their experiment showed that CER of all four genotypes decreased after

collar formation at a rate of about 15 to 20% per week. They grew one

crop in the greenhouse during a four week period and another in the

field during a six week period. The CER measurements were done in

leaves previously marked and the rates were measured at an approximate

interval of one week on clear days.

Another possible reason for the decrease in photosynthetic rates

can be ascribed to increases in nonstructural carbohydrates (NSC) in

the leaves. Decreased photosynthetic rates with a concurrent increase

in NSCwereobserved in soybean following pod removal (Mondal et al.,

1978). On the other hand, an increase in photosynthetic rates of

leaves during fruit formation has also been observed in soybeans

(Dornhoff and Shibles, 1979; Ghorashy et al., 1975). This effect has

been hypothesized to be due to an increased demand for photosynthates

by the developing fruit with a resulting decrease in NSC. Decreased

NSC concentration has been thought to stimulate photosynthesis by

alleviating end product inhibition by soluble sugars (Neales and

Incoll, 1968), or by decreasing starch concentration of leaves

(Nafzinger and Koller, 1976; Thorne and Koller, 1974; Upmeyer and

Koller, 1973). High starch levels may inhibit net leaf photosynthesis

by starch granules physically shading the chloroplasts, by increasing

biochemical carboxylation resistance, or by increasing the C02

diffusion pathlength due to physical swelling of chloroplasts

(Nafzinger and Koller, 1976).

Hageman et al. (1976) reviewed their attempts to screen and select

corn varieties for activity of specific essential enzymes (aldolase,

glucose 6-phosphate dehydrogenase, trisephosphate dehydrogenase, and








18

nitrate reductase). Genetic differences in activities of single enzymes

were found among cultivars; however, these did not provide a metabolic

explanation for hybrid vigor in dry matter production, because crosses

did not exhibit heterotic enzyme activity when compared with the

parental inbreds. On the basis of their failure to find single enzyme

activities to account for heterosis, they suggested that an efficiently

organized total metabolic system is the characteristic of a superior

corn variety.















MATERIALS AND METHODS

This study was conducted at the Agronomy Farm of the University

of Florida during the 1978 and 1979 growing seasons. The soil used

in 1978 was a poorly drained, loamy, silicious, hyperthermic Arenic

Paleudult (Kendrick loamy sand). In 1979, the soil was a taxajunct

classified as loamy, mixed, thermic Arenic Hapludalf (Jonesville

fine sand) with excellent drainage.

Rainfall, solar radiation, and maximum and minimum temperatures,

collected near the plots at the Agronomy Farm Weather Station, were

averaged over 10-day periods coinciding with harvest dates. These

data for 1978 and 1979 are presented in Figs. 1 and 2. Anthesis dates

were recorded in both years when 50% of the plants in each plot were

shedding pollen. General information on fertilizers and pesticides

is presented in Table 1.

In 1978, the experiment was seeded on June 9. The corn cultivars,

single-cross hybrid Pioneer Brand 3369A and inbred line Iowa B37, were

planted in a complete randomized design with four replications. The

seeds were hand planted on square spacing of approximately 45 cm for

the hybrid and 30 cm for the inbred. Two or three seeds were placed

at each planting point to insure uniform stands. Fifteen days after

emergence the plants were thinned to one per planting point. Final

plant populations were 4.8 and 10.8 plants per m2 for the hybrid and

inbred, respectively. Nitrogen was applied 30 days after planting at













SOLAR RADIATION
SOLAR RADIATION


TEMPERATURE

---r --- ^ MAX.


MJ/r
24-
19-
14-

C
35
32
29
26
23
20


PRECIPITATION


I I I I


33 43


13 23


53 63 73 t8


DAYS AFTER PLANTING


Climatological data for the 1978 experimental period.
Averages of 10-day periods coinciding with harvest
dates.


MIN.


mTI
20-

15-
10-

5


Figure 1.


I















MJ/m2
M/m SOLAR RADIATION
25


TEMPERATURE
-MAX.


PRECIPITATION


5


4 -


25 45


I I


, I


65 85 105' IL5


DAYS AFTER PLANTING


Climatological data for the 1979 experimental period.
Averages of 10-day periods coinciding with harvest
dates.


15

C
34,


22-


I0


mn
401


20


Figure 2.











Table 1. Fertilizers and pesticides used in themaize growth analysis
experiments of 1978 and 1979.


Product Rate kg/ha Application Date

1978 Experiment (9 June through 25 August)


Fertilizers:
Dolomite
4-8-16
Nitrogen
Nitrogen

Nematicides:
Carbofuran
DBCP

Herbicides:
Butylate
Atrazine

Insecticide:
Carbaryl


2000.0
600.0
80.0
30.0


1.5 ai
12.0 ai


3.0 ai
2.0 ai


0.5-1.0 1/ha ai


1 month before planting
1 month before planting
30 days after planting
45 days after planting


1 week before planting
1 week before planting


Pre-emergence
Pre-emergence


When necessary


1979 Experiment (21 March through 23 July)


Fertilizers:
4-8-16
Nitrogen
Nitrogen

Herbicides:
Butylate
Atrazine

Nematicides:
Carbofuran

Insecticide:
Carbaryl


600.0
40.0
40.0


3.0 ai
2.0 ai


1.5 ai


days
days
days


before planting
after planting
after planting


10 days before planting
10 days before planting


At planting


0.5-1.0 1/ha ai When necessary


0.5-1.0 1/ha ai


When necessary










different rates because of the different plant populations. The

densities used gave similar LAI values for both cultivars throughout

the critical part of the experimental period.

Sampling began 23 days after planting and continued at intervals

of 10 days until day 73. The last sampling at day 78 had a 5-day

interval. Samples were taken from each plot beginning at one end and

moving successively across the field, leaving one or two border rows

between sampling sites. The plants were removed from the soil with

a shovel to insure extraction of most of the root weight. From the

third harvest until the last sampling date, the roots were left in the

soil on the assumption that minimum additional root growth was taking

place (Hanway, 1963, 1971; Whaley et al., 1950).

Total dry matter production of both hybrid and inbred cultivars

was calculated for harvests 3 to 6 by adding the root weight of

harvest 2 to the other plant components on each respective harvest

date. Six harvests were taken, each consisting of three subsamples

as follows:

i. Ten plants per plot were harvested to measure the total

fresh weight. Ear fresh weight was determined separately.

ii. An average plant was selected from each plot and used to

determine fresh and dry weight of plant components: roots, stalk

(stem and sheaths), leaves, and ears. These plant components were

dried at 60 C for three days. Leaf area was measured with a photo-

electric planimeter (Hayashi Denko Co., Ltd., Automatic Area Meter,

Type AAM-5) and used to calculate LAI. The ratio dry weight to fresh

weight of the whole plants, and of the ears, was used to estimate

total as well as ear dry weights of the 10-plant sample.








24

iii. Six plants from each plot were sampled to estimate soluble

solid concentrations in the internodes. An American Optical 0 to 25%

Brix hand refractometer was used. The Brix readings were measured in

the second, fourth, sixth, and eighth internodes, beginning from the

base. Brix readings were taken until day 83.

In 1979, four cultivars were studied: Coker 77, a closed-pedigree,

high yielding hybrid; Maiz Criollo, a racial accession from Cuba; and

Chapalote and Nal-Tel, two ancient Mexican races. Chapalote and Nal-Tel

are races believed to have arised from primitive sources without

hybridization (Wellhausen et al., 1952). The experiment was hand-planted

on March 21 in a split-plot arrangement with four replications. Ten

main plots, each representing a harvest date, were arranged in such a

way that two border rows of Coker 77, planted continuously in the

middle of the experimental area, separated each replication into two

sets of five main plots. Additionally, two border rows of Coker 77,

in the outside of the main plots, were planted to insure equal competi-

tion among cultivars. The sub-units consisted of two rows per cultivar

without border separation between sub-units in the same main plot.

Each sub-unit contained 24 planting sites. One or two seeds were placed

at each planting site. Twenty plants were used for sampling and two

plants, each at the row's ends, were utilized as guard plants between

sub-units of the other main plots. Missing sites were replanted with

plants of equal age and size, resulting in nearly perfect stands for

all cultivars. Final plant population was 4.3 plants per m2. Harvest

dates and cultivars were randomly assigned to main plots and sub-units,

respectively, by means of a table of random numbers. Overhead irrigation








25

was applied at planting to encourage uniform germination and provide

adequate soil moisture during periods of low rainfall.

Sampling began 34 days after emergence. The second sampling

was made 11 days later. Subsequent sampling continued at 10-day

intervals until 125 days after planting with a total of 10 harvests.

Each sample consisted of three sub-samples as follows:

i. Five plants were selected from each sub-plot and used to

estimate the internode density in Brix readings. The readings were

made on alternate internodes beginning in the second internode at

ground level. Juice from the internode was obtained by squeezing the

basal end with pliers. Several drops of juice were placed onto the

glass surface of an American Optical 0 and 25% Brix hand refracto-

meter for its reading. Readings were performed only for the main

stalk.

These five plants were also used to determine'the percent dry

matter distribution of vegetative and reproductive plant components.

A plant consisted of the main stem plus any tillers. From the ears,

a random sample of 100 kernels was weighed to estimate the average

kernel weight (AKW). From the plot of AKW and time the rate of

kernel dry matter accumulation (KGR) was estimated using linear

regression analysis (Steel and Torrie, 1960). Effective seed filling

period (ESFP) was calculated by the ratio AKW to KGR.

Stalk (stems and sheaths), leaf blades, cobs, and kernels were

ground in a Wiley mill with 1-mm screen. Cobs and kernels were ground

again to pass through a 40 mesh screen. Total available carbohydrates

(TAC) were determined in the ground material by the procedure outlined

in Appendix B. The fractions included in the TAC determination are:








26
the reducing sugars, glucose and fructose; the transport sugars which

are nonreducing, mainly sucrose; and the storage carbohydrates, mainly

sucrose and starch.

ii. Ten plants in each sub-unit were harvested and dried in a

convection oven at 60 C for four days. The measured total dry weight

was added to the total dry weight of the five-plant sample, such that

total dry weight of 15 plants was used to calculate the CGR and ear

growth rate (EGR) of each cultivar. Dry matter distribution of the

15-plant sample, in grams per m2 and for each variety, was estimated

by multiplying its total dry weight by the percent dry matter calculated

from the 5-plant sample.

iii. A representative plant from each sub-unit was sampled for

leaf-area determination. Leaf area was measured with a Lambda Instru-

ment Corp., LI-3100 Area Meter, and utilized to estimate LAI.

Total available carbohydrates, in grams per m2, were calculated

by multiplying each component (stalk, leaves, cobs, and grain) of

the 15-plant sample by the percentage TAC in each part.

Crop growth rate and EGR for each cultivar were calculated by

simple linear regression analysis applied during the linear phase of

the 15-plant sample total and ear dry-matter accumulation curves

(Steel and Torrie, 1960).

Effective ear filling period (EEFP) was estimated by the quotient

of final yield and EGR. Number of kernels per m2 was calculated by

dividing the product of ear yield times shelling percentage by AKW.

In all rates of dry matter accumulation determinations, separate

linear regression equations were computed for each replication. The

slopes of these lines were used as treatment variables for statistical








27

analysis of dry matter accumulation rates. All characteristics

observed or calculated were tested by analysis of variance and ranked

by Duncan's Multiple Range procedure at the 0.05 level of probability.

Statistical analyses were done with the use of SAS 79.3 Statistical

Analysis System by Barr et al. (1979). Analysis of variance and
regression analysis were performed using the ANOVA (analysis of

variance) and the GLM (general linear models) procedures.|















RESULTS AND DISCUSSION

1978 Experiment

Vegetative Yields

Late planting in 1978 together with poor soil drainage resulted

in unfavorable conditions for a proper development of both the hybrid

and inbred cultivars. Prine and Schroder (1965) showed that late

planting decreased the growth cycle of the semi-prolific hybrid Florida

200 by more than 30 days from planting to 50% silking. They found

that yield for maize planted on May 8 was 40% lower than that planted

March 8. In 1978, rainfall during the month of June was adequate for

crop growth. However, rainfall in July and August was 30% and 17%

higher, respectively, than the 70-year rainfall average for the same

months in the Gainesville area (McCloud, 1979). The high rainfall

in July and August, poor soil drainage, and high temperatures caused

stunted plants and shortened the growth cycle of the cultivars (Valle,

1978). A high relative humidity also increased leaf, stalk, and ear

diseases, which severely decreased yields (Valle, 1978; Chapman et

al., 1978).

Vegetative yields were taken throughout the growing season (Fig.

3). Differences in total dry weight between cultivars at day 23 were

not statistically significant. However, from day 43 through 78 total

dry weights for the hybrid were significantly greater than for the

inbred. The stalk dry weight of the hybrid increased to a maximum of




























-I *


33


43


DAYS AFTER PLANTING
Total, stalk, leaves, roots, and ear dry weight accumulation
Pioneer Brand 3369A and the inbred line (I) Iowa B37 studied


for the hybrid (H)
in 1978.


560


(--

LQ

>.


450


330


210-


90


TWH



TWI
SWH
SWI

LWH
LWI
RWH
RWI


Figure 3.


53


63


73 78








30

337.3 gm-2 at day 73 and then declined. Peak stalk dry weight for

the inbred was 279.Ogm-2 at day 63. Leaf dry weight increased for

both cultivars until day 43. Both cultivars maintained a plateau in

the leaf weight component from day 43 to 73. Maximum leaf weight at

day 73 for the hybrid and inbred were 157.8 and 122.0 g m-2, respectively.

Statistical significance (p = 0.05) in the leaf dry weights between

the two cultivars were found from day 43 until the end of the experi-

ment.

Pollination occurred at day 53 for the hybrid and 55 for the

inbred. Maximum dry ear weight for the hybrid was 30.5 g m-2 at day

78. From day 63 to 73 (the period of linear ear growth) the hybrid

accumulated 34% in the stalks of the total dry weight produced in

this period, 52% in the leaves, and 14% in ear growth. There was no

reproductive component in the inbred.

Crop Growth and Ear Growth Rates

The rate of dry matter accumulation (CGR) was calculated for both

cultivars from day 23 to 63 after planting. The CGR values for hybrid

and inbred were 12.2 and 9.1 g m-2 day-', respectively. These CGR values

were significantly different at the 0.05 level of probability when

ranked by Duncan's Multiple Test procedure. Therefore, with the data

obtained and the conditions of this experiment, mean CGR values for

hybrid and inbred compared at nearly equal LAI were significantly

different, indicating differences in net photosynthesis between them.

However, in an earlier study with the same cultivars, Valle (1978) was

unable to detect a statistically significant difference for the CGR's

for the before anthesis period, although significant differences were

found after anthesis.








31

The EGR, the rate at which the ear was filled, was computed for

the hybrid from day 63 to 73 and is expressed by the equation:

Y = -16.6 + 0.64 X.

Brix Readings

Since by day 55 it was apparent that the hybrid and the inbred

line would produce abnormally low yields, it was decided to investigate

the level of soluble solids accumulated in the stalks. The hypothesis

was that photosynthate that could have gone to the ear would accumulate

mainly in the stalk. Data presented in Table 2 show that the mean

Brix readings per plot for the hybrid and the inbred at day 83 after

planting (columns 9 and 10) were higher for the inbred line. The means,

compared using a t-test, were significantly different at the 0.05

level of probability. These results tend to indicate that the photo-

synthate produced by the inbred line, which could have filled the ear,

was accumulated in the stalk to a much greater extent than in the

hybrid corn; this suggested that the sink capacity of the inbred was

lower.


1979 Experiment

Cultivar Characteristics

The cultivars studied during the 1979 growing season were chosen

because of their similar characteristics when grown in Florida (Table

3). The similar height of the cultivars facilitated the field layout

used, since seeds of the ancient races, Chapalote and Nal-Tel, as

well as Maiz Criollo were scarce.

Emergence of all cultivars began approximately one week after

planting. Stands in all plots were nearly perfect; however, skips







Table 2. Mean Brix readings per internode and per plot for the hybrid corn Pioneer Brand 3369A,
and the inbred Iowa B37 studied in the 1978 growing season.


Days Internode
after 2 4 6 8 Per Plot
planting Hybrid Inbred Hybrid Inbred Hybrid Inbred Hybrid Inbred Hybrid Inbred

----------------------------- % ---------------------------------

63 6.5 a* 7.0 a 5.8 a 6.6 a 6.0 a 6.6 a 7.5 a 6.4 a 6.4 a 6.6 a

73 2.1 a 0.7 a 3.5 a 0.9 b 3.2 a 1.5 a 3.7 a 1.3 a 3.1 a 1.1 b

78 1.1 a 0.8 a 1.6 a 1.5 a 1.6 a 1.7 a 0.9 a 2.0 a 1.3 a 1.5 a

83 1.6 a 1.0 a 0.8 b 1.6 a 1.8 a 3.4 a 1.4 a 3.1 a 1.4 b 2.3 a


Numbers with the same letter within internode and dates are not significantly different at the
0.05 level of probability according to a t-test.











Table 3. Characteristics of the cultivars studied in the 1979 growing
season.t

Cultivar Plant Ear Leaves Ears Tillers Anthesist
height height

--- m ------ --- number/plant ----

Chapalote 2.8 1.4 12.7 1.8 2.0 66

Coker 77 2.9 1.4 15.4 1.6 0.1 72

Maiz Criollo 2.8 1.6. 16.0 1.1 0.1 71

Nal-Tel 2.6 1.4 14.2 1.8 0.3 65

t Mean of 30 plants. The measurements were done 125 days after
planting.

t Days from planting.








34

were replanted with seedlings of similar age and size. Anthesis for

Chapalote, Coker 77, Maiz Criollo, and Nal-Tel occurred at day 65, 71,

72, and 66, respectively (Table 3). These dates closely agreed with

unpublished results for 1978 of Dr. E. S. Horner (Professor of Agronomy,

University of Florida). The early maturing Chapalote had an average of

two tillers per plant at the end of the growing season as compared with

few or none for the other cultivars. The late maturing Coker 77 and

Maiz Criollo produced approximately two or three more leaves than the

other two cultivars. The cultivars began to show signs of senescence

(dead lower leaves) in the period between days 95 and 105 in Chapalote

and Nal-Tel, and at day 115 and 125 in Maiz Criollo and Coker 77,

respectively. A high LAI in Coker 77 and Maiz Criollo was maintained

for longer periods than in Chapalote and Nal-Tel. The LAI of Chapalote

was similar to that of Coker 77 during its reproductive phase (Fig. 4).

Nal-Tel had the lowest LAI.

Total Dry Weight

Total dry matter accumulation in all cultivars followed a typical

sigmoidal curve (Fig. 5). Total dry weights were not statistically

different among cultivars for the first 55 days of crop growth. By

day 65, Chapalote, Maiz Criollo, and Coker 77 had produced more dry

weight than Nal-Tel. However, the dry weight of Coker 77 and Maiz

Criollo did not differ statistically from that of Nal-Tel. Total dry

weights for Chapalote and Coker 77 at day 75 were significantly greater

than those ofMaiz Criollo and Nal-Tel due to higher weights of their

stalk and leaf components.

From day 85 until the end of the experiment, the total dry weight

of Coker 77 significantly differed from the other cultivars. This


























34 45 55 65 75 85 95


105 115


DAYS AFTER PLANTING


Leaf area index for the maize cultivars grown in 1979. CH = Chapalote;
MC = Maiz Criollo; NT = Nal-Tel. Arrows indicate anthesis dates.


CO = Coker 77;


-J


CO


Figure 4.








2500


2000h


CO


.MC

CH
NT


1500F


coJ
0"'
#

I-

0
Lu

>.
Q2:


500-



35 45 55 65 75 85 95 105 115 125

DAYS AFTER PLANTING


Total dry matter accumulation for the maize cultivars grown in 1979.
Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel. Arrows
indicate anthesis dates.


CH =


1000


Figure 5.








37

difference was mainly the result of its high ear dry weight. During

this period Nal-Tel had consistently lower total dry weights. Chapalote

and Maiz Criollo were intermediate.

Peak dry weight for Coker 77 was 2476 g m-2, recorded at day 115.

Chapalote, Maiz Criollo,and Nal-Tel had peak dry weights of 1838, 1848,

and 1563 g m-2, respectively, which were measured at day 95 in Chapalote,

day 105 in Nal-Tel, and day 125 in Maiz Criollo. While Chapalote,

Coker 77, and Nal-Tel showed decreased total weight at day 125, Maiz

Criollo showed increases as a result of ear weight increase.

Root Dry Weight

Root dry weight increased in all cultivars until day 75, after

which a plateau was maintained throughout the experimental period.

Average root dry weights during the plateau were 123, 193, 163, and 81

g m-2 for Chapalote, Coker 77, Maiz Criollo, and Nal-Tel, respectively.

Mean root weight of Coker 77 was significantly greater than those of

Chapalote and Nal-Tel.

Stalk Dry Weight

Dry weight in the stalk (Fig. 6) differed significantly among the

four cultivars. Peak stalk weights for Chapalote, Coker 77, Maiz

Criollo, and Nal-Tel were 980, 1003, 873, and 855 g m-2, respectively.

After day 85 all cultivars showed a decline in stalk weight, but the

degree of decrease varied widely among them. The rate of decline in

Chapalote was markedly more pronounced than in the other cultivars.

Stalk dry weight in Nal-Tel declined rapidly after day 85 but less

rapidly than in Chapalote.

Decreases in stalk weight occurred at the initiation of the ear

linear phase which began at day 85 in Coker 77, Maize Criollo, and









1000 -


750[


500


NT


250h


35 45 55 65 75 85 95 105 115 125

DAYS AFTER PLANTING


Stalk dry matter accumulation for the maize cultivars grown in 1979.
Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel. Arrows
indicate anthesis dates.


c~J
E

I-
2:
(-9



QZ
0


CO
MC


Figure 6.


CH =


0,








39

Nal-Tel. However, Chapalote increased stalk weight until day 85, but

its linear ear growth phase began at day 75. Since Chapalote tillered

profusely (up to 12 tillers were counted in several plants before

and after anthesis) the increase in stalk dry weight was likely the

result of tiller growth. Nal-Tel continued increasing stalk weight

from anthesis to the beginning of its linear ear growth. This period

was longer than those of the other cultivars. The continued stalk

growth into linear ear fill reduced the amount of photosynthate

available for ear growth. The decrease in stalk dry weight after day

85 in all cultivars is assumed to be due to translocation of assimilates

to the growing kernels.

Leaf Dry Weight

Leaf dry weight in all cultivars increased rapidly until new leaf

formation was completed at about day 65 (Fig. 7). After day 65 Coker 77

had the highest leaf weight, whereas Nal-Tel had the lowest; for the

latter even the slope of its linear increase leaf weight phase was

distinctly different.. Peak leaf-weight components were 345, 350, 300,

and 217 g m-2 for Chapalote, Coker 77, Maiz Criollo, and Nal-Tel,

respectively. From day 65 the leaf component of Chapalote, Coker 77,

and Maiz Criollo formed plateaus for periods varying from 20 to 50 days

until leaf senescence started; Coker 77 had the longest and Chapalote

the shortest plateau. After reaching its peak weight at day 75, the

leaf dry weight of Nal-Tel showed a steady decrease until the end of

the experiment. The decline in leaf weight was more pronounced in

Chapalote and Maiz Criollo than in Coker 77 or Nal-Tel.












CO


Cu
E


r
(9
LU
$-
w

0


35 45 55 65 75 85 95 105 115 125
35 45 55 65 75 85 95 105 115 125


DAYS AFTER


PLANTING


Leaf dry matter accumulation for the maize cultivars grown in 1979. CH =
Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel. Arrows
indicate anthesis dates.


400


320


2401


CH
NT


160F


80


Figure 7.


ol










Ear Dry Weight

Dry matter in the ear component differed significantly among

cultivars (Fig. 8). From day 85 throughout day 125, Coker 77 had a

significantly greater ear weight than the other cultivars. The ear

weight of Chapalote was the lowest from day 105 until the experiment

ended, while Maiz Criollo and Nal-Tel were between the two extremes.

Maximum ear weights were 1146, 578, 776, and 607 g m-2 for Coker 77,

Chapalote, Maiz Criollo, and Nal-Tel, respectively. Ear dry weight

of Coker 77 at the final harvest was 1023 g m-2.

Dry Matter Distribution

Root, stalk, leaf, and ear computed as a percentage of the cul-

tivars' total dry weight are presented in Table 4. Root percentages

were higher in the vegetative phase. The decrease in root percentage

during the reproductive phase was the result of root dry weight

plateaus from anthesis, or shortly after, until the end of the

experiment, while the total dry weight of the cultivars continued to

* increase. From day 65 to day 125 the percentage of total dry matter

comprising the stalk component was lower in Coker 77 and Maiz Criollo

than in Nal-Tel or Chapalote. The stalk component percentage of

Coker 77 was the lowest. Stalk component percentages of Chapalote

and Nal-Tel were higher than that of Coker 77 and Maiz Criollo due

to continued growth of tillers in Chapalote and stalk weight increase

in Nal-Tel between day 65 and 85.

Coker 77 had higher ear percentages than the other cultivars;

Coker 77 had the highest and Chapalote the lowest. From day 85 to 115

Maiz Criollo had the highest leaf component percentage ranging from

13.3 to 19.5%; it was also the variety with more leaves (Table 3).
















CO


MC
NT
CH


A or I I I


85


95


105


125


DAYS AFTER PLANTING


Ear dry matter accumulation for the maize cultivars grown in 1979.
Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel.


CH =


1200


800F


N




I-
(.9



0


400


75


Figure 8.


D


0











Table 4. Dry matter distribution as percent of the total dry weight of the maize cultivars
grown in 1979.


Days Plant Components
after Roots Stalks NLeaves Ear
planting CHt CO MC NT CH CO MC NT CH CO MC NT CH CO MC NT
--------------------------.-----. ---- % ----------------------..---------------

34 17.0 14.6 13.0 15.1 33.0 33.3 32.0 33.3 50.0 52.1 55.0 51.6

45 11.6 10.0 11.5 9.4 36.2 40.2 36.3 42.0 52.2 49.8 52.2 48.6

55 10.5 11.2 14.3 10.1 45.1 46.5 42.2 49.4 44.4 42.3 43.5 '40.5

65t 11.6 13.7 19.2 12.6 56.9 49.1 49.5 59.0 31.5 37.2 31.3 28.4

75j 10.3 18.0 15.0 10.8 61.1 58.4 59.1 65.3 25.3 20.5 24.0 19.9 3.3 3.1 1.9 4.0

85 8.5 12.6 18.0 6.6 62.6 54.8 54.3 66.6 16.5 19.1 19.5 16.2 12.4 13.5 8.2 10.6

95 6.3 8.3 8.5 5.2 53.3 45.2 49.8 59.0 17.0 16.3 18.4 14.2 23.4 30.2 23.3 21.6

105 6.0 7.6 5.8 5.8 52.6 40.0 49.4 45.4 12.8 13.6 15.3 12.3 28.6 38.8 29.5 36.5

115 10.8 8.5 10.5 5.0 45.0 32.4 40.6 49.7 12.3 12.8 13.3 10.3 31.9 46.3 35.6 35.0

125 5.2 6.0 5.4 4.0 42.2 36.3 41.8 43.5 12.5 12.1 10.8 9.2 40.1 45.6 42.0 43.3


t CH = Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel
SAnthesis date for Chapalote and Nal-Tel.
Anthesis date for Coker 77 and Maiz Criollo.








44
Although Chapalote and Nal-Tel tasseled at day 66 and 65, respec-

tively, the high vegetative component weight up to or well into the

ear linear phase is evidence that these cultivars continued distributing

photosynthate to vegetative growth. Stalk and leaf component

percentages were higher in both cultivars at day 75 and 85 than for

Coker 77 and Maiz Criollo. Coker 77 and Maiz Criollo, in spite of

their later anthesis at day 72 and 71, respectively, invested a lower

fraction of their assimilates into their stalk and leaf components

before and after anthesis, and began linear increase in ear weight

sooner than the ancient races. In other words, Coker 77 and Maiz

Criollo set kernel number and began to fill them with less apportioning

of photosynthate to vegetative growth.

Crop Growth Rate

The early exponential phase of the total dry matter sigmoidal

curve covered the first 45 days of crop growth (Fig. 5). The cultivars

increased dry weight at a linear rate from approximately day 45 to

day 85. Vegetative crop growth rates (CGRv) were calculated from day

45 to day 65 in Chapalote and Nal-Tel, and from 45 to 75 for Coker 77

and Maiz Criollo. These periods correspond to beginning of linear

total weight increase to anthesis.

Crop growth rates during the vegetative phase for Chapalote,

Coker 77, Maiz Criollo, and Nal-Tel are presented in Table 5. These

values are the slopes of the respective linear regression equations.

Coefficients of determination for each equation were greater than

0.986. The difference in CGRv between Nal-Tel and the other three

cultivars is attributed to the lower LAI of Nal-Tel (Fig. 4). It has

been shown that the rate of dry matter production in corn increases










with increasing LAI and percent light interception (Hanway, 1962;

Ragland et al., 1965; Williams et al., 1965a, 1968). Chapalote,

Coker 77, and Maiz Criollo had comparable LAI values during most of

the experimental period.

Since the CGRv values for Chapalote, Coker 77, and Maiz Criollo

were not statistically different, presumably, they also had very

similar canopy photosynthesis and potential to produce high yields.

Crop growth rate measured from the beginning of the linear phase prior

to ear development reflects the rate of net photosynthesis, and hence,

assimilate production rate that could be available for ear growth.

This assumes, however, that the photosynthate produced would be used

exclusively to fill grain, that the rate does not change during grain

filling, and the sink capacity is adequate to utilize it.

From the beginning of linear increase in ear weights the rates

of total dry matter accumulation decreased for all cultivars. Crop

growth rates during linear ear growth (CGRr) for Chapalote, Coker 77,

Maiz Criollo, and Nal-Tel are presented in Table 5. Coefficients of

determination for the linear regression equations explained more than

90% of the variability in the sum of squares for total dry matter.

The CGRr values for Chapalote and Coker 77 were not statistically

different from each other, but were significantly different from the

CGRr of Maiz Criollo and Nal-Tel.

The decrease in total biomass growth rate during the reproductive

period could have been caused by a decrease in photosynthesis with

decrease in solar radiation, light interception, leaf aging, or because

more photosynthate was required in the production of dry matter in the

seed than in the vegetative portion. This last reason, although









Table 5. Crop growth rates, EGR, and distribution index for the maize cultivars grown in 1979.


Cultivars Days CGRvt DIvt Days CGRrt Dirt Days EGR

g m-2 day-1 g m-2 day-1 g m-2 day-1

Chapalote 45-65 37.6 a* 0.51 b 75-95 23.7 a 0.81 c 75-95 19.2 b

Coker 77 45-75 39.5 a 0.77 ab 85-115 24.0 a 1.27 b 85-115 30.4 a

Maiz Criollo 45-75 34.3 a 0.57 b 85-105 11.3 c 1.74 a 85-105 19.7 b

Nal-Tel 45-65 24.7 b 0.88 a 85-105 13.9 bc .1.56 ab 85-105 21.7 b

t CGRv and CGRr are the CGR measured from the beginning of the linear phase to anthesis and during the
linear ear growth rate, respectively.

SDIv and DIr are the ratios of EGR divided by CGRv and CGRr, respectively.
* Values within columns with the same letter are not significantly different at 0.05% level of
probability according to Duncan's multiple range procedure.










47

important, may not have been the cause of the decrease in total biomass

growth rate, since the vegetative portion of a corn plant has a chemical

composition similar to the seed (Morrison, 1947; Sinclair and de Wit,

1975). The energy required to produce a unit of seed weight or a unit

of vegetative component per gram of photosynthate is nearly equal.

These relationships are presented in Table 6.

Production value (Penning de Vries et al., 1974) is defined as

the weight of the end product divided by the weight of the substrate

required for its formation. The production value can be used to

determine the amount of glucose required for synthesis of plant com-

ponents provided that the chemical composition is known. For example,

one gram of maize vegetative matter requires 1.09 grams of glucose while

one gram of seed and one gram of cob require 1.29 and 1.05 grams of

glucose, respectively. Using a shelling percentage of 83, the ear yield

component of the plant requires 1.25 grams of glucose. The ratio of the

glucose required for the yield component to the vegetative component

is 1.15. The 15% increase in photosynthate required to produce the ear

component accounts for only a small part of the decrease in total bio-

mass production in the reproductive phase.

A decrease in solar radiation was an improbable cause for the

decrease in total biomass growth rate during reproductive growth, since

the average daily irradiance during reproductive growth, June and

July, was the highest of the experimental period (McCloud, 1980).

Leaf area index maintained plateaus during most of the vegetative and

reproductive growth (Fig. 4). Thus, light interception can be assumed

the same in both periods.











Table 6. Estimation of glucose required for synthesis for the
vegetative, seed, and cob components of amaize plant.


Component % PVt Glucose required
for synthesis


Vegetativet

Carbohydrate

Protein

Lipids

Grain

Carbohydrate

Protein

Lipids

Cobst

Carbohydrate

Protein

Lipids


80

6

2



84

10

5



86

2

0.4


g g-1



0.853

0.620

0.351



0.853

0.620

0.351



0.853

0.620

0.351


g g-1


0.938

0.097

0.057



0.985

0.161

0.142



1. 008

0.032

0.011


t Production Value (Penning de Vries
+ Chemical composition from Morrison
Chemical composition from Sinclair


et al., 1974)
(1947)
and de Wit (1975).








49

Most of the decrease in crop growth during ear development (CGRr)

may have resulted from a decrease in apparent photosynthesis or CER

(Shibles, 1976) as Vietor et al. (1977), Crosbie et al. (1977), and

Wilhelm and Nelson (1978b) have shown. These studies showed decreases

in photosynthetic rates with leaf aging sufficient to account for the

decrease in growth rate (CGRr) during the reproductive phase measured

in this experiment. There was also rain deficit during the grain

filling period. Irrigation as supplied may not have been as uniform

as expected; dry soil caused wilting and hence reduction in photo-

synthesis.

It should be recalled that the increase in dry weight in Chapalote

during the vegetative, and part of the reproductive growth phases,

was the result of main stalk growth as well as growth of tillers

most of which were barren. Thus, CGRv as a measurement of dry matter

increase for crop growth that could be available for ear growth would

be applicable only to varieties which allocate photosynthate more

completely to ears. The high CGRv of Chapalote was a composite of

potentially available photosynthate for ear growth and photosynthate

invested into tiller growth. The CGRr of Chapalote thus decreased

either because photosynthesis decreased as leaves aged or it may have

decreased because of lack of sink.

The change in growth rate for the period after anthesis and during

linear ear growth may be exemplified better in Maiz Criollo. This is

a cultivar that did not tiller and had a high CGRv not statistically

different from that of Chapalote or Coker 77. However, its total dry

matter accumulation rate changed drastically during the period of

reproductive growth. This reduction in growth rate, as stated above,








50
likely could have resulted from a decreased canopy photosynthesis which

assimilate production had to be diverted into two sinks, i.e., ear

growth and stalk growth, as did Chapalote. However, the decrease in

dry weight for the leaf and stalk components after day 95 and 105,

respectively, suggestsremobilization and translocation of assimilates

for ear growth (Figs. 6 and 7).

These considerations are also applicable to Coker 77 and Nal-Tel;

although these cultivars did not continue increasing stalk weight after

the beginning of linear ear growth. Coker 77 had almost double CGRr

which was maintained for a longer period and also less translocation

of assimilates to the ear than the other cultivars, as is evident by

its lower decrease in stalk and leaf dry weights during the reproductive

period.

Ear Growth Rate

The cultivars began to increase ear dry weight at a linear rate

around day 75 for Chapalote and day 85 for the other cultivars (Fig. 8).

Ear growth rates were computed using linear regression analysis (Steel

and Torrie, 1960). These rates are presented in Table 5. The EGR

of Coker 77 was significantly greater than the EGR of Chapalote,

Nal-Tel, and Maiz Criollo, while the latter three did not differ

significantly from each other.

The EGR is the rate at which the ear is filled. The CGRv,

calculated prior to ear development, is taken as an estimation of the

rate of potentially available photosynthate for ear development. The

quotient of EGR by CGRv is an estimate of the crop's relative increase

in ear weight as compared to weight increases in the vegetative

fraction, i.e., an estimation of distribution of dry matter for ear








51

growth. These distribution indices (Dlv) for Chapalote, Coker 77, Maiz

Criollo, and Nal-Tel were 0.51, 0.77, 0.57, and 0.88, respectively.

This means, for example, that Chapalote produced 51% as much as it

could have produced had all photosynthate been available at the same

rate during seed filling as it was during vegetative growth and 100%

of it were allocated to seeds, assuming that grain growth requires

equal photosynthetic energy of vegetative growth.

The distribution index in the reproductive phase (DIr), calculated

by the ratio of EGR to CGR, is presented in Table 5. Ratios greater

than 1.0 resulted because of the decrease in growth rate during the

reproductive phase, probably caused by decline in canopy photosynthesis

as leaves aged. The DIr ratios may also be interpreted as an indica-

tion of translocation to the ear of assimilates, previously stored in

vegetative parts, when the demands of the ear became greater than the

photosynthate produced. This translocation maintained the ear growth

rate constant for most of the filling period.

Ear Effective Filling Period

The presumed linear period over which the ear increases in dry

weight until it reaches mature weight is referred to as the effective

ear filling period (EEFP). It was calculated by dividing the final

yield by the EGR (Table 7), and hence, is a relative measurement of

the length of the ear filling period.

Several studies have shown that lengthening the life of a crop

increased productivity (Alberda, 1962; Daynard et al., 1971; Van

Dobben, 1962). However, the filling period is the period in which

assimilate is distributed into the yield component of the plant. Thus,

to increase yield, this is the period that should be lengthened.







Table 7. Summary of related yield parameters of the maize cultivars grown in 1979.

Cultivars
Chapalote Coker 77 Maiz Criollo Nal-Tel

Final ear yield (g m-2) 578.0 c* 1023.0 a 776.0 b 607.0 c

EGR (g m-2 day-') 19.2 b 30.4 a 19.7 b 21.7 b

EEFP (days) 30.1 b 33.7 ab 39.4 a 28.0 b

Shelling percentage (%)t 84.2 ab 81.5 b 81.3 b 86.2 a

AKWT (mg kernel-') 183.6 c 297.5 a 266.3 b 211.5 c

KGR (mg kernel-1 day-') 5.0 c 8.5 a 7.5 b 7.1 b

ESFP (days) 36.7 a 35.0 ab 35.5 ab 29.8 b

Kernel number (kernels m-2) 2650.0 a 2802.0 a 2370.0 b 2474.0 b

* Means within each row followed by the same letter do not differ significantly at the 0.05
level of probability according to Duncan's multiple range test.

t Shelling percentage at the final harvest date. It was obtained from the 5-plant sub-sample.

t Average-kernel weight at the final harvest date. It was obtained from 100-kernel weights.








53

Duncan et al. (1978) found that differences in the EFP, among several

peanut varieties and one soybean cultivar, accounted for from 7 to 37%

of the yield difference among cultivars. Gay et al. (1980) concluded

that a significant portion of the yield difference between an old,

low-yielding soybean cultivar and a new high-yielding cultivar was due

to an increase in the filling period.

The EEFPsfor Chapalote, Coker 77, Maiz Criollo, and Nal-Tel are

presented in Table 7. The difference in EEFP between Coker 77 and

Chapalote explained 17% of their yield difference. The EEFP also

explained 30% of the difference in yield between Coker 77 and Nal-Tel.

However, the greater EGR of Coker 77 explained most of the yield

differences.

Kernel Growth Components

The weight of 100 kernels, taken at each harvest during the

reproductive period, allowed the development of a curve of dry matter

accumulation for individual seeds (Fig. 9). The mean rate of dry

matter increase in single kernels (KGR) was calculated during linear

kernel growth using regression analysis. Single kernel growth rate

is genetically controlled, with short-term environmental conditions

having minimal effects on the growth rate (Osafo and Milbourn, 1975;

Poneleit and Egli, 1979; Tollenar, 1976; Duncan et al., 1965), and

as a result of remobilization of assimilates it is relatively independent

of current photosynthate supply (Duncan et al., 1965; Poneleit and Egli,

1979).

Significant differences were found among cultivars in KGR (Table

7). Coker 77 had the highest KGR, and Chapalote the lowest.










300


240


CO
MC


NT
CH


180h


120


60


0


/-I ,,---I I I I


85


95


105


115


125


DAYS AFTER PLANTING


Kernel dry matter accumulation for the maize cultivars grown in 1979.
CH = Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel.


L.
G)

0)
E


Figure 9.








55

Final average kernel weights (AKW) were significantly different

among cultivars at the 0.05 level of probability (Table 7). Effective

seed filling period (ESFP) was also determined for the cultivars (Table

7). The ESFP is defined as the quotient of average kernel weight and

the average rate of dry matter accumulation during the linear phase

of grain growth (Hatfield and Ragland, 1967; Daynard et al., 1971).

The ESFP is the time it would take for kernel development if development

had proceeded at the same rate from pollination to maturity.

The rate of dry weight accumulation in the ear is a direct function

of the number of kernels actively growing. The increase in ear weight

occurs at an increasing rate as the number of actively growing kernels

continues to increase. In corn, the period when actively growing

kernels are added is short, i.e., no more than 10 days (Duncan et al.,

1965). The rapid beginning of ear growth in Chapalote indicated that

the number of actively growing kernels increased rapidly, since a sum

of linear growth rates by the parts, the kernels, must add to increase

in linear growth rate by the whole, the ear. The difference between

EEFP and ESFP in Chapalote seems to be in that the kernels grew rapidly

at early stages, but after the 95-105 day period the rate of kernel

weight increase slowed drastically in such a way that after day 95

total ear dry weight increases were not apparent (Fig. 8). Also,

Chapalote had a relatively high kernel number per m2, which did not

fully compensate for its low yield, probably as a result of lower

kernel weight (Table 7). Slow growing kernels which may result in

large kernel number (Dreyer, 1980) would not give higher yields per

se, since the kernel must also have the capacity to grow large.








56

Coker 77 had a higher KGR, kernel weight, and kernel number than

the other cultivars. This would explain its higher yield.

Total Available Carbohydrates

The percentages of TAC for the different plant components are

presented in Table 8. Percent TAC in the stalk decreased linearly in

all cultivars during the first 55 days of crop growth. Between day 55

and day 85 percent TAC increased to a plateau which ended at day 105

in Nal-Tel, day 115 in Chapalote and Maiz Criollo, and day 125 in Coker

77. Leaf percent TAC also decreased linearly during the first 55 days

of growth. During the rest of the experiment leaf percent TAC

increased to a maximum and then decreased at the end of the experiment.

Percent TAC in the cob component decreased rapidly in Nal-Tel, and

maintained plateaus, from day 85 to 105 in Chapalote and from day 85

to 115 in Coker 77 and Maiz Criollo. The percent TAC in the grain was

higher in Maiz Criollo and Coker 77 than in the ancient races. Coker

77, the best yielding variety, maintained greater percentage TAC in

vegetative components (leaf, stalk, and cob) during reproductive growth

than the other varieties; this may indicate greater photosynthate

availability.

Total available carbohydrates (TAC) designates the sum of starch,

sucrose, and reducing sugars. The TAC are carbohydrates readily available

to the plant as a source of energy. Stalk and leaf TAC weights were

calculated by multiplying the fraction TAC (Table 8) by the stalk and

leaf weights. The cob TAC weight was estimated by multiplying ear

yield by shelling percentage; the product was subtracted from ear yield

and multiplied by the cob TAC fraction; TAC weight for the grain was










Table 8. Percentages of total available carbohydrates (TAC) for stalks, leaves, cobs, and
grain of the maize cultivars studied in 1979.


Days ___________ Plant Components________
after CStalIks t leaves _____ Cobs ______ _______ Grain c N
plrantin CH o C MC NT CH CO MC YNT CH CO MC NT CH CO MC NT
-------------------------------------------------------------------........................... ..................................................................------------------------------------------------------------------
34 13.5 bc 19.0 a 10.8 c 16.0 ab* 7.4 a 10.0 a 7.4 a 9.1 a
45 7.4 b 11.3 ab 7.5 b 13.0 a 4.1 a 4.3 a 4.6 a 4.8 a
55 4.0 bc 6.2 a 3.1 c 5.6 ab 1.0 a 1.1 a 1.0 a 1.0 a
65 12.3 a 12.5 a 7.1 a 12.2 a 2.7 b 4.4 a 3.1 ab 3.0 b
75 9 14.7 c 22.5 4 13.8 d 17.2 b 4.4 a 4.6 a 4.4 a 4.2 a
85 20.7 b 24.8 a 16.1 c 19.0 b 2.8 ab 3.8 a 2.1 b 2.5 ab 13.1 c 20.2 b 29.0 a 16.5 bc 55.0 ab 52.6 c 58.3 ab 65.1 a
95 19.7 ab 23.0 a 16.8 b 19.4 ab 4.0 b 6.3 a 4.1 b 2.4 b 11.6 b 20.4 a 20.1 a 14.7 ab 49.1 c 76.0 a 71.0 a 60.0 b
105 21.0 abc 24.2 a 18.8 bc 16.0 c 3.2 b 9.1 a 5.4 b 3.3 b 13.1 c 28.4 a 20.5 b 8.6 d 49.6 b 69.8 a 59.8 ab 61.7 a
115 16.0 b 25.0 a 15.8 b 9.0 c 2.0 c 7.2 a 4.8 b 0.1 d 6.0 c 20.8 a 17.7 b 4.1 c 64.5 a 72.5 a 74.0 a 62.5 a
125 13.3 b 24.0 a 11.0 bc 8.4 c 1.4 bc 6.7 a 2.6 b 0.7 c 2.0 c 15.4 a 9.6 b 2.2 c 60.8 b 65.3 ab 68.2 a 62.1 b

Values with same letter within row and plant component are not statistically different
according to Duncan's multiple range procedure.
t Stalks = stem, sheaths, and husks.
f CH = Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel.
Anthesis date for Chapalote and Nal-Tel.
SAnthesis date for Coker 77 and Maiz Criollo.







58

obtained by multiplying ear yield by shelling percentage which product

was multiplied by the TAC fraction in the grain.

The TAC weights for stalks of Chapalote, Coker 77, and Nal-Tel

at day 34 did not differ statistically; however, the stalk TAC of

Chapalote was not significantly different from that of Maiz Criollo,

which was the lowest.

From day 34 to the end of the experiment, Coker 77 had signifi-

cantly higher TAC weights in its stalk and leaves than the other

cultivars (Figs. 10 and 11). Peak stalk TAC weight in Coker 77 was

250 g m-2 at day 85. Coker 77 had one of the slowest remobilization

rates of stalk TAC. Leaf TAC increased from 3 g m-2, at day 34, to a

maximum of 30 g m-2 at day 105, decreasing to 18 g m-2 at the final

harvest.

Peaks of stalk and leaf TAC for Maiz Criollo were 164 and 15 g m-2,

respectively, at day 105, decreasing to 85 and 5 g m-2 at day 125.

Stalk TAC of Chapalote and Nal-Tel peaked at 207 and 163 g m-2

at day 105 and 85, respectively. Leaf TAC, in both races, peaked at

day 75 with weights of 15 and 9 g m-2, respectively.

Total available carbohydrates in the cob component of Coker 77 and

Maiz Criollo were significantly higher than in Chapalote and Nal-Tel

from day 85 throughout the end of the experiment (Fig. 12). The cob TAC

of Coker 77 was almost double that of Maiz Criollo. Peak TAC weights

for the cob of Chapalote, Coker 77, Maiz Criollo, and Nal-Tel were 15,

56, 26, and 10 g m-2, respectively. Peak weights were recorded at day

85 for Nal-Tel, day 95 for Chapalote and Maiz Criollo, and day 105 for

Coker 77. From peak dates, TAC in the cob decreased until the end of

the experiment.






240-

%200


160


120


801


40


35 45 55 65 75 85 95 105 115


AFTER PLANTING


Figure 10.


Stalk TAC weight in the maize cultivars grown in 1979. CH = Chapalote;
CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel. Arrows indicate anthesis dates.


CH


- CO









"oNT



125


DAYS








30.0
Cq
22.5

- 15.0
2 15.0
bJ


7.5


35 45 55 65 75 85 95 105 115


AFTER PLANTING


Figure 11.


Leaf TAC weight in the maize cultivars grown in 1979. CH = Chapalote; CO =
Coker 77; MC = Maiz Criollo; NT = Nal-Tel. Arrows indicate anthesis dates.


MrCO




MC


DAYS


125


















..----------MC


85 95 105 115 125


DAYS AFTER PLANTING
Figure 12. Cob TAC weight in the maize cultivars grown in 1979. CH = Chapalote; CO =
Coker 77; MC = Maiz Criollo; NT = Nal-Tel.








62

Total available carbohydrates in the grain increased rapidly in all

cultivars. Grain TAC in Coker 77 was significantly higher than grain

TAC of the other cultivars; Coker 77 was followed by Maiz Criollo and

finally Nal-Tal and Chapalote (Fig. 13).

From the beginning of grain TAC increase, at day 85, until maximum

grain TAC weight was reached, at day 115 in Coker 77 and day 125 in

Chapalote, Maiz Criollo, and Nal-Tel, they gained 649, 243, 409, and

277 grams TAC per m2, respectively. Assuming that the decrease in TAC

in the other components (from their maximum to their minimum weight)

is translocated to the grain, it would explain 9, 26, 13, and 21% of

the final yield of the cultivars in the same order. Coker 77 and

Maiz Criollo had more TAC in leaf and cob than Chapalote and Nal-Tel.

Apparently high cob TAC may be indicative of a good driving mechanism.

The assumption that the summation of the decrease in TAC weight

in the different components is translocated to the ear has to be viewed

with caution, since it is possible that a fair amount of that TAC could

have been respired. However, it is worth noting that the decrease of

TAC in the leaf component of Coker 77 was much lower than in the other

cultivars. Also, its stalk TAC declined quite slowly. This could have

resulted from greater photosynthate production.

The decrease in TAC in the various plant components, assumed to

indicate carbohydrate translocation to the grain during the reproductive

phase, was greater as canopy senescence progressed. As mentioned before,

canopy senescence began at day 95 and 105 in the ancient races, day 115

in Maiz Criollo, and was appreciable only at day 125 in Coker 77.







700

,600


LU
300

200
c 200


I00


CO

MC

NT
CH


85 95 105 115 125


DAYS AFTER PLANTING


Figure 13.


Grain TAC weight in the maize cultivars grown in the 1979 growing season.
CH = Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel.










Brix Readings

Percent Brix readings in corn cultivars, measured either in sap

from the whole stalk or internode by internode, could be used as an

indication of inadequate sink capacity or inadequate photosynthesis.

It is reasonable to assume that photosynthate that is not translocated

to the ear should accumulate, mainly in the stalk and then in leaves

and roots. Also, if photosynthate is decreasing due to stress, the

ear could withdraw assimilates from reserves to fill its kernels. The

main storage of assimilates are the lower internodes, because they have

greater capacity than the top internodes thus containing more of the

sap in which soluble solids are stored, and because photosynthate

produced by leaves in the top internodes is rapidly utilized by the

growing ears. Thus, it would be in the lower internodes that a change

in Brix should reflect accumulation or withdrawal of assimilates more

accurately.

Refractometric readings per plot in the four cultivars studied are

shown in Fig. 14. The influence of high Brix in the top internodes of

Coker 77 could be the cause for the higher Brix readings per plot

during the last part of its growth cycle. However, its lower inter-

nodes (2nd, 4th, and 6th), as well as the lower internodes of the other

three cultivars, increased by more than 100% from the vegetative to the

reproductive phase.

Average percent Brix readings (APBR) in the different internodes

are presented in Figs. 15, 16, 17, and 18. The figures show only the

APBR until the 10th internode. Chapalote's APBR increased rapidly

until day 85, from which the 6th, 8th, and upper internodes maintained

plateaus until day 105. The 2nd and 4th internodes continued increasing






















75 85


95


105 115 125


DAYS


AFTER PLANTING


Figure 14. Average percent Brix readings per plot in the cultivars grown in 1979.
CH = Chapalote; CO = Coker 77; MC = Maiz Criollo; NT = Nal-Tel.


I0

9
8
7


CO

CH
MC
NT


4k-


---


55


65
























95


105 115


125


DAYS AFTER PLANTING


Figure 15.


Average percent Brix readings per internode in Coker 77. Smaller numbers
indicate lower internodes. Arrow marks anthesis date.


8Q


x
cn
M
031-


55


65


75


85























95


105 115


AFTER PLANTING


Figure 16.


Average percent Brix readings per internode in Nal-Tel.
indicate lower internodes. Arrow marks anthesis date.


Smaller numbers


61


4F


55


65


75


85


DAYS


125











I0
8


6F


{i / pI p I I


55


65


75


DAYS


85


95


105


115


125


AFTER PLANTING


Figure 17.


Average percent Brix readings per internode in Chapalote. Smaller numbers
indicate lower internodes. Arrow marks anthesis date.


10-

8-
























75 85 95


105


DAYS AFTER 'PLANTING


Figure 18.


Average percent Brix readings per internode in Maiz Criollo. Smaller numbers
indicate lower internodes. Arrow marks anthesis date.


12F


X
X
QM
OQ


6


10= 12


8
6


55


65


115


125








70

APBR from day 85 throughout day 125 but at a slower rate. In Chapalote

as well as in Nal-Tel, the 6th and 8th internodes were usually the

internodes bearing ears. Nal-Tel APBR in internodes 2, 4, and 6

increased until day 95, but decreased markedly at day 105. Average

percent Brix readings for the 6th, 8th, and 10th internodes were very

similar at day 105 and 115.

Internode APBR patterns for Coker 77 and Maiz Criollo were similar.

APBR increased in a linear manner in Coker 77 until day 85. From day

85 to 95 the APBR of the 2nd, 4th, and 6th internodes decreased

sharply and leveled-off in the 8th. From day 95 until the end of the

experiment all the internodes of Coker 77 increased APBR. The ears of

Coker 77 and usually one ear in Maiz Criollo were located generally

in the 8th and/or 10th internode. The difference between the pattern

of Maiz Criollo and that of Coker 77 was that the rate of APBR increase

in Maiz Criollo until day 105 was slower. Also, the decrease in APBR

at day 95, mainly in the lower internodes, was not as pronounced as

in Coker 77.

The lower values of the APBR of the lower internodes of Coker 77

during part of its linear ear growth phase were not statistically

different from those of Maiz Criollo, Chapalote, or Nal-Tel. However,

they may indicate that Coker 77 had a greater sink capacity, which not

only used photosynthate produced by the canopy, but also utilized

photosynthate stored in those internodes.

Partitioning Coefficient

The partitioning coefficient, or partitioning factor (Duncan et

al., 1978), is defined as the division of recent assimilates between

reproductive growth as opposed to vegetative growth. In a determinant








71

crop, particular attention is given to the partitioning that occurs

just as the final fruit number per plant is determined. This is because,

before the final seed number is determined, there are not enough seeds

to utilize all the assimilates potentially available for kernel growth.

Thus, the plant may continue to grow vegetatively, i.e., produce

tillers, or store the assimilates. After final kernel number has been

determined, actively growing kernels develop priority for photosynthates,

i.e., a polarization of assimilates to the growing kernel established

in the early phases of embryo development (Loomis, 1945); however,

actively growing kernels may utilize more assimilate than is produced

by redistribution or translocation of photosynthates from reserves as

the season advances or weather conditions are temporarily unfavorable.

The partitioning coefficient (PC) for the cultivars was calculated

by the equation PC = (Y.KGR) / (CGRv.AKW) (Duncan et al., 1980). In

this equation Y represents the final yield, KGR is the rate of dry

matter increase in individual kernels corrected for energy content and

energy of formation, CGRv is the rate of total dry matter accumulation

during the vegetative period also corrected for energy content and

energy of formation. The CGRv is a measurement of dry matter produc-

tivity, and in the context of the formula it is equated as an estima-

tion of net photosynthesis during the period in which kernel number

was set; AKW is the average kernel weight equated as a measurement of

the average final capacity of individual kernels to accommodate dry

matter, i.e., average kernel size (Table 7).

ThePCsof Chapalote, Coker 77, Maiz Criollo, and Nal-Tel were

0.45, 0.87, 0.75, and 0.99, respectively. This factor is interpreted

as an estimate of the fraction of photosynthate partitioned to kernel








72

growth, as opposed to vegetative growth or storage at the period in

which potential maximum kernel was set. In fact, PC is.important at

this moment since it would determine the number of kernels that may

develop into final yield, provided that climatic and nutritional

conditions are favorable.

The lower PC of Chapalote is in agreement with earlier considera-

tions about distribution of photosynthate between main stalk growth

and tiller growth. Chapalote was still growing tillers in the middle

of its linear ear growth phase, presumably, partitioned less of its

assimilates to ear development.

The PC is limited by factors other than photosynthate supply,

since increases in TAC in vegetative components occurred before and

after anthesis. In other words, cultivars like Chapalote, Maiz Criollo,

and Nal-Tel, probably had to satisfy the needs of two sinks, the

reproductive and the vegetative sinks. Thus, the PC limiting kernel

number also acted to satisfy vegetative needs. However, once vegeta-

tive needs were satisfied translocation of assimilates from vegetative

components occurred due to leaf senescence and decrease in leaf photo-

synthesis, and because one of the components of sink capacity, final

kernel size, was yet to be satisfied. However, in the period of kernel

number adjustment, basal kernels may begin to grow sooner than kernels

at the tip of the ear, simply, because they are receiving photosynthate

more directly. Thus, an explanation for the lower weight of tip kernels

may be their shorter filling periods. This may be caused by a late

beginning of their linear growth rates and an earlier cessation of

development, probably due to atrophy of vascular bundles as basal

kernels stop growing.










Yield Dynamics

The four cultivars differed significantly in final ear dry weight.

The ancient races had the lowest yield. The yield of Maiz Criollo was

34% and 28% higher than that of Chapalote and Nal-Tel, respectively.

The hybrid, Coker 77, yielded 32% more than Maiz Criollo, and almost

doubled the yield of the ancient races. The total yield increase of

Coker 77 was 59% greater than the average yield of the three cultivars

and 73% greater than the average yield of Chapalote and Nal-Tel.

The capacity for dry matter accumulation of the cultivars as

measured by the CGRv did not differ significantly. The statistically

lower CGRv of Nal-Tel was caused primarily by its lower LAI. Crop

growth rate is a measurement of the integrated metabolic processes

that the plant performs for carbon fixation. Among its more important

components are the photosynthetic and respiratory rates. In this

experiment a direct measurement of these rates was not done. However,

the net result of these processes, the CGRv, was not different among

Chapalote, Coker 77, and Maiz Criollo. This tends to indicate potential

for similar yields.

Corn, a determinant plant, ceases vegetative development at

anthesis or shortly thereafter (Hanway, 1971). As the plant changes

from the vegetative to the reproductive phase, the PC determines

allocation of photosynthate for ear development. Chapalote, with the

smaller PC, continued distributing assimilates to tiller growth.

The tillers were not only barren and, therefore, represented a

diversion of growth potential from the ears, but also shaded main

stalks. Shading, to some extent, could have decreased ear dry matter








74

accumulation by reducing photosynthesis of the main ear-bearing stalk.

This may have caused a poor estimate of the CGRv for the main stalk in

Chapalote. If the PC could have been computed for the main stalk

only, it might have been higher. Nal-Tel continued allocation of photo-

synthate into the stalk component for a longer period than the other

cultivars anthesiss occurred at day 65 and beginning of linear ear

growth at day 85), again diverting growth potential from ears. Nal-Tel

had a high PC, but also had a lower photosynthetic rate (CGRv) which

did not produce enough assimilate for a high yield.

Diversion of growth potential from ears is closely shown in Maiz

Criollo which increased TAC in the stalk component well into its linear

ear growth phase. This may have resulted because of its lower PC. No

explanation for the lower PC of Maiz Criollo is evident in the data

obtained.

The rate of total day matter increase during the reproductive

period (CGRr) varied widely among cultivars, and although the CGRr for

Chapalote and Coker 77 were similar, the CGRr of Coker 77 was maintained

for a longer period. This fact reflects the greater ability of Coker

77 to maintain a higher rate of photosynthesis and higher LAI during

seed filling. The decrease in CGRr in the four cultivars is assumed

to be caused mainly by a decrease in canopy photosynthesis as the leaves

aged. This decrease was more pronounced in the ancient races and Maiz

Criollo than in Coker 77.

Filling periods, estimated as EEFP or ESFD, did not provide

explanation for the higher yield of Coker 77. The explanation for the

higher yield of Coker 77 with respect to Maiz Criollo and Chapalote

(the cultivars with CGRr not significantly different from Coker 77)








75

appeared to be its greater PC that triggered the development of more

kernels and thus, a greater sink which better utilized photosynthate

produced and/or translocated.















SUMMARY AND CONCLUSIONS

During the 1978 growing season, the hybrid maize Pioneer Brand

3369A and the inbred Iowa B37 were planted (in a completely randomized

design with four replications) at populations which provided conditions

of nearly equal LAI to allow comparisons. This study showed that

soluble solids were accumulated to a higher degree in the stalk

component of the inbred line. This suggested that the higher yield of

the hybrid was caused by its higher PC.

In 1979 four cultivars were compared in a split-plot arrangement

with four replications. The cultivars were: two ancient races, Chapalote

and Nal-Tel; a Cuban accession, Maiz Criollo; and a high yielding hybrid

developed in the south-east USA, Coker 77. Growth analysis indicated

that the rate of dry matter production in the vegetative phase (CGRv)

for Chapalote, Coker 77, and Maiz Criollo were not statistically dif-

ferent. The difference of CGRv between Nal-Tel and the other cultivars

was probably the result of its lower LAI.

The similar CGRv of Chapalote, Coker 77, and Maiz Criollo sug-

gested a similar potential for higher yields. However, the CGRv of

Chapalote included a heavy growth of tillers and thus only the CGRv

of the main stalk could be considered potential assimilate for ear

growth.

The partitioning coefficient (PC), used as an estimate of the

distribution of assimilates for ear growth as opposed to vegetative

growth or storage at the period of kernel number set, was higher in

76








77

Coker 77 than in Chapalote or Maiz Criollo. Nal-Tel had the highest

PC but also the lower photosynthetic rate (lowest CGRv) which was not

enough to set a greater sink capacity, thus its low yield.

Coker 77 maintained a higher LAI and total dry matter accumulation

rate during reproductive growth (CGRr) than the other cultivars. Also,

the hybrid had a greater rate of accumulation of ear weight (EGR) than

Chapalote or Maiz Criollo.

It follows that Coker 77 had a better combination of sink capacity

in terms of kernel number and size than Chapalote or Maiz Criollo.

Chapalote had a relatively high kernel number that did not fully

compensate for its lower yield, probably because of its lower kernel

size. Total available carbohydrates (TAC) measured in the stalk, leaf,

cob, and grain were higher in the hybrid than in the other cultivars.

High percentage TAC in cobs of Coker 77 suggested a better driving

mechanism. Translocated TAC from vegetative components contributed 9,

26, 13, and 21% to the final ear yield in Coker 77, Chapalote, Maiz

Criollo, and Nal-Tel, respectively.

The results of this experiment support the conclusion that under

conditionsof equal LAI, high PC, which determines greater sink capacity,

and a high production of photosynthate during reproductive growth are

the physiological parameters that cause high yield.















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APPENDIX A















AMYLOGLUCOSIDASE-INVERTASE PROCEDURE FOR HYDROLYZING
TOTAL AVAILABLE CARBOHYDRATES (STARCH, SUCROSE) TO REDUCING SUGARS


1. Weigh 0.1 g of ground, throughly mixed plant material into a 5 ml

Erlenmeyer flask.

2. Add 5 ml of distilled water, cap the flasks with marbles and boil

for 3 to 5 minutes.

3. To the cooled flask add 5 ml of 0.2 N acetate buffer, and 1 ml of

enzyme mix. Place flasks in a 44 C water-bath for 10 to 12 hours.

4. Remove from bath and cool it.

5. Take aliquots (between 0.2 to 0.5 ml) and put into 15 ml test tubes.

6. Add deionized water (between 5.5 and 5.8 ml) and shake.

7. Take aliquots (between 0.2 and 0.5 ml) and put into 15 ml test

tubes.

8. Add 1.0 ml of alkaline reagent in each flask, boil for 20 minutes

and then cool.

9. Add 1.0 ml of arsenomolybdate reagent in each flask, fill to 10 ml

with deionized water and mix well.

10. Read absorbance at 540 nm with a blank solution as zero. Use set

of glucose standards prepared with same procedure for calibrating

regression line.

Acetate Buffer: Mix 3 parts of 0.2 N acetic acid and 2 parts of

0.2 N sodium acetate. Titrate final buffer solution to pH 4.8 by addition

of either solution. Add a few crystals of thymol to prevent growth of

microorganisms.








88

Enzyme mix for 50 ml fresh daily: Add 1.25 g of amyloglucosidase,

1.25 ml invertase, and 3.75 ml of 0.2 N acetate buffer to 45 ml of de-

ionized water.

Alkaline reagent: dissolve 25 g of anhydrous sodium carbonate,

25 g of potassium sodium tartrate, 20 g of sodium bicarbonate, and

200 g of anhydrous sodium sulfate in 700 ml of deionized water and

then dilute to one liter. Dissolve 6 g of cupric sulfate in 40 ml of

deionized water followed by one drop of concentrated sulfuric acid.

Combine the two solutions.

Arsenomolybdate reagent: dissolve 25.0 g of ammonium molybdate

tetrahydrate in 450 ml of deionized water, then add 21 ml of concen-

trated sulfuric acid. In separate solution dissolve 3.0 g of disodium

arsenate in 25 ml deionized water. Combine the two solutions.

Calculate TAC in percentage by:

%TAC (OD slope + intercept) (Dilution factors) 100
wt. (mg)


















APPENDIX B

TABLES: SOIL FERTILITY ANALYSIS, DRY WEIGHT OF PLANT
COMPONENTS FOR THE 1978 AND 1979 GROWING SEASONS, TOTAL
AVAILABLE CARBOHYDRATES, AND PERCENT BRIX READINGS




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