Retrospective eses and Dissertations Iowa State University Capstones, eses and Dissertations 1979 Physiological characters in maize (Zea mays L.) and their relationship to stalk rot Hashem Moustafa Soliman Iowa State University Follow this and additional works at: hps://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons , Agriculture Commons , Agronomy and Crop Sciences Commons , Plant Biology Commons , and the Plant Pathology Commons is Dissertation is brought to you for free and open access by the Iowa State University Capstones, eses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective eses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Recommended Citation Soliman, Hashem Moustafa, "Physiological characters in maize (Zea mays L.) and their relationship to stalk rot" (1979). Retrospective eses and Dissertations. 7249. hps://lib.dr.iastate.edu/rtd/7249
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Retrospective Theses and Dissertations Iowa State University Capstones, Theses andDissertations
1979
Physiological characters in maize (Zea mays L.)and their relationship to stalk rotHashem Moustafa SolimanIowa State University
Follow this and additional works at: https://lib.dr.iastate.edu/rtd
Part of the Agricultural Science Commons, Agriculture Commons, Agronomy and CropSciences Commons, Plant Biology Commons, and the Plant Pathology Commons
This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State UniversityDigital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State UniversityDigital Repository. For more information, please contact [email protected].
Recommended CitationSoliman, Hashem Moustafa, "Physiological characters in maize (Zea mays L.) and their relationship to stalk rot" (1979). RetrospectiveTheses and Dissertations. 7249.https://lib.dr.iastate.edu/rtd/7249
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Universify Microfilms
Infe-national 300 N. ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WCl R 4EJ, ENGLAND
8000174
SOLIMAN, HA5HEK HOUSTAFA PHYSIOLOGICAL CHARACTERS IN MAIZE (ZEA MAYS L . l AND THEIR KELATIDNSHIP TO STALK ROT.
IOWA STATE UNIVERSITY, PH.D. , 1979
UniversiW Micrailms
International 300 N. ZEEB ROAD. ANN ARBOR. Ml 48106
Physiological characters in maize (Zea mays L.)
and their relationship to stalk rot
by
Hashem Moustafa Soliman
A Dissertation Submitted to the
Graduate Faculty in Partial Fulfillment of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Department t Agronomy Major: Crop Production
and Physiology
Approved;
In Ch rge of M r Work
the Major Department
For the Grad ée College
Iowa State University Ames, Iowa
1979
Signature was redacted for privacy.
Signature was redacted for privacy.
Signature was redacted for privacy.
ii
TABLE OF CONTENTS
Page
Dedication iii
INTRODUCTION 1
REVIEW OF LITERATURE 3
Photosynthetic Rate 3
MATERIALS AND METHODS 19
Experiment 1 19
Experiment 2 20
Experiment 3 21
RESULTS AND DISCUSSION 28
Experiment 1 28
Experiment 2 38
Experiment 3 43
GENERAL DISCUSSION 67
Experiment 1 67
Experiment 2 71
Experiment 3 72
SUMMARY AND CONCLUSIONS 75
BIBLIOGRAPHY 79
ACKNOWLEDGMENT S 89
iii
DEDICATION
To My Father and My Mother
My Sister and All My Brothers
1
INTRODUCTION
Maximum yield is the major concern of plant scientists.
It concerns botanists, geneticists, biochemists, plant
In 1976, the samples were stored in a refrigerator
freezer to the end of the growing season. This determination
in 1977 took place in the same day the plants were sampled
from the field.
Nonstructural carbohydrate (NSC) determination
The plant samples were dried at 100°C for 2 hours and at
70°C for 48 hours. The dry samples were ground through a
40-mesh screen and thoroughly mixed in a paper bag. Just
27
before NSC analysis the plant material was dried at 70°C for
3 hours, translocated to a desiccator and allowed to cool to
room temperature.
Extractions were made by placing 200 mg of sample in a
test tube with 25 ml of 0,8 N sulfuric acid and refluxing for
one hour in a boiling yjater bath. The solution was filtered
and washed with 25 ml of 0.8 N sulfuric acid and hydrolyzed
for one hour more. The solution was filtered again and washed
with water. The filtrate was neutralized and increased to
100 ml with water (Smith et al., 1964). The reducing power of
all extracts was determined by dinitrosalicylic acid (Miller,
1959).
28
RESULTS AND DISCUSSION
Experiment 1
Carbon dioxide exchange rate (CER)
The CER varied among the 16 inbred lines (Table 2) for
both years in the field and for the greenhouse experiments.
The range was from 26.6 to 59.0 mg CO2 cm hr in 1976, and
13.3 to 41.8 mg CO dm hr in 1977. Inbred lines B67, B14,
B57, and B76 consistently showed high CER in all environments
and WF9, C103, and 187-2 consistently showed low CER in all
environments. These ranges were comparable to those reported
for maize inbreds grown in temperate climates (Heichel and
Musgrave, 1969), and those reported by Crosbie et al. (1977).
In 1977, the CER increased with increases in photosyn-
thetic photon flux density (PPFD) for almost all inbreds
(Table 2). The CER response to different PPFD levels varied
among inbred lines- For example, when exposed to 200 and
2000 [iE sec cm B57 rate increased from 16.8 to 41.8 mg
CO2 dm hr (262% increase), while C103 increased from 11.5
to 16.2 mg CO2 dm hr (68% increase). The variation between
the inbred lines was small in low PPFD levels, but it increased
with increasing PPFD levels (Table 2). Similar data were re
ported by Hesketh and Moss, 1963).
Table 2. The CO2 exchange rates (CER, mg CO2 dm hr ) at different photosyn-thetic photon flux density (PPFD), stalk rot ratings fDiplodia (D) and Fusarium (F)], and leaf area per plant for the 16 inbred lines grown in the field in 1976 and 1977
1976 1977
Stalk CER rot 2000 fiE la Stalk rot CER
ratings sec~l (dm^/ ratings 200 fiE 500 p.E 2000 jiE dm2/ D cm~2 plant) D F sec~lcm~2 plant)
Table 5. Mean squares from analysis of variance of stalk rot ratings»CO2 exchange rate (CER), sucrose level, nonstructural carbohydrate (NSC) level, and leaf area per plant (LA) for experiment 1 in 1976
Source of
variation
Degree of
freedom
Stalk rot rating
( Dicilodia) Sucrose level Source
of variation
Degree of
freedom
Stalk rot rating
( Dicilodia) CER S-20 S-45 S-45I
Replication 2 0,82 246.7** 0.73 3.64 6.69
Ihbreds 15 0.87 407.2** 2.28 8.2** 2.87
Error 30 0.59 40.6 1.70 2.82 4.73
Source of
variation
Degree of
freedom
NSC level Source of
variation
Degree of
freedom S-20 S-45 S-45I LA
Replication 2 0.19 22.3 13.7 5281 .7
Inbreds 15 32.2* 32.2* 33.7 1224832 .1**
Error 30 13.9 16.05 25.7 141905 .5
*,**SignifiLcant at 0,05 level and 0.01 level of probability, respectively.
Table 6. Mean squares from analysis of variance of stalk rot ratings, COg exchange rate (CER), sucrose level, nonstructural carbohydrate (NSC) level, and leaf area per plant (LA), experiment 1 in 1977
CER
Source of variation
Stalk rot ratings 200 E 500 E 2000 E Sucrose level Source of variation DF Diplodia Fusarium
-1 -2 S-20 S-45 S-451
Source of variation DF Diplodia Fusarium S-20 S-45 S-451
In 1976, the inbred lines showed a negative correlation
between stalk rot rating and sucrose levels only at S-45I
(Table 7). In 1977, the correlations for Diplodia showed a
significant negative correlation only at S-45. Fusarium
showed a significant negative correlation at S-20 and S-45,
but not at S-45I (Table 7),
These results were comparable to those reported for 12
inbred lines by Craig and Hooker (1961). Many other workers
have reported that resistance to stalk rot is associated with
a high carbohydrate level in the stalks (Koehler, 1960;
Holbert et al., 1935; Zuber et al., 1957; Wysong and Hooker,
1966). A similar relation was found in wheat and Thvphula
idahoensis (Kiyomoto and Bruehl, 1977), finger millet
(Eleusine coracona (L)) and Helminthosporium nodulosum
(Vidhyasekaran, 1974a) 0 However, some investigators have
reported little to no relationship between sugar concentration
Table 7. Correlation coefficients between stalk rot ratings or CO2 exchange rate (CER, mg CO2 dm~ hr~l) and sucrose level, nonstructural carbohydrate (NSC) level, or leaf area per plant (LA) for the 16 inbred lines in 1976 and 1977
1976 1977
CER CER 2000_|I E stalk rot ratina 200 n. E 500 F I . E 2000 U . E
rating sec _i _o Diplodia cm~"2 Diplodia Fusarium sec cm
F-0 = control; F-1/2T = 5C% of the leaf blades above the ear were removed; F-1/2B = 50% of the leaf blades below the ear were removed; F-T = 100% of the leaf blades above the ear were removed; F-B = 100% of the leaf blades below the ear were removed.
40
Table 9. Stalk rot ratings as affected by inbred lines and defoliation treatments in 1976 and 1977
Defoliation treatments
1976 1977 Defoliation treatments B70 B14 B70 B14
FO 3.73 3.08 2.45 1.95
F-1/2T 3.53 2.87 2.78 2.52
F-1/2B 3.74 3.06 3.00 2.39
F-T 3.36 3.20 2.77 2.22
F-B 3.53 2.38 2.89 2.50
X 3.58 2.92 2.91 2.31
C.V. 23.5 14.6
1935; Koehler, 1953; Pappelis, 1963a,b). The cause for
these conflicting results is not Known; perhaps it is due to
different environments and/or varieties.
There was no interaction in stalk rot rating between
inbred lines and defoliation treatments either year (Tables
10, 11). These results indicate that both the inbred lines
and the defoliation treatments acted independently on stalk
rot. However, B70 had higher ratings than B14 both years
under all defoliation treatments (Table 9).
Table 10. Mean squares from analysis of variance for stalk rot ratings, sucrose level, and nonstructural carbohydrate (NSC) level for experiment 2 in 1976
Stalk Sucrose level NSC level source or variation DF
Table 14. Correlation coefficients between defoliation treatments and stalk rot ratings, sucrose levels, or nonstructural carbohydrates (NSC) levels in 1976 and 1977
Defoliation treatments
Sample time 1976 1977
Stalk rot ratings S-45 -.17 .1
Sucrose level (%) S-20 -.07 - .41*
S-45 .08 —.47**
S-45I .09 -.29
NSC level {%) S-20
i> I—f
1 -.40*
S-45 -.09 -.49**
S-45I -.19 -.51**
*,**Significant at 0.05 and O.Ol levels of probability, respectively.
plant density increased the stalk rot ratings with moderately
resistant and susceptible cultivars, but failed with resis
tant cultivars.
The interaction between plant density and inbred lines
was not significant either year (Tables 19, 20). These re
sults indicate that both maize density and inbred lines acted
independently on stalk rot ratings.
Table 15, Stalk rot ratings, sucrose levels, nonstructural carbohydrate (NSC) levels, leaf area per plant, and leaf area index as affected by plant densities in 1976 and 1977
Table 15, Stalk rot ratings as affected by inbred lines and ear removal in 1976 and 1977
treatments B70 B14 B70 B14
E 4.09 3.61 2.74 2.83
EO 3.51 3.05 2.41 2.56
X 3.80 3.33 2.57 2.70
C.V. 11.9 12.4
Table 17. Stalk rot ratings and leaf area per plant as affected by plant densities in 1976 and 1977
denïïty Stalk rot ratings., LA (dmVplant)
treatments B70 B14 B70 B14
P-1
P-1
P-2
P-3
X
C.V.
3.79
4.06
3.56
3.80
1976
3.24
3.00
3.75
3.33
11.9
29.7
31.5
30.4
30.5
35.1
36.7
33.1
35.0
5.02
1977
P-1 2.67 2.61 55.5 74.3
P-2 2.72 2.78 61.7 66.3
P-3 2.34 2.70 59.2 72.1
X 2.57 2.70 58.8 70.9
C.V. 12.4 20.0
50
Table 18, Stalk rot ratings as affected by plant densities, inbred lines, and ear removal in 1976 and 1977
Plant density treatments
B70 B14 Plant density treatments E EC E e o
1976
P-1 4.05 3.53 3.57 2.91
F-2 4.44 3.67 3 . 3 0 2.67
P-3 3.80 3.34 3.93 3.57
X 4.10 3.51 3.60 3.05
C.V.
1977
11.9
P-1 2.78 2.55 2.66 2 . 5 6
P-2 3.00 2 . 4 4 2.94 2 . 6 1
P-3 2.44 2.24 2.89 2.50
X 2.74 2.41 2.83 2 . 5 6
C.V. 12.4
Nonstructural carbohydrate (NSC) levels and sucrose levels as affected by plant density
Increasing plant density decreased NSC level both years
at S-20, but at S-45 and S-45I plant density decreased NSC
level only in 1977 (Tables 15, 19, 20). The decrease in NSC
level from lowest to highest plant density was 23.5% and 5%
at S-20 in 1976 and 1977, respectively, and 21.3% at S-45,
5 1
Table 19. Mean squares from analysis of variance for stalk rot ratings, sucrose, and nonstructural carbohydrate (NSC) level, and leaf area per plant (LA) for experiment 3 in 1976
Source of variation DF
Stalk rot
ratings
Sucrose level
8-20 S-45
Replicates 2 0.25 0.23 0.87
Plant density (p) 2 0.07 0.01 2.06
Error (a) 4 0.78 1.32 0.88
Inbreds ( I) 1 2.00 100.03** 0.31
P X I 2 1.19 2.12 4.34
Error (b) 6 0.33 0.50 1.81
Ear (E) 1 2.91** 27.65** 86.21**
P X E 2 0.081 0.32 1.36
I X E 1 0.0003 0.42 0.69
P X I X E 2 0.013 0.71 7.74*
Error (c) 12 0.18 0.45 1.95
*,**Significant at 0.05 and O.Ol levels of probability, responsibility.
52
NSC level
S-45I S-30 S-45 S-45I LA
3.43 2.40 17.04 14.39 3236.6
2.60 135.78* 16.33 24.05 171315.43
1.57 7.77 20.45 24.15 58328.1
0.51 42.79 221.3** 340.71** 1774947.8**
4.90** 50.57 7.58 2.82 64791.5
0.39 16.54 13.91 9.07 37035.9
26.7** 233.8** 328.5** 71.54* 235828.4
3.23 12.04 9.90 0.18 82050.5
1.22 4.88 13.14* 0.92 173212.7
0.37 4.46 0.19 19.66 119922.9
2.04 8.27 7.53 10.26 26974.8
Table 20. Mean squares from analysis of variance for stalk rot ratings, sucrose, and nonstructural carbohydrate (NSC) levels, and leaf area per plant (LA) for experiment 3 in 1977
Table 30. Correlation coefficients between plant density or ear removal and stalk rot rating, sucrose level, nonstructural carbohydrate (NSC) level, or leaf area per plant (LA) in 1976 and 1977
1976 1977
Sample Plant Ear Plant Ear time density removal density removal
Stalk rot ratings S-45 .08 .44** .13 .40*
Sucrose (%) S-20 -.01 .43** .12 .28
S-45 -.05 .74** .09 .21
S-45I -.20 .54** -.08 .18
NSC (%) S-20 -.54** .50** -.16 .30
S-45 .19 .60** -.39* .27
S-45I .01 .30 -. 20 .07
LA (dm/plant) - -.08 - .03 -
67
GENERAL DISCUSSION
Experiment 1
Inbred lines varied in CER both years. This gave me the
opportunity to find a correlation between CER and stalk rot
susceptibility. Reducing the PPFD levels of measurement in
1977 reduced CER in all inbreds. The ranking of inbreds as
to CER at different PPFD levels did not change significantly.
This means that the relationship between stalk rot suscepti
bility and CER would not vary when CER was measured at dif
ferent light levels.
The CER range was comparable to those reported by
Crosbie (1975) and Heichel and Musgrave (1959). Usually C4
crop species (such as maize) have been considered capable of
higher CER than C3 species. The 16 inbred lines, however,
did not exhibit a higher CER than those reported for alfalfa
(Pearce et al., 1959), oats (Criswell and Shibles, 1971),
or soybeans (Dornhoff and Shibles, 1970).
The inbred lines varied in stalk rot rating in 1977,
but did not in 1976. These differences may be due to the hail
damage and drought conditions during grain filling which
occurred in 1976, Pappelis (1970) reported that injuries to
plants change the rate of cell death which is accompanied by
a similar change in stalk rot response.
Using the average of the two years, the inbred lines can
be ranked according to their reaction to Diplodia stalk rot»
reduction of leaf area will reduce both grain yield and stalk
carbohydrates.
72
Defoliation did not significantly increase stalk rot
ratings. No differences in stalk rot ratings were found by
removing either top or lower leaves. The hail damage in 1976
made it difficult to conduct the defoliation treatments which
probably affected the 1976 results and caused higher stalk rot
ratings than for 1977, The results indicate that stalk rot
ratings of both B14 and B70 reacted the same way to defolia
tion treatments. Gates and Mortimore (1972) found an increase
in stalk rot ratings by removing leaves. He reported that
upper leaves of resistant plants contributed more to stalk rot
reduction than those of susceptible plants and attributed this
to greater photosynthetic products. There was no indication
of this in my experiments.
Defoliation reduced NSC and sucrose levels in the stalk
but did not increase the stalk rot ratings. This indicates
that there was no relation between NSC and sucrose levels
and stalk rot ratings. However, the control plants (no
defoliation) had the lowest stalk rot ratings in 1977.
Experiment 3
Plant density reduced NSC at S-20 both years and at S-45
and S-45I in 1977, but never reduced sucrose levels in either
year. This reduction in NSC might be due to the competition
for water, minerals, and light among plants in the plant i
canopy. Increasing plant density reduces the amount of light
intercepted by the leaves which reduces total plant CER.
73
Singh and Nair (1975a) found that increasing plant density
from 60,000 to 90,000 plants/ha resulted in a decline of dry
matter accumulation in different plant parts, though the
decline was not statistically significant.
Increasing plant density did not change stalk rot rat
ings either year. This experiment was conducted both years
under nonirrigated conditions. The results showed that B70
is more resistant than B14 if the drought occurred before the
grain filling period (as it was in 1977), and more susceptible
than B14 if the drought occurred after grain filling period
(in 1976), This may be due to the fact that B70 plants form
larger ears than B14 under normal conditions and draw more
carbohydrate from the stalk to the ear and thus increase
stalk cell death and susceptibility to stalk rot. Gupto et
al. (1970) found that increasing plant density failed to in
crease stalk rot ratings. However, Timiti (1977) and Doupink
and Wysong (1970) found that stalk rot increased with in
creasing plant density. The differences between different
studies might be due to the differences between the inbred
lines used and the environmental conditions.
Removal of ears from inbred plants increased NSC and su
crose levels at all sample periods both years with few excep
tions. Removal of the ear will cause photosynthetic products
to accumulate in leaves and stems. McAllan and Phipps (1977)
reported that removal of ears from maize plants after flowering
was shown to cause an increase in leaf-soluble sugars and
74
starch compared to plants with ears. Allison and Weinmann
(1970) and Bunting (1975) reported that soluble carbohydrate
content of sterile maize was appreciably higher than that of
fertile maize. Loomis (1934) found that the developing ear
has first priority of the use of sugars produced by the
plant. If the supply of sugars is not sufficient for both
grain development and vegetative cell maintenance, grain
formation is accompanied by senescence of the cells of roots
and stalk,
Removal of ears from inbred plants significantly reduced
the stalk rot ratings both years. This might be due to that
the defruited plants remained green and in good physiological
condition until harvest. Also, it may be because the vigorous
root growth continued throughout the growing season in de-
fruited plants while root growth is usually sharply curtailed
after silking (Loomis, 1934). Similar results have been re
ported by Pappelis (1957) and Koehler (1950). Pappelis et al.
(1973) and Pappelis and Boone (1966) reported that both removal of
ears and poor seed set delays nodal cell death and whole plant
death which was well-correlated to plant resistance.
Plant density did not change sucrose levels and slightly
reduced NSC levels but did not increase stalk rot ratings.
Ear removal increased sucrose and NSC and decreased stalk
rot ratings. However, the correlation coefficient for carbohy
drate levels and stalk rot rating was not significant either
year. Low and negative correlation was found both years.
75
SUMMARY AND CONCLUSIONS
The relationship between carbohydrate and stalk rot has
been reported by many investigators# although the correlations
have been low and inconsistent. The results from this study
are in agreement with those results. The carbohydrates are
the main energy source for plants to maintain the physiological
processes which will affect the rates of cell death and the
severity of stalk rot. Hence, the spread of disease or-
ganisms in stalks depend on senescence in stalk tissues.
Data from this study demonstrated that s
1. The 16 inbred lines varied in stalk rot ratings
(Diplodia and Fusarium) in 1977, but not in 1976.
2. The differences in results between the two years
indicated that the environmental conditions could
alter the severity of stalk rot. Stalk rot ratings
in inbred lines were different under irrigated and
nonirrigated conditions. The hail damage in
1976 increased the stalk rot ratings and
decreased the differences between inbred lines.
3. The CER of inbred lines were different and were
ranked the same in all environments.
4. A low but significant negative correlation between
CER and stalk rot was found in 1977 for Diplodia.
Nonsignificant but negative correlations were found
for other Diplodia measurements and for Fusarium.
76
The 16 inbred lines varied in NSC levels and sucrose
levels both years, except for the inoculated plants
(S-45I) in 1976.
Sucrose and NSC levels declined with maturity for
the 16 inbred lines, with few exceptions and this
decline was higher for sucrose levels than for NSC
levels.
Low, significant, negative correlations were found
between NSC level and Diplodia and Fusarium, stalk rot
ratings at all sample periods in 1977, but only at
S-45I in 1976.
Low and inconsistent, negative correlations were
found between sucrose level and stalk rot ratings.
The drop in sucrose and NSC levels at S-45 was higher
in susceptible plants than in resistant plants.
Stalk rot organisms caused a drop in NSC and sucrose
levels in stalk. This drop was higher in resistant
plants than in susceptible plants.
The relationships between CER and NSC and sucrose
levels were different in 1976 than in 1977. The
correlation was negative in 1976 and positive in
1977. This may be due to the nonirrigated and irri
gated conditions in 1976 and 1977, respectively.
Leaf area per plant for the 16 inbred lines was
quite different for both years. It did not affect
stalk rot ratings either year and it had a negative
77
correlation with CER.
13. Removing leaf blades above or below the ear did not
affect the stalk rot ratings. However, the control
treatment had the lowest stalk rot ratings in 1977.
Both B14 and B70 reacted in the same way to defolia
tion levels.
14. Removing leaf blades above the ear reduced NSC and
sucrose levels in the stems more than removing leaf
blades below the ear.
15. No correlation was found between NSC or sucrose
levels and stalk rot ratings in this experiment.
16. Plant density did not affect stalk rot ratings or
sucrose levels either year.
17. Plant density did affect NSC both years except at
S-45 and S-45I in 1976.
18. Removing ears decreased stalk rot ratings and in
creased sucrose and NSC levels both years, except
for plants inoculated with stalk rot (S-45I) in
1977.
19. A nonsignificant, negative, correlation was found
between stalk rot rating and NSC and sucrose levels
both years in experiment 3,
Under the theory that carbohydrate levels in maize stalk
can affect the spread of stalk rot organisms in stalk tissues,
this study was conducted to relate CER to carbohydrate levels
78
and to stalk rot. Although I have been unable to relate
CER and carbohydrate levels in stalks we were able to corre
late CER to stalk rot in maize inbreds and to correlate car
bohydrate levels to stalk rot ratings. However, more re
search is required to document these results.
79
BIBLIOGRAPHY
Allison, J.C.S. 1969. Effect of plant population on the production and distribution of dry matter in maize. Ann. Appl. Biol. 63: 135-144.
Allison, J.C.S. 1971. Analysis of growth and yield of inbred and crossbred maize. Ann. Appl. Biol. 68; 81.
Allison, J.C.S., and D. J. Watson. 1966. The production and distribution of dry matter in maize after flowering. Ann. Bot. 30; 365-381.
Allison, J.C.S., and H. Weinmann. 1970. Effect of absence of developing grain on carbohydrate content and senescence of maize leaves. Plant Physiol. 46; 435-436.
Allison, J.C.S., J. H. Wilson, and J. H. Williams. 1975a. Effect of partial defoliation during the vegetative phase on subsequent growth and grain of maize. Ann. Appl. Biol. 81; 367-375.
Allison, J.C.S., J. H. Wilson, and J. H. Williams. 1975b. Effect of defoliation after flowering on changes in stem and grain mass of closely and widely spaced maize. Rhod. J. Agric. Res. 13; 145-147.
Bargida, L. P., J. DeLortlaval, and G. Viroben. 1975. The occurrence of stalk rot Fusarium of maize in dependence on row distance and susceptibility of hybrid cultivars. (German, Engl, summary). Zacker Pflanzenbau 14; 160-164.
Black, L. L,, D. T. Gordon, and P. H. Williams. 1968. Carbon dioxide exchange by radish tissue infected with Albugo Candida measured with infrared CO- analyzer. Phytopathology 58; 173-178.
Bonaparte, E.E.N.A., and R. I. Brown. 1976. Effect of plant density and planting date on leaf number and some developmental events in corn. Can. J. Plant Sci, 56; 691-698.
Bonner, J., and J. E. Varner. 1976. Plant biochemistry. Academic Press, New York.
Broadhead, D. M. 1973. Effect of deheading on stalk yield and juice quality of Rio sweet sorghum. Crop Sci. 13; 395-396.
80
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ACKNOWLEDGMENTS
My heartfelt thanks to Dr. R. B. Pearce, the chairman
of my graduate study committee, for his sincere criticism,
valuable suggestions, continuous help, and encouragement
throughout this work and in the preparation of this manuscript.
I am deeply indebted to my thesis advisors, who gave so
unselfishly of themselves to help my research and my personal
development.
I owe a debt of gratitude to Dr. C. A. Martinson for his
valuable help and for providing me the use of his laboratory
facilities.
Thanks also are due to Dr. I. C. Anderson, Dr. W. A.
Russell, Dr. T. B. Bailey, and Dr. J. J. Mock for their
encouragement and great help throughout this work.
A special word of thanks and gratitude must be bestowed
on the Agronomy Department of Cairo University, who supported
me during this study.
I also want to thank all those who helped me directly
or indirectly. My friends, Sami Saad ElDin and his wife
Mervat, I.O.I. Agwatu and his wife Ngozi, the Yarges family, f
and Nabil Mohammed and his wfie Tahani, for their enduring
courage, understanding and moral support during this study.
Finally, I want to express thanks to all the staff and tech
nicians in the Agronomy Department, Ain Shams University,