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 Title Page
 Acknowledgement
 Table of Contents
 Abstract
 Introduction
 Review of literature
 Materials and methods
 Results and discussion
 Conclusion
 References
 Biographical sketch














Title: Screening for resistance to Meloidogyne incognita (Kofoid and White) Chitwood in Aeschynomene and Desmodium spp. and herbicide effects on Aeschynomene americana L. /
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Title: Screening for resistance to Meloidogyne incognita (Kofoid and White) Chitwood in Aeschynomene and Desmodium spp. and herbicide effects on Aeschynomene americana L. /
Physical Description: v, 72 leaves : ; 28 cm.
Language: English
Creator: Pasley, Sherman F
Publication Date: 1981
Copyright Date: 1981
 Subjects
Subject: Meloidogyne incognita -- Control   ( lcsh )
Aeschynomene   ( lcsh )
Desmodium   ( lcsh )
Agronomy thesis Ph.D
Dissertations, Academic -- Agronomy -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (Ph.D.)--University of Florida. 1981.
Bibliography: Bibliography: leaves 68-71.
Statement of Responsibility: by Sherman F. Pasley.
General Note: Typescript.
General Note: Vita.
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Bibliographic ID: UF00099239
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000901859
notis - AEL0702
oclc - 016470722

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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
    Abstract
        Page iv
        Page v
    Introduction
        Page 1
        Page 2
        Page 3
    Review of literature
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Materials and methods
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
    Results and discussion
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
    Conclusion
        Page 66
        Page 67
    References
        Page 68
        Page 69
        Page 70
        Page 71
    Biographical sketch
        Page 72
        Page 73
        Page 74
        Page 75
Full Text














SCREENING FOR RESISTANCE TO Meloidogyne incognita
(KOFOID AND WHITE) CHITWOOD IN Aeschynomene AND
Desmodium SPP. AND HERBICIDE EFFECTS ON
Aeschynomene americana L.







BY

SHERMAN F. PASLEY


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







UNIVERSITY OF FLORIDA


1981
















ACKNOWLEDGEMENTS


I wish to express my sincere thanks to my advisor,

Dr. K. H. Quesenberry, for his advice concerning my disser-

tation and classwork.

I am grateful to the Department of Agronomy for

financial assistance as well as materials in my dissertation.

I am indebted to my committee for their suggestions

concerning my dissertation.

I appreciate the technical assistance and advice given

me by the Nematology faculty and staff.

My special thanks go to my wife, Kaye, whose encourage-

ment and efforts make this dissertation as much hers as

mine.

















TABLE OF CONTENTS


Page
ACKNOWLEDGEMENTS. . . . . . . . ... ii

ABSTRACT . . . . . . . . .. . . . iv

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

REVIEW OF LITERATURE . . . . . . . . 4

MATERIALS AND METHODS . . . . . . . .. 11

Part 1 . . . . . . . . . . 15

Part 2 . . . . . . . . . . 21

RESULTS AND DISCUSSION . . . . . . ... 25

Part 1 . . . . . . . . . . 25

Part 2 . . . . . . . . .. . 59

CONCLUSION . . . . . . . . .. . . 66

REFERENCES . . . . . . . . . . . 68

BIOGRAPHICAL SKETCH . . . . . . . ... 72















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


SCREENING FOR RESISTANCE TO Meloidogyne incognita
(KOFOID AND WHITE) CHITWOOD IN Aeschynomene AND
Desmodium SPP. AND HERBICIDE EFFECTS ON
Aeschynomene americana L.

By

Sherman F. Pasley

December 1981

Chairman: Dr. Kenneth H. Quesenberry

Major Department: Agronomy


Root-knot nematodes (Meloidogyne spp.) are endemic in

Florida. In Part 1 of this study, a rapid and simple

greenhouse technique for screening large numbers of lines for

resistance to Meloidogyne incognita (Kofoid and White)

Chitwood was evaluated on 29 lines from five species of

Aeschynomene and two species of Desmodium. The lines were

grown in M. incognita infested and non-infested field plots,

and were identified as resistant or susceptible on the basis

of nematode reproduction and effect on dry matter yields.

These variables were highly correlated to visual gall scores.

Visual gall scores from lines grown in the greenhouse in M.

incognita infested soil were poorly correlated with root








and shoot biomass, vigor, and degree of nodulation but did

correctly identify the resistance or susceptibility of 27 of

the 29 lines. This indicates that the initial screening of

Aeschynomene and Desmodium lines for resistance to M. incognita

can be conducted in the greenhouse. The lines were grown in

the greenhouse in Meloidogyne arenaria (Neal) Chitwood infested

soil, and lines appearing to be resistant were identified.

Some herbicide-nematode combinations are more detrimental

to plant growth than the additive effects of each. In Part 2,

a commercial source of Florida Common American jointvetch

(Aeschynomene americana L.), thought to be resistant to M.

incognita, and a susceptible plant introduction of A. americana

were grown in a M. incognita infested field. Methyl bromide

treated plots were used to assess the effects of the herbi-

cides Trifluralin, Ethalfluralin, and Paraquat on A. americana

and non-fumigated plots to assess the effects of the herbi-

cides on M. incognita. The latter effects could not be

determined because weed competition was so severe and soil

populations of M. incognita so variable. Dry matter yields

were significantly higher in Trifluralin treated subplots

than in Paraquat treated subplots. There were no significant

herbicide effects on degree of nodulation, nitrogenase

activity, percent stand, or percent dry matter. Each source

of Florida Common American jointvetch may require screening

for resistance to Meloidogyne spp. because the source used

exhibited galling symptoms in non-fumigated plots.















INTRODUCTION


The primary goal of the Florida grassland research

program is to find the most economical way to supply enough

quality forage to attain an 80 to 85% calf crop and produce

calves of 500 or more pounds at nine months of age. One

of the stated objectives to accomplish this is to determine

the best legume(s) to use in improving established bahiagrass

(Paspulum notatum Flugge) pastures (Anonymous, 1978).

Breeding for disease and pest resistance is a paramount

consideration in a forage legume program because chemical

control measures are becoming uneconomical and the forage

legume will probably be grown on the same site for several

years which encourages disease and pest buildup. Root-knot

nematodes (Meloidogyne spp.) are endemic in Florida and,

according to Lamberti (1979), the southern root-knot nematode

[Meloidogyne incognita (Kofoid and White) Chitwood] is the

most important of the Meloidogyne complex in subtropical

climates because of its widespread distribution, wide host

range, and effect on overall yield reduction.

To keep a breeding program within manageable limits,

a plant breeder must continually evaluate and discard

unpromising material as soon as possible and routinely

screen new germplasm for desirable characteristics. One









approach to screening forage legumes for resistance to the

southern root-knot nematode involves planting these legumes

in fields thought to be infested with the nematode. Sub-

sequent evaluations, including visual observations of plant

growth, examination of the roots for galling symptoms, or

yield measurements may be conducted to assess the effects

of the nematode on the plant. Visual evaluations are usually

for characteristics such as vigor and stanC. Equating plant

appearance to the effects of the nematode is speculative,

as nematode effects may be exacerbated by or confused with

the effects cf other plant pests, plant diseases, variation

in soil conditions, or by the nature of the genetic material

under consideration. Root galling symptoms, however, are

more direct indicators of the effect of the nematode on

the plant. Field infestations of nematodes are rarely

uniform and a plant that may appear to be unaffected by

nematodes may in fact be an escape.

Replicated yield trials are often conducted in fields

thought to be infested with nematodes in order to assess the

effects of the nematodes on the plant. Replicated yield

trials are costly in terms of the labor and space they

require. For maximum efficiency, only the most promising

lines should enter these costly trials. As a consequence,

yield trials are rarely conducted on material that has not

been previously selected by the plant breeder. To aid in

this selection process, a reliable and cost-efficient means









is needed to initially screen relatively large numbers of

forage genotypes for resistance to the southern root-knot

nematode. This preliminary process must be relatively

simple and be highly correlated to the effects of the nema-

tode on the plant under field conditions. Yield trials are

often treated with herbicides because herbicides are con-

sidered cost-efficient when compared with the alternative

of hand-weeding. Because yield trials are a test of the

breeder's earlier selection efforts, more information

concerning the effects of specific herbicides on the plant

by nematode interaction is needed in order for the breeder

to choose a herbicide that will not confound the results of

his costly yield trials.

The objectives of this research were (1) to evaluate

the use of a greenhouse procedure as a preliminary means

of screening lines of Aeschynomene and Desmodium spp. for

resistance to the southern root-knot nematode, (2) to

compare greenhouse results with the effects of the nematode

on these same lines in the field, and (3) to evaluate the

effects of certain selected herbicides on the nematode by

legume interaction under field conditions.















REVIEW OF LITERATURE


The 1967-68 losses in the U. S. in grass and legume

nay due to nematodes were estimated at $118,767,300.00

(Feldmesser, 1971). Root-knot nematodes are a major group

of plant-pathogenic nematodes affecting crop production and

rank among the top five major plant pathogens because of

their worldwide distribution, extensive host range, and

involvement with fungi and bacteria in disease complexes.

The most widespread and most important agronomic species

are M. incognita, Meloidogyne javanica (Treub) Chitwood,

Meloidogyne hapla Chitwood, and Meloidogyne arenaria (Neal)

Chitwood, in that order (Lamberti, 1979). Sasser (1979b)

reported that the estimated losses in the tropics (defined

for convenience as the area between the Tropic of Cancer

and the Tropic of Capricorn) due to Meloidogyne spp.

averaged 12.69% for all major crops. He considered these

estimates conservative and stated ". . the direct losses

each year are hundreds or thousands of times greater than

the amounts which will be expended . for research on

means for alleviation of damage caused by nematodes

[Meloidogyne spp.] .. ." (1979b, p. 366). In Florida,

Dickson (1973) estimated that M. arenaria cost peanut

(Arachis hypogea L.) producers 1.6 million dollars in 1972.









The southern root-knot nematode complex is made up

of at least four races based on the parasitism of host differ-

entials. The races of M. incognita are distributed throughout

the world and are morphologically indistinguishable (Sasser,

1979a).

The life cycles of Meloidogyne spp. are similar and

can be generalized. Second stage larvae hatch from eggs

which may be free in the soil or embedded in a gelantinous

matrix which may adhere to the root tissue of the host plant.

These larvae migrate to and invade new root tips in the zone

of intense meristematic activity. They penetrate the cortex,

establish themselves with their anterior in contact with the

vascular cylinder and, in susceptible hosts, induce the

formation of giant cells upon which they feed. Galls

generally form at this stage. During their development,

the larvae undergo three moults. The mature females secrete

a gelatinous matrix in which they lay 500-1,000 or more

eggs. The number of generations per year is highly variable

and is influenced by factors such as nematode species, soil

temperature, soil moisture, soil nutrient status, and host

species. Almost all eggs hatch under optimum conditions

but there is always a variable proportion of eggs that remain

alive with their development arrested at an early stage.

Many of these dormant eggs are resistant to environmental

stress and nematicides (Guiran and Ritter, 1979).

Breeding for resistance to the southern root-knot

nematode is important because eradication on a large scale









basis is economically impractical and control through crop

rotation has limited effectiveness because the nematode is

polyphagous (Agrios, 1969). Further, it has been observed

that resistance in low value crops such as forages often

produces yields equal to those obtained with soil fumigants

(Good, 1972; Netscher and Manhoussin, 1973). The movement

to low energy technology agriculture coupled with the manu-

facturing restrictions placed on soil fumigants containing

1,2-dibromo-3-chloropropane has placed additional emphasis

on breeding for resistance to nematodes in general

(Fassuliotis, 1979). Some efforts in breeding for resistance

to M. incognita have been spectacular as was the case with

'NC 95' tobacco (Nicotiana tabacum L.) which saved growers

millions of dollars (Moore, Jones, and Gwynn, 1962).

Relative to Meloidogyne spp., most breeding efforts have

been directed toward the southern root-knot nematode.

Over 235 cultivars in 15 major crop species, including

forage legumes, have been selected or developed for resistance

to M. incognita. The notable exceptions from this list are

vegetable cultivars from Cucumis and Cucurbita spp. and

eggplant (Solanum melongena L.). In the latter cases,

resistance is either non-existent or in a sexually incompatible

form (Fassuliotus and Rau, 1963; Birat, 1966; Fassuliotis,

1979).

Generally, root-knot nematode larvae invade the roots

of both susceptible and resistant plants. Resistance is

usually expressed by larvae that fail to develop into









reproductive adults (Webster, 1975). According to Fassuliotis

and Dukes (1972), galling does not necessarily indicate

nematode development. Such lack of nematode development

may be of little value if the galling still causes crop

loss. A plant breeder is concerned with breeding plants

that can withstand nematode attack and yield as well as

plants not attached by the nematode (Fassuliotis, 1979).

Nematclogists usually advocate using some index that

includes nematode reproduction when screening for resistance

to M. incognita (Fassuliotis, 1967; Taylor, 1971). There

are numerous laboratory, greenhouse, and field methods used

to screen for resistance or sources of resistance to

Meloidogyne spp. Dropkin, Davis and Webb (1967) screened

seedlings infested with root-knot larvae on agar slants with

the assumption that seedling response corresponded to older

plant response. Fassuliotis and Corley (1967) used plastic

growth pouches to screen seedlings for resistance and Carter,

Nietro and Veech (1977) used rag dolls, normally used for

seed germination tests, for the same purpose. These

aforementioned methods of screening for resistance do not

involve any measurements of nematode reproduction and can

be conducted in the laboratory.

Most screening tests are conducted in the greenhouse

because most plants can be uprooted, indexed for resistance

and then replanted (Barrons, 1939; Bailey, 1940; Fassuliotis,

1979). Field plots are desirable because large populations

can be grown and those plants classified as resistant can









then be selected for desirable agronomic or horticultural

traits. This would not be recommended for initial screening

because field plots are rarely uniformly infested (Fassuliotis,

1979). If greenhouse facilities are inadequate for initial

screening and field plots are used, the method of Ross and

Brim (1957) may preclude selecting escapes because a highly

susceptible plant is planted in close proximity to a test

plant and both are evaluated at the same time. The majority

of the methods for assaying nematode reproduction are rather

laborious and seem beyond the capabilities of many breeding

programs. According to Holbrook (1981), the method used by

Fenner (1962) to determine nematode mortality can be used

to highlight egg masses on the roots of nematode-infested

plants. This may be an indirect means of assaying nematode

reproduction and might be less laborious and/or complicated

than many other methods used for this purpose.

Root-knot nematodes often interact with other plant-

pathogenic organisms causing crop losses more severe than

would be expected from the additive effects of each organism.

Some of these interactions include Meloidogyne-Fusarium

(Powell, 1963), Meloidogyne-Verticillum (McClellan, Wilhelm,

and George, 1955), Meloidogyne-Phytophthora (Nusbaum and

Chaplain, 1952) and Meloidogyne-Rhizoctonia (Batten and

Powell, 1971). It seems the nematode provides an entry

point for the disease organism and/or predisposes the

plant to attack.









Meloidogyne-herbicide interactions are less well

documented but Griffin and Anderson (1978) did report that

the combination of trifluralin (a,a,a,-trifluoro-2,6-dinitro-

N,N-dipropyl-p-toluidine) and M. hapla reduced plant height

and weights of tomato (Lycopersicon esculentum L.) and

alfalfa (Medicago sativa L.) more than the additive effects

of the nematode and the herbicide. Griffin and Anderson

(1979) found that EPTC (S-ethyl dipropylthiocarbamate)

reduced the resistance of 'Nev Syn XX' alfalfa to M. hapla.

They also found that chlorpropham isopropyll m-chlorocarbin-

ilate) and DCPA (dimethyl tetrachloroterephthalate) severely

reduced the root growth of alfalfa thereby reducing infec-

tion by M. hapla because of fewer infection sites. Johnson,

Dowler, and Hauser (1975) reported that soil-applied

herbicides (unspecified types) did not significantly affect

nematode population densities.

In Florida, land is frequently cleared and vegetables

planted year after year until the buildup of soil pests,

including nematodes, and diseases makes vegetable production

uneconomical. Then, grass pastures are often planted on

this land with the idea that grass is a less suitable host

to the pests and diseases and will reduce the soil popula-

tions of pests and diseases while making the land economically

productive. This practice often precludes the use of some

forage legumes in these pastures. Kretschmer, Sonoda,

and Snyder (1980) report that 'Florida' carpon desmodium





10


[Desmodium heterocarpon (L.) DC.], a tropical forage legume

released in Florida, is highly susceptible to root-knot

nematodes and should not be planted in areas infested with

these nematodes. They did report that Florida Common

American jointvetch (Aeschynomene americana L.) was resis-

tant to Meloidogyne spp. Rhoades (1980) reported that A.

americana exhibited a high degree of resistance to M.

incognita and might have use as a cover crop for the purpose

of reducing soil populations of M. incognita.















MATERIALS AND METHODS


The study was conducted in two parts. In Part 1,

18 genotypes from five species of the genus Aeschynomene

and 11 genotypes from two species of the genus Desmodium

were screened for resistance to the southern root-knot

nematode (Tables 1, 2, and 3). These genoytpes were

selected because of their potential as forage legumes in

the state of Florida (Quesenberry, personal communication*)

and the availability of sufficient seed to complete this

part of the study. Aeschynomene americana, Desmodium

barbatum (L.) Benth. and Oerst., and D. heterocarpon were

the genera and species of primary interest. Aeschynomene

brasiliana (Poir.) DC., Aeschynomene indica L., Aeschynomene

rudis Benth., and Aeschynomene villosa Poir. in Lam. were

included to increase the scope of the experiment. Since

each of these latter species was represented by only one

or two genotypes, no generalizations about a particular

species were attempted. The central hypothesis in Part 1

of this study was that root gall scores could be used to

identify genotypes that were susceptible to the southern



*K. H. Quesenberry, Associate Professor, Department
of Agronomy, University of Florida, Gainesville, Florida,
1979.











Table 1. Source and identification
Aeschynomene americana.


of genotypes of


Entry Identificationt Origin


P.I. 421680


Florida


Florida Common


IRFL 1982

IRFL 2054


P.I. 420304

P.I. 420313

P.I. 420314

CIAT 2868


CIAT 9666


CIAT 9881


CIAT 9882


Florida
(Commercial)

Brazil

Leticia
Colombia

Australia


Australia

Australia

Valle del Cauca
Colombia

Mato Grosso
Brazil

Choco
Colombia

Choco
Colombia


t P.I. = USDA plant introduction number; IRFL = Indian
River Field Lab number assigned by Dr. A. E. Kretschmer,
Jr.; CIAT = Centro Internacional de Agricultura number,
Cali, Colombia.











Table 2. Source and identification of genotypes of
Aeschynomene spp.



Entry Species Identificationt Origin



12 brasiliana CIAT 7011 Herrera
Panama

13 "IRFL 2017 Brazil

14 indica P.I. 420283 Australia

15 P.I. 420288 Australia

16 rudis CIAT 9875 Antioquia
Colombia

17 villosa IRFL 2925 Yumbo
Colombia

18 "IRFL 2929 Lologuerrero
Colombia



t CIAT = Centro Internacional de Agricultura Tropical
number, Cali, Colombia; IRFL = Indian River Field Lab
number assigned by Dr. A. E. Kretschmer, Jr.; P.I. =
USDA plant introduction number.











Table 3. Source and identification of genotypes of
Desmodium spp.



Entry Species Identificationt Origin


barbatum


"


CIAT 3010


CIAT 3125


CIAT

CIAT


heterocarpon

"


3239

3563


CIAT 3116

P.I. 317049

'Florida'
Carpon

P.I. 317049

CIAT 3669

CIAT 3671

CIAT 3670


Cochabamba
Bolivia

Vichada
Colombia

Belize

Monagas
Venezuela

(ex Florida)

India

India


India

India

Fiji Islands

Fiji Islands


t CIAT = Centro Internacional de Agricultura Tropical
number, Cali, Colombia; P.I. = USDA plant introduction
number.

t Received as P.I. 317049 from the Southern Regional Plant
Introduction Station and as IRFL #854 from Dr. A. E.
Kretschmer, Jr.

Received as D. heterocarpon but identified by some as
D. heterocarpon var. ovalifolium.









root-knot nematode. Essential to this hypothesis was the

correlation between gall scores and the effect of the nema-

tode on the plant (plant growth) and between gall scores and

the effect of the plant on the nematode (nematode reproduction).

In part 2 of this study, two genotypes of A. americana

were studied to determine the effects of three herbicides

on the legume and the southern root-knot nematode. 'Treflan'

(a,a, a,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine),

'Sonalar' (N-ethyl-N(2-methyl-2-propenyl)-2,6-dinitro-4-

(trifluoromethyl)benzenamine), and Paraquat (l,l'-dimethyl-

4,4'-bipyridinium ion) were the herbicides selected because

of their effects on the weeds that were expected to be the

major source of competition.





Part 1


Greenhouse 1980


On 15 January 1980, seeds from each entry were mechan-

ically scarified and germinated in Petri dishes. The

seedlings were planted in 20.5 cm 'Conetainers' filled with

a 3:1 mixture of sterilized Pomona sand (sandy, siliceous,

hyperthermic Ultic Haplaquod) and vermiculite. The mixture

had been amended with sufficient ground limestone to raise

the pH to 6.0 (determined with a 'Coleman metrion IV' pH

meter). The seedlings were inoculated at planting with

'Nitragin' 'EL' culture Rhizobium cowpeaa type).









The seedlings were placed in a growth room with a 13-

hour day length and daytime and nighttime temperatures of

32 and 26DC, respectively, in an attempt to simulate late

spring and early summer light an3 temperature conditions in

mid-Florida. The seedlings were watered when necessary

and amended biweekly with a phosphorous-potassium solution.

Light intensity in the growth room could not be increased

beyond 100 gEm sec After eight weeks, the seedlings

were moved to a greenhouse because of very slow plant growth.

Daytime and nighttime temperatures in the greenhouse ranged

from 43 to 24C, respectively.

On 26 March 1980, the seedlings were infested with M.

incognita eggs separated from the roots of 'Rutgers'

tomato plants by the method of Hussey and Barker.(1973).

Three levels of infestation were used: no infestation;

1 egg/g soil; and 10 eggs/g soil.

Six and 10 weeks after infestation, three plants

selected at random from each entry-treatment combination

wtre visually scored for degree of root galling, degree of

vigor, and degree of nodulation. Galling was scored on a

0-5 scale where 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls,

3 = 11-30 galls, 4 = 31-100 galls, and 5 = over 100 galls.

Vigor was scored on a 0-5 scale; 0 = a dead plant and 5 =

a very vigorous plant. Nodulation was also scored on a 0-5

scale; 0 = no nodules and 5 = a well nodulated plant. In

addition, root and top weights were determined for each

plant.









Field 1980


In the summer of 1980, the study was continued at the

Agronomy Farm and the Beef Research Unit (BRU). The Agronomy

Farm is located near the campus of the University of Florida,

Gainesville, Florida, and is typified by Kendrick fine sand

(loamy, siliceous, hyperthermic Arenic Paleudult). The BRU

is located approximately 10 miles north of Gainesville,

Florida, and is typified by Pomona sand. The soil pH at

both locations was 5.6 or above (determined by the Florida

Cooperative Extension Service, Gainesville, Florida).

On 10 May 1980, seeds from all entries were mechanically

scarified and germinated in Petri dishes. The seedlings

were inoculated with 'Nitragin' 'EL' culture Rhizobium (cow-

pea type) and planted in 20.5 cm 'Conetainers' or in 'Speedling'

trays filled with a 1:1 mixture of sterilized Pomona sand

and 'Jiffy Mix' (peat + vermiculite). On 4 June 1980,

one-half of the seedlings of each entry were infested with

one M. incognita egg/g soil; the eggs obtained as described

previously.

Both locations were fertilized with 448 kg/ha of 0-10-20

fertilizer that had been amended with 'FTE 503' (contains the

equivalent of 9.6% B203, 3.8% CuO, 25.7% Fe203, 9.7% MnO,

0.3% MoO3, and 8.7% ZnO by weight) at the rate of 20

kg/metric ton of fertilizer. After fertilization, the soil

fumigants 'D-D' (AI 1,3-dichloropropene and 1,2-dichloro-

propane) at the rate of 128 1/ha and 'Telone II' (AI, 1,3-









dichloropropene) at the rate of 173 1/ha were applied at

the Agronomy Farm and the BRU, respectively, in an attempt

to reduce the soil population of the southern root-knot

nematode. The fumigants were applied with a chisel appli-

cator at a depth of approximately 20 cm with an inter-

chisel spacing of 45 cm. A minimum of two weeks between

fumigant application and planting elapsed to alleviate any

phytotoxic effects of the fumigants.

On 18 and 25 June, the seedlings were transplanted

at the Agronomy Farm and the BRU, respectively. Because

of seed quantity, it was necessary to conduct this experiment

on spaced plants. The paired-plot technique was used with

three replications at each location with one plot planted

with non-infested plants and its sister plot planted with

infested plants of the same genotype. A plot consisted of

a row of nine plants with an intra-row spacing of 0.5 m

and an inter-row spacing of 1.0 m. Throughout this exper-

iment, supplemental irrigation was provided when necessary

and weed control was accomplished by hand.

Three dry matter harvests were made at 6-week intervals

beginning eight weeks after transplanting. A harvest

consisted of hand-cutting three randomly selected plants

from-each plot, excluding end-of-row plants. The remaining

unharvested plants in each plot were cut back to the same

height as those plants harvested for dry matter.

Seventeen weeks after transplanting, one randomly

selected plant was dug with a shovel from each plot. The









root system was visually scored for degree of root galling

on the same 0-5 scale used previously. Approximately 10

grams of root material were cut into 5 mm pieces and

incubated for 24 hours using a modified Baermann technique

(Dunn, personal communication*) for the purpose of assaying

nematode reproduction. Three sub-samples were drawn to

count M. incognita larvae, the counts averaged for each

plot and adjusted to reflect nematode numbers per 10 grams

of root material.



Greenhouse 1981


In January 1981, the 1980 greenhouse experiment was

conducted again because of missing data, to check repeat-

ability of the results, and to obtain additional data. On

5 January, 15 seeds from all entries were mechanically

scarified and germinated in Petri dishes. The germinating

seedlings were planted in 10.3 cm diameter plastic pots.

Pots were used instead of 'Conetainers' because it had

been hypothesized that the slow plant growth seen in the

1980 greenhouse experiment may have been due, in part, to

the limited volume of the 'Conetainers.'" The pots were

filled with sterilized Pomona sand that had been amended with

ground limestone to bring the pH to 6.0 (determined with

a 'Coleman metrion IV' pH meter) and with a 448 kg/ha


*R. A. Dunn, Extension Nematologist, Department of
Entomology and Nematology, University of Florida, Gainesville,
Florida, 1980.








equivalent of 0-10-20 fertilizer containing 20 kg of 'FTE

503' per metric ton of fertilizer. The decision to use

soil instead of a soil-vermiculite mixture was made because

of the difficulty encountered previously in separating root

material from the vermiculite. The seedlings were not

inoculated with Rhizobium because some of the entries

nodulated poorly or not at all in the preceding experi-

ments. The seedlings were placed in a greenhouse where

daytime and nighttime temperatures ranged from 32 to 220C,

respectively. All plants were watered when necessary and

fertilized biweekly with a 12-10-20 fertilizer containing

trace elements.

On 24 January, one-third of the plants from each entry

were infested with 10 M. incognita eggs/g soil; one-third

were infested with 10 M. arenaria eggs/g soil; and the

remaining third served as a check. The nematode eggs were

obtained as previously described.

Ten weeks after infestation, all plants were scored

for degree of root galling and degree of root growth. Root

galling was visually scored on the 0-5 scale used previously

Degree of root growth was assayed by two methods. The first

was a visual evaluation on a 0-5 scale; 0 = normal root

growth and 5 = little or no secondary root growth. The

second method was to immerse the root system of each plant

in 500 ml of water and record the amount of water the root

system displaced. Two D. heterocarpon genotypes reported

to be resistant to Meloidogyne spp., IRFL #1699 and #1946









(Kretschmer et al., 1980), were added to this experiment as

entries #30 and #31. They were infested with M. arenaria

and M. incognita and scored for degree of root galling but

not for root growth.





Part 2


In May of 1981, the study was continued at the Agronomy

Farm on the same site used in Part 1 of the study. A

commercial seed source of Florida Common American joint-

vetch, thought to be resistant to M. incognita (Kretschmer

et al., 1980; Rhoades, 1980), and entry #9, found to be

susceptible to the southern root-knot nematode in Part 1

of the study, were used in an attempt to assess the effects

of the herbicides on A. americana and M. incognita.

The site was fertilized at the rate of 448 kg/ha with

an 0-10-20 fertilizer that had been amended with 20 kg of

'FTE 503' per metric ton of fertilizer. Subsequent to

fertilization, 16 4 x 8 meter plots were fumigated with

methyl bromide at the rate of 2.2 kg/9.8 m The purpose

of the fumigation was to remove as much Competition as

possible so that the effects of the herbicides on the legume

could be assessed. A split-split-split-plot design of eight

replications was used. A whole plot consisted of two 4 x 8

meter areas (one fumigated and one non-fumigated) to which

one genotype of Aeschynomene was planted, a subplot consisted









of one 4 x 8 meter area (fumigated and non-fumigated), and

a sub-sub-plot consisted of one 2 x 4 meter area to which a

herbicide treatment was applied: check, 'Treflan', 'Sonalan',

or Paraquat. This design was chosen inasmuch as herbicide

effects were the area of primary interest.

Immediately prior to planting, one sub-sub-plot in

each subplot was sprayed with 'Treflan' at the rate of 0.56

kg/ha and incorporated with a rototiller. Following this,

the entire site was cultipacked and hand-broadcast with seed

that had been mechanically scarified and coated with a mixture

of 'Pel-gel' sticker and 'Nitragin' 'El' culture Rhizobium

cowpeaa type). Sufficient seed, based on a 25% emergence

rate, was broadcast in an effort to assure one plant every

25.8 cm2. Immediately following planting, the site was

cultipacked and one sub-sub-plot in each subplot was sprayed

with 'Sonalan' at the rate of 1.0 kg/ha. The entire site

was sprinkler-irrigated the same day and irrigation was

subsequently provided as often as possible in an effort to

aid germination and emergence. After seedling emergence,

irrigation was provided when necessary. On 28 May, one sub-

sub-plot in each subplot was sprayed with Paraquat at the

rate of 0.25 kg/ha.

During the period 29 June to 2 July, two plants from

each sub-sub-plot in the fumigated subplots were selected

at random, dug, and assayed for nitrogenase activity (C2H2

reduction). Acetylene reduction assays were not conducted

on non-fumigated sub-plots because of severe weed growth.









Tops and roots of those plants dug were separated and the

root system scored for degree of galling and nodulation

using the scales previously described. The root system of

each plant was placed in individual 0.96 glass jars the

tops of which had been fitted with serum stoppers. A

volume of air equal to the volume of acetylene to be

injected was withdrawn from the jars and the reaction

initiated by acetylene injection to 10% (v/v). At 30

and 60 minutes after acetylene injection, 0.5 ml was with-

drawn from each jar and assayed with a 'Varian' model 940

gas chromatograph for acetylene and ethylene. The tops

and roots from each plant assayed were dried and weighed.

Acetylene reduction values were adjusted to nM/hr/g of plant

biomass.

On 8 July, a 1 x 3 meter area of each sub-sub-plot

was harvested for dry matter yield with a 'Carter' plot

harvester. Prior to harvest, each sub-sub-plot was visually

scored for percent Aeschynomene and the dry matter yield

was adjusted to reflect the amount of Aeschynomene harvested

based on this visual estimate. After harvest and on 13

August, two plants selected at random from each sub-sub-

plot in non-fumigated subplots were dug and the root system

visually scored for degree of root galling using the scale

described previously.

Data from both parts of the study were analyzed at the

Northeast Regional Data Center of the State University

System of Florida, Gainesville, FL 32611, using the





24



Statistical Analysis System (SAS) on an 'Amdahl 470 V/6-II'

computer with OS/MVS Release 3.8 and JES 2/NJE Release 3.0.

Because the data were unbalanced in the sense that there

were unequal numbers of entries in different species, the

data were analyzed by species.















RESULTS AND DISCUSSION


Part 1


Greenhouse 1980


As indicated previously, plant growth was less than

satisfactory. Roots of some entries were necrotic at both

sampling dates which may have been due to the effects of the

southern root-knot nematode but was probably compounded by

the conditions in the growth room. Galling symptoms were

more pronounced and thus easier to score at the higher

infestation rate and at the 10-week sampling date.

Seven of the 11 genotypes of A. americana tested

appeared to be susceptible to the southern root-knot

nematode (Table 4). No reason can be given to explain why

entry #9 showed galling symptoms at the 6-week sampling

date but not at the 10-week sampling date. Vigor was the

only variable significantly correlated to gall scores but

the correlation coefficient of -0.17 seemed too low to be

of any value (Table 5). It is not surprising that top

weight, root weight, vigor, and degree of nodulation are

significantly correlated. In effect, the first three

variables are indirect measurements of each other and because










Table 4. Gall scores in response to Meloidogyne incognita
for 11 genotypes of Aeschynomene americana at two sampling
dates and two rates of infestation (Greenhouse 1980).



Sampling Date

6-week 10-week
Entry
1 egg/g 10 eggs/g 1 egg/g 10 eggs/g
soil soil soil soil


gall scores
1 0.0 0.0 0.0 0.0

2 0.0 0.0 0.0 0.0

3 0.0 0.0 1.3 1.3

4 0.0 0.0 0.0 2.0

5 0.0 0.0 0.0 0.0

6 0.0 0.0 0.0 2.0

7 0.0 2.0 3.0 4.0

8 1.0 0.0 0.0 0.0

9 3.0 3.0 0.0 0.0

10 2.0 0.0 0.0 4.0

11 3.0 2.0 0.0 3.0



t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.










Table 5. Correlation of gall scores with top weight, root
weight, plant vigor, and degree of nodulation in response
to Meloidogyne incognita for 11 genotypes of Aeschynomene
americana (Greenhouse 1980).



Top Root Plant Nodulation
Weight Weight Vigor Score



Gall -0.01 0.08 -0.17* -0.01
Scores

Top 0.79** 0.40** 0.35**
Weight

Root 0.31** 0.34**
Weight

Plant 0.53**
Vigor



*, ** Significance at the 5 and 1% probability level,
respectively.








no nitrogen fertilizer was provided the plants, degree of

nodulation would be expected to have a direct bearing on

plant growth.

Two of the genotypes tested in the remaining species

of Aeschynomene showed gal ing symptoms in response to

M. incognita (Table 6).

One of the four genotypes of D. barbatum tested

appeared to be susceptible to M. incognita (Table 7).

The positive significant correlation between gall scores and

top weight may not be meaningful (Table 8). The southern

root-knot nematode is expected to adversely affect the growth

of susceptible plants, so this correlation should be

negative for significance. The positive significant corre-

lation between gall scores and root weight may be meaningful

because the root system of a heavily galled plant might

weigh more than the healthy root system of a plant of the

same genotype.

All genotypes of D. heterocarpon tested seemed to be

susceptible to the southern root-knot nematode (Table 7).

As was the case with entry 49, entry #25 showed galling

symptoms at the 6-week sampling date but not at the 10-

week sampling date. The lack of a significant correlation

between gall scores and the other variables and the signifi-

cant correlations among the variables top weight, root

weight, vigor, and degree of nodulation (Table 9) are

similar to the correlations in A. americana (Table 5) and




















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Table 8. Correlation of gall scores with top weight, root
weight, plant vigor, and degree of nodulation in response
to Meloidogyne incognita for seven genotypes of Desmodium
barbatum (Greenhouse 1980).



Top Root Plant Nodulation
Weight Weight Vigor Score



Gall
Scores 0.25* 0.43* 0.07 0.16

Top
Weight 0.90** 0.63** 0.63**

Root
Weight 0.62** 0.64**

Plant
Vigor 0.88**



*, ** Significance at the 5 and 1% probability level,
respectively.









Table 9. Correlation of gall scores with top weight, root
weight, plant vigor, and degree of nodulation in response
to Meloidogyne incognita for four genotypes of Desmodium
heterocarpon (Greenhouse 1980).



Top Root Plant Nodulation
Weight Weight Vigor Score



Gall
Scores -0.01 0.03 -0.04 0.09
Scores

Top
Weight 0.93** 0.75** 0.66**

Root
eight 0.74** 0.69**
Weight

Plant
Vigor 0.83**



**Significance at the 1% probability level.








would seem to indicate that factors other than the southern

root-knot nematode affected top weight, root weight, vigor,

and degree of nodulation.



Field 1980


Degree of root galling was the standard by which the

effectiveness of treatments was to be judged and yield

differences between treatments within entries was the measure-

ment of the effect of M. incognita on the plant. Thus, if

the non-infested treatment is galled due to indigenous

soil populations of M. incognita to an extent equal to the

infested treatment, the effect of the southern root-knot

nematode on a genotype could not be determined. Nematodes

were counted to determine if those entries that galled

also supported nematode reproduction, not to determine if

there were differences in the level of nematode reproduction

among those entries that galled. It would seem that the

environment would have to be narrowly defined and rigidly

controlled in order to detect true inter-line differences

in levels of nematode reproduction because of the number

of factors that can affect nematode reproduction.

The data from the Agronomy Farm indicate that treat-

ments were ineffective because those lines that galled did

so whether in infested or non-infested plots (Tables 10,

11, and 12). The data from the BRU indicate that, with the

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those lines that galled did so only in infested plots.

These differences may have been due to differences in the

levels of soil populations of M. incognita and/or differ-

ences in the effectiveness of the soil fumigants used at

the two locations. Entry #16 appeared to show galling

symptoms at the Agronomy Farm but not at the BRU. This

may have been due to a misclassification because the roots

of this entry were rather necrotic when sampled at both

locations.

Those lines that galled also supported nematode

reproduction and some ungalled lines appeared to support

nematode reproduction at both locations. Every effort

was made to wash all soil from the root systems of those

plants assayed for nematode reproduction but it is possible

that some soil adhered to the root system and the nematodes

seen from ungalled root systems may have been from the

soil although Fassuliotis, Deakin, and Hoffman (1970) did

report that normal nematode reproduction occurred on some

lines of Phaseolus spp. that showed no galling symptoms in

response to root-knot nematodes.

Because of these location differences, the BRU results

were concluded to be the more valid estimate of the effects

of M. incognita on yield. There were significant treatment

differences for yield in the 11 genotypes of A. americana

tested at the BRU (Table 13). Yields in non-infested plots

generally increased with date of harvest and yield differences








Table 13. Dry matter yields for three harvest dates for
11 genotypes of Aeschynomene americana grown in non-
infested plots and plots infested with Meloidogyne
incognita (Beef Research Unit 1980).



Date of Harvest
Entry Treatmentt
17 July 28 August 3 October


g /3


plants


L.S.D. (0.05)


t 1 = non-infested plots;


2 = infested with M. incognita.


t Those entries showing gall symptoms in infested plots.








between infested and non-infested plots tended to increase

with date of harvest for those entries showing gall symptoms.

Gall scores were significantly correlated to all other

variables for the genotypes of A. americana tested at the

BRU (Table 14). Because nematode numbers were considered

an indication of nematode reproduction on a plant and yield

differences between infested and non-infested plots an

indication of the effect of the southern root-knot nematode

on the plant, it seems that field gall scores are quite

useful for predicting the susceptibility of A. americana

genotypes to M. incognita. It is of interest that the

correlation between gall scores and nematode numbers

improved when the log of nematode numbers was used in the

correlation. This was probably due to the fact that gall

scores were fairly consistent across replications whereas

nematode numbers were highly variable.

There were significant treatment differences for yield

in the genotypes of D. barbatum tested at the BRU although

not in the entry that showed gall symptoms in infested

plots (Table 15). The significant yield differences

between treatments for entry #21 are of interest because

the root system of this entry from an infested plot was not

galled but did show a marked reduction in secondary root

growth when visually compared with the root system of a plant

from a non-infested paired-plot. This may be an example

of a resistant but intolerant genotype. That is, this






40






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Table 15. Dry matter yields for three harvest dates for
four genotypes of Desmodium barbatum grown in non-
infested plots and plots infested with Meloidogyne
incognita (Beef Research Unit 1980).



Date of Harvest
Entry Treatmentt
17 July 28 August 3 October


g/3 plants


1 103 63 80
19
2 59 69 84

201 27 35 30
0 2 29 9 0

1 1 145 176 160
2 69 124 88

1 56 131 78
2 74 145 80

L.S.D. (0.05) 35 64 65


t 1 = non-infested
incognita.


$ Indicates those entries
plots.


plots; 2 = plots infested with M.


showing gall symptoms in infested









genotype does not gall or support nematode reproduction

but suffers a significant yield reduction in the presence

of the southern root-knot nematode.

Gall scores were significantly correlated to all other

variables in the genotypes of D. barbatum tested at the

BRU (Table 16). The correlation between gall scores and

yields) is rather low, probably because entry #21 suffered

a significant yield reduction without galling. But gall

scores and nematode numbers were highly correlated and

because nematode reproduction is generally accepted as a

measure of susceptibility, it would seem that field gall

scores are an effective indication of the susceptibility of

D. barbatum genotypes to M. incognita.

Four of the seven genotypes of D. heterocarpon tested

at the BRU had significant yield differences between treat-

ments in the last two harvests (Table 17). The L.S.D.,

in general, exceeded the yields of the remaining three

genotypes at all harvests.

Gall scores were significantly correlated to all other

variables except the first harvest dry matter yields in the

genotypes of D. heterocarpon tested at the BRU (Table 18).

As was the case with A. americana, and probably due to the

same reason, the correlation between gall scores and log

of nematode numbers showed a marked improvement over the

correlation between gall scores and nematode numbers. It

would seem that field gall scores can be used as a measure

of the susceptibility of genotypes of D. heterocarpon to

M. incognita.










Table 16. Correlation of field gall scores with dry matter
yields from three harvests and with nematode numbers for
four gentoypes of Desmodium barbatum grown in non-
infested plots and plots infested with Meloidogyne
incognita (Beef Research Unit 1980).



Harvest Harvest Harvest Total Nematode
1 Yield 2 Yield 3 Yield Yield Numbers


Gall -0.38** -0.51** -0.52** -0.52** 0.90**
Scores

Harvest0.66** 0.86** 0.89** -0.34**
1 Yield

Harvest 0.80** 0.92** -0.45**
2 Yield

Harvest 0.96** -0.46**
3 Yield

Total -0.46**
Yield



**Significance at the 1% probability level.










Table 17. Dry matter yields for three harvest dates for
seven genotypes of Desmodium heterocarpon grown in non-
infested plots and plots infested with Meloidogyne
incognita (Beef Research Unit 1980).



Date of Harvest
Entry Treatmentt
17 July 28 August 3 October


g/3 plants


L.S.D. (0.05)


t 1 = non-infested
incognita.


plots; 2 = plots infested with M.


$ Those entries showing gall symptoms in infested plots.













O) U L -x
S' 4 *.*

0 44 0 a) .
O Qm 0n %
S- o o oC
0 Z I I I

4J -P b,-

0 0

O i m V 4N m N
'3 N c r-
o 0 0 o N m


S00
" I I I I






6 C r i i m r

O- O-T o o o o
'0 JC " E >< I
0C 0
4- 4- 4






E 1. LO -a ++
(tr4 "A 02 r
Enm Q) co
. > *4 r N
oO 0 0 N N







0 0 0 0 Ci
O H-i





o o o o
4-) a ) a 41
O0




10 -} m -
RC 2 00

1Cm


*-0 I4- > 0
>l- >O 0 a mH . O





Q4 rO r. - pM >
0 0 r. C ,
H 4 0 N I 0 ~
4.0 W 4







. 4 -H UH
CCC) En A 4A
i c mi 4-'3 4J 4 -' 1 r-
> a ) mH- H I ,r-I En,-1 0 p
S"OO Ul) WO) a) a) 0 V) 4WJ 0)
4 l ) o >-H >. >.H-4 fH mdr*
-A c0 4 o >4 >i 4 >I 4ji a) E Lo
m n L) rd (a ra O --i W
p 0 UOi =E =N = m Ei 1 ZZ Z









Greenhouse 1981


Because field gall scores were generally higher than

greenhouse gall scores, Taylor's (1971) description of a

very resistant plant was used to divide greenhouse gall

scores into two categories: a score of less than 2 indi-

cated a resistant plant and a score of 2 or more indicated

a susceptible plant. By this standard, 1981 greenhouse

gall scores identified the resistance or susceptibility to

M. incognita (as determined at the BRU) for 10 of the 11

genotypes of A. americana with entry #9 being misclassified

as resistant (Table 19). The 1980 greenhouse gall scores

also correctly identified 1C of the 11 genotypes with entry

#8 being misclassified as resistant. There appeared to be

variability for resistance to M. arenaria within A. americana

(Table 20). Gall scores in response to M. arenaria appeared

to be of a lesser magnitude than gall scores in response to

M. incognita. Certain entries which galled in response to

M. arenaria did not in response to M. incognita and vice

versa. This suggests that two different genetic mechanisms

exist within A. americana for resistance to M. arenaria

and M. incognita.

The significant correlation between gall scores and

root volume for A. americana (Table 21) do not seem meaning-

ful when the data are examined (Table 22). In some entries,

the non-infested root system had a larger volume than the

infested root system; in other entries the opposite was










Table 19. Gall scores in response to Meloidogyne incognita
for 11 genotypes of Aeschynomene americana [Beef Research
Unit (BRU) 1980, Greenhouse 1980 (GH80), and Greenhouse
1981 (GH81)].



Entry BRU GH80 GH81


-- gall scores

1 O.0(R)t 0.0(R) 0.0(R)

2 0.0(R) 0.0(R) 0.0(R)

3 0.0(R) 1.3(R) 0.0(R)

4 5.0(S) 2.0(S) 5.0(S)

5 0.0(R) 0.0(R) 0.0(R)

6 5.0(S) 2.0(S) 5.0(S)

7 4.0(S) 4.0(S) 5.0(S)

8 4.3(S) 0.0(R) 3.8(S)

9 5.0(S) 3.0(S) 0.7(R)

10 5.0(S) 4.0(S) 5.0(S)

11 5.0(S) 3.0(S) 5.0(S)



t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.

$ R = resistant and S = susceptible to M. incognita.










Table 20. Gall scores in response to two species of
Meloidogyne for 11 genotypes of Aeschynomene americana
(Greenhouse 1981).




Nematode
Entry
M. arenaria M. incognita


Sgall scores


t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over -100 galls.




49







Table 21. Correlation of gall scores with root volume and
with visual root scores for 11 genotypes of Aeschynomene
americana (Greenhouse 1981).



Root Visual
Volume Root Scores



Gall Scores -0.29** 0.84**

Root Volume -0.36**



**Significance at the 1% probability level.










Table 22. Root volume as affected by two species of
Meloidooyne for 11 genotypes of Aeschynomene americana
(Greenhouse 1981).



Treatment
Entry
Untreated M. arenaria M. incognita


ml


8.8

7.5

8.8

10.0

6.3

6.3

5.0

7.5

7.5

7.5

6.3


10.0

8.8

8.8

6.3

10.0

5.0

5.0

8.8

7.5

7.5

5.0


t Those lines showing gall symptoms in
arenaria.

t Those lines showing gall symptoms in
arenaria and M. incognita.

Those lines showing gall symptoms in
incognita.


response to M.


response to M.


response to M.









true. The significant correlation between gall scores and

visual root scores may be biased in that the evaluator might

unconsciously assign a more severe visual root score to a

heavily galled plant than to a healthy plant. Thus, in A.

americana, an assessment of root growth may be useful only

in those entries not showing gall symptoms.

Dunn (personal communication*) believes that heavy

root galling indicates susceptibility to M. incognita. By

this description, the 1980 BRU results failed to identify

the susceptibility of entries #13, #16, and #17 and the 1981

greenhouse results failed to identify the susceptibility of

entry #15 to M. incognita for the seven genotypes of

Aeschynomene spp. used in the study (Table 23). Resistance

can be modified by plant genotype and environmental factors

(Rohde, 1965). Dropkin (1969) found that 'Nematex' tomatoes

grown at a soil temperature of 280C were highly resistant

to M. incognita acrita but at a soil temperature of 330C

seedlings were fully susceptible. Conversely, he observed

that the resistance of the African horned cucumber (Cucumis

metuliferus E. May) to M. incognita acrita increased as

soil temperatures rose from 28 to 320C. These observations

may explain, in part, the differences between the 1980 BRU

and 1981 greenhouse results because the conditions in the

field were not the same as those in the greenhouse. Plant



*R. A. Dunn, Extension Nematologist, Department of
Entomology and Nematology, University of Florida,
Gainesville, Florida, 1981.










Table 23. Gall scores in response to Meloidogyne incognita
for four species of Aeschynomene [Beef Research Unit
(BRU) 1980, Greenhouse 1980 (GH80), and Greenhouse 1981
(GH81)].



Entry Species BRU GH80 GH81


---gall scores -


12 brasiliana 0.0(R)f ND 0.8(R)

13 0.0(R) ND 3.0(S)

14 indica 5.0(S) 4.0(S) 2.0(S)

15 2.0(S) ND 0.5(R)

16a rudis 3.7(S) 0.0(R) 4.3(S)

17 villosa 0.0(R) 0.0(R) 2.3(S)

18 2.5(S) 0.0(R) 2.7(S)


t 0 = no galls, 1 =
galls, 4 = 31-100

$ R = resistant and


1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, and 5 = over 100 galls.

S = susceptible to M. incognita.


ND = no data due to death of plants.

Found to be resistant at the BRU and susceptible at the
Agronomy Farm.









growth of these Aeschynomene spp. was so poor in the 1980

greenhouse experiment that no generalizations of this seg-

ment of the 1980 greenhouse experiment can be made. There

did appear to be variability for resistance to M. arenaria

within the seven genotypes of Aeschynomene spp. (Table 24).

Both the 1980 and 1981 greenhouse gall scores correctly

identified the resistance or susceptibility to M. incognita

for four genotypes of D. barbatum (Table 25). There

appeared to be variability for resistance to M. arenaria

within the genotypes of D. barbatum tested (Table 26).

Those genotypes that galled or did not gall did so to both

M. arenaria and M. incognita. Also, the magnitude of the

gall scores in response to the two nematodes seemed similar.

The variables gall scores, root volume, and visual

root scores were significantly correlated within the geno-

types of D. barbatum (Table 27). In contrast to A.

americana, the non-infested entries generally had a larger

root volume that did those same entries that were infested

with M. arenaria or M. incognita (Table 28), indicating that

an assessment of root growth may be useful in D. barbatum

although these results were based on only four genotypes.

The 1980 and 1981 greenhouse gall scores correctly

identified the susceptibility to M. incognita for seven

genotypes of D. heterocarpon (Table 25). Entries #30 and

#31 seemed to be resistant to both M. incognita and M.

arenaria (Table 26). There appeared to be variability for

resistance to M. arenaria in the nine genotypes of










Table 24. Gall scores
Meloidogyne for four
1981).


in response to two species of
species of Aeschynomene (Greenhouse


Nematode
Entry Species
M. arenaria M. incognita


--- gall scores


12 brasiliana 2.0 0.8

13 2.5 3.0

14 indica 3.0 2.0

15 1.3 0.5

16 rudis 5.0 4.3

17 villosa 0.3 2.3

18 0.0 2.7



t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.










Table 25. Gall scores in response to Meloidogyne incognita
for two species of Desmodium [Beef Research Unit (BRU)
1980, Greenhouse 1980 (GH80), and Greenhouse 1981 (GH81)].



Entry Species BRU GH80 GH81


gall scores -

19 barbatum 0.0(R)$ 0.0(R) 1.0(R)

20 4.3(5) 3.5(S) 3.5(S)

21 0.0(R) 0.0(R) 0.0(R)

22 0.0(R) 0.0(R) 1.0(R)

23 heterocarpon 5.0(S) 4.0(S) 2.8(S)

24 5.0(S) 2.0(S) 4.0(S)

25 5.0(S) 2.0(S) 3.0(S)

26 5.0(S) 3.5(S) 3.8(S)

27 5.0(S) 4.5(S) 4.5(S)

28 5.0(S) 2.5(S) 3.8(S)

29 5.0(S) 3.0(S) 4.0(S)



t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.

$ R = resistant and S = susceptible to M. incognita.










Table 26. Gall scores in response to two species of
Meloidogyne for two species of Desmodium (Greenhouse
1981).



Nematode
Entry Species
M. arenaria M. incognita


--- gall scores


barbatum







heterocrpon


t 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.





57






Table 27. Correlation of gall scores with root volume and
with visual root scores for four genotypes of Desmodium
barbatum (Greenhouse 1981).



Root Visual
Volume Root Scores



Gall Scores -0.41** 0.59**

Root Volume -0.61**



**Significance at the 1% probability level.










Table 28. Root volume as affected by two species of
Meloidogyne for two species of Desmodium (Greenhouse
1981).



Treatment
Entry Species
Untreated M. arenaria M. incognita


ml


barbatum


heterocarpon

"


5.0

4.0

4.0

5.0

5.0

10.0

5.0

6.3

10.0

5.0

5.0


t Those lines showing galling symptoms
M. arenaria and M. incognita.


in response to both








D. heterocarpon tested. Those entries that galled did so

in response to both M. arenaria and M. incognita and gall

scores in response to both nematodes were of the same

general magnitude. There is no evidence to conclude that

two different genetic mechanisms exist within D. heterocarpon

or D. barbatum for resistance to M. arenaria and M. incognita.

The variable gall scores, visual root scores, and root

volume were significantly correlated (Table 29), and the

root volume of non-infested plants was generally greater

than the root volume of infested plants for the seven

genotypes of D. heterocarpon tested (Table 28). It would

seem, therefore, that some method of assessing root growth

may also be useful in D. heterocarpon.





Part 2


The performance of the genotypes in fumigated subplots

was intended to be used to assess herbicide effects and

the performance in non-fumigated subplots used to assess the

effects of the herbicide on the southern root-knot nematode

and on the genotypes. Weed competition -in the non-fumi-

gated subplots was so severe that no assessment of dry

matter yields, nitrogenase activity, or percent dry matter

was attempted. Gall scores in fumigated subplots were used

to determine the effectiveness of the fumigant.




60







Table 29. Correlation of gall scores with root volume and
with visual root scores for seven genotypes of Desmodium
heterocarpon (Greenhouse 1981).



Root Visual
Volume Root Scores



Gall Scores -0.31** 0.76**

Root Volume -0.36**



* Significance at the 1% probability level.








Fumigation appeared to be effective because no root

galling was observed in either genotype in the fumigated

subplots (Table 30). There were significant herbicide

effects on dry matter yields in fumigated subplots for both

genotypes (Table 31). No herbicide treatment was, however,

significantly different from the check. Herbicides did not

seem to affect nitrogenase activity, percent dry matter,

or degree of nodulation in either genotype (Tables 30, and

31).

In the non-fumigated subplots, there were no signifi-

cant herbicide effects for degree of root galling or percent

stand (Table 32). Root galling scores were highly variable

across replications which would seem to indicate that

relying on field infestations of the southern root-knot

nematode for studying herbicide by nematode interaction is

unsatisfactory. Also, the genotype of A. americana thought

to be resistant to root-knot nematodes (Kretschmer et al.,

1980; Rhoades, 1980) showed galling symptoms which would

seem to require that each seed source of Florida Common

American jointvetch be screened for resistance to

Meloidogyne spp. before using it in a breeding program or

before planting it in root-knot nematode infested fields.

Percent stand, percent dry matter, and dry matter

yields were highest in 'Treflan' treated sub-sub-plots.

Whether this was due to the effects) of 'Treflan', or

because 'Treflan' treated sub-sub-plots were tilled just










Table 30. Herbicide effects on nodulation and root galling
for two genotypes of Aeschynomene americana in fumigated
subplots (Agronomy Farm 1981).



Genotype

Herbicide Florida Common CIAT #9666

Nodulationt GallS Nodulationf Gallf


scores


None 5.0 0.0 5.0 0.0

'Treflan' 4.9 0.0 5.0 0.0

'Sonalan' 4.8 0.0 4.9 0.0

Paraquat 5.0 0.0 4.8 0.0

L.S.D. (0.05) 0.6 0.8



f 0 = no nodules and 5 = a well nodulated plant.

4 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30
galls, 4 = 31-100 galls, and 5 = over 100 galls.
















Sr m N
m r C0 I










3N N (N
oh ,-I u"

ml -4


0

C U






O 1
0










-Eo
-(-4












0









Co
0










4-1 a
I'a














4-4>O
a o





OMH







S44
01 0

O 0





'0 >1
o -u- 0
Q4- 4'-)



rna'


4e N




o.
H






(N















co




(7 1
. 0
r (N







0 0












H
N






A H
3 0


N a
C0 a r
0 O HC
to (N (


Ln



0 0 4


0 0 '

SH 0 4 CO


m (N N


DH Co N








D0 0 (7 (N


N N (N
















CD ko C -"sr n

H IN CN IN H








H H 0 0 IN


un
41
4- 0



C @r









WI








EO
Oc








S0
M -i

o

0








40
SE


















OW



4-'0
0


o c







00m


c o
0


E -40
r00
E 0


















0t
Ifl


^cl
8^;-


m IN

m 0
n -H N
r4 Iz o
(-A 1-4 "


H 0 H H 0








o o 0 0 N


6p
r-
IN


o o

m 00c c
'T CN CN


0
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0 0 4 -
0 0 1


S -4 0 4 Do
o E o 0
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En
rl~-rl


CN





65



prior to planting, or a combination of both cannot be

concluded. Conversely, Paraquat treated sub-sub-plots had

a higher percent stand and lower dry matter yields than

the check treatment. This would seem to indicate that

Paraquat reduces weed competition but has a detrimental

effect on Aeschynomene growth.















CONCLUSION


Genotypes resistant to M. incognita were identified

in A. americana, A. brasiliana, A. villosa, and D. barbatum.

One genotype of D. barbatum was identified as resistant but

intolerant to the southern root-knot nematode. Visual root

gall scores from plants grown in the field in plots infested

with M. incognita and in check plots were highly correlated

with plot yields and nematode reproduction. Visual root

gall scores from plants grown in the greenhouse and

infested with M. incognita were generally effective in

identifying susceptible genotypes of A. americana, D.

barbatum, and D. heterocarpon and seem quite suitable as a

preliminary technique for screening large numbers of geno-

types of these species. Visual vigor scores, degree of

nodulation, and root and shoot weights of nematode-infested

plants grown in the greenhouse were not useful for identifying

nematode-susceptible genotypes. Root volume and visual root

growth scores may be useful for assessing the effects of the

nematode on the plant. Genotypes in the aforementioned

species were identified that appeared to be resistant or

susceptible to the peanut root-knot nematode.

There were significant differences in the effects of

the herbicides 'Treflan', 'Sonalan', and Paraquat on dry









matter yields of two genotypes of A. americana. There were

no significant herbicide effects on degree of nodulation,

degree of root galling, nitrogenase activity, percent dry

matter, or percent stand. 'Treflan' treated sub-sub-plots

had the highest dry matter yields, percent dry matter, and

percent stand while Paraquat treated sub-sub-plots had a

higher percent stand and lower dry matter yields than check

sub-sub-plots. No information was gained concerning the

effects of the herbicides on M. incognita and the field

did not seem a suitable environment for assessing herbicide

by nematode interactions because of the variability noted

in the degree of root galling symptoms across replications.

The study did point out that herbicide selection could

influence a study of nematode effects on dry matter yields.

Florida Common American jointvetch has been reported as

resistant to Meloidogyne spp. but the source of Florida

Common used in Part 2 of this study showed galling symptoms

which would seem to indicate that all sources of Florida

Common may not be resistant to Meloidogyne spp.













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Advances in parasitology. Academic Press, London.















BIOGRAPHICAL SKETCH


Sherman F. Pasley was born in Ross Township, Rossville,

Illinois. He attended grade school in Judyville, Indiana,

End high school in Williamsport, Indiana. He served 20

years with the United States Air Force. He received a

3.S. in Agronomy at Washington State University and an

M.S. at the University of Minnesota. He is married to the

former Kaye S. Busby.










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




Kenneth H. Quesenberry, Chairmanj-
Associate Professor of Agronomy-



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




Stephen L. ibrecht
Assistant Professor of Agronomy



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



sepH H. 'Conrad
CProfessor of Animal Science



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




Robert A. Dunn
Associate Professor of
Entomology and Nematology










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




Kuell Hinson
Professor of Agronomy



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

December 1981




Dean,/ college of Agriclture


Dean for Graduate Studies and
Research




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