Influence of maturity and fruit yield on susceptibility to leafspot diseases of peanuts (Arachis hypogaea L.)

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Title:
Influence of maturity and fruit yield on susceptibility to leafspot diseases of peanuts (Arachis hypogaea L.)
Uncontrolled:
Arachis hypogaea
Leafspot diseases of peanuts
Physical Description:
viii, 48 leaves : ill. ; 28 cm.
Language:
English
Creator:
Miller, Ivan Lee, 1954-
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Subjects / Keywords:
Peanuts -- Disease and pest resistance   ( lcsh )
Leaf spots   ( lcsh )
Agronomy thesis Ph. D
Dissertations, Academic -- Agronomy -- UF
Genre:
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1981.
Bibliography:
Bibliography: leaves 44-47.
Statement of Responsibility:
by Ivan L. Miller.
General Note:
Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 028124797
oclc - 07842896
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AA00017656:00001


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INFLUENCE OF MATURITY AND FRUIT YIELD ON SUSCEPTIBILITY
TO LEAFSPOT DISEASES OF PEANUTS (Arachis hypogaea L.)









By

IVAN L. MILLER


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 sincerely thank Dr. A. J. Norden, advisor and chairman

of my supervisory committee, for his advice and encouragement through-

out my work at the University of Florida. My appreciation also to

Drs. D. W. Gorbet, D. A. Knauft,R. C. Littell, and R. D. Berger for

serving on my supervisory committee, and to Dr. L. F. Jackson, a

former member of my committee, who gave many useful suggestions about

the pathological aspects of my research. Ms. Lauryl Burton greatly

assisted in flower bud removal during the summer of 1979. Mr. Harry

Wood gave a great deal of appreciated, practical advice about growing

my experiment.

I am deeply thankful to my wife, Fonda, for the many sacrifices

she made so that I could continue my education and the many evenings

she spent alone while I removed floral buds. I wish to also thank

my father, Floyd Miller, who instilled in me the love of growing

things.

















TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS................ ............................. ii

LIST OF TABLES....................................... ..... .......iv

LIST OF FIGURES................................ ..............vi

ABSTRACT................................................vii

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

LITERATURE REVIEW.................................................. 2

MATERIALS AND METHODS.................... ............. .........10

RESULTS............................. ................... .......14

Leafspot Measurements.....................................14
Pod Yield...............................................27

DISCUSSION................. ................................36

SUMMARY AND CONCLUSIONS.........................................42

LITERATURE CITED.................... ......... ...... ............ 44

BIOGRAPHICAL SKETCH........ ........... .. ............. ........ 48















iii
















LIST OF TABLES


Number Page

1 Relative yielding ability, maturity, and peak
flowering of the three cultivars used in this
experiment.............. ...... ............ .........12

2 Mean effect of fungicidal spray and removal of
flower buds on leaf retention ratings of three
peanut cultivars 135 days after planting in 1979......15

3 Analysis of variance for the effect of fungicidal
spray and removal of flower buds on leaf reten-
tion ratings for three peanut cultivars in 1979.......16

4 Mean effect of fungicidal spray and removal of
flower buds on the number of lesions per plot
sample (10 leaves) at 10 day intervals for three
cultivars in 1980.................................... 21

5 Analysis of variance for the effect of fungicidal
spray and removal of flower buds on the number of
lesions per plot sample (10 leaves) at 10 day
intervals for three peanut cultivars in 1980..........22

6 Mean effect of fungicidal spray and removal of
flower buds on pod yield (g/plot) for two harvests
of three peanut cultivars in 1979 and 1980............28

7 Analysis of variance for the effect of fungicidal
spray and removal of flower buds on the pod yield
for two harvests of three peanut cultivars in
1979 and 1980..................................... ..29

8 Mean effect of fungicidal spray and removal of
flower buds on the percent of sound mature kernels
for two harvests of three percent cultivars in
1979 and 1980.................................. 32

9 Analysis of variance for the effects of fungicidal
spray and removal of flower buds on the percent of
sound mature kernels for two harvests of three
peanut cultivars in 1979 and 1980....................33










Number Page

10 Mean effect of fungicidal spray and removal of
flower buds on the yield of sound mature kernels
(kg/hectare) for two harvests on three peanut
cultivars in 1979 and 1980.............................34

11 Analysis of variance for the effects of fungicidal
spray and removal of flower buds on the yield of
sound mature kernels for two harvests of three
peanut cultivars in 1979 and 1980......................35
















LIST OF FIGURES


Number Page

1 Photograph of the six reproductive treatments in
the sprayed block of the 1979 experiment 135 days
after planting.............. ......... .. .... ........19

2 Graph of the mean effects of flower bud removal and
chemical fungicides on the number of lesions per
plot sample for Early Bunch in 1980....................24

3 Graph of the mean effects of flower bud removal
and chemical fungicides on the number of lesions
per plot sample for Florunner in 1980..................25

4 Graph of the mean effects of flower bud removal
and chemical fungicides on the number of lesions
per plant sample for Dixie Runner in 1980..............26
















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


INFLUENCE OF MATURITY AND FRUIT YIELD ON SUSCEPTIBILITY TO
LEAFSPOT DISEASES OF PEANUTS (Arachis hypogaea L.)

By

Ivan L. Miller

June 1981

Chairman: A. J. Norden
Major Department: Agronomy

Three peanut, Arachis hypogaea L., cultivars were evaluated for

amount of leafspot diseases and yield. The objectives of this experi-

ment were to examine the relationship of yield and maturity to

susceptibility to leafspot diseases in peanuts.

The three cultivars, Early Bunch, Florunner, and Dixie Runner,

differing in yield and maturity were grown two years at Gainesville,

Florida. To further regulate reproductive efficiency, the initial

floral buds were removed from half the plots. Additionally, the

experiment was divided into two blocks with one receiving fungicidal

spray.

Removing the initial floral buds appeared to reduce the amount of

leafspot disease and extend maturity for all cultivars in both sprayed

and unsprayed blocks. Leaf retention was greater for Early Bunch and

Florunner plots with controlled reproductive efficiency than corre-

sponding plots with unrestricted flowering in 1979. Dixie Runner

vii










showed little difference between reproductive treatments. Lesion

numbers per plot sample in 1980 indicated a similar response to con-

trolling reproductive efficiency. The two higher yielding cultivars

had fewer lesions in the plots with restricted flowering than those

with uncontrolled reproductive efficiency.

Pod yield of Early Bunch, the highest yielding cultivar, was

reduced most by floral bud removal. The yield of Florunner was

reduced slightly and that of Dixie Runner the least. Mean yield and

leafspot disease differences due to flower removal were greater in

the unsprayed block.

These experiments indicate that reducing the initial fruiting

of peanut plants reduces the amount of leafspot disease and based

on leaf retention, delays plant maturity. Also, that cultivars

respond differently to flower removal relative to yield and to leaf-

spot disease control.


viii
















INTRODUCTION

The costs of producing peanuts (Arachis hypogaea L.), both

economically and environmentally, are increasing greatly. A part of

these costs is involved with controlling leafspot diseases which

occur wherever peanuts are grown. Resistance to these diseases would,

therefore, contribute to the production of peanuts throughout the

world. Peanut breeders have observed great variability in resistance

within the genus from almost immunity to high susceptibility. However,

the most resistant lines have been in species other than the cultivated

peanut.

Within the cultivated species of peanut very little variability

has been found. A number of characteristics may be involved with the

degree of resistance in a particular peanut cultivar or line. Late

maturing, spreading or semi-bunch types with large green leaves that

have low yields have been more resistant. The inability to develop

high yielding, resistant cultivars also associated low yield with

resistance. Additionally the size of stomatal apertures has been

shown to affect susceptibility.

The objective of this research was to examine the relationship

of yield and maturity to susceptibility to leafspot diseases in three

peanut cultivars.
















LITERATURE REVIEW

Leafspot diseases of peanuts occur throughout the world in

almost all peanut production areas. Losses due to these diseases

range from 10% to 50% when adequate control measures are not taken.

Berkeley (1875) first described the pathogens which incite these

diseases as Cladosporium personatum. The classification of these

pathogens varied for about 45 years until specimens and reports were

compared, and Woodroof (1933) determined that there were two species

of Cercospora inciting the leafspot disease. The two pathogens were

identified as Cercospora arachidicola Hori and Cercospora personata

(Berk. and Curt.) Ellis and Everhart. Jenkins (1938) identified

the perfect stages of Mycosphaerella arachidicola and Mycosphaerella

berkeleyii. Deighton (1967) recently transferred Cercospora personata

to the genus Cercosporidium naming it C. personatum.

The pathogens overwinter on crop debris on the soil (Hemingway,

1954; Kucherek, 1975; Wolf, 1916) or on volunteer plants (Hemingway,

1954). Leaves infected with these pathogens fall to the ground.

Mycelia persist in the diseased leaves for six months or more and

upon favorable conditions the following year, readily sporulate pro-

ducing inoculum for the initial disease cycle of that season. Conidia

are also thought to persist from season to season (Hemingway, 1954).

The sexual stage of these pathogens is reported to be a survival struc-

ture (Jenkins, 1938; Woodroof, 1933) but is not considered to be

important in nature.








3

Conidia are splashed from the soil to the leaves of young peanut

plants by rain, blown from sporulating lesions by wind (Hemingway,

1954) or transmitted by insects (Wolf, 1916). Conidial germination

occurs when the temperature is within the range of 200 C to 300 C,

and the air is nearly saturated with a relative humidity of 96.5% or

more (Jenson and Boyle, 1965, 1966). Germination may occur from one

or more of the conidial cells within three to eight hours (Jenkins,

1938). Abdou et al. (1974) found 95% to 99% of the conidia germinated

48 hours following inoculation under controlled conditions. Germ

tubes of both pathogens have been reported to penetrate the epidermal

cell walls (Jenkins, 1938), but further observations showed that most

entered through open stomata (Abdou et al., 1974; Jenkins, 1948) about

six days after inoculation. Abdou et al. (1974) reported germ tubes

appeared to be attracted to open stomata in some peanut lines. In

both pathogens the distal ends of the germ tubes enlarged and pene-

tration pegs formed entering the stomata.

Following penetration, secondary mycelia formed. Cercospora

arachidicola produced intercellular hyphae at first; and then, following

the death of the cells in advance of the growing mycelia, cell walls

were penetrated (Abdou et al., 1974; Jenkins, 1938; Woodroof, 1933).

The secondary mycelia of C. personatum grew intercellularly with the

production of haustoria, and the cells were not killed in advance of

the growing hyphae. As the mycelia spread in the host tissue, cells

collapsed and produced the necrotic spot (Abdou et al., 1974; Jenkins,

1938). Lesions caused by C. arachidicola usually were surrounded by

pale yellow halos in early stages while halos formed around mature

lesions of C. personatum (Jenkins, 1938; Woodroof, 1933).










4

Both pathogens produced stromata, often in the stomatal chambers.

Differences between stromatal development of the two pathogens were

shown. Stroma developed on the lower or on both surfaces of C.

personatum lesions but primarily on the upper surface of C. arachi-

dicola lesions (Abdou et al., 1974; Jenkins, 1938; Woodroof, 1933).

Under favorable conditions the stroma produced conidiophores about

two weeks following infection (Abdou et al., 1974). The conidiophores

emerged through the stomata or ruptured the epidermis.

Early research (Woodroof, 1933), showing that the pathogens

overwintered in peanut residues, suggested the measures first used to

control these diseases: sanitation and crop rotation. Burning and

deep plowing all residues were recommended (Hemingway, 1954). Wolf

(1916) found that rotation by itself reduced but did not eliminate

leafspot. Hemingway (1954) suggested at least two years between crops

of peanuts on the same land. Mazzani and Allievi (1971) found great

differences between fields of peanuts grown consecutively for seven

years and those with six years fallow between crops. Plants in the

fields grown continuously in peanuts had about 45 lesions on 100% of

their leaves, while those plants which were grown with six years

fallow between crops averaged about two lesions on 52% of the leaves.

In addition, plant life was lengthened 20 days, yield increased 70%,

and fruit and kernel weight and kernel percentage were greater for

the crop grown in rotation. Kucharek (1975) reported that a one

year rotation reduced the number of lesions per leaflet about 90%









5

during the early growing season. This reduction occurred in adjacent

fields, one under rotation, the other not. Differences existed whether

or not fungicide control was used.

Planting time has been shown to affect the amount of leafspot

occurring in a particular crop. Delaying planting decreased leafspot

occurrence in a study in Africa (Farrell et al., 1967) and in India

(Nath and Kulkarni, 1967). In Africa and India the later plantings

develop in dryer environments and are lower yielding, whereas in the

southeastern United States later plantings are frequently exposed to

higher humidity and often show greater disease.

Farrell et al. (1967) also showed that decreasing plant density

decreased leafspot diseases. The authors suggested two possible reasons

for the reduction in lesion number. First, with higher densities or

narrow spacings, the leaf canopy is tighter increasing the moisture

retained within the canopy. High humidity is one of the requirements

for germination and infection by the spores. Secondly, there is a

dilution effect with the wide spacings, in that the plants produce

more leaves and, therefore, with equal infection have fewer lesions

per leaf. Reducing row spacing to increase yield was effective only

when fungicides were used.

Fungicides have been the only effective means of controlling

leafspot throughout the growing season. Initially sulfur dust was

used in the United States, but in other areas the use of fungicides

was not considered economically feasible until higher yielding culti-

vars and better fungicide application methods were developed (Hemingway,

1954). It was shown that fungicide effectiveness was greater at

higher densities or narrow spacings (Farrell et al., 1967). Present








6

recommendations are to apply fungicides every 10 to 14 days beginning

four to eight weeks after planting with four to six applications during

the growing season.

A large number of organic fungicides have replaced the sulfur-

copper dusts and sprays originally used to control leafspot. Sulfur

is sometimes added to these fungicides to improve their efficiency.

In 1973 races of both C. arachidicola and C. personatum were found to

be tolerant to a fungicide benomyll) used extensively in the control

of leafspot (Backman et al., 1977).

The cost of controlling leafspot diseases with fungicides is

rapidly increasing and some of the chemicals may pose a threat to the

environment. It has also been shown that the fungicides affect kernel

quality by upsetting the balance of pathogenic fungi and their antago-

nists (Backman et al., 1977; Hammond et al., 1976). Additionally,

they found that other pathogens were influenced through leafspot con-

trol using fungicides. The frequency of white mold, Sclerotium rolfsii,

was greater with the use of some chemicals.

Producing high yielding cultivars that are also leafspot resistant

has not been accomplished thus far. Genotypes with useful levels of

resistance have been reported (Abdou et al., 1974; Aulakh et al., 1972;

Hassan and Beute, 1977; Hemingway, 1954; Nur and Ibrahim, 1968; Sowell

et al., 1976; Monasterious, 1980). However, breeders have been unable

to utilize this resistance to date. Higgins (1956) reported that in

hundreds of crosses he was unable to combine resistance to leafspot

and high yield, and that there was a positive correlation between

susceptibility to leafspot and maturity.








7

Hemingway (1954) assessed 75 peanut cultivars for resistance to

leafspot diseases and found 25 that showed some resistance. The

following year these resistant cultivars were evaluated, and the four

that were determined to be very resistant had dark green foliage, were

longer season cultivars, and had bunch or semi-bunch growth habits.

Other studies (Aulakh et al., 1972; Nur and Ibrahim, 1968) found that

spreading and semi-bunch types were significantly more resistant than

bunch types. Sowell et al. (1976) examined 1400 plant introductions

and found three that had significantly less disease than the suscep-

tible cultivars included in the test. The yield of these plant

introductions were also significantly lower than the cultivar,

Florunner, and the maturity significantly later. Mazzani et al.

(1972) found that of the 474 lines they evaluated, the lines which

had large yields had high disease incidence. Positive relationships

between light green foliage and large leaves with high disease also

were shown.

Gibbons and Bailey (1967) associated resistance to leafspot

diseases with small stomatal apertures. Mazzani et al. (1972) and

Hasson and Beute (1977) found no relationship between aperture size

and resistance among the lines they studied. Abdou et al. (1974)

reported that the germination tubes were attracted to the stomatal

openings in susceptible lines but not to the stomata of resistant

lines. Results from their study led to the conclusion that the culti-

vated species of Arachis did not contain useful levels of resistance

to leafspot diseases. Several other species within the genus

show high resistance or immunity to the leafspot pathogens. The

wild relatives of the cultivated peanut that showed this resistance








8

were dark green, produced few if any fruit and were either very late

maturing or perennials.

Many plant diseases have been associated with some factor of plant

nutrition. Bledsoe et al. (1946) examined the effects of several

nutritional deficiencies (phosphorus, potassium, calcium, magnesium,

sulfur, and several micronutrients) on the peanut plant. Of all these,

only plants with deficiencies in magnesium showed leafspot disease

more severe than the controlled plants. Magnesium deficiency symptoms

became apparent 24 days after magnesium was withheld from the plant.

Four days later lesions of C. arachidicola appeared on the leaves

which showed the first magnesium deficiencies. Progress of the

disease continued following the same development as that of the

magnesium deficiency.

The disease of the plants growing in magnesium deficient soil

developed while the plants were producing fruit. Magnesium deficient

plants produced more flowers and gynophores than those in any other

mineral deficient soil. It has been shown that the fruit may take up

calcium from the soil (Bledsoe and Harris,1950), and that its applica-

tion in the form of gypsum increases both the production of fruit and

the plants susceptibility to leafspot. Much of the magnesium in the

leaves of the magnesium deficient plants was mobilized and transported

to the gynophores and fruit, greatly lowering the percentage magnesium

in the leaves compared to those in soil with no added nutrients. Burk-

hart and Collins (1941) reported that magnesium is also concentrated

in the kernels. This may explain why production of a large number of

fruit could increase the susceptibility of peanut plants to leafspot

diseases.








9

Whether or not reduced magnesium in the leaves is the direct or

indirect cause of susceptibility to leafspot has not been determined.

Bhagsari and Brown (1976) showed that cultivated peanut lines trans-

located more of the photosynthetically assimilated 14C than did wild

relative species. Smith (1954) reported that production of flowers

and gynophores is inhibited by an increasing number of developing

fruit.

These reports, plus observations that leafspot disease symptoms

in the field generally are first noted at flowering,suggest that

leafpot disease susceptibility may indeed be related to reproduction.

It appears that the fruit may withdraw some substance from the vegeta-

tive plant parts which induces susceptibility to leafspot and the

larger the sink, i.e. fruit set, the greater the susceptibility.
















MATERIALS AND METHODS

The experiments reported here were grown during 1979 and 1980

as randomized, complete block designs with six treatments. In 1979

the field plots were on the Green Acres Agronomy Farm, Gainesville,

Florida, and in 1980 on the University of Florida Campus Agronomy

Farm, Gainesville, Florida. Cultural practices during both years

were those recommended for commercial peanut production. Rainfall

was augmented with irrigation to maintain adequate moisture for

plant growth, and fertilizer was applied at recommended levels prior

to planting. Two applications of gypsum were made each year after

flowering had commenced. Weeds were controlled through the use of

herbicides and hand cultivation.

In 1979, plots were one row 6.1 m (20 ft) long with 30 cm (1 ft)

between plants and 91 cm (3 ft) between plots. Plots were 4.3 m

(14 ft) long in 1980 with all other spacings the same as the previous

year. The experiment was divided into two blocks, one received

fungicidal spray for leafspot control, and the other remained

untreated for the duration of the experiment. The treatments were

replicated within each spray regime four times.

The six reproductive treatments consisted of three cultivars:

high, moderately high, and low yielding, each with a plot in which

the reproductive efficiency was controlled until peak flowering and a

control plot with unrestricted flowering. The three cultivars differed

10








11
in yield, days to maturity, and peak flowering (Table 1). Early Bunch,

the highest yielding cultivar, has the shortest maturity. Florunner

has a moderately high yield and intermediate maturity. Dixie Runner

is the lowest yielding and latest maturing of the three cultivars.

The reproductive efficiency was controlled by removing floral

buds prior to fertilization. The majority of the floral buds were

removed from 1900 hours (7:00 P.M.) until 2300 hours (11:00 P.M.)

daily after they had enlarged, and the peanut leaflets had folded

together. The remainder were removed the following morning prior to

0930 hours (9:30 A.M.) to insure that fertilization had not occurred.

The number of plants in which the reproductive efficiency was control-

led decreased from 20 plants per plot initially to five plants per

plot because it was too time-consuming to remove all the flowers from

20 large plants.

Seeds were planted by hand in mechanically opened furrows. The

first experiment was planted 2 May 1979 and the second experiment

1 June 1980. Upon emergence, plantings were thinned to one plant per

30 cm. Plants began flowering about 30 days after planting both years.

Floral bud removal began with the first flowers and continued until

76 days, 83 days, and 90 days after planting for Early Bunch, Florunner,

and Dixie Runner, respectively.

The relative amounts of leafspot disease for each plotwereesti-

mated in 1979 by visual leaf retention ratings on 17 September prior

to the second harvest of Early Bunch. A one to five rating scale was

used with one being totally defoliated and five retaining a full canopy.

In 1980 samples of 10 leaves were chosen randomly from each plot at















Table 1. Relative yielding ability, maturity, and peak flower-
ing of the three cultivars used in this experiment.


Cultivar Relative Maturity* Peak
Yield Flowering*

Early Bunch High 125 130 78

Florunner Mod. High 135 140 83

Dixie Runner Low 140 145 90


*Days from planting.










10 day intervals and the number of lesions counted to assess the

severity of disease.

Plots were harvested at the average physiological maturity for

the respective cultivars and again 15 days later. Early Bunch was

harvested at 125 and 140 days after planting, Florunner at 135 and

150 days, and Dixie Runner at 145 and 160 days after planting. Plants

were loosened from the soil with a potato fork and then lifted and

picked by hand. After the plants were removed, the soil was sifted

to gather any remaining pods. After harvest the fruit samples were

dried, weighed, and graded following standard Federal-State Inspec-

tion Service grading procedures.

The least significant differences (LSD) in the following analysis

of variance tables are appropriate for comparing the treatment means.

However, since variation depends on the size of the mean, different

LSD values are needed to compare two small means than to compare two

large means. Additionally, because of restraints on the field

layout of this experiment no test is possible for spray regime main

effect differences.

















RESULTS

Means for leaf retention ratings, number of lesions per plot,

pod yield, percent sound mature kernels and sound mature kernel yield

are presented in Tables 2, 4, 6, 8, and 10, respectively. The cor-

responding analysis of variance are presented in Tables 3, 5, 7, 9,

and 11. Graphs of the mean lesion number per plot for Early Bunch,

Florunner, and Dixie Runner are shown in Figs. 2, 3, and 4, respec-

tively.


Leafspot Measurements

Cercospora arachidicola lesions appeared as the plants began

flowering about 30 days after planting in 1979. This disease,

however, was present for only a short time, even in the unsprayed

plots. Cercosporidium personatum lesions were first observed about

85 days after planting corresponding to approximately peak bloom

for the three cultivars. Development of C. personatum progressed

at about the same rate on all plots for 14 days, after which time

visual differences were seen between the plots in which the floral

buds had been removed and those with uncontrolled flowering.

Leaf retention ratings (Table 2) indicate that bud removal

had a large effect on the high and moderately high yielding cul-

tivars, and a lesser effect on the low yielding cultivar. Analysis

of variance (Table 3) showshighly significant (P<0.01) differences















Table 2. Mean effect of fungicidal spray and removal of flower
buds on leaf retention ratings of three peanut culti-
vars 135 days after planting in 1979.



Cultivar Treatment Rating*

Early Bunch Spray Flower buds removed 3.5
Control 2.0
No spray Flower buds removed 2.7
Control 1.5

Florunner Spray Flower buds removed 3.7
Control 3.0
No spray Flower buds removed 3.0
Control 2.5

Dixie Runner Spray Flower buds removed 4.0
S Control 3.7
No spray Flower buds removed 3.0
S Control 3.0

LSD .05 0.8


* 1 = No leaves;
four ratings.


5 = Full canopy; data represents mean of













Table 3. Analysis of variance for the effect of fungicidal spray
and removal of flower buds on leaf retention ratings
for three peanut cultivars in 1979.


Source of Variation df Mean Squares

Spray regimes (S) 1 6.0

Replications within spray
regimes 6 2.6**

Reproductive treatments (T) 5 3.5**

SxT 5 0.1

Error 30 0.6


** Significant at the 0.01 level of probability.











among the six reproductive treatments. Leaf retention ratings were

higher for the lower yielding cultivars and under the spray regime.

Leaf retention ratings for Early Bunch, the high yielding cul-

tivar, were significantly (P<0.05) improved by flower-bud removal

and fungicidal spray, 3.5 compared to 1.5 (Table 2). Ratings

were improved by the floral removal treatment in both the sprayed

and unsprayed plots. However, the ratings for the plots with un-

restricted flowering in the sprayed block were not significantly

different from those of the plots with restricted flowering in the

unsprayed block.

Florunner, the moderately high yielding cultivar, showed

similar differences between reproductive treatments and spray

regimes. Unsprayed plots with uncontrolled reproductive efficiency

showed significantly (P<0.05) less leaf retention than the sprayed

plots with bud removal. All other comparisons for this cultivar

were not statistically different.

Leaf retention ratings for Dixie Runner, the low yielding

cultivar, ranged from 4.0 for the controlled reproductive efficiency

plots in the sprayed block to 3.0 for both reproductive treatments

in the unsprayed block. The only significant difference in ratings

was between these extremes, with both not significantly different

from the sprayed plots with uncontrolled flowering.

Dixie Runner with uncontrolled flowering and no fungicide

spray retained as many leaves as the higher yielding cultivars with

controlled flowering and fungicide sprays. In both the sprayed











and unsprayed blocks the three cultivars with controlled repro-

ductive efficiency showed no significant (P<0.05) differences in

leaf retention. F tests showed that spray regimes were not

significantly different nor were there significant spray regime

by reproductive treatment interactions.

Figure 1, a photograph taken 135 days after planting in 1979,

shows that where the floral buds were removed leaves were retained

almost uniformly in all the cultivars (the green area appearing

horizontally across the three cultivars in the photograph).

However, where flowering was not controlled, Early Bunch, Flo-

runner, and Dixie Runner lost progressively fewer leaves in that

order.

The summer of 1980 was very dry and the peanut leafspot

diseases were late. Only a few C. arachidicola lesions were

found relatively late in the season. Again, there was no build-

up of this pathogen and, as in 1979, it soon disappeared.

Cercosporidium personatum began to show up about 80 days after

planting, and with a brief period of rain the population increased

very rapidly in the unsprayed plots. Following another period

of dry weather the number of lesions per plot decreased from 30

August to 10 September and then increased again until a maximum

of about 750 lesions per plot sample was reached. There were

highly significant (P<0.01) differences among reproductive treat-

ments and spray regimes by reproductive treatment interactions at

all sampling dates (Table 5).












































Fig. 1. Photograph of the six reproductive treatments in the sprayed
block of the 1979 experiment 135 days after planting.








20
On the first sampling date (20 August 1980--Table 4), no signifi-

cant differences were found in the sprayed block. In the unsprayed

block where the number of lesions was much greater, significant

(P<0.05) differences are shown only between reproductive treatments

of the high yielding cultivar and between the high yielding cultivar

and the other lower yielding cultivars. In the sprayed block the

lesion numbers per plot sample ranged from 10 for Dixie Runner with

.controlled flowering to 66 for Early Bunch with uncontrolled flowering.

In the unsprayed block the range was from 129 for Florunner with buds

removed to 699 for Early Bunch with unrestricted flowering. The varia-

tion among samples within a plot was large as reflected by the least

significant difference.

Lesion numbers increased from the first to the second sampling

for the reproductive treatments of Early Bunch in the unsprayed blocks.

Early Bunch had significantly (P<0.05) more lesions than the other

two cultivars. Number of lesions per plot in the sprayed block ranged

from 19 for Dixie Runner with controlled reproductive efficiency to 90

for Early Bunch with uncontrolled flowering. In the unsprayed blocks

the range was from 254 to 766 for Florunner with controlled reproductive

efficiency and Early Bunch with uncontrolled flowering, respectively.

Variation within samples at the second sampling date was less than

at the first.

The number of lesions per plot on the third sampling date was

reduced relative to the first two sampling dates, particularly in the

unsprayed block. Differences between treatments within blocks were

small and insignificant statistically, except for the Early Bunch

reproductive treatments in the unsprayed block which were different

(P<0.05) from each other and from the other treatments.










Table 4. Mean effect of fungicidal spray and removal of flower buds on the number of
lesions per plot sample (10 leaves) at 10 day intervals for three cultivars
in 1980.


Cultivar Treatment Date
8/20 8/30 9/10 9/20 10/10

Early Bunch Spray Flower buds removed 66 71 25 113 653
S Control 57 90 40 240 761
No spray Flower buds removed 699 713 215 5311 745
S Control 496 766 312 755 763

Florunner Spray Flower buds removed 11 22 16 81 350
S Control 23 46 21 103 574
No spray Flower buds removed 136 254 51 225 483
S Control 129 281 56 353 719

Dixie Runner Spray Flower buds removed 10 19 10 51 166
S Control 20 26 12 122 238
No spray Flower buds removed 137 288 62 279 328
S Control 200 300 60 357 492


75 43 25 63 78


LSD .05












Table 5. Analysis of variance for the effect of fungicidal spray and removal of flower buds on the
number of lesions per plot sample (10 leaves) at 10 day intervals for three peanut culti-
vars in 1980.


Source of Variance


8/20


Mean Squares
Sampling date
8/30 9/10


Spray regimes (S) 1 864,033 1,806,528 133,141 2,650,800 206,981

Replications within spray
regimes 6 171,131** 312,168** 22,515** 454,329** 38,265**

Reproductive treatments (T) 5 139,885** 140,983** 29,289** 104,129** 345,329**

S x T 5 94,713** 88,945** 20,389** 40,897** 13,780**

Error 30 8,102 3,127 380 4,426 3,715

* Significant at the 0.05 level of probability.

** Significant at the 0.01 level of probability.


9/20


10/10








23

After the third sampling the number of lesions began to increase.

On the fourth sampling date lesion numbers in the sprayed plots ranged

from 51 for Dixie Runner with controlled reproductive efficiency to 240

for Early Bunch with uncontrolled flowering. In the unsprayed plots,

the range was from 225 for Florunner with bud removal to 755 for Early

Bunch with unrestricted flowering. More of the treatments were

significantly (P<0.05) different at this sampling.

In the sprayed block the two treatments of Early Bunch were

significantly (P<0.05) different from each other, while those of the

other two cultivars showed no differences. There were no significant

differences among the three cultivars with controlled flowering. Plots

of Early Bunch which had uncontrolled reproductive efficiency had

significantly more lesions than those of the other cultivars treated

similarly.

In the unsprayed plots the reproductive treatments of each culti-

var were significantly different. The plots with uncontrolled flower-

ing had significantly (P<0.05) more lesions than those in which floral

buds had been removed. Again, Early Bunch had significantly more

lesions in both reproductive treatments than the other cultivars.

In the final sample many of the treatments were approaching the

maximum number of lesions observed. Lesion numbers in the sprayed

block ranged from 166 to 761 for Dixie Runner with controlled repro-

ductive efficiency and Early Bunch with uncontrolled flowering,

respectively. The same cultivars had similar minimum (328) and

maximum (763) lesion numbers, respectively, in the unsprayed block.

Only the plots of Early Bunch from which the flowers were

removed in the sprayed block were significantly (P<0.05) different




























I'.





"\


/
I


/---"""""


/
/ /




/ !
/ !


/


I

I
I
;1
I
I


spray -COntrol
sproy-buds
removed
S pray -control
Spray -buds
removed


8-20 8-30 9-10 9-20
SAMPLING DATE


Fig. 2. Graph of the mean effects of flower bud removal and
chemical fungicides on the number of lesions per plot
sample for Early Bunch in 1980.


800


600

Z
O
S500
-J
_J
U-
0
400
w
Zn

Z 300"




















700



600"


z
0
(n 500

LL
_j
0
400
UJI
CD


------ No sproy-control
---- No soroy- buds removed
Spray control
Spray-buds removed


/


200 / /


,,/ /
o .' //




8-20 8-30 9-10 9-20 10-10
SAMPLING DATE




Fig. 3. Graph of the mean effects of flower bud removal and
chemical fungicides on the number of lesions per plot
sample for Florunner in 1980.

















.----- No spray-control
---- No spray- buds removed
----Spray control
---. Spray- buds removed


j


600'



500



400


300


2001 /


100


I' t
t
S\\ /
\\,' /
I I /


'k.,
I
4 4


8-30 9-10
SAMPLING


-4--


-e -00


9-20
DATE


SFig. 4. Graph of the mean effects of flower bud removal and
chemical fungicides on the number of lesions per plant
sample for Dixie Runner in 1980.


10-10









27

in numbers of C. personatum lesions from the others (Table 4). Flo-

runner plots with controlled reproductive efficiency had significantly

fewer lesions than those with unrestricted flowering in both the sprayed

and unsprayed blocks. Differences in reproductive treatments of Dixie

Runner were significant only in the unsprayed block. Early Bunch

treatments had significantly more lesions than the other treatments

except for the Florunner plots with uncontrolled reproductive efficiency

in the unsprayed block. In the sprayed block Early Bunch had signifi-

cantly more lesions than Florunner which had significantly more lesions

than Dixie Runner.

Graphs plotting the mean C. personatum lesion number per plot

sample for the three cultivars presented in Figs. 2, 3, and 4 show

similar trends. Fungicidal .spray applications resulted in slower

increases in pathogen population, but the lesion numbers followed the

same general pattern as those of the unsprayed plots. Differences

between treatments were greatest when the pathogen population was

large, until the population approached maximum size.

A serious occurrence of peanut rust (Puccinia arachidis) caused

a large amount of premature leaf abscision throughout the 1980 experi-

ment, irrespective of the treatment, confounding the effects of the

leafspot diseases. This prevented obtaining meaningful leaf retention

ratings in 1980.

Pod Yield

Data from 1979 and 1980 harvests (Table 6) show the effects of

controlling the pathogen population and the reproductive efficiency

on yield. Differences among reproductive treatments and the spray

regime by reproductive treatment interaction were highly significant

(P<0.01) in both years.













Table 6. Mean effect of fungicidal spray and removal of flower buds on
for two harvests of three peanut cultivars in 1979 and 1980.


pod yield (g/plot)


Cultivar Treatment 1979 Harvest 1980 Harvest
First Second First Second

Early Bunch Spray Flower buds removed 561 552 534 545
S Control 830 820 792 807
No spray Flower buds removed 170 174 212 211
S Control 446 439 432 445

Florunner Spray Flower buds removed 628 641 528 584
S Control 679 703 597 615
No spray Flower buds removed 438 452 415 423
S Control 534 531 432 470

Dixie Runner Spray Flower buds removed 262 283 273 299
S Control 322 366 329 384
No spray Flower buds removed 390 400 384 412
Control 405 451 397 471


LSD .05


182


170 47 33
















Table 7. Analysis of variance for the effect of fungicidal spray and
removal of flower buds on the pod yield for two harvests of
three peanut cultivars in 1979 and 1980.


Source
of Variation


df 1979
First


Mean Squares
Harvests 1980 Hi
Second First


harvests
Second


Spray regimes (S) 1 268,667 280,923 203,685 214,508

Replications 6 109,077** 105,741** 34,766** 38,424**

Reproductive
treatments (T) 5 150,153** 133,037** 93,322** 86,822**

S x T 5 98,478** 93,366** 76,085** 80,923**

Error 30 28,775 25,688 1,249 1,051


* Significant at the 0.05

** Significant at the 0.01


level of

level of


probability.

probability.








30

Yields of the first harvest in 1979 ranged from a high of 830

grams for Early Bunch with uncontrolled flowering in the sprayed block

to a low of 170 grams per plot with controlled flowering in the un-

sprayed block. Bud removal significantly (P<0.05) reduced the yield

of Early Bunch in both the sprayed and unsprayed blocks. The yield

of Florunner and Dixie Runner was not significantly reduced by control-

ling reproductive efficiency during the initial flowering period.

The yields of Early Bunch and Florunner were higher in the sprayed

than in the unsprayed block while the yields of Dixie Runner were

greater in the unsprayed.

The second harvest, made 15 days after the initial harvest of

each cultivar, was very similar to the first. The yields of Early

Bunch were slightly reduced or the same as (-10 to +4 grams per plot)

the first harvest. Florunner and Dixie Runner showed increased yields

per plot, -3 to +24 grams and 10 to 46 grams, respectively.

Yields of the 1980 harvest followed the same trends as the 1979

harvest. Early Bunch again had the highest and lowest yielding treat-

ments in the first harvest of 792 grams and 212 grams per plot. In

the sprayed block the plots with controlled reproductive efficiency

had a significantly (P<0.05) lower yield than plots with unrestricted

flowering. Early Bunch also showed significant differences between

reproductive treatments in the unsprayed block, while the other culti-

vars had no significant differences.

In the second harvest Early Bunch showed slight increases (11 to

15 grams per plot) in yield for all treatments except the controlled

reproductive efficiency treatment in the unsprayed block which remained











the same. All treatments of Florunner had greater yields (8 to 56

grams per plot) than at the first harvest. Yields of the Dixie Runner

treatments also increased (28 to 74 grams per plot) from the first

harvest.

The percent sound mature kernels (SMK) (Table 8) show that

Florunner and Dixie Runner had a higher percent SMK than Early Bunch.

Data were very consistent from year to year. Early Bunch showed the

only significant (P<0.05) decrease in percent SMK of the plots with

controlled flowering (63 to 55). Fungicidal spray reduced the SMK

percentage of Florunner and Dixie Runner from 82 to 74 and 74 to 72

percent, respectively, where reproductive efficiency was controlled.

A significant treatment variation and spray regime by reproductive

treatment interaction.

Computing the SMK yield per hectare (Table 10), one of the more

important factors in commercial production, shows that Early Bunch

with uncontrolled flowering had the highest yield of all treatments,

ranging from 3900 to 4000 kg/hectare (3471 to 3560 lb/acre). The

yield was consistently higher, although no significantly so in every

case. The second highest yielding treatment was Florunner with un-

restricted reproductive efficiency ranging from 3200 to 3800 kg/hectare.

There was little difference between the SMK yields of the two repro-

ductive treatments of either Florunner or Dixie Runner within a

block. Only the unsprayed plots of Dixie Runner in the second harvest

of 1980 shows significant (P<0.05) differences.










Table 8. Mean effect of fungicidal spray and removal of flower buds on the percent of
sound mature kernels for two harvests of three peanut cultivars in 1979 and
1980.


Cultivar Treatment 1979 Harvests 1980 Harvests
First Second First Second
Early Bunch Spray Budsremoved 61.4 65.5 65.2 65.6
S Control 67.0 65.0 69.3 67.3
No spray Budsremoved 39.5 51.2 60.1 58.4
S Control 62.0 62.8 63.4 64.4

Florunner Spray Buds removed 73.8 74.3 74.3 75.8
S Control 74.3 74.5 74.8 75.7
No spray Buds removed 81.7 81.5 82.0 83.7
S Control 74.3 74.9 74.5 75.6

Dixie Runner Spray Buds removed 73.8 70.5 71.5 71.2
S Control 73.1 73.0 74.2 73.9
No spray Buds removed 74.4 73.8 75.3 74.9
S Control 72.3 72.2 73.1 73.5


LSD .05


3.9















Table 9. Analysis of variance for the effects of fungicidal spray and
removal of flower buds on the percent of sound mature kernels
for two harvests of three peanut cultivars in 1979 and 1980.


Source df
of Variation


Mean
1979 Harvests
First Second


Squares
1980 Harvests
First Second


Spray regimes (S) 1 81.6 13.9 0.3 0.3

Replications within
spray regimes 6 20.3 16.3 0.8 0.5

Reproductive
treatments (T) 5 790.0** 431.6** 227.6** 343.3**

S x T 5 216.6** 106.3** 54.2** 54.5**

Error 30 18.6 25.6 7.5 1.3


* Significant at the 0.05

** Significant at the 0.01


level of

level of


probability.

probability.











Table 10.


Mean effect of fungicidal spray and removal of flower buds on the yield of
sound mature kernels (kg/hectare) for two harvests on three peanut cultivars
in 1979 and 1980.


1979 Harvests 1980 Harvests
Cultivar Treatment First Second First Second

Early Bunch Spray Flower buds removed 2425 2612 2502 2570
S Control 4025 3837 3947 3909
No spray Flower buds removed 477 656 917 885
S Control 2000 1985 1971 2064

Florunner Spray Flower buds removed 3325 3420 3126 3355
S Control 3627 3774 3213 3181
No spray Flower buds removed 2580 2653 2447 2550
S Control 2853 2852 2315 2556

Dixie Runner Spray Flower buds removed 1327 1432 1407 1531
S Control 1679 1887 1759 2043
No spray Flower buds removed 2080 2127 2077 2221
S Control 2180 2342 2088 2488


LSD .05


902


838 283 188












Analysis of variance for the effects of fungicidal spray and removal of flower
buds on the yield of sound mature kernels for two harvests of three peanut
cultivars in 1979 and 1980.


Source of Variation


Mean Squares
df 1979 Harvests 1980 Harvests
First Second First Second


Spray regimes (S) 1 6,191,243 6,303,586 5,711,130 4,878,150

Replications within
spray regimes 6 2,706,989** 2,641,060** 987,799** 879,199**

Reproductive treatments (T) 5 4,839,944** 4,045,710** 2,699,039** 2,562,007**

S x T 5 2,680,914** 2,493,422** 2,090,921** 2,208,356**

Error 30 727,301 657,142 45,802 30,260

* Significant at the 0.05 level of probability.

** Significant at the 0.01 level of probability.


Table 11.
















DISCUSSION

The mechanical restraints on performing these experiments neces-

sitated sampling only five plants per replication for leafspot disease

ratings and yield. However, even under these conditions many of the

treatment differences were large enough to be statistically signifi-

cant. The plants which were handled in the process of removing the

floral buds were smaller than plants which did not have the flowers

removed. This effect has been reported elsewhere (Williams et al.,

1975). How this response may have affected the results was not

determined.

In these experiments,as reported in other studies (Nath and

Kulkarni, 1967; Ramakrishna and Apparao, 1968),the leafspot diseases

appeared in the field when the plants had begun flowering. Cercospora

arachidicola, in agreement with its common name "early leafspot,"

produced the first lesions. This pathogen produced few lesions in

both 1979 and 1980, and C. personatum was the predominant pathogen.

Cercosporidium personatum began to produce lesions about mid-

season on all plots. In 1979 visual differences between treatments

were not apparent for several weeks. Between 14 to 21 days after

lesions were initially seen, the plots in the unsprayed block began

to show differences between the cultivars and between the flower

removal treatments. The foliage of Early Bunch with uncontrolled

reproductive efficiency became increasingly lighter green and the









37
numbers of lesions were noticeably higher than on the other cultivars.

Plots with controlled reproductive efficiency had fewer lesions than

those with unrestricted flowering for all three cultivars.

Differences in disease ratings increased until prior to harvest

when leaf abscision resulted in yet another difference between the

treatments. The cultivars with uncontrolled flowering shed different

amounts of their leaves. Early Bunch lost the most leaves followed

by Florunner, while Dixie Runner showed little leaf loss. Plots in

which initial floral buds were removed retained more leaves than their

counterparts with unrestricted flowering. As the plants matured the

amount of leaf loss in plots with controlled flowering, while much

less than that of the other plots, was greater for Early Bunch and

Florunner than for Dixie Runner.

In 1980, counts of leafspot lesions showed that fungicical sprays

delayed the incidence of disease. About the same number of lesions were

produced on all three cultivars through the first 100 days of growth.

Cultivar differences then became apparent. Early Bunch, the highest

yielding and earliest maturing cultivar, developed large numbers of

lesions on plots which had unrestricted flowering. The number of lesions

per plot for Florunner and Dixie Runner also had increased but to a

lesser degree. Plots of Early Bunch which had the initial floral buds

removed had similar numbers of lesions to the lower yielding cultivars.

At the last sampling date in the sprayed plots, both treat-

ments of Early Bunch had about the same number of lesions as

the unsprayed plots indicating that fungal control merely delayed

the increase in lesions numbers as reported by Plaut and Berger

(1980). In the case of Early Bunch this delay continued until










harvest time which is desired for chemical control of disease.

Neither Florunner nor Dixie Runner reached as high numbers of lesions

in the sprayed plots, but the number of lesions rapidly increased

for these cultivars as well.

In the unsprayed plots lesion numbers showed greater changes

and greater differences between treatments. The number of lesions

per plot sample increased from a very few to several hundred in a

short period of two weeks. Initially, differences between the

floral removal treatments of a cultivar were small, but as the

number of lesions per plot increased these differences increased.

From the first sampling Early Bunch had the largest number of

lesions, while Florunner and Dixie Runner had similar numbers

through the fourth sampling date. Florunner had rapidly increasing

lesion numbers from the fourth to the fifth sampling, whereas Dixie

Runner had a gradual increase in lesion numbers.

Plots with unrestricted flowering had a larger number of lesions

than the plots with controlled reproductive efficiency after the

third sampling for all three cultivars. The difference between the

two treatments was greatest in the unsprayed plots. Significant

spray regime by reproductive treatment interaction for lesion number

confirms that controlling reproductive efficiency had a greater

effect on the different cultivars for lesion numbers in the unsprayed

than sprayed plots. Sprayed plots of Early Bunch and Florunner with

uncontrolled reproductive efficiency had more lesions than the treat-

ments with controlled efficiency in the unsprayed plots. At the last

sampling the number of lesions per plot sample indicated a similar trend









39

for Dixie Runner. The number of lesions increased more for sprayed

plots with unrestricted flowering than for unsprayed plots with con-

trolled flowering.

Yields of the three cultivars were as expected in the sprayed

block when flowering was allowed to proceed as normal. Early Bunch

had a greater yield than Florunner, which outyielded Dixie Runner.

Of greater interest are the effects of the different treatments on

yield. Early Bunch showed the greatest decrease in yield because of

removing the initial floral buds. The yield of Florunner was not

significantly reduced by bud removal in the first year's experiment.

In the second year slight reductions occurred in the unsprayed plots

for both the first and second harvests. Dixie Runner also showed

yield differences in the second year's study. Hemsey et al. (1974)

found, for the cultivar, Colorado Manfredi, that removing flowers

until 40 days after planting increased yields over controls. It is

possible in this study that the crucial flowering period for the lower

yielding cultivars was late enough in the season that the yields were

not greatly reduced by removing floral buds for the period of the

treatment.

Yields for the second harvests showed different results in 1979

and 1980. In 1979, plots in which the reproductive efficiency had

been controlled, showed the largest increase in yield between the

first and second harvest. However, in the second year both repro-

ductive treatments of Florunner and Dixie Runner had greater yields

in the second harvest. The increases in 1979 could be explained

by greater fruit filling in plots with controlled flowering because

of the greater capability for photosynthesis by the remaining leaves








40

than of the other treatments between harvests. In 1980, the increase

in yield for plants with unrestricted flowering may have involved fil-

ling a larger number of immature fruit.

Fungicide sprays increased yields of all treatments except those

of Dixie Runner. Fungicide sprays reduced the differences in yield

between reproductive treatments. Williams et al. (1976) reported that

50% defoliation increased growth rate per pod. Possibly the defoliation

that occurred in the unsprayed plots of Dixie Runner resulted in a

greater growth rate of the fruit than that in the unsprayed plots.

Removing the initial floral buds had little effect on percent SMK

in the sprayed plots. Unsprayed Early Bunch showed a dramatic decrease

in percent SMK while Florunner had a moderate increase. The three

cultivars showed differing effects from fungicidal sprays for leafspot;

SMK's for Early Bunch increased with leafspot control sprays while

Florunner, and Dixie Runner to a lesser extent, had a decreased SMK

percentage. The latter had been noted before (Backman et al., 1977)

and is thought to involve an imbalance of the soil pathogens and

antagonistic fungi and bacteria. From the SMK yield data we see that

Early Bunch shows a significant decrease when buds are removed and

plots not sprayed. Dixie Runner showed a similar response to bud

removal in the second year while Florunner only showed a response to

leafspot control for SMK yield. These results may be related to the

effect of bud removal on pod yield.

Considering both yield and the amount of leafspot, the data show

that with lower yields the numbers of leafspot lesions are also lower

prior to maturity. Early Bunch which exhibited the greatest decrease

in yield from controlling the reproductive efficiency also had the










largest differences in leaf retention ratings (1979) and lesion

numbers (1980). Shortly after physiological maturity little dif-

ference was seen between the reproductive treatments of Early Bunch.

Dixie Runner which has smaller yield differences between reproductive

treatments also showed the least effect on leafspot disease.

Nevill and Evans (1980) performed a study in which flowers were

removed after the initial three weeks of flowering. They reported no

decrease in leafspot, and suggested that reports of resistance to

leafspot diseases in conjunction with low yield was related to a

greater number of leaves. Thus, they stated that a random leaf sample

would indicate a smaller number of lesions or less disease but would

not actually be greater resistance. Williams et al. (1976) found in

the cultivars he studied that removing pods did not significantly

increase plant growth rate. This study indicated that decreasing the

yield, or at the least removal of the initial flowers does indeed

increase leafspot disease resistance or delay the most severe effects

of leafspot disease.

An important difference between these studies involving flower

removal and those of Nevill and Evans is that they allowed flowering

to proceed for three weeks at a time when plants were very small. At

this time the new fruit require a larger proportion of the photosyn-

thate produced by the plant than later in the season. In this study

flower buds were removed for the initial 48 to 60 days of flowering,

and this allowed the plants to mature to a greater extent before the

fruit began forming a large sink for photosynthate and other nutrients.

This may be the major reason for the different results obtained from

the two investigations.















SUMMARY AND CONCLUSIONS

The objective of the studies reported in this dissertation was

to determine the effects of yield and maturity on the susceptibility

of three peanut cultivars to leafspot diseases. The three cultivars,

Early Bunch, Florunner, and Dixie Runner differed in yield and maturity.

Early Bunch, the highest yielding cultivar matures earliest. Flo-

runner and Dixie Runner are moderately high yielding and low yield-

ing, respectively, with Dixie Runner maturing latest of the three

cultivars.

Each cultivar was subjected to two treatments, one in which the

reproductive efficiency was allowed to remain as normal and the second

in which initial flowering was restricted. The second treatment was

to reduce the yield and did so significantly in Early Bunch. Florunner

and Dixie Runner, however, showed slight yield reduction because of

bud removal. The two higher yielding cultivars showed significant

reductions in disease measurements when flower buds were removed,

whereas Dixie Runner had about the same amount of disease in plots

with either controlled or uncontrolled reproductive efficiency.

Leaf abscision or plant maturity was delayed by removing the

initial reproductive organs. The differences between reproductive

treatments increased as pathogen numbers increased. Lesion numbers

increased for all treatments and from indications based on Early Bunch

eventually reach a maximum for all treatments.

42









43
In addition to the reproductive treatments the experiment was

grown in two blocks, one of which received leafspot control. The

results of restricted and nonrestricted flowering followed the same

trends in both blocks. Early Bunch showed the greatest effect from

controlling reproductive efficiency and leafspot diseases. Dixie

Runner had higher yields in the unsprayed plots.

The results from this experiment indicate that reducing the

initial fruiting of peanut plants will reduce the amount of leafspot

occurring and delay plant maturity. They also indicate that cultivars

respond differently to flower removal relative to yield and to leaf-

spot control.

Further study could show how long fruiting must be delayed to

get a reduction in disease. Also, a study of this type could indicate

at what point higher yielding cultivars begin to lose yield. Addition-

ally the possibility of using photoperiod responses to develop lines

which flower later and thereby reducing leafspot diseases, may be worth

examining.
















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Elston, J., C. Harkness, and D. McDonald. 1976. The effects of
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BIOGRAPHICAL SKETCH

Ivan L. Miller was born in Washington, Iowa, on April 6, 1954,

to Floyd and Ruth Miller. At the age of five he moved to Florida with

his family where he attended Blountstown Elementary and Wewahitchka

and Blountstown High Schools, graduating from the latter in 1972.

After attending Gulf Coast Community College in Panama City, Florida,

for one year he enrolled at the University of Florida. In June 1975,

he received his Bachelor of Science degree in agronomy and enrolled in

Iowa State University. He married the former Fonda Joy Shaw in August

1977. After receiving his Master of Science degree in 1978 from Iowa

State University in plant breeding he returned to the University of

Florida. Since his return he has pursued his Ph.D. degree in agronomy

(plant breeding) which he will receive in June 1981. He is a member

of the American Society of Agronomy, Crop Science Society of America,

and Gamma Sigma Delta honor society.








I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.



A./ Norden, Chairman
P rfessor of Agronomy


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.




Richard D. Berger I
Professor of Plant Pathology


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.




Daniel W. Gorbet
Associate Professor of Agronomy


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.


'.

David A. Knauft
Assistant Professor of Agronomy










I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.



Ramon Littell
Associate Professor of Statistics


This dissertation was submitted to the Graduate Faculty of the College
of Agriculture and to the Graduate Council, and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.

June 1981


Dea?4 College of Agric Lture


Dean, Graduate School







































UNIVERSITY OF FLORIDA
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