Common cocklebur (Xanthium strumarium L.) interference with peanut (Arachis hypogaea L.)

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Title:
Common cocklebur (Xanthium strumarium L.) interference with peanut (Arachis hypogaea L.)
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xi, 87 leaves : ill. ; 29 cm.
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Fiebig, William W., 1948-
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Thesis (Ph. D.)--University of Florida, 1990.
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Includes bibliographical references (leaves 93-96).
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by William W. Fiebig.
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Typescript.
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Vita.

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COMMON COCKLEBUR (Xanthium strumarium L.) INTERFERENCE
WITH PEANUT (Arachis hypoqaea L.)











By

WILLIAM W. FIEBIG


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





UNIVERSITY OF FLORIDA


1990


















This work is dedicated to my dear wife
and children whom the Lord gave me in Africa
and so shall I try to repay Him with
my dedicated work in Africa when we return.













ACKNOWLEDGEMENTS


I wish to extend my sincere appreciation to Dr. D. A. Knauft,

Chairman, and Dr. D. G. Shilling, Cochair, for their direction and

support during this research project. Their guidance and suggestions

were pivotal to the completion of this project. Their interest and

enthusiasm were continual sources of encouragement.

I also thank Drs K. L. Buhr, C. K. Hiebsch, and J. H. Conrad for

serving on my committee. I wish to thank H. Wood for his continual

assistance in providing the necessary inputs for disease and insect

control in the field trials.

Most of all, I want to thank my wife and children for their love,

patience, and support through some very difficult times.














TABLE OF CONTENTS


ACKNOWLEDGEMENTS...................................

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

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

ABSTRACT......................................... ...

CHAPTERS

I INTRODUCTION.................................


II THE RELATIVE COMPETITIVENESS OF PEANUT
(Arachis hypoqaea L.) AND MECHANISMS OF
INTERFERENCE BY COMMON COCKLEBUR (Xanthium
strumarium L.).................................

Introduction................................
Materials and Methods .........................
Results and Discussion.........................


III RESPONSE OF FOUR PEANUT GENOTYPES TO
INTERFERENCE FROM COMMON COCKLEBUR.............

Introduction................................
Materials and Methods ..........................
Results and Discussion ........................


IV SUMMARY AND CONCLUSIONS .......................

APPENDIX

A Data from Density Studies..................

B Data from Replacement Studies..............

C Field data at 45 DAP.........................


page
...... iii

...... vi

...... viii

...... x


......43

..... 43
..... 46
..... 49


............ 73



............ 77

............ 79

............ 8 1







D Field data at 90 DAP.................................... 85

E Field data at 135 DAP .................................... 89

LITERATURE CITED................................................ 93

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
















































v













LIST OF TABLES


TABLE

2.1 Average shoot dry weight (gm 180 cm2 -1)
of peanut and common cocklebur grown at
different plant density levels.................

2.2 Average shoot dry weight (gm plant"1)
of peanut and common cocklebur grown at
different plant density levels..................

2.3 Influence of fertilization levels
[ml 10X Hoaglands (-N) wk'1] on shoot dry
weight of peanut and cocklebur..................


2.4 The additive effect of common cocklebur
interference in peanut....................

2.5 Average shoot dry weight (gm pot"1) of
peanut and common cocklebur when grown in
monoculture and in mixture................

2.6 Average shoot dry weight on a per plant
basis of peanut and common cocklebur
when grown in monoculture and in mixture..

2.7 Relative yield (RY) and relative yield
total (RYT) of shoot dry weight of peanut
and common cocklebur when grown in
monoculture and in mixture................

2.8 The influence of interference on relative
crowding coefficients (RCC) of peanut and
common cocklebur shoot dry weight.........

2.9 The effects of shoot (SC) and/or root (RC)
competition on shoot dry weight of peanut
when grown in association with common
cocklebur.................................


................... 24



................... 26



................... 29




................... 30



................... 37




................... 39


2.10 The effects of
competition on
cocklebur when


shoot (SC) and/or root (RC)
shoot dry weight of common
grown in association with


peanut .....................................


............ 16


... ... ... ... .. 40








3.1 Shoot dry matter yield as affected by
interference from common cocklebur 45 DAP
in four genotypes of peanut................................. 50

3.2 Shoot dry matter yield as affected by
interference from common cocklebur 90 DAP
in four genotypes of peanut............................... 54

3.3 Shoot dry weight of common cocklebur (CB)
when grown with four genotypes of peanut during
two growing seasons..................................... 57


3.4 Shoot dry matter yield as affected by
interference from common cocklebur 135 DAP
in four genotypes of peanut................

3.5 Pod dry matter yield as affected by
interference by common cocklebur 90 DAP
in four genotypes of peanut.................

3.6 Pod dry matter yield as affected by
interference by common cocklebur 135 DAP
in four genotypes of peanut.................


................. 59



................. 65



................. 68













LIST OF FIGURES


page


Average shoot dry weight (gm 180 cm2 1)
of peanut and common cocklebur grown
at different density levels........................


Average shoot dry weight (gm plant"')
of peanut and common cocklebur grown at
different plant density levels..............

Average number of nodes and leaf
area (cm2) of peanut and common cocklebur
grown at different density levels...........

Leaf and stem dry weight (gm plant') of
peanut and common cocklebur grown at
different density levels.....................

Average shoot dry weight (gm pot"')
of peanut and common cocklebur grown
in monoculture and mixture...................

Relative yield (RY) and relative yield
total (RYT) of shoot dry weight of peanut
genotype NC 7 and common cocklebur grown
in monoculture and in mixtures..............


Relative yield
total (RYT) of
genotype 8143B
in monoculture


.......... 18



.......... 20


.......... 21



.......... 27




.......... 31


(RY) and relative yield
shoot dry weight of peanut
and common cocklebur grown
and in mixtures.........................


Relative yield (RY) and relative yield
total (RYT) of leaf and stem dry weight
of peanut genotype NC 7 and common
cocklebur grown in monoculture and in
mixture............................................. 33

Relative yield (RY) and relative yield
total (RYT) of leaf and stem dry weight
of peanut genotype 8143B and common
cocklebur grown in monoculture and in
mixture.............................................. .. 34


viii


FIGURE

2.1


... 15


2.3



2.4



2.5


2.6







Shoot dry weight
with and without
cocklebur in the


at 45 DAP (1987) of peanut
competition from common
field.......................


Shoot dry weight at 45 DAP (1989) of
peanut with and without competition from
common cocklebur in the field...............

Growth and development of common cocklebur,
with and without peanut, in the field
(shoot dry weight) during the 1987 and
1989 growing seasons ........................


Shoot dry weight
with and without
cocklebur in the

Shoot dry weight
with and without
cocklebur in the


Shoot dry weight at 135
peanut with and without
common cocklebur in the

Shoot dry weight at 135
peanut with and without
common cocklebur in the


at 90 DAP (1987) of peanut
competition from common
field.......................

at 90 DAP (1989) of peanut
competition from common
field.......................


DAP (1987) of
competition from
field................

DAP (1989) of
competition from
field................


.......... 56



.......... 60



.......... 61



.......... 62


Pod dry weight at 90 DAP (1987) of peanut
with and without competition from
common cocklebur in the field.......................... 66

Pod dry weight at 90 DAP (1989) of peanut
with and without competition from
common cocklebur in the field.......................... 67

Pod dry weight at 135 DAP (1987) of peanut
with and without competition from
common cocklebur in the field......................... 69

Pod dry weight at 135 DAP (1989) of peanut
with and without competition from
common cocklebur in the field.......................... 71


3.2


3.3


3.4


.......... 52




.......... 53


3.5


3.6



3.7


3.8


3.10


3.11













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


COMMON COCKLEBUR (Xanthium strumarium L.) INTERFERENCE
WITH PEANUT (Arachis hypoqaea L.)

By

WILLIAM W. FIEBIG

May, 1990

Chair: Dr. D. A. Knauft
Cochair: Dr. D. G. Shilling
Major Department: Agronomy

Greenhouse studies were conducted to determine the effects of

interference by common cocklebur on the relative yields of two genotypes

of peanut, NC 7 and 8143B. Density studies showed that intraspecific

competition occurred with four plants per pot. Replacement series

experiments showed peanut genotype NC 7 contributed 50% less relative

yield (RY) in shoot dry weight than common cocklebur at a 2:2 mixture

ratio, while peanut genotype 8143B and common cocklebur contributed

equally at a 2:2 ratio. Partitioning studies were conducted to

determine the mechanism of interference of common cocklebur on peanut.

NC 7 showed less percent inhibition (PI) in shoot dry weight when

competing only above-ground with common cocklebur versus only below-

ground competition with common cocklebur. Genotype 8143B had little

difference in PI of shoot dry weight yield under either above- or below-

ground competition with common cocklebur. Full competition (above- and







below-ground) resulted in significant shoot dry weight yield reductions

in NC 7, but not in 8143B.

Field experiments were conducted to determine the effects of

interference by common cocklebur on four peanut genotypes. NC 7

produced the greatest pod dry weight in weed-free plots in 1987 and

1989, yet suffered the greatest yield reduction under interference from

common cocklebur in both years. Genotype 8143B was less susceptible to

the influence of interference from common cocklebur and had the highest

pod yield when competiting with common cocklebur. Genotypes BL-8 and

BL-10 produced the greatest amount of vegetative dry matter, and pod

yield of these lines was greater than NC 7 when competing with common

cocklebur.












CHAPTER I

INTRODUCTION


Yield loss from weed competition in food crops is a common problem

of farmers throughout the world, especially in the less developed

tropical and semitropical regions of the world (Holm, 1969). Production

practices in developed countries utilize cultural, chemical, and

mechanical methods for weed control. In the less developed countries

where small scale subsistence farming systems predominate, weed control

is a manual and time-consuming task. Time constraints on the allocation

of tasks within a household often result in weed infestations of fields,

and weeding is not done when needed to avoid yield reductions. If it is

possible to develop cultivars with improved weed resistance, food

production increases could potentially be achieved.

A considerable amount of research has been reported on the amount

of time a crop must be maintained weed free to avoid yield reductions

(Walker et al., 1989). According to Hauser et al. (1975), if peanuts

(Arachis hvpooaea L.) remain free of Florida beggarweed [Desmodium

tortuosum (Sw.) DC.] or sicklepod (Cassia obtusifolia L.) for four weeks

after crop emergence, yields were not reduced. Chamblee et al., (1982)

reported that interference by broadleaf signalgrass [Brachiaria

platyphylla (Griseb.) Nash] significantly reduced peanut yields at a

weed density of less than 4 plants 10 m'1 of row. According to Hill and







2

Santelmann (1969), pigweed (Amaranthus hybridus L.) and large crabgrass

[Digitaria sanquinalis (L.) Scop.] interference for four or more weeks

significantly reduced peanut yields. York and Coble (1977) reported

that, in peanut, fall panicum (Panicum dichotomiflorum Michx.)

interference for even two weeks after crop emergence resulted in a 28%

yield reduction, that fall panicum emerging as late as eight weeks after

crop emergence reduced seed yields 15%, and that as few as 0.2 fall

panicum plants m"' of row reduced seed yields 25%.

Differences in the ability to compete with weeds vary among crop

species. Hamdoun (1977) reported 62-80% yield reductions due to weeds

in peanut. Yield losses due to weeds in sorghum (Sorqhum bicolor L.)

were less than 45% in a study by Kock et al.(1982). Genetic variation

in competitive ability has also been reported within crop species.

McWhorter and Barrentine (1975) found that 'Bragg' soybeans [Glycine max

(L.) Merr.] had yield reductions of 7% compared with 20% for other

soybean cultivars when mechanical weed management was compared with the

use of herbicides. Winter wheat (Triticum aestivum L.) yield reductions

from 9 to 21% at one location and from 20 to 41% at another location,

depending on the cultivar, were reported by Challaiah et al. (1986).

These genetic differences within a species for competitive ability

against weeds indicate that plant breeders could potentially produce

cultivars with enhanced weed resistance. However, little work has been

done on the development of techniques to identify crop varieties or

breeding lines that resist damage from weeds.

The crop-weed interaction is species specific and the development

of techniques for selection of weed-resistant cultivars will vary with









and among crop and weed species. Peanut and common cocklebur (Xanthium

strumarium L.) will be used in this study to develop techniques for the

identification of weed-resistant varieties or breeding lines and to

assess the mechanisms of the resistance. Relative to other crop plants,

the low-growing vegetative characteristics of peanut make it

particularly susceptible to shading by broadleaf weeds, which is often

the main component of above-ground competition. Wilson et al., (1980)

found that a field bean cultivar with greater weed suppression ability

shaded the ground quicker than a cultivar which exhibited less

competitive ability. In assessing differences among crop species,

William and Warren (1975) indicated that the faster growing, leafier

species such as green beans or cucumbers (Cucumis sativus) were more

competitive than slower growing plants such as okra (Hibiscus

esculentus) or plants with limited shading ability such as garlic.

Common cocklebur is a fast-growing, broadleaf weed that competes

vigorously above and below the ground (Davis et al., 1967).

Previous studies have generally been descriptive with little work

reported on the development of procedures to identify crop cultivars or

breeding lines that are more competitive with weeds. This research

examined the specific system of common cocklebur competition with the

peanut crop to determine which characteristics of the peanut plant are

most affected by weed competition. Genetic differences among peanut

lines were assessed for competitive ability and the mechanisms of weed

interference were examined in greenhouse studies. Peanut genotypes with

a diverse genetic background (e.g., growth habit, partitioning rate,

time to maturity, etc.) were tested in the field to verify if the







4
competitive traits of peanut identified through a series of greenhouse

studies correlated with peanut yields.













CHAPTER II

THE RELATIVE COMPETITIVENESS
OF PEANUT (Arachis hypoqaea L.) AND MECHANISMS
OF INTERFERENCE BY COMMON COCKLEBUR (Xanthium strumarium L.)

Introduction

Competition is a complex phenomenon that is governed by various

biological (e.g., growth habit, time to maturity, etc.), environmental

(e.g., light intensity over growing season, amount and/or distribution

of rainfall, etc.), and proximity factors (Radosevich, 1987). The

factors of proximity include plant density, species proportion, and

spatial arrangement among individuals. Mechanisms of interference which

are influenced by these factors are important in understanding the

relative competitiveness of one plant with another.

The stress created by the proximity of neighboring plants may be

absorbed in an increased mortality risk for whole plants or their parts,

reduced reproductive output, reduced growth rate, delayed maturity

and/or reduced reproduction (Harper, 1977). Rice (1974) defined

competition as the removal of some factor from the environment that is

needed by other plants sharing the same space, and allelopathy as the

addition of a chemical compound to the environment by a plant that has a

harmful effect on another plant. Interference caused by a weed in a

crop may result in yield losses through competition and/or allelopathy

(Dekker and Meggitt, 1983). Muller (1969) suggested that the term

interference should include both competition and allelopathy.







6

Various weed and crop associations have been studied and differing

levels of competitiveness have been reported among and within many plant

species (Zimdahl, 1980; Stewart, 1981). Peanut has a relatively low-

growing vegetative characteristic compared with other crop plants which

makes it particularly susceptible to weed interference (Hamdoun, 1977;

Chamblee et al., 1982).

Plant density (PD) or the number of plants per unit area is

important to competition studies because of the relationship between

plant yield, number of individuals and resources available in the system

(Radosevich, 1987). Plant growth response is a function of the

available resources above and below the ground and is a measure of

intraspecific competition. Competition for these resources (e.g.,

light, water, and nutrients) influences plant growth, which responds in

a plastic manner to the amount of available resources. Therefore, when

studying competition, density studies must be conducted to determine the

number of plants per unit area necessary to assure that interference

between the weed and crop species will occur.

When interspecific competition is studied, proportion of plant

species per unit area becomes another factor to consider (Radosevich,

1987). An analysis of the nature of interaction between different

plants (Hall, 1974a, 1974b), such as crop and weed, has demonstrated the

value of the replacement series experiment, based on experimental

procedures developed by de Wit (1960). In this type of study, the two

plant species (e.g., crop and the weed) are grown at different

proportions and their growth in mixture is compared with that in

monoculture.









Another method which has been used to evaluate plant competition

is an experimental design where it is possible to partition the growth

habit of the plant species being evaluated to study three different

mechanisms of interference (MI): above ground (competition for light and

space); below ground (competition for nutrients and moisture) and

allelopathy (chemical interaction) (Hall, 1974a; Snaydon, 1979).

A limitation of many studies of mixed stands is that yield is

frequently the only plant characteristic assessed. Jolliffe et al.

(1984) suggested that observations of other plant characteristics (leaf

area, dry matter partitioning, etc.) might help explain the

physiological basis of yield variations in monocultures and mixtures.

Spitters (1983) concluded that interplant competition is better measured

by biomass than by the yield of any plant part, because dry matter

distribution within the plant varies with competitive stress.

The objective of this research was to identify characteristics of

peanut which are affected by interference from common cocklebur. If

differences are found among peanut genotypes in the degree with which

certain characteristics are affected, these criteria could be used to

rank peanut lines from the most competitive (least affected by common

cocklebur) to the least competitive lines.

Greenhouse experiments were conducted to study the effects of

interference by common cocklebur on two peanut genotypes. Additive

studies were utilized to study the effect of increasing plant densities

of common cocklebur on peanut growth. Replacement series experiments

were utilized to determine the relative competitiveness of the two

peanut genotypes and common cocklebur. Partitioning studies were








conducted to study the mechanism of interference (above- and/or below-

ground competition) of both the crop and the weed.


Materials and Methods


Methods Common to all Experiments

All greenhouse studies were conducted in a temperature-controlled

greenhouse maintained at 20 OC to 30 OC. Water was applied once or

twice daily as required to avoid stress. The potting medium used in all

experiments was a mixture of 50% Arredondo fine sand (Grossarenic

Paleudult) and 50% vermiculite.' The peanut cultivar NC 7 and Florida

breeding line 8143B2 and commercially obtained common cocklebur seed3

were planted in monoculture and various mixtures according to

experimental design. NC 7 is a Virginia market-type peanut with an

upright (bunch) growth habit. The second peanut genotype, 8143B, is a

runner market-type peanut with a spreading (runner) growth habit. All

experiments were fertilized with a modified (minus nitrogen) 10X

Hoaglands solution at a rate of 50 ml weekI' (Hoagland and Arnon, 1950).

This soil mixture, fertilization level, and moisture regime were used in

all of the following experiments. Pots with NC 7 were planted as border

rows around all reported greenhouse experiments.




1 W. R. Grace & Co., Cambridge, Mass., 02140
2 Seed source: Univ. Florida Peanut Breeding Program

3 Seed purchased from Azlin Seed Co., LeLand, Miss.









Density Studies

A density study was conducted for both peanut genotypes and common

cocklebur to determine the density of each species which was independent

of above ground dry matter production (carrying capacity). Results of

this study were used to establish the appropriate density (carrying

capacity of the system to assure interference would occur) for

interference studies. Peanut genotype NC 7 and 8143B and common

cocklebur were planted in monoculture plant populations of 1, 2, 4, and

8 plants per 180 cm2 using 2-L plastic pots. These experiments were

conducted two times utilizing a randomized complete block design (RCBD)

with four replications.

Plants were harvested 45 days after planting (DAP) by clipping the

plants at the soil surface. Number of nodes, total leaf area (cm2), dry

matter partitioning to leaf and stem (gm), and shoot dry weight (gm) per

180 cm2 were determined. Yield per plant (YPP) was determined by

dividing the total shoot dry weight (gm per 180 cm2) by the total number

of plants.

Analysis of variance was used to determine the effects of

experiment, replication, genotype, and plant density and their

interactions on per unit area and per plant growth responses.

Regression analysis was utilized to determine the relationship between

increasing plant density and shoot dry weight for each peanut genotype

and common cocklebur. Species differences were compared within each

density by the LSD test at the 0.05 significance level.








Fertility Studies

A fertility study was conducted to determine the appropriate

amounts of fertilizer needed to allow the plants to grow without

competition for nutrients and to maximize biomass production. Hoaglands

solution (10X) without nitrogen was applied weekly at 0, 25, 50, 75, and

100 ml per 2-L plastic pot to a monoculture of four plants per 180 cm2

of NC 7, 8143B, and common cocklebur in a RCBD with four replications.

The fertility experiment was conducted two times. Number of nodes, leaf

area (cm2), dry matter partitioning to leaf and stem (gm), and shoot dry

weight (gm) per pot (180 cm2) were measured 45 DAP.


Additive Studies

This experiment was conducted twice to determine the additive

effect of competition by common cocklebur on peanut. These studies were

conducted as RCBD with four replications. A plant density of four

peanut plants per 180 cm2 were kept constant while 0, 1, 2, 3, and 4
common cocklebur plants per 180 cm2 were added to peanut in 2-L pots.

Peanut seeds were sown around the edge of the pot and common cocklebur

seeds were distributed between the peanut seed. In this design, peanuts

were regarded as the indicator species and varying populations of common

cocklebur were used to determine the additive effect of weed density

(WD) on the growth and development of each peanut genotype. Pots were

watered and fertilized as in previous studies. All plants were

harvested 45 DAP and the previously described data were obtained.









Replacement Studies

Replacement series experiments at a total density of four plants

per pot were performed in 2-L plastic pots (surface area of 180 cm2) at

five proportions of peanut to cocklebur: monoculture of peanut (4:0),

3:1, 2:2, 1:3, and monoculture of common cocklebur (0:4). The five

treatments corresponded to 100, 75, 50, 25, and 0 percent peanut

composition, on a per plant basis, within the overall mixture. Aerial

partitions were established using circular columns 15 cm in diameter

made of hardware cloth. Plants were, therefore, restricted to similar

aerial space and prevented from mixing with plants in neighboring pots.

The complete replacement series experiment was conducted three times in

a RCBD with four replications. Excess seed were planted and seedlings

were thinned to desired densities 2-3 days after emergence.

Fertilization with 50 ml of 10X Hoaglands (-N) as reported previously

was applied weekly to reduce competition for nutrients.

Plants were harvested 45 DAP and number of nodes, leaf area (cm2),

dry matter partitioning to leaf and stem (gm), and shoot dry weight (gm)

per pot (180 cm2) were recorded for both peanut genotypes and common

cocklebur to measure the response of each peanut genotype to the

treatments.

Relative yield (RY) and relative yield total (RYT) for each peanut

genotype and common cocklebur were calculated from the various growth

parameters at each mixture ratio according to Harper (1977). The RY of

any given plant species is the yield of the species in mixture divided

by its yield in monoculture. RYT is the total RY of both species in the

system calculated at each of the five proportions.









Relative crowding coefficients (RCC) were calculated at each

interspecific mixture ratio according to de Wit (1960). The RCC of

species A with respect to B is equal to the (mean yield per plant of A

in mixture)(mean yield per plant of B in mixture)-' divided by the (mean

yield per plant of A in monoculture)(mean yield per plant of B in

monoculture)-.

The data were subjected to analysis of variance to determine

contributions of the main effects (experiment, replication, genotype,

and mixture ratio) and their interactions. Where three-way interactions

between experiment, genotype, and mixture ratio were non-significant

(P>0.05), the data from each experiment were combined. Differences

between species within each mixture ratio were determined using the LSD

test at the 0.05 level of significance. Regression analysis was

utilized to establish the relationship between each peanut genotype and

common cocklebur shoot dry matter production as affected by changes in

species ratio. Regression analysis was performed to determine the

relationship between RY and species ratio. Diallel diagrams (Harper,

1977) were constructed to graphically illustrate the interaction of each

peanut genotype with common cocklebur.


Partitioning Studies

To evaluate the relative extent to which above- and/or below-

ground interference influenced the overall interaction between each

peanut genotype and common cocklebur, three different mechanisms of

interference were studied using a partitioning technique: above- and/or

below-ground competition (light, nutrients, and moisture) and









allelopathy (chemical interaction). Each genotype was grown in a

greenhouse in wooden cases with a surface area of 30 x 30 cm which were

divided into 15 x 30 x 15 cm soil compartments. Aerial compartments

were rectangular columns 15 x 30 x 60 cm made of hardware cloth such

that plant species in each experimental unit were restricted to similar

aerial space and prevented from mixing with plants in neighboring

experimental units.

Different arrangements of the above- and below-ground partitions

and of plant species gave four forms of competition: no competition

(NC); root competition only (RC); shoot competition only (SC); and both

root and shoot competition (FC). Four plants of each species were used

in each competition treatment. In the NC treatment, each species grew

alone in the specified space. In the FC treatment, both species grew

together above and below the ground in the specified space. In the SC

treatment, both species grew together in the above-ground space, but

were separated into the specified below-ground compartments. In the RC

treatment, each species grew in separate aerial compartments, but grew

in the same below-ground compartment. At 45 DAP, plants were harvested

and separated by species, dissected, and oven dried as described

previously to measure the different growth parameters in response to the

treatments.

Partitioning experiments were conducted twice and arranged in a

RCBD with four replications per experiment. The data were subjected to

analysis of variance to determine the significance (P<0.05) of the main

effects (experiment, genotype, and type of competition) and interactions

on the species growth parameters and percent inhibition (PI). Where








two-way interactions involving the separate experiments were non-

significant (P>0.05) the data from the experiments were combined. The

LSD test (P<0.05) was used to compare mean values for each competition

treatment.


Results and Discussion


Density Studies

Yield-density relationships are generally linear in monocultures

at very low plant densities (PD) because of the lack of intraspecific

interference (Jolliffe et al., 1984). At higher densities, the plants

compete intraspecifically and the total yield of the stand is restricted

by the total availability of resources in the system. Mean yield of the

system is, therefore, a function of density in monocultures and stand

yield may become constant as PD in the system increases. In this study,

increases in PD resulted in a constant increase in shoot dry weight per

180 cm2 for both peanut genotypes (Fig. 2.1). Total shoot dry weight of

8143B increased in a near linear fashion, while NC 7 had a much higher

negative quadratic component in the regression equation above four

plants per 180 cm2. Average shoot dry weights showed significant

genetic differences in yield performance of NC 7 and 8143B when grown at

four plant densities (Table 2.1). Common cocklebur yields increased up

to four plants per 180 cm2. Above this PD, severe elongation and

lodging caused a reduction in shoot dry weight per 180 cm2 for common

cocklebur.







15









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t-->-- \ > C 0
0 l og
) D <, O
c ', \ 0 o





oo r L n1
CD



FC) 0<





8 II "" L1 ,--4
f--'l OCD "<









CoU) 4qxieM








Table 2.1. Average shoot dry weight (gm 180 cm2 -1) of peanut and
common cocklebur (CB) grown at different plant density levels.


# Plants/180 cm2 a

Genotype 1 2 4 8


--------------- gm 80 cm2 --------------

NC 7 5.2 8.0 13.7 18.0

8143B 2.3 2.6 4.4 8.0

CB 10.4 12.6 20.0 14.6


LSDo.05 for comparison within columns = 2.6


a Means were calculated from eight replications of two experiments.









As plant density in the system increased, intraspecific

interference increased and the shoot dry matter accumulation per plant

decreased as a function of PD (Fig. 2.2). Common cocklebur suffered a

greater shoot dry weight reduction than peanut with increasing PD.

Shoot dry weight of each peanut genotype was affected in a similar

manner with increasing PD, differing only in the degree of their genetic

differences in growth habit. The number of nodes, leaf area, and dry

matter production per plant for both peanut genotypes and common

cocklebur decreased above a plant density of one plant per 180 cm2

indicating that intraspecific interference was occurring (Table 2.2;

Fig. 2.3, 2.4).

An increase in density for each peanut genotype and common

cocklebur grown in monoculture, resulted in diminishing returns for all

growth parameters measured on a per plant basis. This indicates that

intraspecific competition was occurring and, therefore, each peanut

genotype and common cocklebur was at or approaching density independent

yield. This density study was conducted to determine the carrying

capacity of the system for both plant species. Common cocklebur

achieved the carrying capacity at four plants per 180 cm2. Even though

both peanut genotypes exhibited an increase in total yield per 180 cm2

as PD increased, there was a decrease in shoot dry weight yield per

plant which indicated that intraspecific interference was occurring.

Because shoot dry weight per 180 cm2 continued to increase (although at

a reduced rate), yield was not totally independent of density even at

the highest PD. However, a density of four plants per 180 cm2 was

chosen for the replacement series and partitioning experiments because




















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Table 2.2. Average shoot dry weight (gm plant"') of peanut and common
cocklebur (CB) grown at different plant density levels.

# plants/180 cm2 a

Genotype 1 2 4 8


--------------- gm plant- --------------

NC 7 5.2 4.0 3.4 2.3

8143B 2.3 1.3 1.1 1.0

CB 10.4 6.3 5.0 1.8


LSDo.os for comparison within columns = 1.2
a Means were calculated from eight replications of two experiments.












Density Study
Average No. of Nodes per Plant

o NC 7 A 8143B 0 Cocklebur


\






-----------A ------------------------


0--------------
----
~ I i _
'" ^--


S 2 3 4 5 6
Plant Density per 180 sq. cm.


Density Study
Rveroge Leaf Rrea per Plant


7 8


0 1 2 3 4 5 6 7 8
Plant Density per 180 sq. cm.


Figure 2.3 Average number of nodes and leaf area
(cm2) of peanut and common cocklebur
grown at different density levels.








21



Density Study
Rverage Leaf Dry Weight (gm/plant)
5
o NC 7 A 81438 o Cocklebur

C
4--

a.





_j/ ------------

0 2 3 4 5 6 7






Plant Density per 180 sq. cm.



Density Study
Rveroge Stem Dry Weight (gm/plont)


o "jC 7 a 8143B 0 Cocklebur
7-

O
C \
c4-






3
\\
-- --- -A------------------------------------












0 2 3 4 5 6 7 8
7 -




0 .










Plant Density per 180 sq. cm.
o 2






Plant Density per 180 sq. cm.


Figure 2.4 Leaf and stem dry weight (gm plant"')
of peanut and common cocklebur grown
at different density levels.









unacceptable elongation and lodging occurred for plant densities of

eight plants per 180 cm2 and per plant dry weight yields were not

indicative of normal plant growth. The density study demonstrated the

genetic differences in plant growth habit between the two peanut

genotypes grown under greenhouse conditions (Fig. 2.1, 2.2).


Fertility Studies

No significant differences in shoot dry weight were observed in

the response to the levels of fertilizer added to either peanut genotype

or common cocklebur according to the analysis of variance (P>0.05).

Similar trends were seen for the number of nodes, leaf area, leaf and

stem dry weight (data not shown). Significant differences were observed

in the shoot dry weights between the two peanut genotypes and common

cocklebur (Table 2.3). It was assumed that the soil used in all the

greenhouse studies, which came from a field with a previous history of

peanut production, had a sufficient fertility level to result in no

further response to added nutrients. To avoid possible nutrient stress,

50 ml of 10X Hoaglands solution (-N) was added weekly to all

experiments.


Additive Studies

Increasing weed density in both peanut genotypes had little if any

impact on peanut growth during the six week study. Significant

differences in shoot dry weight showed the genetic differences in growth

habit between the two peanut genotypes in this study (Table 2.4). Shoot

dry weight of both genotypes was not significantly affected by the









Table 2.3. Influence of fertilization levels [ml Hoaglands
on shoot dry weight of peanut and cocklebur8.


NC 7 8143B Cocklebur



Fert. Level --------------- gm pot ---------------

0 ml 17.9 8.2 1.5

25 ml 17.8 8.9 1.4

50 ml 20.7 8.3 1.4

75 ml 17.9 9.2 2.0

100 ml 20.4 9.1 2.2


LSDo Q5 for row comparisons between
level = 2.6


genotypes within fertility


a Means were calculated from eight replications of two experiments.


(-N) wk-I]







24

Table 2.4. The additive effect of common cocklebur (CB) interference in
peanut.


Peanut : CB Ratio

Genotype 4:0 4:1 4:2 4:3 4:4


--------------------- gm pot' --------------------

NC 7 12.7 13.2 11.8 11.8 12.2

8143B 5.8 5.3 5.2 5.3 5.8

LSDo.o5 for column comparisons within mixture ratio = 3.0

CB(w/NC 7) --- 1.2 1.0 2.4 1.7

CB(w/8143B) --- 0.4 0.8 1.0 1.1

LSDo.o5 for column comparison within mixture ratio = 0.8



a Means were calculated from eight replications of two experiments.









addition of 1, 2, 3, or 4 common cocklebur plants grown in a mixture

with four peanut plants according to the analysis of variance (P>0.05).

These data indicated that when common cocklebur is grown with four

peanut plants in 2-L pots, higher densities of common cocklebur or

longer periods of interspecific competition are required. Spatial

arrangements may also have affected the results. Peanut seeds were

planted around the edge of the pot and the common cocklebur seeds were

randomly placed between the peanut. Plants were not restricted to

aerial compartments in this study and the peanut plants may have been

able to spread sufficiently to avoid competition for light and/or space.



Replacement Studies

Effects of interference by common cocklebur on peanut shoot growth

and development can be seen by the total shoot dry weight of peanut and

common cocklebur in the system (Table 2.5). Both peanut genotypes and

common cocklebur suffered shoot dry weight yield reductions as the

percentage of the other species increased in the system. NC 7 suffered

a greater yield reduction than 8143B at all proportions in mixture with

common cocklebur which is demonstrated by the linear regression

equations (Fig. 2.5). The slope of the regression line for shoot dry

weight reduction for NC 7 is more than twice that of 8143B.

Differences in shoot dry weight response of the monoculture yields

of the two peanut genotypes and common cocklebur illustrate the

different growth rates of each species (Table 2.5; Fig. 2.5). NC 7 has

a more rapid growth rate than 8143B, which would suggest a better-

developed root system and perhaps a greater capacity for nitrogen









Table 2.5 Average shoot dry weight (gm pot"') of peanut and common
cocklebur (CB) when grown in monoculture and in mixturea.


peanut : cocklebur ratio

Genotype 4:0 3:1 2:2 1:3 0:4


---------------------- gm pot1 -------------------

NC 7 12.1 8.8 6.1 3.5 ---

8143B 4.8 3.9 2.8 1.7 ---

CB(w/NC 7) --- 0.8 1.4 1.6 1.4

CB(w/8143B) --- 0.6 0.9 1.1 1.4



LSDo.05 column comparisons within mixture ratio = 1.3

a Means were calculated from 12 replications of three experiments.






























































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CI
C,




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0)


4






04
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C



0 (


00
4O






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Ok

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28

fixation at an early growth stage. Significant differences in shoot dry

weight between the two peanut genotypes were observed at all proportions

on a per plant basis also (Table 2.6). According to the analysis of

variance, there were no significant differences (P>0.05) in either

peanut genotype at all mixture proportions on a per plant basis (Table

2.6).

Due to large differences in biomass of the two species, data on a

relative basis was used for a direct comparison of their

competitiveness. Relative yield (RY) data demonstrated the greater

competitiveness of common cocklebur against NC 7 compared with 8143B

(Table 2.7). The RY of any given plant species is the yield of the

species in mixture divided by its yield in monoculture. At the 2:2

species mixture ratio, common cocklebur shoot dry weight accounted for

the majority of the total dry matter production for both species (RYT)

when grown in association with NC 7 (Fig. 2.6, 2.8). At this mixture

ratio, RY values for common cocklebur shoot dry weight were

approximately twice that of the corresponding RY values of NC 7 (Fig.

2.6). In contrast, the RY contribution to the system of 8143B and

common cocklebur at a 2:2 mixture ratio based on shoot dry weight

werenearly equal (Fig. 2.7). Genetic differences in the competitive

ability of 8143B compared with NC 7 are suggested because at the 2:2

species mixture ratio, 8143B contributed nearly equal in shoot dry

weight, leaf and stem dry weight to the RYT of the system (Fig. 2.7,

2.9). This indicates that 8143B and common cocklebur were equally

competitive at a 2:2 mixture ratio.








Table 2.6 Shoot dry weight on a per plant basis of peanut and common
cocklebur (CB) when grown in monoculture and in mixture.


peanut : cocklebur ratio

Genotype 4:0 3:1 2:2 1:3 0:4


---------------------- gm plant ---------------------

NC 7 3.0 3.0 3.0 3.5

8143B 1.2 1.3 1.4 1.7

CB(w/NC 7) --- 0.8 0.7 0.6 0.4

CB(w/8143B) --- 0.6 0.5 0.3 0.4



LSDoQ5 for column comparisons of peanut genotypes within mixture
ratio = 0.7
a Means were calculated from 12 replications of three experiments.









Table 2.7. Relative yield (RY)
dry weight of peanut and common
and in mixture .


30
and relative yield total (RYT) of shoot
cocklebur (CB) when grown in monoculture


peanut : cocklebur ratio
Genotype 4:0 3:1 2:2 1:3 0:4


NC 7 RY 1.00 0.73 0.50 0.29 0.00

CB (w/NC 7) RY 0.00 0.54 0.99 1.18 1.00

RYT 1.00 1.27 1.49 1.47 1.00

8143B RY 1.00 0.80 0.58 0.36 0.00

CB (w/8143B) RY 0.00 0.41 0.65 0.76 1.00

RYT 1.00 1.21 1.23 1.12 1.00


a Means were calculated from 12 replications of three experiments.



































































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Replacement Study
Relative Yield Data: NC 7
Leaf Dry Weight


4:0 3:1 2:2 1:3
Peanut : Cocklebur Ratio


Replacement Study
Relative Yield Data: NC 7
Stem Dry Weight


:0

ure 2.8


3:1 2:2 1:3 0:4
Peanut : Cocklebur Ratio
Relative yield (RY) and relative yield
total (RYT) of leaf and stem dry weight
of peanut genotype NC 7 and common
cocklebur grown in monoculture and in
mixture.


a]
> 1.


a
Q:


o NC 7 A CB a RYT



-o-

-A'



0
^^*o^^0


(0







0.


4

Fig












Replacement Study
Relative Yield Data: 8143B
Leaf Ory Weight
2.0
o 8143B a CB o RYT



-3

.' -. .
--a.


a"---------- -.


0 0


0.0 ----------- ---------
4:0 3:1 2:2 1:3 0:4
Peanut Cocklebur Ratio



Replacement Study
Relative Yield Data: 8143B
Stem Ory Weight
2.0
o 81438 a CB a RYT




N-O
0 ,-0 -------------- 0--- _-

> 1.0a'^ ..-*


0: -- -




0.0
0.0'- ---------------------
4:0 3:1 2:2 1:3 0:4
Peanut : Cocklebur Ratio
Figure 2.9 Relative yield (RY) and relative yield
total (RYT) of leaf and stem dry weight
of peanut genotype 8143B and common
cocklebur grown in monoculture and in
mixture.









Mutual benefit (Harper, 1977) is suggested from the replacement

series diallel diagrams of the relative yields and relative yield totals

(Fig. 2.6, 2.7), since both species in the mixtures produced more shoot

dry matter than would be expected (e.g., RYT>1) if each species produced

as in pure stands. Expected yields arise from equal competition.

Actual and expected yield contributions of NC 7 to the system were

nearly equal at all proportions, while the relative yield of common

cocklebur grown in association with NC 7 was much greater than expected

(Fig. 2.6). Relative yields of 8143B and common cocklebur were also

greater than expected, yet common cocklebur did not benefit as greatly

in its association with 8143B as it did with NC 7 (Fig. 2.7). These

studies suggested that there are no allelopathic interactions between

these two plant species because both peanut genotypes and common

cocklebur yielded equally or greater than expected and RYTs were greater

than one.

The intersection of the curves of the relative yields of peanut

and common cocklebur represent that proportion at which each species

contributes equally to the total productivity of the system. The

intersection of the NC 7 and common cocklebur curve lies near a 3:1

ratio (Fig. 2.6), while 8143B contributes equally near a 2:2 ratio

(Fig.2.7). This suggests genetic differences in their ability to

compete for resources and shows that 8143B is not as affected by inter-

specific competition when compared with NC 7. The slower growth rate of

8143B may not demand above- and/or below-ground resources to the degree

which NC 7 does for its vigorous growth and, therefore, less effect from

inter-specific competition was observed in 8143B. Another possibility









is that NC 7 provides common cocklebur with some sort of advantage to

escape the effects of inter-specific competition for available resources

and becomes more competitive than common cocklebur grown in association

with 81438. The greater relative yield total of the system with NC 7

compared with that of 81438 is due to the greater biomass accumulation

of common cocklebur in association with NC 7 (Table 2.7).

Measurements of change in relative yield is one method of

evaluating how two plant species interact when grown in mixtures. DeWit

(1960) proposed another method to assess relative competitive abilities

of the species by calculating the relative crowding coefficient (RCC).

A greater RCC value indicates a greater relative competitiveness. De

Wit (1960) states that when the product of the relative crowding

coefficients equals one, plant species "compete for the same space" and

are "mutually exclusive" and compete for the same resources. The

products (RCCp x RCCcB) of the relative crowding coefficients for both

NC 7 and 8143B with common cocklebur were nearly or equal to 1.00

suggesting that they are competing for the same above- and/or below-

ground resources (Table 2.8).

These results also indicate that 8143B is the genetically superior

genotype as a competitor with common cocklebur in a mixture because the

RCC values of 8143B were much greater at all proportions than NC 7. The

RCC values of common cocklebur were greater in association with NC 7

than when grown with 8143B which suggests that common cocklebur was more

competitive when grown with NC 7.









Table 2.8. The influence of interference on relative crowding
coefficients (RCC) of peanut and common cocklebur (CB) shoot dry
weight.


Peanut:CB ratio RCCp RCCcs RCCxRCCCB



3:1 NC 7 1.35 0.74 1.00

8143B 1.97 0.51 1.00

2:2 NC 7 0.51 1.97 1.01

8143B 0.90 1.11 1.00

1:3 NC 7 0.24 4.11 0.99

8143B 0.47 2.12 1.00



a Means were calculated from 12 replications of three experiments.









Partitioning Study

Neither peanut genotype suffered a significant shoot dry

weight reduction due to interference by common cocklebur under above-

ground (SC) competition (Table 2.9). Leaf dry weight was more affected

by SC than stem dry weight in both peanut genotypes.

Under root competition (RC), NC 7 had greater PI values for

leaf, stem, and shoot dry weight than 8143B (Table 2.9). This suggests

that below-ground competition affects the peanut genotypes differently

and to a greater degree than above-ground competition with common

cocklebur.

Root and shoot competition (FC) caused a significant

(P<0.05) reduction in leaf, stem, and shoot dry weight of NC 7 (Table

2.9). Full competition had no significant effect on leaf, stem, and

shoot dry weight of 8143B. NC 7 had greater PI values under the

influence of interference from common cocklebur than 8143B on leaf,

stem, and shoot dry weights when in full competition.

Common cocklebur leaf, stem, and shoot dry matter

accumulation was not inhibited when grown in association with NC 7

compared to its growth in monoculture (Table 2.10). In contrast, common

cocklebur showed greater than 40% inhibition of leaf, stem, and shoot

dry matter accumulation when grown under RC and FC in association with

8143B. This suggests that common cocklebur is somehow escaping the

effects of competition when grown with NC 7 and is susceptible to

interference when growing in association with 8143B. Inhibition of

leaf, stem, and shoot dry matter accumulation of common cocklebur grown

with 8143B is greatest when under the influence of RC or FC suggesting









Table 2.9. The effects of
shoot dry weight of peanut
cocklebur (CB)a.


shoot (SC) and/or root (RC) competition on
when grown in association with common


(a) Leaf Dry Wt. (g pot"') No RC RC

No SC NC 7 8.4 7.3 (13)b
81438 5.4 5.0 (7)
SC NC 7 7.8 (7) 6.0 (29)
8143B 5.0 (7) 4.2 (22)
LSDo.os = 1.3

(b) Stem Dry Wt. (g pot"1) No RC RC

No SC NC 7 5.9 5.5 (7)
81438 3.0 3.1 (0)
SC NC 7 5.8 (2) 4.3 (27)
81438 3.0 (0) 2.4 (21)
LSDo.o5 = 1.0

(c) Shoot Dry Wt. (g pot') No RC RC

No SC NC 7 14.3 12.8 (10)
8143B 8.4 8.1 (4)
SC NC 7 13.6 (5) 10.3 (28)
8143B 8.0 (5) 6.6 (21)
LSDo.os = 2.3

a Means were calculated from eight replications of two experiments.
b Percent inhibition (PI) values are given in parentheses next to the
absolute dry weight values.









Table 2.10. The effects of shoot (SC) and/or root (RC) competition on
shoot dry weight of common cocklebur (CB) when grown in association with
peanut'.

(a) Leaf Dry Wt. (g pot"') No RC RC

No SC NC 7 avg. 1.6 (0)b
8143B 1.5 0.9 (46)

SC NC 7 1.7 (0) 1.3 (13)
8143B 1.3 (13) 0.8 (47)

LSDo.o0 = 0.6

(b) Stem Dry Wt. (g pot-') No RC RC

No SC NC 7 avg. 1.4 (0)
8143B 1.1 0.6 (45)

SC NC 7 1.8 (0) 1.5 (0)
8143B 1.1 (0) 0.6 (45)

LSDo.os = 0.8

(c) Shoot Dry Wt. (g pot"') No RC RC

No SC NC 7 avg. 3.0 (0)
8143B 2.6 1.5 (42)

SC NC 7 3.5 (0) 2.8 (0)
8143B 2.4 (8) 1.4 (46)

LSDo.os = 1.4

a Means were calculated from eight replications of two experiments.

b Percent inhibition (PI) values are given in parentheses next to the
absolute dry weight values.









that below-ground competition is the primary mechanism of interference.

This study corroborates results from replacement studies where

common cocklebur appeared to gain some sort of advantage and escaped

from the effects of inter-specific competition when grown with NC 7

compared with 8143B. It has been hypothesized that NC 7 may develop a

more vigorous root system and common cocklebur benefits from the

nitrogen fixation. Another possibility may be that the peanut genotype

may alter the rhizosphere (e.g., soil bacterium, etc) to the benefit of

common cocklebur.

This would suggest two further experiments to clarify this point.

The series of experiments previously described were fertilized with a

modified 10X Hoaglands solution minus nitrogen. Nitrogen could be added

to the soil of the above-ground mode of competition to determine if

common cocklebur is still more competitive against NC 7 than 8143B. A

second experiment would be to repeat the below-ground mode of

competition of the partitioning study with and without activated

charcoal. If the addition of charcoal lowers or alleviates RC, then

allelopathy may be a component of common cocklebur's interference

strategy, since the charcoal would absorb potentially phytotoxic

compounds.

Results from this study suggest that the primary mechanism of

interference of common cocklebur in peanut occurs below the ground. The

effects of interference is enhanced under full competition. As was seen

in the replacement study, peanut genotype 8143B is not affected by

interference to the degree in which NC 7 is, suggesting that 8143B is

the genetically superior genotype to avoid yield reductions due to







42

interference by common cocklebur. It may be that the slower growth

habit of 8143B compared with the more vigorous growth habit of NC 7

allows 8143B to avoid the effects of competition for available

resources. This is also suggested by the fact that common cocklebur

suffered no inhibition in growth when grown in association with NC 7,

yet suffered greater than a 40% inhibition when grown in the RC and FC

forms of competition with 8143B.












CHAPTER III

RESPONSE OF FOUR PEANUT GENOTYPES
TO INTERFERENCE FROM COMMON COCKLEBUR


Introduction

Weed control practices and most weed studies are designed to

minimize competition of weeds with crop plants. However, the parameters

and dynamics of competitive pressure exerted by the weed on the crop

plant remain undefined for most weed-crop situations (Hauser et al.,

1975). Most of the research reported in the literature deals with the

effects of weed competition on crop yield. Jolliffe et al. (1984)

suggested that the study of other plant characteristics (including leaf

area and dry matter partitioning) may allow a better determination of

the effects of weed competition on crop yield.

Numerous studies have been conducted to determine when peanuts are

most susceptible to weed interference and how long weed-free conditions

must be maintained to avoid yield reductions. Chamblee et al. (1982)

reported that season-long competition of 16 broadleaf signalgrass

[Bracharia platyphylla (Griseb.) Nash] plants 10 m-1 of row reduced

peanut seed yield 28%. In the same study, they found that broadleaf

signal grass must be removed within six weeks of peanut planting, or

peanuts maintained weed-free for the first six weeks of growth, to

achieve maximum peanut yield. Hill and Santelmann (1969) reported that

peanut seed yields were not reduced by smooth pigweed (Amaranthus







44

hybridus L.) and large crabgrass [Digitaria sanquinalis (L.) Scop.] that

emerged six weeks after peanut planting, or when smooth pigweed and

large crabgrass were removed within three weeks after planting. A full-

season infestation of large crabgrass reduced peanut yield 25%. York

and Coble (1977) reported that fall panicum (Panicum dichotomiflorum

Michaux.) interference for only the first two weeks after planting

reduced peanut yield 28%. In addition, fall panicum emerging eight

weeks after planting reduced seed yields 15% and as few as 0.2 fall

panicum plants m-1 of row reduced seed yields 25% when competition

occurred over the entire growing season.

Common cocklebur (Xanthium strumarium L.) is one of the most

serious weed problems in the southeastern United States (Barrentine,

1974; Gosset, 1971; Waldrep and McLaughlin, 1969). The ability of

common cocklebur to compete with agronomic crops in the field has been

documented. In a three-year study, Barrentine (1974) showed that full-

season competition of common cocklebur reduced 2-yr. average yields of

soybeans [Glycine max (L.) Merr.] from 10% for densities of 3300 common

cocklebur plants ha-' (approx. 6 plants 17 m'1 row) to 52% from season-

long competition with 26000 common cocklebur plants ha-'. Gosset (1971)

reported a 50% yield reduction with 14 common cocklebur plant 3.1 m-' of

soybean row. Buchanan and Burns (1970) showed that full-season

competition with common cocklebur at a density of eight plants 7.3 m1

of row reduced seed yields of cotton approximately 60%.

Research has also been conducted to better understand why common

cocklebur is such a competitive species. The competitiveness of common

cocklebur may be the result of its potential for rapid growth and high








water and nutrient requirements (Geddes et al., 1979). Barrentine and

Oliver (1977) reported that reductions in soybean leaf area index, plant

dry weight, and crop growth rate were good indicators of the time at

which common cocklebur began competing with soybean. Common cocklebur

may grow to heights of 150 cm and can have a root depth and radius of

2.9 and 4.3 m, respectively (Davis et al., 1967). Common cocklebur

plants often start forming a canopy over the crop plants before the

beginning of the reproductive period of many crop species. This can

result in reduced flowering, increased pod abortion, and poor seed fill

(Carter and Hartwig, 1963).

Several weed competition studies have investigated changes in the

vegetative characteristics of crop species in response to common

cocklebur competition and have shown that vegetative characteristics are

not as responsive to weed competition as seed yields of cotton (Buchanan

and Burns, 1971; Buchanan and McLaughlin, 1975). Common cocklebur also

has been shown to affect soybean height, stem diameter, number of pods

per plant, seed grade, leaf area, dry weight, crop growth rate, and the

amount of foreign material present in seed samples (Barrentine and

Oliver, 1977; Eaton et al., 1976). McWhorter and Hartwig (1972)

reported yield losses ranging from 63% to 75% for six soybean varieties

from season-long competition with 7400 to 16500 common cocklebur

plants ha1.

Differences in the ability to compete with weeds vary among crop

species. Hamdoun (1977) reported 62-80% yield reductions due to full-

season competition by weeds in peanut. Yield losses due to weeds in

sorghum (Sorghum bicolor L.) were less than 45% in a full-season study









by Kock et al. (1982).

Genetic variation in competitive ability has also been reported

within crop species. McWhorter and Barrentine (1975) found that 'Bragg'

soybeans had yield reductions of 7% compared with 20% for other soybean

cultivars when mechanical weed management was compared with the use of

herbicides. Winter wheat (Triticum aestivum L.) yield reductions from 9

to 21% at one location and from 20 to 41% at another location, depending

on the cultivar, were reported by Challaiah et al. (1986).

Little work has been done on the development of techniques to

identify crop varieties or breeding lines that resist damage from weeds.

If there are sufficient genetic differences within a species for

competitive ability against weeds, plant breeders could potentially

produce cultivars with enhanced weed resistance.

The objective of this study was to evaluate the relative effects

of interference by common cocklebur on the growth and development of

different peanut genotypes under field conditions. Peanut

characteristics affected by common cocklebur interference and their

correlation with crop yield were evaluated.



Materials and Methods


Experiments were conducted in 1987 and 1989 at the University of

Florida Agronomy Farm west of Gainesville on an Arredondo fine sand

(Grossarenic Paleudult). Four peanut genotypes were planted on 18 June,

1987 in a randomized complete block design (RBCD) with three

replications. The same four genotypes were planted on 14 April, 1989 in









a RBCD with four replications. Two treatments were studied in these

experiments, the four genotypes and their yield response when grown with

and without common cocklebur. The four peanut genotypes were chosen for

their genetic variablity in plant growth (vegetative and reproductive)

characteristics that may affect competition with weeds. NC 7 is a

Virginia market-type peanut with an upright (bunch) growth habit. The

second peanut genotype, 8143B, is a runner market-type peanut with a

spreading (runner) growth habit. The third peanut genotype, BL-8, also

has a spreading growth habit, yet grows much more vigorously throughout

the growing season than 8143B. The fourth peanut genotype, BL-10, has

an upright growth habit, but does not grow as vigorously or begin to

partition assimilates to pod formation as early in the growing season as

NC 7 (Knauft and Gorbet, 1990).

Plots consisted of four rows spaced 91 cm apart and rows were 6 m

long. Peanut seed were hand planted at a density of 18-20 seed m-' of

row and thinned to a density of 10 plants m-1 of row. Each peanut

genotype was planted in plots with and without common cocklebur.

Commercially purchased de-spined common cocklebur seed' were planted the

same day as peanut in peat pots in the greenhouse and were transplanted

to the south side of the peanut row 10 cm from the peanut plants when

the peanuts were approximately 4-5 cm tall. Ten to twelve common

cocklebur plants were transplanted to each plot approximately every 2 m


1 Azlin Seed Service, Inc. Leland, Miss.









of row. Common cocklebur plants harvested were chosen at random, from

the two middle rows. All plots were kept free of all other weeds over

the growing season by hoeing and hand-pulling.

These experiments were conducted in a manner which allowed a

comparison of the four peanut genotypes in their ability to compete with

common cocklebur. An increment of one meter of peanut row surrounding a

neighboring common cocklebur plant was harvested three times over the

growing season each year to determine potential interference effects due

to the weed. The one meter of peanut row was divided into two

increments: one in which peanut plants were within 25 cm of the common

cocklebur plant (total length of 0.5 m) and another in which the peanut

plants were 25 to 50 cm from the common cocklebur plant (total length of

0.5 m). The same increment (1.0 m) of peanut row was randomly harvested

in plots without the weed and comparisons were made of relative

differences in competitive ability between peanut genotypes in the

increments adjacent to the common cocklebur plant. Vegetative harvests

were conducted three times over the growing season each year at 45, 90,

and 135 days after planting (DAP). All plants within the designated

distance increment from the common cocklebur plant were hand-harvested

and the root was cut at the base of the plant. After peanut plants were

removed from each increment, the common cocklebur plant was clipped at

the soil surface. Plants were dissected into leaves, stems, and in the

case of peanut, pods, from which dry weights were determined. The main

effects of the experiment were year of study, replication, peanut

genotype, and cocklebur treatment (with and without). Distance

increment from the common cocklebur plant harvested was a subplot effect









and harvest interval (45, 90, and 135 DAP) was a sub-subplot effect.

Because genotype x year interactions were significant (P<0.05) data from

each year was analyzed separately.


Results and Discussion


Shoot Dry Matter Yield

Main effects, two and three way interactions were all highly

significant (P<0.01) in each year the experiment was conducted. Because

three way interactions were significant, the shoot dry weight yields for

each genotype in each distance increment within harvest interval for

each year are presented separately.

At 45 days after planting (DAP), NC 7 was the only peanut genotype

which was significantly (P<0.05) affected by the interspecific

competition by common cocklebur in 1987 (Table 3.1; Fig. 3.1). In 1989

at 45 DAP, there were no significant shoot dry weight yield reductions

in any of the peanut genotypes with common cocklebur compared with the

plots which were weed free (Fig. 3.2). Common cocklebur plant growth

during the first 45 DAP was not sufficient to significantly affect

peanut plant growth due to interspecific competition, except that of NC

7 in 1987 (Fig. 3.3).

Interspecific competition by common cocklebur resulted in

significant (P<0.05) shoot dry weight yield reductions in three of the

four peanut genotypes at 90 DAP in 1987 (Table 3.2). There were no

significant reductions in shoot dry weight in either distance increment

by 8143B. NC 7, BL-8, and BL-10 suffered significant yield reductions









Table 3.1 Shoot dry matter yield as affected by interference from
common cocklebur (CB) 45 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987
------------- gm 0.5 m2 -1 ------------

NC 7 110.0 67.3 61.2

8143B 58.2 56.1 49.8

BL-8 111.3 114.7 109.5

BL-10 106.4 107.0 91.6

LSD.os = 46.9 for column comparison of genotype within increment

LSD 0o = 44.1 for row comparison within genotype
1989

------------- gm 0.5 m2 -1 ------

NC 7 116.5 108.1 79.2

8143B 87.6 88.1 69.1

BL-8 89.0 79.8 68.6

BL-10 86.2 82.1 70.2

LSD.05 = 46.3 for column comparison of genotype within increment

LSD.o5 = 42.6 for row comparison within genotype







51









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Table 3.2. Shoot dry matter yield as affected by interference
from common cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)


Genotype



NC 7

8143B

BL-8

BL-10

LSD.05 = 46.9 fo

LSD.05 = 44.1 fo




NC 7

8143B

BL-8

BL-10

LSD.05 = 46.3 fc

LSD.05 = 42.6 fo


1987

------------- gm 0.5 m2 -1 ------

322.4 243.9 174.1

252.9 262.9 242.0

331.0 338.1 205.3

346.0 274.6 261.1

ir column comparison of genotype within increment

ir row comparison within genotype
1989

------------ gm 0.5 m2 -1----

401.4 218.5 144.8

228.4 172.0 133.4

319.9 269.8 185.1

352.8 221.2 116.2

ir column comparison of genotype within increment

ir row comparison within genotype








of 46.0, 38.0, and 24.5%, respectively, in the 0-25 cm increment of

peanut row from the common cocklebur plant (Fig. 3.4). NC 7 and BL-10,

which have the upright growth habit, suffered significant (P<0.05) yield

reductions in shoot dry weight in the 25-50 cm increment from the common

cocklebur plant, while the two genotypes with the spreading growth habit

(8143B and BL-8) had no shoot dry weight reduction in the 25-50 cm

increment. Similar effects from common cocklebur interference in

soybean were reported by Barrentine and Oliver (1977) where plant growth

was significantly reduced when soybeans were 0-20 cm from the common

cocklebur plant and that dry matter yields increased as the distance

from the common cocklebur plant increased.

In 1989, at 90 DAP, all four peanut genotypes suffered significant

(P<0.05) shoot dry weight yield reductions in the 0-25 cm and 25-50 cm

increment from the common cocklebur plant when compared with their shoot

dry matter yield in weed-free plots (Table 3.2). Common cocklebur shoot

dry weights at 90 DAP in 1989 were almost twice that of common cocklebur

plants in 1987 which allowed the common cocklebur to be more competitive

and cause shoot dry matter reductions in all four genotypes (Fig. 3.3;

Table 3.3). The main reason for this difference in the growth and

development of common cocklebur was a function of planting date. Common

cocklebur is very sensitive to photoperiod and due to the late planting

date in 1987, began flowering and partitioning to seed development very

early in the growing season. In 1989, due to the earlier planting date,

common cocklebur had much more time for growth and development before

beginning partitioning to seed development.

















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Table 3.3. Shoot dry weight of common cocklebur (CB) when
grown with four genotypes of peanut during two growing seasons.

1987
DAP

Genotype 45 90 135
------------- gm plant" --------------

NC 7 6.0 153.0 350.0

8143B 21.3 258.3 480.3

BL-8 13.0 269.0 482.0

BL-10 25.3 294.7 350.0

Control 26.8 318.9 320.3

LSD.o5 for column comparison within days after planting (DAP) = 111.9

1989
NC 7 9.0 390.0 692.5

8143B 10.8 443.0 720.5

BL-8 6.2 452.2 720.0

BL-10 10.8 474.5 721.8

Control 10.8 540.8 590.2

LSD for column comparison within days after planting (DAP) = N.S.






58

Genetic differences between the four peanut genotypes were seen in

shoot growth rate and competitive ability under the influence of common

cocklebur interference to a greater degree in 1989 than in 1987 at 90

DAP (Fig. 3.4, 3.5). Shoot dry weights of all peanut genotypes showed

similar yield trends each year in the treatment without common cocklebur

interference. In 1987, NC 7 and BL-10 were the only genotypes to suffer

significant shoot dry weight reductions in the 25-50cm increment. In

1989, all four genotypes showed significant (P<0.05) shoot dry weight

reductions.

At 135 DAP, interference from common cocklebur resulted in

significant (P<0.05) shoot dry weight reductions of all peanut genotypes

in both years in the 0-25 cm increment compared with weed-free shoot dry

matter yield (Table 3.4). In 1987, the common cocklebur plants had

already started to senesce due to the late planting date of the field

trial and, therefore, were not as competitive late in the season because

there was little canopy left for shading. As a result, 8143B and BL-10

had no significant shoot dry weight reductions in the 25-50 cm increment

(Fig. 3.6). In 1989, only peanut genotype 8143B showed no significant

shoot dry weight reduction in the 25-50 cm increment (Fig. 3.7). In

both years, BL-8 and BL-10 produced significantly more shoot dry matter

than NC 7 and 8143B in all treatments at 135 DAP (Fig. 3.6, 3.7).

The comparison of the genetic differences between the four

genotypes in shoot dry matter production in these studies corroborate

the description of the variability in growth characteristics of the same

peanut genotypes as reported by Knauft and Gorbet (1990). NC 7 is

characterized as having a vigorous early season growth rate and most of









Table 3.4. Shoot dry matter yield as affected by interference from
common cocklebur (CB) 135 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987


NC 7

8143B

BL-8

BL-10

LSD.os

LSD.os



NC 7

8143B

BL-8

BL-10

LSD.os

LSD5os


------------- gm 0.5 m2 -1

420.1 369.2 236.4

360.3 332.7 319.6

519.9 471.6 355.8

515.6 497.0 459.9

= 46.9 for column comparison of genotype within increment

= 44.1 for row comparison within genotype
1989
------------- gm 0.5 m2 -1

471.6 374.4 297.1

380.2 349.0 286.6

568.8 521.8 446.4

545.4 432.5 393.5

= 46.3 for column comparison of genotype within increment

= 42.6 for row comparison within genotype







60









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its vegetative growth occurs early in the growing season. In contrast,

8143B has a much slower growth rate and produces less vegetative dry

matter over the growing season than the other genotypes. In their

study, BL-8 produced the greatest amount of vegetative dry matter

compared with the other genotypes over the growing season, esp. later in

the growing season. BL-10 also produced more vegetative dry matter than

NC 7 and 8143B over the growing season, yet grew at a lesser rate than

BL-8 late in the growing season.

Results from these field experiments indicated that the peanut

genotypes which have a spreading rather than an upright growth habit are

less susceptible to interference from common cocklebur. In addition,

genetic characteristics such as duration of vegetative development and

the time and rate of partitioning of assimilates to pod development

could play an important role in the ability of certain peanut genotypes

to avoid dry matter yield reductions due to weed interference.

Studies conducted in the greenhouse indicated that the primary

mechanisms of interference were below-ground and that 8143B was less

affected than NC 7 by interference from common cocklebur. Results from

the field experiments were based on similar observations and 8143B was

the peanut genotype which was least affected by interference from common

cocklebur. These data suggest that it is possible to screen peanut

genotypes in the greenhouse over a six week growing period, based on a

knowledge of the vegetative characteristics which allow a competitive

advantage, to select peanut genotypes for field verification as to their

competitiveness with common cocklebur.









Pod Dry Matter Yield

NC 7 produced significantly (P<0.05) more pod dry matter at 90 DAP

than the other three peanut genotypes in 1987 in plots that were weed-

free and when under competition in the 25-50 cm increment (Table 3.5;

Fig. 3.8). NC 7 and BL-10 produced significantly more pod dry matter

than 8143B and BL-8 in all three treatments. NC 7 and BL-10 begin

partitioning assimilates to pod development earlier during the growing

season than the other two genotypes (Knauft and Gorbet, 1990). At 90

DAP in 1987, all four genotypes suffered significant pod yield

reductions due to interference by common cocklebur in the 0-25 cm

increment, yet did not show significant reductions in the 25-50 cm

increment.

Common cocklebur interference caused greater pod yield reductions

in 1989 than in 1987 at 90 DAP (Table 3.5; Fig. 3.9). In 1987, 8143B

had the highest percent inhibition (43%) while in 1989 all four

genotypes had greater than 60% inhibition in the 0-25 increment (Fig.

3.8, 3.9). For each treatment (weed-free, 0-25 cm, 25-50 cm), NC 7

yielded significantly more pod dry matter than the other three genotypes

studied in 1989 at 90 DAP as it did in 1987 (Table 3.5). All four

genotypes had significant yield reductions in the 0-25 cm increment from

common cocklebur in 1989. BL-8 and 8143B, which begin partitioning to

pod development later than NC 7 and BL-10, had the lowest pod yield in

the weed-free treatment each year of the study at 90 DAP.

NC 7 and BL-10 had significantly greater pod yield in the weed-

free treatment than 8143B and BL-8 at 135 DAP in 1987 as they did at 90

DAP (Table 3.6; Fig. 3.10). Under the influence of interference by









Table 3.5. Pod dry matter yield as affected by interference by common
cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987


NC 7

8143B

BL-8

BL-10

LSD.os

LSD.os



NC 7

81438

BL-8

BL-10

LSD.os

LSD.os


------------- gm 0.5 m2 -1 ------

130.1 119.2 84.0

66.4 55.4 38.1

71.4 62.2 50.5

90.0 91.5 72.4

= 14.0 for column comparison of genotype within increment

= 12.8 for row comparison within genotype
1989

------------- gm 0.5 m2 -1 -------------

120.0 62.2 40.2

72.4 40.6 25.6

49.8 37.8 18.9

78.4 37.9 16.8

= 13.6 for column comparison of genotype within increment

= 12.6 for row comparison within genotype

















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Table 3.6. Pod dry matter yield as affected by interference by common
cocklebur (CB) 135 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)


Genotype


1987


------------- gm 0.5 m2 -1-----

193.3 139.6 104.4

147.9 135.3 131.9

153.3 146.8 112.8

179.3 164.3 157.3

= 14.0 for column comparison of genotype within increment

= 12.8 for row comparison within genotype
1989

------------- gm m 2 -1------

223.5 134.3 103.5

159.4 136.0 121.8

172.8 135.3 114.8

190.0 141.0 115.0

= 13.6 for column comparison of genotype within increment

= 12.6 for row comparison within genotype


NC 7

8143B

BL-8

BL-10

LSD.os

LSD.o5



NC 7

8143B

BL-8

BL-10

LSD.os

LSD.o5








69








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common cocklebur, BL-10 had significantly higher pod yields at 135 DAP

than the other three genotypes in both treatments with common cocklebur.

In both years of the study at 90 DAP, 8143B had significantly less

pod dry weight than NC 7 in the 0-25 cm increment treatment (Table 3.5),

yet at 135 DAP it had significantly greater pod yield than NC 7 (Table

3.6). According to Knauft and Gorbet (1990), 81438 begins partitioning

assimilates to pod development later than NC 7 and has a relatively high

partitioning rate over the growing season.

In 1989 at 135 DAP, NC 7 produced significantly more pod dry

matter than the other peanut genotypes in the weed-free treatment (Table

3.6). Under the influence of interference from common cocklebur, 8143B

yielded significantly (P<0.05) more pod dry matter at 135 DAP in 1989

than NC 7 in the 0-25 cm increment as it did in 1987. There were no

significant pod yield differences due to common cocklebur interference

between genotypes 81438, BL-8, and BL-10 in 1989 in either increment

treatment (Fig 3.11).

According to Knauft and Gorbet (1990), NC 7 has a vigorous early

season growth habit and begins partitioning assimilates to pod

development well before the other three genotypes. This could account

for the significant (P<0.05) pod dry matter yield of NC 7 at 90 DAP in

the weed-free treatment each year. Later in the growing season, the

common cocklebur plant develops a canopy over the peanut row while NC 7

is partitioning much of its energy to pod growth and cannot adjust

partitioning to produce more leaf matter to avoid shading effects.

Shoot dry weights of all four genotypes were highly correlated (r=0.90,

P<0.01) with pod dry matter production in both years of the study.


















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Peanut genotypes that produce more vegetative and less pod dry

matter early in the growing season due to their growth habits and/or

partitioning rates may be more competitive with weeds later and be able

to avoid serious yield reductions over the entire growing season. Some

crops, such as peanut, are poor competitors with weeds, and therefore,

the cost to control the weeds can be high, and if the weeds are not

adequately controlled, serious yield losses can occur (Walker et al.,

1989). It would be to the advantage of the grower if cultivars could be

developed with an improved competitive ability with weeds. Little work

has been reported on the development of weed resistant cultivars or of

an effort to develop a selection criterion of above-ground plant

characteristics which would allow a plant breeder to determine genetic

differences in competitive ability of crop plants such as peanut.

This study suggests that it is possible to identify peanut

genotypes with genetic differences in competitive ability with common

cocklebur. Vegetative characteristics, such as length of partitioning

period to leaf and stem growth, time of partitioning to pod development,

and rate of partitioning appeared to affect the degree of severity of

the effects of interference by common cocklebur on shoot and pod yield

reductions in the four peanut genotypes studied. Through studies of the

growth characteristics of the crop and an understanding of the

characteristics most affected by interference by the weed, it would seem

feasible that crop genotypes could be identified which are more

competitive with weeds.












CHAPTER IV

SUMMARY AND CONCLUSIONS

This research addressed how interference from common cocklebur

affects the growth and development of peanut in a mixed stand. The

relative competitiveness of peanut genotypes and mechanisms of

interference by common cocklebur under greenhouse conditions were

investigated. The response of peanut genotypes to interference from

common cocklebur grown under field conditions was evaluated.

Replacement series studies demonstrated that peanut genotype 81438

competed more effectively with common cocklebur over a six week period

than genotype NC 7 under greenhouse conditions. NC 7 exhibited a more

vigorous growth habit and shoot dry weight accumulation in the

greenhouse, yet suffered greater shoot dry weight yield reductions when

grown in association with common cocklebur than did peanut genotype

81438. Leaf and stem dry matter accumulation contributed equally to

this effect. On a relative basis, 8143B contributed equally to the

relative yield total of the system in a 50:50 mixture. Common cocklebur

contributed approximately twice the relative yield than NC 7 in a 50:50

mixture. This suggests genetic differences in competitive ability

between the two peanut genotypes.

Partitioning studies in the greenhouse indicated that the

mechanism of interference of common cocklebur on peanut occurs both

above- and below-ground for the first six weeks of growth in the









greenhouse.

Field experiments demonstrated the genetic differences in

competitiveness between four genotypes of peanut to interference by

common cocklebur. NC 7 grew very vigorously early in the growing season

and produced significantly greater pod dry matter yields compared with

the other three genotypes when grown without common cocklebur

interference. Peanut genotype, 8143B, produced less shoot dry matter

during the growing season and had the lowest pod dry weight both years

when grown without the influence of interference by common cocklebur.

Genotypes, B1-8 and BL-10, produced significantly more shoot dry matter

than NC 7 and 8143B during the growing season without common cocklebur

interference, yet produced significantly less pod dry matter.

When grown under the influence of interference by common

cocklebur, NC 7 suffered the greatest yield reduction in shoot and pod

dry matter yield compared with the other genotypes. Peanut genotype

8143B grew more slowly early in the growing season, esp. in 1987, yet

continued to produce vegetatively throughout the growing season and

suffered little shoot or pod dry matter yield in either year. Genotype

BL-8 and BL-10 produced more shoot dry matter than NC 7 and 8143B over

the growing season each year. Pod dry matter yield of BL-8 was

consistent over both growing seasons, while BL-10 had the highest pod

dry matter yield in 1987 under the influence of interference by common

cocklebur.

The four peanut genotypes which were examined in this research

project differ in plant growth habits, partitioning rates, and results

from these studies show genetic differences in competitive ability to









withstand the effects of interference from common cocklebur. These

results suggest the possibility of developing peanut genotypes that

could have a genetic advantage over other genotypes in their ability to

avoid yield losses due to weed interference.

Some crops, such as peanut, are poor competitors with weeds. The

cost to control weeds in these crops can be high, and, if the weeds are

not adequately controlled, serious yield losses can occur. It would be

advantageous to the grower if cultivars could be developed with an

improved ability to compete with weeds. Little work has been reported

on the development of weed-resistant cultivars or of an effort to

develop a selection criterion of above-ground characteristics which

would allow a plant breeder to determine differences in the competitive

ability of crop plants, such as peanut.










APPENDIX









Table A.1. Number of nodes produced when peanut and common
cocklebur are grown at different plant density levels.

Plant Density per Pot
Genotype 1 2 4 8
--------------- nodes pot" ------------
NC 7 37.7 61.1 107.0 161.5

8143B 26.8 35.2 64.0 105.2

CB 9.5 15.6 32.6 33.8

LSD.o05 for column comparison within density level = 20.5



Table A.2. Leaf area produced when peanut and common
cocklebur are grown at different plant density levels.

Plant Density per Pot
Genotype 1 2 4 8
---------------- cmz pot" -------------
NC 7 570.5 839.9 1428.2 1839.8

8143B 253.8 326.5 598.9 910.5

CB 801.2 907.5 1322.0 1139.8

LSDo.os for column comparison within density level = 323.4









Table A.3. Leaf dry matter produced when peanut and common
cocklebur are grown at different plant density levels.

Plant Density per Pot
Genotype 1 2 4 8
---------------- gm pot" --------------
NC 7 3.0 4.4 7.5 10.0

8143B 1.3 1.6 2.4 4.4

CB 4.0 4.6 6.8 5.3

LSDo.os for column comparison within density level = 1.4



Table A.4. Stem dry matter produced when peanut and common
cocklebur are grown at different plant density levels.

Plant Density per Pot
Genotype 1 2 4 8
--------------- gm pot" -------------
NC 7 2.2 3.6 6.2 8.0

8143B 1.0 1.1 1.9 3.6

CB 6.4 7.9 13.2 9.3

LSD.o05 for colum comparison within density level = 1.2









Table B.1. Number of nodes produced of peanut and common
cocklebur when grown in monoculture and in mixture.

peanut : cocklebur ratio
Genotype 4:0 3:1 2:2 1:3 0:4
---------------- nodes pot"---------------

NC 7 98 76 55 31

8143B 73 53 40 22 --

LSDo.05 for column comparison within mixture ratio = 8.3

CB(NC7) -- 6 12 17 22

CB(8143B) -- 7 12 17 22

LSD5o.o for column comparison within mixture ratio = N.S.




Table B.2. Leaf area produced of peanut and common cocklebur
when grown in monoculture and in mixture.

peanut : cocklebur ratio
Genotype 4:0 3:1 2:2 1:3 0:4
----------------- cme pot --------------
NC 7 1082 864 597 363

8143B 568 446 330 203

LSDo.05 for column comparison within mixture ratio = 112.4

CB(NC7) -- 65 115 163 135

CB(8143B) -- 58 108 135 184

LSDo.o5 for column comparison within mixture ratio = N.S.









Table 8.3. Leaf dry matter yield responses of peanut and common
cocklebur when grown in monoculture and in mixture.

peanut : cocklebur ratio
Genotype 4:0 3:1 2:2 1:3 0:4
----------------- gm pot ----------------
NC 7 7.1 5.3 3.7 2.1

8143B 3.0 2.5 1.8 1.0 --

LSDo.o5 for column comparison within mixture ratio = 0.7

CB(NC7) -- 0.3 0.5 0.6 0.6

CB(8143B) -- 0.3 0.5 0.6 0.8

LSDo.os for column comparison within mixture ratio = N.S.




Table B.4. Stem dry matter yield responses of peanut and
common cocklebur when grown at both monocultures and in
mixtures.

peanut : cocklebur ratio
Genotype 4:0 3:1 2:2 1:3 0:4
----------------- gm pot" --------------
NC 7 5.0 3.6 2.5 1.3

8143B 1.8 1.4 1.1 0.6

LSD5o.o for column comparison within mixture ratio = 0.6

CB(NC7) -- 0.3 0.7 0.8 0.6

CB(8143B) -- 0.4 0.6 0.7 0.9

LSDo.o5 for column comparison within mixture ratio = N.S.









Table C.1. Number of nodes as affected by interference from
common cocklebur (CB) 45 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987
------------- # nodes 0.5 m2 -------------

NC 7 321.3 234.7 211.0

8143B 179.7 162.3 138.7

BL-8 235.7 240.3 169.3

BL-10 242.7 233.7 236.3

LSD 0, = 191.5 for column comparison of genotype within increment.

LSD5,, = 165.5 for row comparison within genotype.
1989

------------- # nodes 0.5 m2 -1

NC 7 349.5 323.2 176.5

8143B 222.5 225.5 190.2

BL-8 277.0 221.5 185.8

BL-10 260.2 227.2 181.8

LSD05, = 204.6 for column comparison of genotype within increment.

LSD5,, = 112.3 for row comparison within genotype.










Table C.2. Leaf area as affected by interference from common
cocklebur (CB) 45 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

GRnntvnp 1987


-------------- cm2 --

4712.0 2853.0 2475.0

3319.7 2446.7 2055.7

4052.0 3412.3 3002.3

2744.3 2605.7 2579.7

2629.1 for column comparison of genotype within

2570.4 for row comparison within genotype.
1989


NC 7

81438

BL-8

BL-10

LSD.os

LSD.os




NC 7

8143B

BL-8

BL-10

LSD.os

LSD.o5


Sincrement.


Sincrement.


----------------cm2

5342.5 4681.2 2303.8

2588.0 2329.0 1753.8

3472.2 2587.5 2149.0

3428.0 2522.2 2087.8

= 3136.3 for column comparison of genotype within

= 1840.1 for row comparison within genotype.


rr










Table C.3. Leaf dry matter yield as affected by interference
from common cocklebur (CB) 45 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987

------------- gm 0.5 m2 -1 -------------

NC 7 55.2 34.6 28.0

8143B 27.9 26.5 23.3

BL-8 50.3 53.5 53.0

BL-10 54.5 54.7 46.2

LSD 05 = 19.1 for column comparison of genotype within increment.

LSD. 0 = 19.4 for row comparison within genotype.
1989

------------- gm 0.5 m2 -1 -------------

NC 7 64.8 58.7 42.0

8143B 47.8 45.4 35.2

BL-8 49.0 40.5 34.2

BL-10 47.8 43.4 37.4

LSD.05 = 23.8 for column comparison of genotype within increment.

LSD 05 = 12.2 for row comparison within genotype.









Table C.4. Stem dry matter yield as affected by interference
by common cocklebur (CB) 45 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)


Genotype



NC 7

8143B

BL-8

BL-10

LSD.05 = 22.2 fo

LSD.05 = 20.2 fo




NC 7

8143B

BL-8

BL-10

LSD.o5 = 24.3 fo

LSD.05 = 13.3 fo


1987

------------- gm 0.5 m2 -1------

54.8 32.7 33.3

30.3 29.6 26.5

61.0 61.1 56.5

52.0 52.3 45.5

ir column comparison of genotype within increment.

ir row comparison within genotype.
1989

------------- gm 0.5 m2 -1----------

51.7 49.4 37.2

39.8 42.7 33.9

40.0 39.3 34.4

38.4 38.7 32.8

ir column comparison of genotype within increment.

ir row comparison within genotype.








Table D.1. Number of nodes as affected by interference from
common cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987

------------- # nodes 0.5 m2 -1---

NC 7 1167.3 773.7 545.3

8143B 1133.0 1025.7 873.3

BL-8 1302.7 1148.3 698.7

BL-10 1134.7 1000.3 742.7


191.5

165.5











204.6

112.3


for column comparison of genotype within increment.

for row comparison within genotype.
1989

------------- # nodes 0.5 m2 -1 -------

296.0 640.2 484.5

1065.5 831.0 507.0

1395.5 1142.8 767.2

1323.8 953.5 490.8

for column comparison of genotype within increment.

for row comparison within genotype.


LSD.0o =

LSD.0o =



NC 7

8143B

BL-8

BL-10

LSD.o =

LSD.o =









Table D.2. Leaf area as affected by interference
from common cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987
---------------- cm2--- -------

NC 7 19306.0 12011.3 7946.7

8143B 10704.3 8974.3 8600.7

BL-8 23389.3 19259.0 10297.0

BL-10 20136.7 17438.0 10826.3

LSD 05 = 2629.1 for column comparison of genotype within increment.

LSD.o5 = 2570.4 for row comparison within genotype.
1989
---------------- cm2 ---------

NC 7 28928.5 13874.5 9526.0

8143B 16360.2 11369.0 6818.5

BL-8 27523.0 20888.5 14613.8

BL-10 25443.5 17508.5 9663.2

LSD.o = 3136.3 for column comparison of genotype within increment.

LSD.0o = 1840.1 for row comparison within genotype.









Table D.3. Leaf dry matter yield as affected by interference
from common cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(O-25cm)

Genotype 1987

------------- gm 0.5 m2 -1-----

NC 7 153.8 116.9 82.3

8143B 122.8 126.6 118.0

BL-8 161.0 165.2 99.3

BL-10 174.9 154.1 118.2

LSD.05 = 19.1 for column comparison of genotype within increment.

LSD.05 = 19.4 for row comparison within genotype.
1989

------------- gm 0.5 m2 -1 ......

NC 7 199.2 104.4 67.8

8143B 108.6 77.1 59.8

BL-8 154.0 129.4 87.7

BL-10 167.3 105.4 56.2

LSD 05 = 23.8 for column comparison of genotype within increment.

LSD.o5 = 12.2 for row comparison within genotype.








Table D.4. Stem dry matter yield as affected by interference
by common cocklebur (CB) 90 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987

------------- gm 0.5 m2 -1 ------

NC 7 168.6 127.0 91.8

8143B 130.0 136.3 124.0

BL-8 170.0 172.9 106.0

BL-10 171.1 153.8 112.8

LSD.05 = 22.2 for column comparison of genotype within increment.

LSD.05 = 20.2 for row comparison within genotype.
1989

------------- gm 0.5 m2 -1-----

NC 7 202.2 114.0 76.9

8143B 119.8 94.9 73.6

BL-8 166.0 140.4 97.4

BL-10 185.4 115.8 60.0

LSD.05 = 24.3 for column comparison of genotype within increment.

LSD.o5 = 13.3 for row comparison within genotype.









Table E.1. Number of nodes as affected by interference from
common cocklebur (CB) 135 DAP in four genotypes of peanut.

w/out CB w/CB (25-50cm) w/CB(0-25cm)

Genotype 1987

------------- # nodes 0.5 m2 -1 ------

NC 7 1263.3 1025.3 835.0

8143B 1474.3 1395.3 1140.3

BL-8 1973.0 1700.0 1189.7

BL-10 1875.0 1650.0 1439.0

LSD.,5 = 191.5 for column comparison of genotype within increment.

LSD 05 = 165.5 for row comparison within genotype.
1989

------------- # nodes 0.5 m2 -1

NC 7 1467.0 1044.8 862.5

8143B 1452.0 1219.5 935.8

BL-8 2617.2 1969.0 1520.8

BL-10 1978.0 1390.8 1068.0

LSD.05 = 204.6 for column comparison of genotype within increment.

LSD.05 = 112.3 for row comparison within genotype.