INFLUENCE OF PLANT RESISTANCE AND NEMATICIDES ON GROWTH AND YIELD OF 
TOMATO (LYCOPERSICON ESCULENTUM) AND ON POPULATION DYNAMICS OF 
ROOT-KNOT NEMATODES (MELOIDOGYNE INCOGNITA AND MELOIDOGYNE 
HAPLA) WITH AN ASSOCIATED STUDY OF ROOT-KNOT NEMATODE 
RESISTANCE IN LETTUCE (LACTUCA SPECIES)
A Thesis
Presented to the Faculty of the Graduate School 
of Cornell University 
in Partial Fulfillment for the Degree of 
Doctor of Philosophy
by
Conrad Komi a Bonsi 
August 1982
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2.21477
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INFLUENCE OF PLANT RESISTANCE AND NEMATICIDES ON GROWTH AND YIELD OF 
TOMATO (LYCOPERSICON ESCULENTUM) AND ON POPULATION DYNAMICS OF 
ROOT-KNOT NEMATODES (MELOIDOGYNE INCOGNITA AND MELOIDOGYNE 
HAPLA) WITH AN ASSOCIATED STUDY OF ROOT-KNOT NEMATODE 
RESISTANCE IN LETTUCE (LACTUCA SPECIES)
Conrad Komla Bonsi, Ph.D.
Cornell University, 1982
The influence of resistant tomato cultivars, chemical applications 
and both in combination on the population dynamics of root-knot nematode 
species (Meloidogyne incognita and Meloidogyne hap!a) and on growth and 
yield of subsequent susceptible tomato crops was studied.
Both growth chamber and field experiments were conducted. High 
initial inoculum densities (P.) of root knot nematode species reduced 
growth but had slight or no effect on growth of resistant cultivars.
Nematode reproduction was positively correlated with the initial 
inoculum density. M. incognita was more virulent than M. hapla on the 
susceptible (Rutgers) tomato. VFN-8 was found to be partially resistant 
to M. hapla.
Continuous cropping of a susceptible cultivar in infested soil 
greatly increased the nematode population and decreased the growth of 
susceptible plants. Resistant cultivars or applications of Vorlex alone 
permitted one (at highest P.'s) and two to three (at lowest P^s)
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susceptible crops to be grown before the nematode population reached a 
plant damaging level. Applications of Vorlex after a crop of resistant 
cultivar resulted in sufficient reductions of the nematode populations 
that at least three successive crops of the susceptible cultivar could 
be grown before the population reached a plant damaging level. A lower 
dosage of chemical was needed when used in combination with a resistant 
cultivar to control root knot nematodes.
In field experiments, Vorlex significantly increased marketable 
yields of tomatoes. Further increases in marketable yields of Rutgers 
tomato were obtained when Vorlex was applied to infested soil that had 
been previously planted to a resistant cultivar. In another study, 
only the resistant tomato seedlings when transplanted after 2 wk from 
highly infested to noninfested soil, grew as well as those transplanted 
from noninfested to noninfested soil.
In the third study, none of either the Lactuca species or the lettuce 
breeding lines tested were resistant to M. incognita and M. javanica.
JL. saliqna and L.. dregeana were resistant to a greenhouse population of 
M. hapla but were susceptible to a field population of M. hapla.
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BIOGRAPHICAL SKETCH
Conrad Komla Bonsi was born on December 11, 1950 in Ghana, W. 
Africa. He attended Evangelical Presbyterian Seconday and Kpandu 
Secondary Schools for his secondary education. He holds a Bachelor 
of Science (HONS) degree in Crop Protection from the University of 
Ghana. He received his Master of Science degree in Plant and Soil 
Science from Tuskegee Institute, Alabama in May 1978.
His interests include gardening, lawn tennis and soccer.
He is a member of the Society of Nematologists and Sigma Xi, 
the Scientific Research Society of America.
ii
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To my mother, Akosua, who didn’t believe,
To my very special friends
Eunice, Akweley, Dilys, and Janice
and
To the taxpayers in Ghana
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ACKNOWLEDGEMENTS
I wish to express my greatest appreciation to Dr. M. B. Harrison, 
who not only served as my advisor and chairman of my Special Committee 
but who was also a guardian and.a true friend that I could always 
count on. He is a man of a big heart and good intentions without 
whose guidance, patience, criticisms and advice, I probably would not 
have completed this study.
I am equally grateful to Dr. W. F. Mai, a man for whom I have a 
lot of admiration and respect. I feel privileged to have been associ­
ated with him for the past four years. I am very grateful for his 
advice, suggestions and criticisms in the preparation of this thesis.
I am also grateful to Dr. W. Kelley, Dept, of Vegetable Crops 
and to Dr. R. W. Robinson, Dept, of Seed and Vegetable Crops, Geneva, 
for serving on my Special Committee and for their invaluable criticisms 
in the preparation of this thesis.
My sincere appreciation also goes to Dr. C. W. Boothroyd, a 
wonderful person and very good friend and teacher. I would like to 
especially acknowledge his generosity for donating several plant 
pathology textbooks and more than 40 volumes of Phytopathology journals 
to the Department of Crop Science, University of Ghana.
I am also grateful to Dr. H. D. Thurston and all the participants 
in the Plant Pathology International Agriculture discussion group for 
sharing their experiences and ideas on Agriculture in the Developing 
world.
My thanks and gratitude go to the Hematology program employees,
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especially Nick, Teresa and Marian; the greenhouse and chamber crew - 
Bill, Tom, Phil and George, for their invaluable help and for providing 
a very comfortable and trusting working environment.
I thank the Department of Plant Pathology for the experience and 
I hope the Department will continue to give foreign students the 
opportunity to acquire this unique experience.
I am equally thankful to the Department of Crop Science, University 
of Ghana for awarding me the scholarship that supported my studies in 
the United States.
My very special thanks to Eunice and Akweley for the love, care, 
understanding and words of encouragement during the most difficult times 
of my career as a graduate student.
My thanks also go to all the Ghanaian students in Ithaca, especially 
Ricky, Phi 1 ipa, Ekow, Richard, Hannah, and most of all Kwaku (my roommate) 
for providing me with a home-like atmosphere in a world several thousands 
of miles away from home.
I am very greateful to Cynthia, Tab, Janice and Ethel for their 
company and special concern in the final months of my stay in Ithaca.
To my colleagues, Tonny, Dale, Sarah, Diane, Jim, Bob, and Jonathan 
I say thank you for everything. It has been wonderful associating with 
you.
My thanks go to Mary Brodie and Roxy Barnum without whose unlimited 
help and patience in typing this thesis, it probably would still have 
been in a handwritten form.
Finally, but not the least, my thanks go to members of my family, 
especially my mother, my brothers Kofi, Kwami, Kudjo, my cousin, Jonas,
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and all my friends in Ghana for their prayers and words of advi 
throughout my career as a student.
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GENERAL INTRODUCTION ....................................... 1
Literature Cited ..................................... 4
Chapter 1. INFLUENCE OF PLANT RESISTANCE AND CHEMICAL 
TREATMENTS ON GROWTH AND YIELD OF TOMATO AND POPULATION 
DYNAMICS OF ROOT KNOT NEMATODES (MELOIDOGYNE INCOGNITA AND
M. HAPLA) ................................................  6
Abstract ............................................  6
Introduction ......................................... 7
Materials and Methods .................................  13
Results.................................................16
Discussion and Conclusions ...........................  23
Literature Cited ..................................... 28
Chapter 2. EFFECT OF VARIOUS PERIODS OF EXPOSURE TO ROOT-KNOT 
NEMATODES ON GROWTH OF RESISTANT AND SUSCEPTIBLE TOMATO TRANS
PLANTS...................................................... 56
Abstract...............................................56
Introduction ........................................  56
Materials and Methods ................................. 57
Results.........   58
Discussion and Conclusions ...........................  60
Literature Cited ..................................... 63
Chapter 3. EVALUATION OF LACTUCA SPECIES AND BREEDING LINES 
OF LACTUCA SATIVA FOR RESISTANCE TO ROOT KNOT NEMATODE SPECIES
(MELOIDOGYNE INCOGNITA, M. JAVANICA, M. HAPLA) .............  69
Abstract.............................................. 69
TABLE OF CONTENTS
Page
vi i
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Introduction .............................................  69
Materials and Methods ....................................  70
Results and Discussion ..................................  71
Literature Cited ......................................... 73
Page
viii
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LIST OF TABLES
1.1 Effects of P. levels of M. incognita on the growth of
3 tomato cullivars and reproduction of the nematode . . .  34
1.2 Effects of Pi levels of M. incognita on growth of three
tomato cultivars and reproduction of the nematode . . . .  35
1.3 Effects of different Pi levels of M. hapla on the shoot
and root weights of two cultivars and a wild species of
Table Page
tomatoes and reproduction of the nematode .............  36
1.4 Effectsof root knot nematode Pi levels and tomato
cultivars followed by Vorlex applications on the growth 
of subsequent Rutgers (susceptible) tomato and 
reproduction of M. incognita .........................  37
1.5 Effects of root knot nematode Pi levels, tomato 
cultivars and Vorlex applications (0, 22.5 and 45 L/ha) 
on the growth of subsequent Rutgers (susceptible) tomato, 
and reproduction of residual populations of M. incognita 38
1.6 Effects of Pi levels, tomato cultivars and Vorlex appli­
cations on the growth of subsequent Rutgers tomato, and
reproduction of residual populations of M. hapla . . . .  40
1.7 Effects of Pi levels, tomato cultivars and Vorlex
applications (0, 22.5 and 45 L/ha) on growth of subse­
quent Rutgers (susceptible) tomato and reproduction of
the residual populations of M. hapla .................  41
1.8 Effects of Pi levels of M. incognita, previous tomato 
cultivar and chemical treatments on dry weight of sub­
sequent crops of Rutgers tomato ....................... 43
1.9 Effects of Pi levels of M. incognita, previous tomato 
cultivar, and chemical treatments on fresh root weight
of subsequent crops of Rutgers tomato .................  45
1.10 Influence of Pn- levels of M. hapla on yield of two 
cultivars of tomato (1980)   47
1.11 Influence of Pi levels and source of resistance on 
population development of M. hapla ...................  48
1.12 Total marketable yield of tomato (cv. Rutgers) as
influenced by initial inoculum density (P i )  of M. hapla, 
plant resistance and chemical treatments (1981) . . . .  . 49
ix
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Table Page
1.13 Influence of plant resistance and chemical applications 
on population development of M. hapla and galling of 
Rutgers tomato (1981) ..................................... 50
2.1 Height and gall index of Rutgers tomato seedlings grown
in root knot nematode infested soil for 2, 4 or 6 weeks 
before repotting to uninfested soil .....................  65
2.2 Height and gall index of Nematex tomato seedlings grown 
in different levels of root knot nematode infested soil 
for 2, 4 or 6 weeks before transplanting to uninfested
soil ........................................................ 66
2.3 Effects of period of exposure of Rutgers tomato 
seedlings to different inoculum densities of root knot 
nematode infested soil on growth and root gall index
of plants repotted to uninfested soil .................  67
2.4 Effects of period of exposure of Nematex tomato 
seedlings to different inoculum densities of root knot 
nematode infested soil on the growth and root gall
index of plants repotted to uninfested s o i l ............... 68
3.1 Evaluation of Lactuca sp. for resistance to greenhouse
populations of M. hapla, M. javanica and M. incognita . . 74
3.2 Evaluation of lettuce breeding lines for resistance to
greenhouse populations of M. hapla, M. javanica and M. 
incognita and a field population of M. hapla ........... 75
3.3 Reactions of selected Lactuca sp. to two initial 
inoculum densities of a greenhouse population of M. 
h a p l a ........................................................ 76
3.4 Reactions of selected Lactuca sp. to a field population
of M. hapla ................................................77
x
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LIST OF FIGURES
Figures 
1 . 1- 1.4
1.5-1.6
1.7-1.8
Population dynamics of M. incognita on successive 
Rutgers tomato plantings grown in infested soil 
of different P-j levels previously planted to either 
susceptible (Rutgers) or resistant (VFN-8 and 
Nematex) tomato cultivars and treated with either 0,
22.5 or 45 L Vorlex/ha....................................51
Population dynamics of M. hapla on successive 
Rutgers tomato plantings grown in infested soil of 
different P-j levels previously planted to either 
susceptible (Rutgers), partially resistant or 
resistant (J_. peruvianum) tomatoes and treated with 
either 0, 22.5 or 45 L Vorl ex/ha......................... 53
Fresh root weight and gall index of subsequent 
Rutgers tomato plantings grown in infested soil of 
different P- levels previously planted to either 
susceptible (Rutgers) or resistant (VFN-8 and 
Nematex) tomato cultivars and treated with either 
0, 22.5 or 45 L Vorlex/ha.................................54
Page
xi
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GENERAL INTRODUCTION
Root-knot nematodes (Meloidogyne spp.) account for significant yield 
losses of vegetable crops grown throughout the world. The most common 
species encountered worldwide are M. incognita, M. .javanica, M. arenaria 
and M. hapla (5); which are pathogenic on tomatoes. M. incognita, M. 
javanica and M. arenaria occur mostly in the tropical and subtropical 
regions where average annual temperature is between 18 to 30°C, while 
M. hapla is limited to the cooler regions of the world. Wong and Mai 
(7, 8, 9), however, found that higher temperatures (21-26°C) are favorable 
for invasion of M. hapla. Once invasion has occurred, the nematodes 
develop readily if temperatures are high; in the regime of 27°C night 
and 30°C day, eggs can be produced in 20 days. It is, therefore, possible 
that M. hapla once introduced in the tropics can survive and cause severe 
crop damage. On the other hand, M. incognita is unable to withstand cold 
temperatures and therefore does not survive long when introduced in the 
fields in temperatre regions.
Because of the wide host range of root knot nematode species that 
attack vegetable crops, the use of plant resistance and chemicals are 
likely to remain more important control mreasures than crop rotation. 
Increases of plant growth and yield of vegetable crops often result from 
applications of broad spectrum fumigants or nematicides such as Vorlex. 
These growth and yield responses are not only due to the control of plant 
parasitic nematodes but also to the control of other non target organisms. 
Thus, frequent or high dosage applications of fumigants and nematicides 
are often used in an effort to produce crops that are of high economic 
value. This, however, can cause serious health and economic problems.
1
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2Current research emphasis is therefore being directed towards other 
forms of control in order to reduce the dependence on chemicals.
One of the control measures being turned to more frequently is the 
use of plant resistance. Plant resistance is an effective, economical 
and environmentally safe method of control. It has been used quite 
effectively in reducing both the populations of root knot nematodes and 
losses caused by their attack (1). The dependence solely on resistant 
cultivars may pose a serious control problem due to the variability 
that can exist in populations of root knot nematodes and the frequent 
occurrence of mixed species in field populations (2, 6). Some resistant 
cultivars are horticulturally unsuitable or culturally unacceptable in 
certain localities. The use of such resistant cultivars more than once 
in a cropping system may therefore be economically unacceptable. It has 
been suggested (2, 3, 5) that in situations of heavy infestations, 
Meloidogyne populations should be reduced by either chemical or cultural 
means before growing a non host or a resistant variety. The use of 
available information can help in developing integrated control systems. 
In these systems non hosts, resistant cultivars, cultural practices and 
periodic nematicide applications can be combined to keep the nematode 
population below the damaging levels. This practice will also help to 
avoid development of resistance breaking biotypes. The importance of 
developing a management system that will combine effective control 
mreasures and permit the continued use of desirable but susceptible 
cultivars but without developing a damaging nematode population cannot 
be overemphasized.
The main objective of this research was to investigate the influence
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3of resistant hosts, chemical treatments, and combinations of the two on 
population dynamics of two root knot nematode species and on the growth 
and yield of subsequent susceptible tomato crops. Research was also 
conducted to study the effect on resistant and susceptible tomato 
transplants of various periods of exposure to root knot nematodes. Also 
several Lactuca species and breeding lines of Lactuca sativa were 
evaluated for resistance to root knot nematode species.
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4Literature Cited
1. Fassuliotis, G. 1979. Plant breeding for root-knot nematode
resistance. Iin Root-Knot Nematodes (Meloidogyne species). 
Systemics, Biology and Control. London, U.K. and New York,
USA. Academic Press, Inc. p. 425-453.
2. Netscher, C. and D. P. Taylor. 1979. Physiologic variation within
the genus Meloidogyne and its implications on integrated control.
In Root-Knot Nematodes (Meloidogyne species). Systemics, Biology, 
and Control. London, U.K. and New York, USA. Academic Press,
Inc. p. 269-293.
3. Netscher, C. and J. C. Mauboussin. 1973. Results of an investiga­
tion of the comparative efficiency of a resistant tomato and certain
nematicides against Meloidogyne javanica. Cah. ORSTOM Ser. Biol.
No. 21.
4. Sauer, M. R. and J. E. Giles. 1957. Effects of some field manage­
ment systems on root knot of tomato. Nematologica 2:97-107.
5. Taylor, A. L. and J. N. Sasser. 1978. Biology, identification and
control of root-knot nematodes (Meloidogyne sp,). North Carolina 
State Univ. Graphics. Ill p.
6. Triantaphyllou, A. C. and J. N. Sasser. 1960. Variation in perineal
patterns and host specificity of Meloidogyne incognita. 
Phytopathology 50:721-725.
7. Wong, T. K. and W. F. Mai. 1973. Pathogenicity of Meloidogyne
hapla to lettuce as affected by inoculum level, plant age at inocu­
lation and temperature. J. Nematol. 5:126-129.
8. Wong, T. K. and W. F. Mai. 1973. Meloidogyne hapla in organic
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5soil: effects of environment on hatch, movement and root invasion.
J. Nematol. 5:130-138.
9. Wong, T. K. and W. F. Mai. 1973. Effect of temperature on growth, 
development and reproduction of Meloidogyne hapla in lettuce.
J. Nematol. 5:139-142.
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Chapter 1
INFLUENCE OF PLANT RESISTANCE AND CHEMICAL TREATMENTS ON GROWTH AND 
YIELD OF TOMATO AND POPULATION DYNAMICS OF ROOT KNOT NEMATODES 
(MELOIDOGYNE INCOGNITA AND M. HAPLA)
Abstract
Both growth chamber and field experiments were conducted to study
the influence of resistant tomato cultivars and applications of Vorlex
(DD MENCS) on the population dynamics of root knot nematode species
and growth and yield of subsequent crops of a susceptible tomato
3 3cultivar. Four initial M. incognita inoculum densities (10 , 5 x 10 , 
104 and 105 eggs/500 orT of soil) and two initial M. hapla inoculum
o o o ^
densities (10 and 5 x 10 eggs/500 cm of soil) were used. Two 
resistant tomato cultivars (Nematex and VFN-8) and a susceptible 
cultivar (Rutgers) were used in studies with M. incognita. A resistant 
tomato species (Lycopersicon peruviarium), partially resistant (VFN-8) 
and susceptible (Rutgers) tomato cultivars were used in studies with M. 
hapla. Field experiments were conducted with M. hapla using the same 
initial inoculum densities of the nematode and the same tomato cultivars 
as in the growth chamber experiments. Vorlex was used at 22.5, 45 and 
90 L/ha in growth chamber studies and at 45 L/ha in field studies. In 
the growth chamber studies both resistant and susceptible tomato plants 
were inoculated with the different initial inoculum density (P.) levels 
of the Meloidogyne sp. Six weeks after inoculation, plant tops were 
removed and the nematode population was determined. Vorlex was applied 
to seven replications of each treatment. An equal number of replicates
6
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7were left untreated. Four weeks after fumigation, pots were replanted 
with seedlings of tl^ e susceptible cultivar and grown for 6 wks. The 
population of the nematode was determined and pots were immediately 
replanted with seedlings of the susceptible cultivar. Three more 
successive plantings of Rutgers were made before the experiment was 
terminated. Continuous cropping of a susceptible cultivar in infested 
soil greatly increased the nematode population and decreased the growth 
of plants. Resistant plants and applications of Vorlex to infested 
soil had similar effects in reducing nematode populations. Resistant 
cultivars alone or Vorlex alone resulted in nematode reduction that 
permitted one (at highest P^) and two to three (at lowest P^s) plantings 
of susceptible crops to be grown before the nematode population returned 
to a damaging level. Applications of Vorlex after growing a resistant 
tomato cultivar resulted in sufficient reductions of the nematode popula­
tions so that at least three successive plantings of the susceptible 
cultivar could be grown before the population reached a damaging level.
In field experiments, applications of Vorlex significantly increased 
marketable yields of the susceptible tomatoes. A further increase in 
yield of Rutgers was obtained when Vorlex was applied to infested soil 
that had been previously planted to resistant tomatoes before growing 
the susceptible cultivar. Fewer nematodes were recovered from the 
infested soil at the end of the second season although heavy galling was 
observed on infected roots.
Introduction
It has been shown by several workers (3, 4, 22, 23, 26, 33, 40) that 
the fundamental quantitative relationships between plant parasitic
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8nematodes and growth and yield of annual crops are primarily the function 
of preplant densities.
Seinhorst (32, 33) observed that the relationship between the 
density of populations of root infecting nematodes and the yield of 
infected plants can be expressed by an equation which showed two 
phenomena; (a) a certain density up to which yield is not affected and 
(b) a certain minimum yield which remained unaffected even at the 
highest densities.
The initial density required to cause significant plant damage and 
yield losses varies with different nematode species (33); the plant 
species, variety (21, 22, 23), age at planting (21, 45) and the environ­
mental conditions (41, 45). Wallace (40) observed that Meloidogyne 
javanica at low numbers stimulated growth of some plant species. In 
some species, top growth was reduced while in another species, there was 
no effect on top growth. Swarup and Sharma (35) observed that 100 M. 
javanica larvae per 400 gm of soil and 1,000 M. incognita larvae per 
400 gm of soil caused significant reduction in growth of tomatoes.
In an experiment conducted by Potter and Olthof (26), in which M. hapla 
was used as inoculum, marketable yields of beet, lettuce and spinach 
tended to be inversely correlated with preplant nematode densities.
Yield losses of marketable produce at highest initial inoculum density 
were 22% for beet, 81% for lettuce and 13% for spinach. In a similar 
experiment, Olthof and Potter (22) showed that yields of cabbage and 
cauliflower were reduced by 9% and 24%, respectively at the highest 
inoculum density. The numbers and fresh weights of potato and onions 
decreased with increase in initial inoculum density but commercial
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9losses were 46% and 64%, respectively. Olthof and Potter (23), in 
another experiment with 'Veebrite' tomatoes, showed that low nematode 
populations stimulated and highest nematode populations suppressed 
vegetative plant growth and yield of marketable produce.
Control of root knot nematodes through development of resistant 
cultivars has gained importance since £he recent increased concern for 
environmental, health and ecological hazards due to pesticide chemicals. 
Successful use of root knot resistance requires the manipulation of 
genetic systems to transfer resistant genes to a susceptible plant that 
has acceptable horticultural characteristics.
Hypersensitivity is the most usual type of resistance response.
This reaction occurs within a few hours after penetration (17, 24, 29, 43). 
The browning reaction of the root, which indicates hypersensitivity, is 
due to an accumulation of phenolic compounds in the tissues around the 
infection sites (5, 25, 34). Resistance to root knot nematodes can be 
modified by the plant's genotype (27, 28) and environmental factors (11). 
Holtzman (10) showed that resistance of tomato to M. incognita was less 
at 30 and 34.5°C than at 20 and 25°C although invasion was not as great 
as in a susceptible cultivar at these temperatures. Dropkin (5) showed 
that the resistant tomato cv. Nematex grown at 28°C and below was highly 
resistant to NT incognita acrita. However, resistance diminished with 
each degree above 29°C and the seedlings were fully susceptible at 33°C. 
Similar temperature effects were observed with beans (7) and sweet potato
(13). Some resistant plants, on the other hand, showed increased re­
sistance as temperature increased. Dropkin (5) observed that the 
resistance of African horned cucumber, Cucumis metulifera, to M. incognita
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10
increased as the temperatures rose from 28 to 32°C. He also observed 
that resistant reactions differed between cultivars within the same 
species.
There are a number of reports on the inheritance of resistance to 
root knot nematode with most reporting one (1, 9, 27, 38, 42), a few 
more than one (2, 9) dominant or incompletely (9) dominant gene(s) for 
resistance. Sidhu and Webster (23) in their study of four genes for 
resistance in tomato against M.. incognita found that two of the genes 
were different rather than either allelic or identical. Two other 
resistant genes were found to be allelic or identical. They, however, 
found no relationship between the third gene (possessed by tomato cv.
Cold Set-1) and the other genes. In another experiment, the same workers 
(27) showed that the F2 and backcross ratios from crosses between Nematex, 
Rutgers and Bonny Best suggest monogenic control of resistance in each 
case. They observed that the resistance expressed by Nematex was 
dominant over the partial resistance of Rutgers and the complete sus­
ceptibility of Bonny Best. It was not evident as to whether the resistant 
genes in cv. Nematex and Rutgers were identical or closely linked. They, 
however, noted that since resistance in Nematex and Rutgers was derived 
from different genetic material, it was quite possible that the resistant 
genes might be allelic or identical but mainfest different levels of 
resistance when influenced by a different genetic background.
Differences in the host-parasite (resistant) reactions are due not 
only to the genetic background of the host but also to the variability 
of different populations of the species of Meloidogyne (19). It is 
therefore possible that when different populations of a species of
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nMeloidogyne are tested against several cultivars of the same host, 
there can be complex host-parasite relationships since variability of 
both host and parasite are involved.
Cultivation of resistant cultivars generally results in reduction 
of populations of root knot nematodes (6, 18, 19, 20, 36). However, 
repeated cultivation of such cultivars may result in a buildup of the 
nematode population (16, 19, 36). Resistant breaking biotypes or 
populations of Meloidogyne spp. have been reported by several workers 
(29, 30, 36, 39). However, resistant varieties of several other crop 
plants other than the crop on which the biotype developed were found to 
be resistant to the new population (30, 39).
Sauer and Giles (31) observed that resistant tomatoes did not 
reduce the nematode population sufficiently to make possible the success­
ful cultivation of a subsequent susceptible crop. Johnson and Campbell
(14) in studies of the effects of cropping systems and nematicides 
found that clean fallow reduced nematode populations more effectively 
than rotation crops of millet, milo, soybean, crotalaria or pigeon 
pea. Furthermore, after 2 years of growing the susceptible crop, 
nematode populations increased to damaging levels and could not be 
controlled by fallowing even when used in combination with fensulfolthion.
Soil fumigation is the most common chemical treatment used to 
achieve economical control of nematodes in agricultural land. The most 
commonly used soil fumigants contain 1,3, dichloropropene as the active 
ingredient. Application rates ranging between 100-500 L/ha have been 
used to increase yields of tomatoes (15). Vorlex, one of the commonly 
used nematicides contains 80% dichloropropene and 20% methylisothiocynata
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12
Vorlex is more effective than 1,3-D alone. It persists longer in soil 
and the two compounds act synergistically in the water phase. It is 
also considered to be a broad spectrum fumigant because of its fungi­
cidal and herbicidal properties. The use of soil fumigants is limited 
because of the need for special equipment, trained personnel, special 
environmental conditions or because of long persistance and phytotoxicity
(15). Various environmental factors as well as method of application 
affect the efficiency of soil fumigation (37, 46).
Guskova (8) showed that application of thiazone at a low dosage 
rate followed by growing the resistant potato variety 'Sagitta' resulted 
in a decrease in the number of viable eggs and larvae of potato cyst 
nematode. The same level of decrease was obtained when the soil was 
treated with 1,000 kg/ha of thiazone alone. Johnson and Campbell (14) 
were able to reduce the population of root knot nematodes to a level 
that allowed growing of a susceptible tomato variety for about 3 seasons 
before damaging population levels were reached by using combinations of 
non hosts and fensulfolthion. Minton et al. (18) showed that there was 
a limited benefit to the subsequent crop from the residual effect of 
DBCP and resistant soybean cultivars when plant resistance and the 
chemical were used for 2 previous years.
Most nematode control studies that involve an integrated approach 
usually deal with one initial population level of the nematodes and one 
chemical dosage level. In this study, different initial root knot 
nematode densities and chemical dosage levels as well as plant resistance 
were used to study their residual effects on population dynamics of root 
knot nematodes and the growth and yield of subsequent susceptible tomato
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crops.
Materials and Methods
A. Growth Chamber Experiments
Meloidogyne incognita and Meloidogyne hapla were obtained from 
populations maintained on Rutgers tomato (L.ycopersicon esculentum) in the 
greenhouse. Eggs were used as inoculum and were extracted from heavily 
infested tomato roots with 0.8% NaOCl solution using a method described 
by Hussey and Barker (12). Two initial inoculum densities (P^ = 1,000 
and 5,000 eggs per 500 cm3 soil) were used. One application rate 
(90 L/ha) of Vorlex (80% dichloropropenes + 20% methyl isothyocynate) 
was used in the first experiment. In subsequent experiments, 22.5 
and 45 L/ha, were used. In experiments involving M. incognita, two 
resistant tomato cultivars, Nematex and VFN-8 and a susceptible 
cultivar, Rutgers, were used. In studies with M. hapla the resistant 
tomato, Lycooersicon peruvianum, and susceptible Rutgers and VFN-8 tomato 
cultivars were used.
In order to avoid contamination, the experiments in which different 
nematode species were used were conducted in separate growth chambers. 
Four week old tomato plants of each cultivar were inoculated with eggs 
of the Meloidogyne spp. at the different P. levels by spreading the 
inoculum on the surface of moist soil in which plants were growing and 
then covering the inoculum with a 4-6 cm layer of moist soil. Plants 
were grown in 12.5 cm pots in a growth chamber with 14 hrs light (22,596 
lux) and 25 + 2°C. They were watered daily and fertilized with 20-20-20 
water soluble fertilizer every 10 days. The experiment was terminated
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6 weeks after inoculation. Roots were washed gently and rated for gall 
index using a rating system of 0 = no galling, 1 = 1-10% galling, 2 = 
11-25% galling, 3 = 26-50% galling, 4 = 51-75% galling and 5 = above 75% 
galling. Roots and soil samples were taken from each replicate and the
3
number of eggs and larvae per gm root and the number of larvae per 100 cm 
soil were determined. Eggs and larvae were extracted from the roots using
0.8% NaOCl solution, and larvae in the soil were extracted by the pie 
pan method (a modification of Baermann funnel method). Fresh weight of 
roots as well as fresh weight and dry weight of shoots were recorded.
3
Number of eggs and larvae per 500 cm of soil was determined.
After root and soil samples had been taken, the remaining roots 
were cut into small pieces, returned to the original pots and mixed 
thoroughly in the soil. Appropriate dosages of Vorlex were then applied 
to 7 of the replicates. A similar number remainted untreated. A small 
amount of water was poured on the soil in all pots. Pots were then 
stored in the laboratory (20 + 2°C) undisturbed for 3 weeks. Prior to 
transplanting, the soil in each pot was cultivated and left to aerate 
for 7 days.
Four week old Rutgers seedlings were then transplanted into all 
the pots and grown in the growth chamber for 6 weeks. Nematode repro­
duction (i.e., gall index as well as egg and larval counts in roots and 
soil) and plant growth (fresh and dry wt.) were determined. This 
procedure was followed 3 more times with successive plantings of Rutgers 
tomatoes without any further applications of the chemical.
A completely randomized design was used and each experiment was 
conducted twice, with all final treatments replicated 7 times unless
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15
otherwise stated.
B. Field Experiments
Microplots were established in the field in 1979 using a similar 
experimental design and the same treatments as in the growth chamber 
experiments. A section of fiberglass screen 120 x 50 cm was wrapped 
around a 30 cm (d) and 45 cm (ht) plastic cylinder with open ends. The 
remaining screening was folded to form a bottom of the microplot. The 
overlapping longitudinal ends were held together by strips of masking 
tape. The cylinder with the screen around it was then inserted in a 
hole dug in the soil. Soil was filled in around the outsides of the 
cylinder. The cylinder was filled with sandy loam soil collected from 
an orchard in New York State. The cylinder was then lifted gently so 
that the screening remained in place, forming walls of the microplot.
Five rows of 18 microplots per row were established, 1 m apart.
The area between the microplots was tilled and the whole area 
was then fumigated with methyl bromide and left undisturbed for 12 days. 
The soil in the microplots was cultivated and allowed to aerate for 1 
week before the inoculum was added.
The inoculum was obtained from a culture of root knot nematode (M. 
hapla) maintained on Rutgers tomato in the greenhouse. Heavily infected 
roots were cut into small pieces and by using a coning technique mixed 
thoroughly in the soil. The number of eggs and larvae per 100 cm soil 
samples were determined. Depending on the treatment, appropriate volumes 
of the infested soil were added to the microplots.
Susceptible red kidney beans were planted in late summer to increase 
the root knot nematode populations. The following spring, soil samples 
were taken from all the infested plots and the population of nematodes
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were determined. Populations were adjusted by adding appropriate 
volume of infested soil or by diluting the soil in the microplot with 
autoclaved soil. Initial population densities of 1,000 and 5,000 eggs 
and larvae/500 cm of soil were used.
Six week old tomato plants of Rutgers, VFN-8 and L, peruvianum 
(PI 2704325) were transplanted on May 28. The experiment consisted of 9 
treatments with 10 replications per treatment in a completely randomized 
design.
Recommended cultural practices for fresh market tomato production 
were followed. Five harvests were made and soil samples were taken at 
each harvest. The tops of the plants were removed at the end of the 
season.
In mid April, of the following year, soil in each microplot was 
mixed with a trowel and soil samples were taken. Vorlex at the rate 
of 45 L/ha was then applied to 5 replications of each treatment. The
experiment now consisted of 18 treatments with 5 replications per treat­
ment because half of all the original treatments were treated with Vorlex
After 4 weeks', the soil in the microplots was mixed thoroughly and 
allowed to remain undisturbed for 2 weeks. Six weed old Rutgers tomato 
plants were then transplanted in all the microplots on the 3rd of June. 
Recommended cultural practices for fresh market tomato production were 
followed. Six harvests were made and soil samples were taken at mid
season (August 15) and at the end of the season (October 4).
Results
A. Effects of P. level, resistant tomatoes and Vorlex applications on 
population dynamics of root-knot nematode species.
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i) Effect of level and resistant tomatoes on reproduction of the 
root-knot nematode species.
Tomatoes resistant to the root knot nematode species supported very 
little or no reproduction of the nematodes whereas Rutgers (susceptible) 
tomato supported high reproduction of the nematodes (Tables 1.1; 1.2 and 
1.3). Higher P^ levels resulted in higher Pf. Although VFN-8 and 
Rutgers are susceptible to M. hapla, reproduction of M. hapla on VFN-8 
was much less than on Rutgers (Table 1.3). Higher final populations of 
nematodes were observed when Rutgers was inoculated with M. incognita 
than when Rutgers was inoculated with the same Pi levels of M. hapla 
(Table 1.1 and 1.3).
ii) Influence of P^  level and resistant tomato on population dynamics
of root-knot nemtade species on subsequent susceptible host plantings.
A subsequent crop of Rutgers grown in infested soil previously 
planted to a susceptible tomato resulted in very large increases in the 
root knot nematode populations (Tables 1.4; 1.5; 1.6 and 1.7). Continuous 
cropping of Rutgers in infested soils previously planted to susceptible 
tomato maintained the population of the nematodes above damaging levels 
regardless of the P.. level (Figs. 1.1A; 1.2A; 1.3A.1.4A; 1.5 A, D and 1.6 
A, D), assuming a previously determined damaging level of 1,000 eggs and
3
larvae/500 cm of soil.
Population dynamics of the root knot nematode species on subsequent 
Rutgers tomato grown in infested soils previously planted to resistant 
tomatoes depended more on the P. level of the nematodes than on the source 
of resistance. At low P. levels (1,000 and 5,000 eggs/500 cm3 of soil) 
resistant cultivars alone did not reduce the populations of the nematodes
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sufficiently enough to allow more than three successive crops to be 
grown before damaging population levels again occurred (Figs. 1.1D, G; 1.2 
D, G; 1.5 G and 1.6 G). At P.. levels of 10,000 and 100,000 eggs of 
M. incognita/500 cm3 of soil, only one additional susceptible crop could 
be grown before damaging population levels again occurred (Figs. 1.3D and 
1.4D, G).
iii) Effects of Vorlex applications on population dynamics of root 
knot nematode species on subsequent plantings of Rutgers.
Applications of Vorlex to infested soil significantly reduced the 
populations of root knot nematode species regardless of the previous 
tomato cultivar (Tables 1.4; 1.5; 1.6 and 1.7). Less control of the 
nematode was achieved when 22.5 L Vorlex/ha was applied than when 45 or 
90 L Vorlex/ha were applied to the infested soil. The dosage level of 
Vorlex as well as the P. level of the nematode affected the population 
dynamics of the root knot nematode species on subsequent Rutgers crops.
3
At low P.j levels of both nematode species (1,000 and 5,000 eggs/500 cm 
of soil) applications of 45 L Vorlex/ha to infested soil previously planted 
to susceptible tomatoes permitted Rutgers to be grown 3 times before 
damaging population levels reoccurred (Figs. 1.1 C; 1.2 C; 1.5 C, F, 
and 1.6 C, F). However, at higher P. levels (10,000 and 100,000 M.
O
incognita/500 cm of soil), the same dosage level of Vorlex reduced the 
nematode population enough to allow only one subsequent crop of Rutgers 
to be grown before damaging nematode populations reoccurred (Figs. 1.3 C 
and 1.4 C). Applications of 22.5 L Vorlex/ha to infested soil previously 
planted to susceptible tomato permitted either two or one successive 
Rutgers crops to be grown at either low or high P. levels, respectively,
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19
before damaging population levels reoccurred (Figs. 1.1 B; 1.2 B; 1.3 B ;
1.4 B; 1.5 B, E; and 1.6 B, E).
iv) Influence of combinations of Vorlex applications and resistant 
tomatoes on population dynamics of root knot nematode species on subsequent 
Rutgers crops.
A much lower residual population of root knot nematodes resulted 
when resistant tomatoes were used in combinations with Vorlex. At low
P. levels, applications of Vorlex at the rate of either 22.5 or 45 L/ha
in combination with resistant plants resulted in sufficient reduction of 
the nematode which permitted more than three successive crops of Rutgers 
to be grown before any substantial reproduction was detected (Figs. 1.1 E, 
F, H, I; 1.2 E, F, H, I; 1.5 H, I; and 1.6 H, I). At higher P^  levels, 
populations of M. incognita on successive Rutgers crops grown in infested 
soil were lower following Nematex and Vorlex than following VFN-8 and 
Vorlex. The combined effects of Nematex and Vorlex allowed more than 4 
successive crops of Rutgers to be grown without nematode populations 
reaching a damaging level (Figs. 1.3 H, I and 1.4 H, I). VFN-8 combined 
with Vorlex permitted 3 successive Rutgers crops to be grown before 
damaging population levels were reached (Figs. 1.3 E, F and 1.4 E, F).
B. Effects of P. level, resistant tomatoes and Vorlex applications on
growth of subsequent Rutgers crops.
i) Effect of Pi level on growth of tomato.
Top dry weight and root fresh weight of resistant tomato were not 
affected significantly when plants were inoculated with different P. 
levels of M, incognita (Tablesl.l and 1.2) or M. hapla (Table 1.3). On 
the other hand, top dry weight of susceptible tomato (Rutgers) decreased 
and fresh weight of roots increased significantly with increase in P.
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level. Although VFN-8 is susceptible to M. hapla, no significant 
decrease from the uninoculated control in top dry weight was observed 
with an increase in the P.. (Table 1.3). A much higher percentage 
decrease in dry weight of shoots was observed when Rutgers was inoculated 
with M. STUDIES ON INSECTICIDE USAGE AND PYRETHROID RESISTANCE INPOPULATION OF ANOPHELES GAMBIAESENSU STICTO(DIPTERA: CULIC1DAE) IN THE GREAER CCRA RGION OF GHANAcognita (12-33% reduction) than when utgers plants were 
inoculated with M. hapla (7-19% reduction) at the same P. levels.
ii) Influence of P^  level and resistant tomato on growth of 
subsequent Rutgers crops.
Generally, top dry weight and root fresh weight of Rutgers tomatoes 
grown in infested soils previously planted to resistant tomatoes were 
not significantly different from the uhinfested controls (Tables 1.3; 1.4 
and 1.5). Both the top dry weight and root fresh weight were significant­
ly lower than the uninfested controls when Rutgers tomatoes were grown in 
infested soils previously planted to susceptible cultivars. Successive 
plantings of Rutgers in soils infested with M. incognita showed fluctu­
ations in growth of the plants depending on the previous Pf (Table 1.8 and 
Figs. 1.7 and 1.8). These fluctuations in data on growth are primarily 
due to the fact that at very high nematode population densities, some 
plants died 3-4 weeks after transplanting. This consequently reduced 
the residual nematode population for the next planting resulting in much 
less damage. In some cases, fresh root weight of plants from successive 
plantings in highly infested soil were significantly lower than roots 
from uninfested controls (Figs. 1.7 and 1.8). This was due to limited 
root growth or severe root pruning resulting from the severe attack of 
the nematodes at high population densities.
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iii) Influence of the combinations of Vorlex and resistant tomatoes 
on growth of subsequent Rutgers crops.
Applications of Vorlex to noninfested soil or soils previously planted 
to resistant tomato had no significant effects on the growth of subsequent 
Rutgers crops (Tables 1.4; 1.5; 1.6 and 1.7). The effects of the 
different dosage levels of Vorlex on the growth of subsequent Rutgers 
crops were not significantly different (Table 1.8 and Figs. 1.7 and 1.8).
At any P.j, resistant tomatoes used in combinations with Vorlex significant­
ly increased the growth of subsequent Rutgers crops when compared to using 
plant resistance alone or Vorlex alone (Table 1.8). Vorlex applied to 
infested soil previously planted to a susceptible cultivar significantly 
increased the growth of subsequent Rutgers crops (Tables 1.4; 1.5; 1.6 
and 1.7).
C. Influence of P^  level, resistant tomato and Vorlex applications on 
.yield of tomatoes in field studies.
The 1980 results indicated a 41% and 42% reduction in total market­
able yields of Rutgers tomato grown in soil infested with 1,000 and 
5,000 eggs and larvae of M. hap!a/500 cm3 of soil, respectively (Table 
1.10). Although there were reductions in the total marketable yields 
of VFN-8 tomatoes (10% and 7% at P^s of 1,000 and 5,000 eggs and larvae/ 
500cm of soil, respectively) these yield reductions were not signifi­
cantly different from those of the uninfested plots. No yield data were 
taken for L, peruvianum because this plant normally does not produce 
edible marketable fruits.
Very little reproduction of the nematode was observed on L, 
peruvianum throughout the season (Table 1.11). The build up of the
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nematode population on VFN-8 was much slower than on Rutgers throughout 
the season. The higher the P^, the higher the final population at the 
end of the season for all cultivars and species of tomato tested.
The yield data for Rutgers planted in all the plots in the 1981 
growing season indicated significant effects from the control of root 
knot nematode due to plant resistance (Table 1.12). Total marketable 
yields of Rutgers grown in infested plots previously planted to L_. 
peruvianum were higher than yields of Rutgers grown in infested plots 
previously planted to Rutgers. Yields of tomatoes grown in infested 
plots previously planted to VFN-8 were 10-16% higher than yields 
obtained when plants were grown in infested plots previously planted 
to U  peruvianum; however, these were not statistically significantly 
different. The effects of resistant tomato ( L  peruvianum) alone in 
controlling the nematode resulted in about 16-53% increase in total 
marketable yield of the subsequent susceptible crop. Yields of Rutgers 
grown in infested plots previously planted to VFN-8 were 26 and 79% 
higher than those obtained from infested plots of the same inoculum 
levels previously planted to Rutgers.
Application of 45 L Vorlex/ha to uninfested plots previously 
planted to Rutgers, VFN-8 or JL. peruvianum resulted in significant in­
creases in yields of Rutgers tomatoes. Vorlex applied to plots 
previously infested with 1,000 or 5,000 eggs and larvae/500 cm^ of soil 
and planted to Rutgers resulted in 45% and 50% increases in marketable 
yields, respectively.
The combined effects of L. peruvianum and Vorlex in reducing nematode 
populations resulted in increased yields of Rutgers in the following
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season by 23 and 84% at P^s of 1,000 and 5,000 eggs and larvae/500 cm 
of soil, respectively. At the same P..S, VFN-8 and Vorlex combined 
increased yields by 50 and 72%, respectively.
Very small numbers of nematode larvae were recovered from the 
infested soil at the beginning of 1981 season (Table 1.13) compared to 
the number recovered at the end of the 1980 season (Table 1.11). There 
was an increase in the population of the nematode in the middle of 
the season but very little or no additional increase in the nematode 
count was made at the end of the season (Table 1.13). Although the 
nematode counts were generally low at the end of the season, fewer or 
no, larvae were recovered from plots to which Vorlex had been applied. 
When roots were examined at the end of the season, very heavy galling 
was observed on roots of plants that were grown in infested plots 
previously planted to Rutgers. Lower gall index ratings were obtained 
where VFN-8 or J_. peruvianum were the previous cultivars and also 
where Vorlex was applied (Table 1.13).
Discussion and Conclusions
Varietal differences in the reaction of plant species to root knot 
nematode are well documented in the literature. Results of this study 
support observations of several workers (3, 22, 23, 26, 33, 36, 45) con­
cerning the reduction in growth and yield of a susceptible cultivar 
when inoculated with high inoculum densities of root knot nematodes.
On the other hand the influence on the growth of the resistant plants 
was affected very slightly. Although gall indices were very high in 
some plants infected by M. incognita (Figs. 1.7 and 1.8), root weights 
were lower than the uninfected plants. This was due to limited root
3
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growth or severe pruning of the roots that resulted from a severe attack 
of the nematodes at high nematode populations. This supports some of 
the observations made by Olthof and Porter (22, 23) of root knot 
nematode attack on some vegetable crops.
Reproduction of M. hapla on VFN-8 was much lower than on Rutgers 
although the two cultivars are known to be susceptible to M. hapla.
This was probably an indication of the manifestation of different levels 
of resistance due to different genetic background (28) since VFN-8 and 
Rutgers may have originated from different genetic material. The higher 
percentage reduction in dry weight of tops of Rutgers tomato inoculated 
with the same P. of M. incognita as M. hapla indicates a more virulent 
action of M. incognita. This was also evident in the reproduction of 
the two species on Rutgers at the temperature at which the experiments 
were conducted. Similar observations were made in field experiments 
conducted by Barker et al. (3) on the pathogenicity of the two species of 
tomatoes.
Significant root knot nematode population reductions were obtained 
by the use of resistant cultivars or application of the nematicide.
At lower P^ levels, much higher population reductions were obtained 
whereas at higher P. levels the effects of either the resistant 
tomatoes alone or chemical applications alone in reducing the nematode 
population did not last long after a crop of a susceptible cultivar. 
Although the application of 90 L Vorlex/ha resulted in the reduction of 
the nematode population below a detectable level, the nematodes were 
not completely eliminated. Some reproduction was observed on the 
subsequent susceptible crops. Such observations have been made for
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several other nematicides (15, 19, 20). Reproduction of the root knot 
nematode species on resistant plants was relatively low. Therefore 
applications of Vorlex after a resistant crop further reduced the 
nematode population thereby permitting several successive susceptible 
crops to be grown without the nematodes reaching a damaging level. 
Significant yield increases were observed in Rutgers tomatoes grown in 
noninfested soil previously planted to Rutgers, VFN-8 or L. peruvianum 
followed by applications of Vorlex in the field experiments. However, 
in the growth chamber experiments, the growth of subsequent Rutgers 
plants grown in noninfested soil previously planted to these cultivars 
and treated with Vorlex were not significantly affected. This was 
probably due to the fact that autoclaved soil was used in the growth 
chamber experiment and very little recontamination of the soil with 
other soilborne organisms occurred. On the other hand, in the field, 
although the entire experimental area was fumigated at the beginning of 
the study (1979) the soil was probably recolonized rapidly with other 
soilborne organisms that could cause a reduction in growth of the plants. 
Thus treatments with a broad spectrum chemical such as Vorlex could 
result in growth responses in the absence of the nematodes.
One of the important ways of maintaining the usefulness of a 
resistant cultivar for controlling root knot nematodes is to avoid 
growing the resistant host in heavily infested soil. This helps to 
reduce the possibility of selecting and developing biological races 
from the existent root knot populations. According to Netscher and 
Taylor (9), if such biological races can be assumed to be independent 
of the number of the root knot nematodes present, then in soils con­
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taining few root knot nematodes these races will be rare or absent. 
Results of this study thus support the observation that the higher the 
P.J, the greater the residual population from the previous crop of the 
resistant cultivar. There is, therefore, a need for an alternate 
control measure before or after growing the resistant cultivar that 
would allow a subsequent susceptible cultivar to be grown without any 
substantial increase in the nematode populations.
In'field studies, Minton et al. (18) observed only limited effects 
in reducing populations of M. incognita the first year after resistant 
soybean cultivars and DBCP had been used in the two previous years. 
Results of this study both in the growth chamber and in the field showed 
substantial effects of resistant tomato cultivars and Vorlex in reducing 
populations of root knot nematode species. Differences in the observa­
tions of the field experiments in this study and those of Minton et al. 
may be due to the different root knot nematode species used, different 
Pis, the different host plants, nematicides, experimental design, 
cultural practices as well as the different temperatures and locations 
of the experiments. Because of the use of tractor drawn agricultural 
equipment in their study, the risks of recontamination might have been 
higher than in this study. Recontamination in this study was kept to 
the minimum by sanitation and contamination prevention. M. hapla is 
known to survive cold weather conditions. However, lower nematode 
counts were recorded at the beginning of the season in 1981 when compared 
to the number recovered at the end of the previous season. This may 
have been due to the severe cold of the 1980-81 winter. The low survival 
of the nematode may also be due to interaction with other soil micro­
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organisms. Based on the 1981 midseason nematode counts, one would 
expect a higher increase in population at the end of the season than was 
observed. This lower nematode count may be due to adverse effects of 
other soil microorganisms on root knot nematodes. Or a chance contamina­
tion of the mid-season soil samples during processing. The field 
experiment supported the observations made in the growth chamber 
experiments on the differences in the pathogenicity of M. hapla to 
Rutgers and VFN-8. There was a lower rate of population buildup on 
VFN-8 than on Rutgers.
Application of Vorlex increased the yield of tomatoes. However, 
a much greater yield was achieved when a resistant cultivar was used 
in combination with chemical application before growing the susceptible 
cultivar. Based on the end of season nematode counts, and gall index 
ratings it appears that the combined effects of plant resistance and 
Vorlex in reducing nematode populations would be much more beneficial 
than either chemical treatment alone or plant resistance alone.
Based on the results of this study, it can be concluded that 
(a) both the frequency and the amount of Vorlex needed to control root 
knot nematodes were reduced when the chemical was used in combination 
with a resistant cultivar in the cropping sequence, (b) the effects of 
plant resistance and chemical treatments were similar in the reduction 
of root knot nematode populations, (c) VFN-8 is partially resistant to 
M. hapla population that was used in the study, and (d) M. incognita 
was more virulent on Rutgers than M. hapla at 25 + 2°C.
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Literature Cited
1. Barham, W. S. and N. N. Winstead. 1957. Inheritance of resistance
to root knot nematodes in tomatoes. Proceedings of the Amer. Soc. 
for Horticult. Sc. 69:372-377.
2. Barham, W. S. and J. N. Sasswer. 1956. Root knot nematode resis­
tance in tomatoes. Proc. Assoc, of South Agric. Workers (Abstr.). 
53rd Annual Conv. (1956). p. 150-151.
3. Barker, K. R., P. B. Shoemaker and L. A. Nelson. 1976. Relation­
ships of initial population densities of Meloidogyne incognita 
and M. hapla to yield of tomato. J. Nematol. 8:232.
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relations of the root knot nematode, Meloidogyne hapla Chitwood 
1949, with tomatoes, onions and lima beans. Plant and Soil 3:47-50.
5. Dropkin, V. H. 1969. The necrotic reaction of tomatoes and other
hosts resistant to Meloidogyne, reversal by temperature. 
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6. Dukes, P. D., R. L. Fery and M. G. Hamilton. 1979. Comparison of
plant resistance and nematicide for control of southern root-knot
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Phytopathol. Soc. S. Div. 4-7 Feb. 1979. Phytopathology 69:1.
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7. Fassuliotis, G., J. R. Dealun and J. C. Hoffman. 1970. Root knot
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resistance. J. Amer. Soc. Hort. Sc. 95:640-645.
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9. Hare, W. W. 1966. Inheritance of resistance of plants to nematodes. 
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10. Holtzmann, 0. V. 1965. Effect of soil temperature on resistance
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11. Holtzmann, 0. V. and J. C. Gilbert. 1967. Factors influencing
resistance of tomato to root knot nematode. Proc. of the 
Symposium on Tropical Nematology. Nov.-Dec. 1967.
12. Hussey, R. S. and K. R. Barker. 1973. A comparison of methods of
collecting inocula of Meloidogyne spp. including a new technique. 
Plant Dis. Reptr. 57:1025.
13. Jatala, P. and C. C. Russell. 1972. Nature of sweet potato
resistance to Meloidogyne incognita and the effects of temperature 
on parasitism. J. Nematol. 4:1-7.
14. Johnson, A. W. and G. M. Campbell. 1977. Effects of cropping
systems and a nematicide on root-knot nematodes and quality and 
yield of tomato transplants. J. Amer. Soc. Hortic. Sci. 102:819-821.
15. Lamberti, F. 1979. Chemical and cultural methods of control.
In Root Knot Nematodes (Meloidogyne sp.), Systemics, Biology and 
Control. London, U.K. and New York, USA.Acad. Press, Inc. p. 405- 
422.
16. McCarter, S. M., C. A. Jaworski and A. W. Johnson. 1978. Effect
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pathogens and on growth of tomato transplants. Phytopathology 68: 
1475-1481.
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30
17. Milne, D. L., D. N. Boshoff and P. W. W. Buchan. 1965. The nature
of resistance of Nicotiana repanda to the root knot nematode,
Meloidogyne ,iavanica. S. Africa Sci. 557-567.
18. Minton, N. A., M. B. Parker and 6. B. Mullinix, Jr. 1977. Effects
of cultivars, subsoiling and fumigation on soybean yields and 
Meloidogyne incognita population. J. Nematol. 10:43-47.
19. Netscher, C. and D. P. Taylor. 1979. Physiologic variation within
the genus Meloidogyne and its implications on integrated control. 
In Root-knot Nematodes (Meloidogyne species), Systemics, Biology 
and Control. London, U.K. and New York, USA, Academic Press, Inc. 
p. 269-293.
20. Netscher, C. and J. C. Mauboussin. 1973. Results of an investiga­
tion of the comparative efficiency of a resistant tomato and 
certain nematicides against Meloidogyne javanica. Cah. 0RST0M 
Ser. Biol. No. 21.
21. Ogbuji, R. 0. 1976. Influence of host age of four crop plants on
infectiveness of Meloidogyne avenaria in Nigeria. Plant Dis.
Reptr. 60:759-761.
22. Olthof, T. H. A. and J. W. Potter. 1972. Relationships between
population densities of Meloidogyne hapla and crop losses in 
summer maturing vegetables in Ontario. Phytopathology 62:981-986.
23. Olthof, T. H. A. and J. W. Potter. 1977. Effects of population
densities of Meloidogyne hapla on growth and yield of tomato.
J. Nematol. 9;296-300.
24. Paulson, R. E. and J. M. Webster. 1970. Cellular response of a
resistant tomato plant to Meloidogyne incognita. J. Parasitol.
56: (4 sec. 2). (Abstr.).
University of Ghana          http://ugspace.ug.edu.gh
31
25. Pi, C. L. and R. A. Rhode. 1967. Phenolic compounds and host
reactions in tomato to injury caused by root knot and lesion 
nematodes. Phytopathology 57:344.
26. Potter, J. W. and T. H. A. Olthof. 1974. Yield losses in fall
maturing vegetables relative to population densities of 
Pratylenchus penetrans and Meloidogyne hapla. Phytopathology 64: 
1072-1075.
27. Sidhu, G. S. and J. M. Webster. 1980. Genetic control of
resistance in tomato (Lycopersicon esculentum). II. Segregations 
for high and low levels of resistance to Meloidogyne incognita. 
Can. J. Genet. Cytol. 22:223-226.
28. Sidhu, G. S. and J. M. Webster. 1975. Linkage and allelic
relationships among genes for resistance in tomato (Lycopersicon 
esculentum) against Meloidogyne incognita. Can. J. Genet. Cytol. 
17:323-328.
29. Riggs, R. D. 1959. Studies on resistance in tomato to root-knot
nematodes. Dissertation Abstr. 19(11):2710.
30. Riggs, R. D. and N. N. Winstead. 1979. Studies on resistance in
tomato to root knot nematodes and on the occurrence of pathogenic 
biotypes. Phytopathology 49:716-724.
31. Sauer, M. R. and J. E. Giles. 1957. Effects of some field manage­
ment systems on root knot of tomato. Nematologica 2:97-107.
32. Seinhorst, J. W. 1970. Dynamics of populations of plant parasitic
nematodes. Ann. Rev. Phytopathol. 8:131-156.
33. Seinhorst, J. W, 1965. The relation between nematode density and
damage to plants. Nematologica 11:137-154.
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32
34. Singh, B. and B. Choudhung. 1973. The chemical characteristics of
tomato cultivars resistant to root knot nematodes (Meloidogyne 
sp.). Nematologica 19:443-448.
35. Swarup, G. and R. D. Sharma. 1965. Root knot of vegetables. IV.
Relation between population density of Meloidogyne incognita var. 
acrita and root and shoot growth of tomato seedlings. Indian 
J. Expt. Biol. 3:197-198.
36. Taylor, D. P. 1975. Observations on a resistant and susceptible
variety of tomato in a field heavily infested with Meloidogyne in 
Senegal. Cah. ORSTOM Ser. Biol. 10:239-245.
37. Thomason, I. J. and M. V. McKenry. 1975. 2lL "Nematode Vectors
of Plant Viruses." (Eds. F. Lamberti, C. E. Taylor and J. W. 
Seinhorst) 423-439. Plenum Press London and New York.
38. Thomason, I. J. and P. G. Smith. 1957. Resistance to tomato to
Meloidogyne javanica and M. incognita acrita. Plant Dis. Reptr.
41:180-181.
39. Triantaphyllou, A. C. and J. N. Sasser. 1960. Variation in perineal
patterns and host specificity of Meloidogyne incognita. Phyto­
pathology 50:724-735.
40. Wallace, H. R. 1971. The influence of the density of nematode
populations on plants. Nematologica 17:154-166.
41. Wallace, H. R. 1970. Some factors influencing nematode reproduction
and growth of tomatoes infected with Meloidogyne javanica. 
Nematologica 16:387-397.
42. Watts, J. W. 1947. The use of Lycopersicon peruvianum as a source
of nematode resistance in tomatoes. Proc. Amer. Soc. Hort. Sci. 
49:233-234.
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33
43. Webster, J. M. and R. E. Paulson. 1972. An interpretation of
ultrastructural response of tomato roots susceptible and resistant 
to Meloidogyne incognita (Kofoid & White) Chitwood. Bulletin 
OEPP No. 6, 33-39.
44. Winstead, N. N. and W. S. Barham. 1957. Inheritance of resistance
in tomato to root knot nematodes. Phytopathology 47:37-38.
45. Wong, T. K. and W. F. Mai. 1973. Pathogenicity of Meloidogyne hapla
to lettuce affected by inoculum level, plant age at inoculation 
and temperature. J. Nematol. 5:126.
46. Wong, T. K., F. C. Harper and W. F. Mai. 1970. Soil fumigation
for controlling root knot of lettuce on organic soil. Plant Dis.
Reptr. 54:368-369.
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Table 1.1. Effects of P. levels of M. incognita on the growth of 3 tomato cultivars and reproduction of 
the nematode.
, Pi 3 (eggs/500 cm
soil
Tomato
cultivar
Plant growth Nematode Reproducti on
Shoot dry 
wt (g)
Root fresh 
wt (g) Gall index
Egg and larvae
/gm roots
Larvae/ 
100 cc soil
0 Rutgers 10.7 b 13.9 a 0.0 a 0.0 a 0.0 a
VFN-8 10.4 b 15.1 ab 0.0 a 0.0 a 0.0 a
Nematex 9.5 b 13.0 a 0.0 a 0.0 a 0.0 a
1,000 Rutgers 8.4 ab 13.9 a 4.5 b 4528.0 b 152.0 b
VFN-8 9.9 a 16.4 ab 0.1 a 1.6 a 0.0 a
Nematex 9.2 b 12.9 a 0.0 a 0.3 a 0.1 a
5,000 Rutgers 7.2 a 19.4 b 5.0 b 7735.0 c 409.0 c
VFN-8 9.4 b 12.8 a 0.0 a 2.0 a 1.5 a
Nematex 10.4 b 12.9 a 0.0 a 6.0 a 1.2 a
Means followed with the same letter in a column are not significantly different at 5% level according to 
Duncan's multiple range test.
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Table 1.2 Effectsof P- levels of M. incognita on growth of three tomato cultivars and reproduction of 
the nematode.
3(eggs/500 cm 
soil)
Tomato
cultivar
Plant growth Nematode Reproduction
Shoot dry 
wt (g)
Root fresh 
wt (g) Gall Index
Eggs and larvae 
/gm roots
Larvae/ 
100 cc soil
0 Rutgers 12.9 c 14.2 a 0 a 0 a 0 a
VFN-8 14.1 c 15.9 ab 0 a 0 a 0 a
Nematex 10.6 be 13.2 a 0 a 0 a 0 a
10,000 Rutgers 6,4 a 20.6 eb 5 b 20148 b 15 a
VFN-8 15.1 c 16.3 ab 0 a 0 a 0.2 a
Nematex 9.7 b 20.4 cb 0 a 0 a 0 a
100,000 Rutgers 5.1 a 27.3 c 5 b 158800 c 1911 b
VFN-8 13.3 c 20.8 cb 0 a 1. 2 a 0.4 a
Nematex 9.4 b 16.3 ab 0 a 0 a 0 a
Means followed with the same letter in a column not significantly different at 5% level according to 
Duncan's multiple range test.
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Table 1.3. Effects of different P. levels of M. hapla on the shoot and root weights of two cultivars 
and a wild species of tomatoes ancT on the reproduction of the nematode.
pi 3
(eggs/500 cm 
soil)
Tomato
cultivar
Plant growth Nematode Reproduction
Shoot dry Root fresh
Gall Index
Eggs and larvae 
/gm roots
Larvae/ 
100 cc soil
0 Rutgers 14.1 a 14.4 a 0 a 0 a 0 a
VFN-8 19.0 b 19.3 ab 0 a 0 a 0 a
L. peruvianum 13.5 a 22.5 c 0 a 0 a 0 a
1,000 Rutgers 13.1 a 21.8 cb 4.7 b 3164 c 239 b
VFN-8 18.8 b 24.8 c 1.3 a 160 b 11.8 a
L. peruvianum 14.0 a 19.4 ab 0 a 0 a 1.4 a
5,000 Rutgers 11.4 a 25.5 c 5.0 b 4928 d 649 c
VFN-8 16.8 ab 23.1 c 1.7 a 394 b 27.4 a
L. peruvianum 14.0 a 23.8 c 0 a 2.8 a 1.0 a
Means followed with the same letter in a column are not significantly different at the 5% level according 
to Duncan's multiple range test.
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Table 1.4. Effect of root knot nematode P.. levels and tomato cultivars followed by Vorlex applications 
on the growth of subsequent Rutgers (susceptible) tomato and reproduction of M. incognita.
Pi 3 
(eggs/500 cm 
soil)
Previous
cultivar
Vorlex 
90 L/ha
Plant growth Nematode Reproduction
Shoot dry 
Wt (g)
Root fresh 
wt (g) Gall index
Eggs & larvae 
/gm roots
Larvae/ 
100 cc soil
0 Rutgers _* 22.4 b 14.5 be 0 a 0 a 0 a
+ 9.6 b 13.9 be 0 a 0 a 0 a
VFN-8 9.4 b 9.8 b 0 a 0 a 0 a
+ 7.9 ab 13.1 b 0 a 0 a Q a
Nematex 10.9 b 11 .8 b 0 a 0 a 0 a
+ 7.4 ab 10.3 b 0 a 0 a 0 a
1,000 Rutgers _ 5.3 a 7.4 a 5.0 b 36601 b 311 b
+ 10.5 b 14.6 be 0.5 a 11 a 0 a
VFN-8 9.2 b 9.6 b 0.6 a 16 a 0 a
+ 9.2 b 11 .2 b 0 a 0 a 0 a
Nematex __ 10.0 b 12.9 b 0.5 a 13 a 1 .8 a
+ 8.2 b 11 .2 b 0 a 0 a 0 a
5,000 Rutgers - 4.1 a 4.5 a 5 b 32842 b 690 b
+ 9.9 b 15.1 be 0 a 12 a 1.7 a
VFN-8 _ 1 1 .6 b 10.1 b 1 .2 a 49 a 2 a
+ 10.7 b 10.6 b 0 a 0 a 0 a
Nematex _ 10.5 b 1 1 .6 b 0.9 a 30 a 0 a
+ 8.8 b 15.1 be 0 a 0 a 0 a
*- = no Vorlex applied; + = Vorlex applied.
Means followed with the same letter in a column are not significantly different at the 5% level according 
to Duncan's multiple range test.
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Table 1.5. Effects of root-knot nematode P. levels, tomato cultivars and Vorlex applications (0, 22.5 
and 45 L/ha) on the growth of subsequent Rutgers (susceptible) tomato and reproduction of 
residual populations of M. incognita.
Pj 3 Plant growth  Nematode Reproduction
(eggs/500 cm Previous Vorlex Shoot dry Root fresh Eggs & larvae Larvae/
soil) cultivar L/ha wt (g) wt (g) Gall index /gm roots 100 cc soil
Rutgers 0 13.3 c 15.0 c 0 a 0 a 0 a
22.5 13.5 c 14.8 c 0 a 0 a 0 a
45.0 13.0 c 15.5 c 0 a 0 a 0 a
VFN-8 0 14.1 c 14.3 c 0 a 0 a 0 a
22.5 13.5 c 18.9 cd 0 a 0 a 0 a
45.0 14.8 c 16.4 c 0 a 0 a 0 a
Nematex 0 10.1 b 15.3 c 0 a 0 a 0 a
22.5 13.0 c 16.0 c 0 a 0 a 0 a
45.0 14.1 c 16.1 c 0 a 0 a 0 a
Rutgers 0 2.4 a 4.5 a 5 c 40811 b 117 be
22.5 10.1 b 13.3 be 0 a 150 a 8 a
45.0 13.0 c 19.9 cd 0 a 40 a 0 a
VFN-8 0 15.5 c 20.6 d 2.6 b 12 a 86 b
22.5 13.3 c 13.9 be 0 a 4 a 0 a
45 10.8 be 13.5 be 0 a Q a 0 a
Nematex 0 14.0 c 20.1 d 1.4 a 14 a 0 a
22.5 13.4 c 15.5 c 0 a 0 a 0 a
45.0 13.7 c 16.0 c 0 a 0 a 0 a
- continued --
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Table 1.5. (Continued;
Rutgers 0 2.1 a 9.0 b 5 c 60832 c 74 b
22.5 12.1 c 19.1 cd 0 a 234 a 0 a
45.0 12.2 c 17.5 cd 0 a 67 a 0 a
VFN-8 0 11.5 be 21.0 d 5 c 51 a 179 c
22.5 11.2 be 16.3 c 0 a 0 a 0 a
45.0 12.0 c 14.3 c 0 a 0.5 a 0 a
Nematex 0 12.1 c 21.7 d 2.6 b 60 a 6.2 a
22.5 12.4 c 15.7 c 0 a 1.0 a 0.2 a
45.0 13.0 c 17.5 cd 0 a 0 a 0 a
Means followed with the same letter in a column are not significantly different at the 5% level according 
to Duncan's multiple range test.
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Table 1.6. Effects of levels, tomato cultivars and Vorlex applications on the growth of subsequent 
Rutgers (susceptible) tomato, and reproduction of the residual populations of M. hapla.
, Pi(eggs/500 
soil)
3
cm Previous 
cultivar
Vorlex 
90 L/ha
Plant growth Nematode Reproduction
Shoot dry 
Wt (g)
Root fresh 
wt (g) Gall index
Eggs & larvae 
/gm roots
Larvae/ 
100 cc soil
0 Rutgers 16.5 ab 16.7 a 0 a 0 a 0 a
+ 15.8 ab 14.4 a 0 a 0 a 0 a
VFN-8 18.4 b 17.5 a 0 a 0 a 0 a
+ 19.5 b 19.5 ab 0 a 0 a 0 a
L. peruvianum _ 19.4 b 18.8 ab 0 a 0 a 0 a
+ 17.7 b 17.8 ab 0 a 0 a 0 a
1,000 Rutgers _ 14.8 a 35.7 c 5.0 c 88800 d 1414 c
+ 18.4 b 17.7 ab 0 a 4 a 0 a
VFN-8 _ 20.8 b 23.0 b 0.6 a 53.8 b 3.0 a
+ 17.4 b 21.2 b 0 a 0 a 0 a
L. peruvianum - 19.0 b 21.4 b 0.4 a 0.4 a 4.0 a
17.4 b 18.7 ab 0 a 0 a 0 a
5,000 Rutgers _ 14.2 a 27.4 be 50 c 78333 d 31.4 b
+ 19.2 b 21.0 b 0 a 10.5 a 0 a
VFN-8 18.1 b 20.5 b 2.4 ab 3108 c 53 a
+ 17.8 b 22.7 b 0 a 0 a 0 a
L. peruvianum - 18.2 b 20.1 b 1.5 a 165 ab 1.0 a
* « nr* \lr>V>1 V -J rt r\ ■ J- —
+ 17.7
i
b 19.9 b 0 a 0 a 0 a
*- = no Vorlex applied; + = Vorlex applied.
Means followed with the same letter in a column are not significantly different at the 5% level according 
to Duncan's multiple range test.
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Table 1.7. Effects of levels, tomato cultivars and Vorlex applications (0, 22.5 and 45 L/ha) on 
growth of subsequent Rutgers (susceptible) tomato and reproduction of the residual 
populations of M. hapla.
(eggs/j>00 cm3 
soil)
Plant growth Nematode Reproduction
Previous
cultivar
Vorlex
L/ha
Shoot dry 
wt (g)
Root fresh 
wt (g) Gall Index
Eggs & larvae 
/gm roots
Larvae/ 
100 cc soil
Rutgers 0 15.6 b 16.5 b 0 a 0 a 0 a
22.5 18.0 c 16.3 b 0 a 0 a 0 a
45.0 15.0 b 17.0 b 0 a 0 a 0 a
VFN-8 0 16.4 b 15.8 b 0 a 0 a 0 a
22.5 15.8 b 20.4 c 0 a 0 a 0 a
45.0 15.0 b 17.4 b 0 a 0 a 0 a
L. peruvianum 0 12.4 b 16.8 b 0 a 0 a 0 a
22.5 15.0 b 17.8 b 0 a 0 a 0 a
45.0 16.4 b 17.6 b 0 a 0 a 0 a
Rutgers 0 4.4 a 6.0 a 5 b 51642 c 248 d
22.5 12.0 b 14.8 b 1 a 64 a 0 a
45.0 15.2 be 20.4 c 0 a 35 a 0 a
VFN-8 0 17.6 b 22.4 c 4 b 624 a 86 ab
22.5 15.6 b 15.6 b 0 a 10 a 0 a
45.0 12.8 b 15.0 b 0 a 0 a 0 a
L. peruvianum 0 16.0 b 21.6 c 1 a 61 a 2 a
22.5 15.4 b 17.0 b 0 a 0 a 0 a
45.0 15.8 b 17.4 b 0 a 0 a 0 a
1,000
—  Continued —
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Table 1.7. Continued
5,000 Rutgers 0 1.6 a 21.3 c 5 b 99834 d 178 c
22.5 14.4 b 20.6 c 1.3 a 78 a 0 a
45.0 14.8 b 19.0 be 0.3 a 30 a 0 a
VFN-8 0 13.2 b 22.7 c 5 b 2040 b 179 be
22.5 13.2 b 17.8 b 1.1 a 14 a 0 a
45.0 14.2 b 15.8 b 0 a 0 a 0 a
peruvianum 0 14.6 b 23.2 c 1 a 40 a 5 a
22.5 14.8 b 17.4 b 0 a 2 a 0 a
45.0 15.0 b 19,0 be 0 a 2 a 0 a
Means followed with the same letter in a column are not significantly different at the 5% level according 
to Duncan's multiple range test.
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Table 1.8. Effect of P. levels of M. incognita, previous tomato cultivar, and chemical treatments on
dry shoot weight of subsequent crops of Rutgers tomato.
Pi 3
(eggs/500 cm Previous Vorlex Top dry wt. of subsequent crops of Rutgers
soil) cultivar L/ha 1 2 3 4
Rutgers 0 10.9 9.6 10.3 8.7
22.5 13.4 6.6 12.6 8.4
45.0 10.8 8.7 13.2 8.5
VFN-8 0 10.4 8.6 12.0 9.8
22.5 9.6 5.7 12.6 10.6
45.0 11.2 11.1 14.0 10.4
Nematex 0 10.7 7.6 13.4 9.0
22.5 10.7 7.5 12.2 8.6
45.0 9.4 9.2 14.0 9.4
Rutgers 0 2.4 9.4 5.8 4.2
22.5 11.6 9.3 9.4 6.6
45.0 11.6 9.4 12.2 4.2
VFN-8 0 9.4 2.1 7.8 8.8
22.5 9.4 9.2 13.4 8.0
45.0 9.7 7.0 12.4 8.4
Nematex 0 10.9 6.7 11.0 7.5
22.5 10.9 9.9 13.0 7.8
45.0 10.9 9.3 12.2 8.3
- Continued -
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Table 1.8. Continued
Rutgers 0 3.1
22.5 12.4
45.0 10.8
VFN-8 0 10.9
22.5 10.9
45.0 11.4
Nematex 0 11.0
22.5 13.4
45.0 10.4
2.8
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5.3 11.4 6.0
7.3 11.0 8.0
7.7 13.6 7.4
2.1 10.4 6.2
6.8 11.6 7.8
8.8 8.8 7.8
6.1 10.0 11.5
8.6 10.2 10.0
7.7 10.8 9.2
2.5 4.5 3.2 -p»-p>
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Table 1.9. Effects of P- levels of M. incognita, previous tomato cultivar and chemical treatments on
fresh root weight of subsequent crops of Rutgers tomato.
(eggs/5(!)0 cm^ Previous Vorlex Root fresh wt. of subsequent crops of Rutgers
soil) cultivar L/ha 1 2 3 4
Rutgers 0 15.7 8.7 18.7 13.0
22.5 21.2 9.6 17.6 12.5
45.0 19.5 9.5 17.6 13.1
VFN-8 0 14.4 10.8 18.6 15.6
22.5 18.8 5.7 18.7 16.2
45.0 18.3 9.7 18.7 14.9
Nematex 0 11.8 8.3 19.2 14.4
22.5 15.7 9.2 18.1 13.3
45.0 15.8 10.2 21.1 13.8
Rutgers 0 14.6 16.5 23.8 20.1
22.5 17.6 9.6 24.8 26.1
45.0 18.3 9.5 24.2 20.2
VFN-8 0 21.5 6.5 27.2 22.7
22.5 16.9 11.3 18.3 16.8
45.0 16.1 10.5 13.2 13.7
Nematex 0 15.4 9.0 17.3 16.8
22.5 19.0 11.4 18.1 17.7
45.0 16.6 8.9 17.5 15.4
-- Continued —
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Table 1.9. Continued
Rutgers 0 19.5
22.5 18.4
45.0 19.1
VFN-8 0 19.5
22.5 17.5
45.0 19.6
Nematex 0 17.9
22.5 19.6
45.0 15.1
6.2
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10.5 28.0 22.9
10.1 26.2 17.6
10.5 23.8 18.1
5.4 26.8 17.9
8.3 17.8 17.2
10.2 23.4 15.7
9.9 27.8 18.5
10.2 23.4 15.7
9.9 16.5 13.6
3.8 5.2 4.3
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Table 1.10. Influence of levels of M. hapla on yield of two cultivars of tomato (1980).
Pi(eggs and larvae 
/500 cm3 soil)
Tomato
Cultivar 1
Yield (g/plant) 
Harvest No.
2 3 4 5
Total marketable yield 
(kg/ha)
0 Rutgers 13 365 1166 2050 648 42420 a
1,000 5 263 782 1117 299 25640 b
5,000 0 196 671 1413 274 24980 b
0 VFN-8 75 382 1190 1825 959 44310 a
1,000 98 213 936 1698 1025 39680 a
5,000 77 352 775 1647 1262 40790 a
Means followed with the same letter are not significantly different at 5% level according to Duncan's 
multiple range test.
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Table 1.11. Influence of Pi levels and source of resistance on population development of M. hapla.
Pi(eggs and~larvae 
/ 500 cm soil)
Previous 
tomato cultivar '
Nematode counts (larvae/100 cc 
Harvest no.
1 3
of soil) 
5
1,000 Rutgers 180 315 920
VFN-8 0 0 13
L. peruvianum 0 0 0.2
5,000 Rutgers 320 946 1294
VFN-8 4 35 65
L. peruvianum 0 0.2 5
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Table 1.12. Total marketable yield of tomato (cv. Rutgers) as influenced by initial inoculum density 
(P^ ) of M. hapla, plant resistance and chemical treatments (1981).
Pi
(eggs & larvae 
/500 cm3 soil)
Previous tomato cultivar 
(1980)
Yield kg/ha 
Chemical treatments 
No Vorlex Vorlex at 45 L/ha
0 Rutgers 45,230 b 53,790 a
1,000 36,070 cd 51,382 a
5,000 27,330 d 42,270 cd
0 VFN-8 47,373 b 55,004 a
1,000 (Better Boy) 45,548 b 54,292 a
5,000 491030 ab 47,142 b
0 L. peruvianum 46,514 b 53,970 a
1,000 41,768 be 44,080 b
5,000 41,844 be 50,244 a
Means followed by the same letter are not significantly different at 5% level according to Duncan's 
multiple range tests.
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Table 1.13. Influence of plant resistance and chemical applications on population development of 
M. hapla and galling of Rutgers tomato (1981).
(Eqgsboo 
cm3 soil)
Previous
tomato Vorlex Larvae/100 cc of soil
cultivar 45 L/ha Beginning of 
season
Mid
season
End of 
season
Gall Index 
End of season
1,000 Rutgers - 15 240 260 4.7
+ 17.6 0 2
VFN-8 - 0.5 50 4 1.0
+ 2.8 0 0
L. peruvianum - 0.3 2.0 3.6 0.8
+ 0 0 0
5,000 Rutgers - 26 620 768 5.0
+ 23 10 2
VFN-8 - 3 100 2.8 2.4
+ 2 0 0
L. peruvianum - 1 4 3.8 1.0
+ 0 0 0
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51
Figure 1.1-1.4.
Population dynamics of M. incognita on successive Rutgers tomato 
plantings grown in infested soil of different P.. levels previously 
planted to either susceptible (Rutgers) or resistant (VFN-8 and 
Nematex) tomato cultivars and treated with either 0, 22.5 or 45 L 
Vorlex/ha.
Figure 1.1 = P^  level of 5,000 eggs/500 cm3 of soil 
Figure 1 . 2 = "  " 1,000 " "
Figure 1.3 = " " 10,000
Figure 1.4 = " " 100,000 1 1
In all the figures,
A, B and C represent applications of Vorlex at either 0, 22.5 or 
45 L/ha, respectively, following a crop of Rutgers;
D, E and F represent applications of Vorlex at either 0, 22.5 or 
45 L/ha, respectively, following a crop of VFN-8; 
and G, H and I represent applications of Vorlex at either 0, 22.5 
or 45 L/ha, respectively, following a crop of Nematex.
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52
>  4
=e 2 
m
t—>
+. 5
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53
Figure 1.5-1.6.
Population dynamics of M. hapla on successive Rutgers tomato 
plantings grown in infested soil of different levels previously 
planted to either susceptible (Rutgers), partially resistant (VFN-8) 
or resistant (J-. peruvianum) tomatoes and treated with either 0, 22.5 
or 45 L Vorlex/ha.
Figure 1.5 = Pi level of 1,000 eggs/500 cm3 of soil 
Figure 1.6= “ " 5,000
In all the figures,
A, B and C represent applications of Vorlex at either 0, 22.5 or 
45 L/ha, respectively, following a crop of Rutgers;
D, E and F represent applications of Vorlex at either 0, 22.5 or 
45 L/ha, respectively, following a crop of VFN-8; 
and G, H and I represent applications of Vorlex at either 0, 22.5 
or 45 L/ha, respectively, following a crop of L_. peruvianum.
Figure 1.7-1.8
Fresh root weight and gall index of subsequent Rutgers tomato 
plantings, grown in infested soil of different P^  levels previously 
planted to either Rutgers VFN-8 or Nematex and treated with either 
0, 22.5 or 45 L Vorlex/ha.
Figure 1.7 = P^  level of 10,000 eggs/500 cm3 of soil 
Figure 1.8 = " " 100,000 " 1
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In all the figures,
A, B and C represent applications of Vorlex at either 0, 22.5 or 
45 L/ha, respectively, following a crop of Rutgers;
D, E and F represent applications of Vorlex at either 0, 22.5 or
45 L/ha, respectively, following a crop of VFN-8;
and G, H and I represent applications of Vorlex at either 0,
22.5 or 45 L/ha, respectively, following a crop of Nematex.
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55
'"■'s. 5  
OJ
5 8
°8 2
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SUBSEQUENT RUTGERS CROPS
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GA
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IN
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X
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Chapter 2
EFFECT OF VARIOUS PERIODS OF EXPOSURE TO ROOT-KNOT NEMATODES ON GROWTH 
OF RESISTANT AND SUSCEPTIBLE TOMATO TRANSPLANTS
Abstract
Experiments were conducted to determine the effects of length of 
time of exposure in root-knot nematode infested soil on growth of 
susceptible and resistant tomato seedlings. Susceptible (Rutgers) and 
resistant (Nematex) tomatoes were grown in soil infested with different 
initial inoculum densities (0, 100, 1,000, 5,000, 10,000, and 50,000 
eggs and larvae/kg of soil) of Meloidogyne incognita for either 2, 4, 
or 6 wk. Seedlings of Nematex were stunted when they were grown in 
soils infested with 10,000 or 50,000 eggs and larvae/kg of soil. They 
grew as well as the uninfested control, however, if in 2 wk they were 
repotted in non-infested soil. Rutgers seedlings were severely 
stunted when they were grown for 2, 4, or 6 wk in infested soil that 
contained more than 1,000 eggs and larvae per kg of soil. Although 
transplants recovered from the nematode attack when they were reported 
in noninfested soil, they did not grow as well as the controls. Before 
the end of 6 wks, all the Rutgers seedlings grown in the highest inoculum 
level soil had died.
Introduction
The use of nematode free planting stocks is often recommended, not 
only to avoid the consequences of nematode infection of the crop but 
also to avoid the possibility of infesting uncontaminated land. Growth 
reductions (7, 10, 11) as well as yield losses (1, 7, 9) often result
56
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when healthy seedlings are transplanted to root knot nematode infested 
soil. The amount of damage caused by root knot nematodes can be 
influenced by the initial inoculum density (1, 7, 9, 10, 11), time of 
inoculation (3, 10) and other environmental and edaphic factors (2, 5,
13). The possibility of regeneration or recovery of damaged roots is 
greater when seedlings infected by root knot nematodes are transferred 
or transplanted to uninfested soil. Lamberti (6) demonstrated the 
importance of transplanting nematode-free seedlings into fumigated soil, 
and he also showed that even infested seedlings may yield well in 
uninfested soil.
The purpose of this study was to investigate the effects of the length 
of exposure period of tomato seedlings to M. incognita on growth of these 
tomato transplants, both before and after transplanting.
Materials and Methods
Eight centimer (dm) pots were filled with autoclaved soil to which 
0, 100, 1,000, 5,000, 10,000 or 50,000 eggs and larvae of M. incognita 
per kg of soil was added. Tomato seeds (3 per pot) were planted in all 
the pots, which were placed randomly on the greenhouse (temperature 
22-26°C) bench and watered daily. Seedlings were thinned to one per 
pot after emergence.
Two weeks after the seeds were sown, the first batch of seedlings 
(7 replications per treatment) were carefully removed from the soil, 
washed in water and transplanted to 12.5 cm (dm) pots filled with 
autoclaved soil. Plant height and root gall index were determined at 
the time of transplanting. The same procedure was followed 4 and 6 wks
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after the seeds were sown. Both the infected and uninfected plants 
were grown for six more weeks after repotting. Plants were watered daily 
and fertilized with soluble 20-20-20 NPK every 10 days. Plant growth 
and root gall index were determined at the end of each experiment. 
Cultivars susceptible (Rutgers) and resistant (Nematex) to M. incognita 
were used. Soil infested with 1,000, 10,000 or 50,000 eggs and larvae/ 
kg of soil were used in the experiments with Nematex. A completely 
randomized design was used. A quantitative scoring index based on 
percent root system galled was used: 0 = no galling, 1 = 1-10% galling,
2 = 11-25% galling, 3 = 26-50% galling, 4 = 51-75% galling and 5 = above 
75% galling.
Results
There was a reduction in height of Rutgers seedlings exposed to 
infested soil for 2 wks at the two highest inoculum densities (Table 1). 
Seedlings repotted in uninfested soil after 2 wks exposure to infested 
soil recovered very quickly from the nematode attack, but the recovery 
was slower for those that were exposed to the two highest inoculum 
density levels (Table 2.3A). Plant height as well as top growth weight 
were lowest at the 50,000 inoculum density. Some galls were observed 
on repotted plants exposed to inoculum densities of 5,000 or more eggs 
and larvae per kg of soil. Rutgers seedlings exposed to M. incognita 
for 4 wks showed severe stunting and galling at inoculum densities 
above 5,000 eggs and larvae (Table 2.1). When plants were repotted 
after 4 wks exposure to infested soil (Table 2.3B), the recovery in 
growth from the nematode attack was slower at higher inoculum densities. 
While the shoots at all inoculum densities were shorter than the
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uninoculated control, significant differences from the control were 
observed only at the highest densities. Galls were observed on roots 
of repotted plants exposed to infested soil for 4 or more weeks. Plants 
exposed to infested soil for 6 wks showed significant differences from 
the uninfested control in growth (Table 2.1). There was stimulation 
of growth at the inoculum level of 100 eggs and larvae/kg of soil. All 
seedlings exposed to 50,000 eggs and larvae/kg of soil died before the 
end of 6 wks. Seedlings exposed to 5,000 and 10,000 eggs and larvae/kg 
of soil were very stunted. Although the seedlings recovered from the 
nematode attack when repotted after the 5 wks exposure (Table 2.3C) to 
1,000, 5,000 and 10,000 inoculum densities, they were not as tall as the 
control. Dry weights of tops and roots were lowest at the highest 
inoculum density. All plants grown in infested soil before transplanting 
were heavily galled. Seedlings that were grown in highly (10,000 and
50.000 eggs and larvae/kg of soil) infested soil for 4 to 6 wks before 
repotting to uninfested soil flowered a week later than those that were 
grown in and repotted to uninfested soil. The effects of exposure of 
seedlings of the resistant cultivar (Nematex) to infested soil were not 
as drastic as those observed when the susceptible cultivar was exposed 
to the same level of inoculum. Seedlings grown for 2 or 4 wks in 
infested soil showed significant differences in height only at the
50.000 inoculum level (Table 2.2). Growing seedlings in infested soil 
for 5 wks resulted in significant reduction in growth at the 10,000 and
50.000 inoculum densities. Some galls were observed on the seedlings
at the highest inoculum level only if they had been grown in the infested 
soil for more than 4 wks at the highest inoculum level. Repotted seed­
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lings after 2 wks growth in infested soil (Table 2.4A) did not show any 
signicant differences from the controls in growth of the plants.
Compared to controls, seedlings grown for 4 or 6 wks in infested soil 
resulted in a decrease in height of the repotted plants, but significant 
differences were only observed at the highest inoculum level (Tables 
2.4B, C).
Discussion and Conclusions 
Survival of transplanted seedlings and subsequent yields of 
transplanted crops are often a reflection of the quality of the seedlings. 
Thus, more emphasis should be directed toward the preparation of the 
nursery material. Although the results of these experiments indicate 
a regeneration and rapid regrowth of seedlings after exposure to 
different levels of inoculum density, they also emphasize the importance 
of the effects of infested soil on the initial and subsequent growth 
and maturity of tomato transplants. Growing seedlings of a susceptible 
cultivar for as little as 2 wks in a highly infested soil could cause 
considerable damage even when transplanted to uninfested soil. Severe 
damage can result when the seedlings are exposed for a longer period 
of time. Since tomato seedlings are normally transplanted 4-8 wks 
after seeding, growing tomato plants in seed beds with soil infested 
with more than 100 eggs and larvae/kg of soil would result in considerable 
loss in yield, even when they are transplanted to uninfested soil. Heavy 
galling observed on roots of transplants of Rutgers seedlings exposed to 
infested soil at higher inoculum densities for 4 or more wks was probably 
due to the fact that some of the females had matured and laid eggs before 
the plants were repotted. The eggs subsequently hatched and the second
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stage larvae reinfected the newly developing roots. Galls on repotted 
plants that were grown in the infested soil for 2 wks were limited to 
roots that had galls on them before they were repotted to uninfested 
soil.
Root necrosis has often been associated with resistance to root 
knot nematodes (8, 14). It is, therefore, possible that in cases where 
there is a heavy infestation of root knot nematodes, severe root necrosis 
could slow the growth of the resistant plant. Results of this experiment 
showed that exposure of seedlings of resistant plants even for 2 wks 
to very high densities could cause a reduction in growth even when 
repotted to uninfested soil. The longer the time of exposure, the more 
the damage, which will subsequently delay maturity and probably reduce 
yield of the crop. This would be especially true when growing seasons 
are short. Vito and Lamberti (12) showed reduction in yield of two 
tomato cultivars resistant to M. incognita, although no gall formation 
was observed on the roots of the resistant cultivars.
Some of the differences observed in growth of the seedlings grown 
in infested soil could also be due to the delay in seed emergence in the 
heavily infested soil. Emergence delay of two to three days was observed 
in some cases. When the seedlings were repotted to uninfested soil, the 
ratios of the initial height, before repotting, to the final height at 
the end of the experiment were much higher for plants that were grown 
in higher inoculum level soil than for those that were grown in uninfested 
or low inoculum level soil. This was probably due to the delay in 
maturity of the repotted plants that were grown in highly infested soil. 
Repotted plants grown in uninfested soil flowered a week earlier than
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those grown in infested soil. Thus, much of the vegetative growth, 
especially growth in height, probably had slowed down in order for the 
photosynthate to be diverted to the reproductive growth at the time that 
the experiments were terminated.
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Literature Cited
1. Barker, K. R., P. B. Shoemaker and L. A. Nelson. 1976. Relationships
of initial population densities of Meloidogyne incognita and M. 
hapla to yield of tomatoes. J. Nematol. 8:232.
2. Bergeson, G. B. 1968. Evaluation of factors contributing to the
pathogenciity of Meloidogyne incognita. Phytopathology 58:49-53.
3. Brodie, B. B. and P. B. Dukes. 1972. The relationship between
tobacco yield and -time of infection with Meloidogyne javanica.
J. Nematol. 4:80-83.
4. Dean, J. L. and F. B. Struble. 1953. Resistance and susceptibility
of root knot nematodes in tomato and sweet potato. Phytopathology 
43:190. (Abstr.).
5. Griffin, G. D. and E. G. Jorgenson. 1969. Effect of soil temperature
on the pathogenicity and reproduction of Meloidogyne hapla on 
Russet Burbank potato. Phytopathology 59:11. (Abstr.).
6. Lamberti, F. 1975. Fumiganti e nematocidid sistemici nella lotta
contro i fitoelminti ipogei. Rep. S.I.F. 26.
7. Olthof, Th. H. A. and J. W. Potter. 1977. Effects of population
densities of Meloidogyne hapla on growth and yield of tomato.
J. Nematol. 9:296-300.
8. Paulson, R. E. and J. M. Webster. 1970. The cellular response of
a resistant tomato plant to Meloidogyne incognita. Parasitology 
56:4. (Abstr.).
9. Potter, J. W. and Th. H. A. Olthof. 1974. Yield losses in fall-
maturing vegetables relative to population densities of Prat.ylenchus 
penetrans and Meloidogyne hapla. Phytopathology 64:1074-1075.
University of Ghana          http://ugspace.ug.edu.gh
64
10. Sigh, N. D. 1975. Effect of inoculum level and plant age on
pathogenicity of Meloidogyne incognita and Rotylehchus reniformis 
to tomato and lettuce. Plant Dis. Reptr. 59:905-908.
11. Swarup, G. and R. D. Sharma. 1965. Root knot of vegetables. IV.
Relation between population density of Meloidogyne javanica and 
Meloidogyne incognita var. acrita and root and shoot growth of 
tomato seedlings. Indian J. Expt. Biol. 3:197-198.
12. Vitro, M. Di, and F. Lamberti. 1976. Reaction of tomato varieties
to populations of Meloidogyne sp. in the glass house. Nematologia 
Mediterranea 4:211-215.
13. Wallace, H. R. 1970. Some factors influencing nematode reproduction
and growth of tomatoes infected with Meloidogyne javanica. 
Nematologica 16:387-397.
14. Webster, J. M. and R. E. Paulson. 1972. An interpretation of
ultrastructural response of tomato roots susceptible and resistant 
to Meloidogyne incognita (Kofoid and White) Chitwood. Bulletin OEPP 
No. 6. 33-39.
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Table 2.1. Height and gall index of Rutgers tomato seedlings grown in 
root knot nematode infested soil for 2, 4 or 6 weeks before 
repotting to uninfested soil.
inoculum density Plant height (cm) Gall index
(eggs and larvae Exposure time (wks) Exposure time (wks)
/kg soil) 2 4 6 2 4 6
0 4.5 14.5 23.0 0 0 0
100 4.7 14.0 28.3 0 2.6 3.5
1,000 3.0 12.5 20.5 1 4.8 4.5
5,000 3.5 4.7 8.0 2 5.0 5.0
10,000 2.8 3.0 4.8 5 5.0 5.0
50,000 2.5 3.1 -
LSD at 5% 1.8 2.6 8.2 1.8 0.7 0.8
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Table 2.2. Height and gall index of Nematex tomato seedlings grown in 
different levels of root knot nematode infested soil for 2, 
4 or 6 weeks before transplanting to uninfested soil.
Inoculum density Plant height (cm) Gall Index
(eggs and larvae Exposure time (wks) Exposure time (wks)
/kg soil) 2 4 6 2 4 6
0 4.5 10.2 21.0 0 0 0
1,000 4.3 10.4 18.6 0 0 0
10,000 4.1 8.0 11.2 1 0 0 1.0
50,000 2.9 7.4 10.6 0 0 2.0
LSD at 5% 0.8 1.5 3.2 NS NS 0.5
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Table 2.3. Effects of period of exposure of Rutgers tomato seedlings 
to different inoculum densities of root knot nematode in­
fested soil on growth and root gall index of plants 
repotted to uninfested soil.
Inoculum density 
(eggs and larvae 
/kg soil)
Shoot
height
(cm)
Plant growth 
Shoot 
dry wt. 
(gm)
Root 
dry wt. 
(gm) Gall Index
A. Exposure for 2 wks
0 38.0 6.2 0.8 0
100 40.3 9.9 0.5 0
1,000 37.8 4.8 0.7 0
5,000 34.2 3.7 0.6 1.0
10,000 32.0 3.7 0.8 1.0
50,000 29.0 3.4 0.6 1.3
LSD at 5% 6.4 2.0 NS 0.4
B. Exposure for 4 wks
0 51.8 11.8 1.7 0
100 48.3 10.5 1.8 1.8
1,000 46.3 9.8 1.8 2.3
5,000 36.8 8.7 1.5 3.5
10,000 35.8 4.6 0.8 4.3
50,000 24.0 4.9 0.9 5.0
LSD at 5% 8.8 3.9 0.5 0.8
C. Exposure for 6 wks
0 55.8 13.5 1.8 0
100 60.0 16.4 2.1 2.8
1,000 45.8 8.9 1.6 4.5
5,000 39.0 6.7 2.0 5
10,000 31.0 3.9 0.7 5
50,000 - - - -
LSD at 5% 4.1 3.9 0.6 1.7
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Table 2.4. Effects of period of exposure of Nematex tomato seedlings
to different inoculum densities of root knot nematode infested 
soil on the growth and root gall index of plants repotted to 
uninfested soil.
Inoculum density 
(eggs and larvae 
/kg soil)
Shoot 
hei ght 
(cm)
Plant growth 
Shoot 
dry wt. 
(gm)
Root 
dry wt. 
(gm) Gall Index
A. Exposure for 2 wks
0 36.8 8.7 1.1 0
1,000 36.4 7.5 1.1 0
10,000 34.6 6.7 0.7 0
50,000 32.6 7.6 1.0 0
LSD at 5% 3.6 NS 0.2 NS
B. Exposure for 4 wks
0 40.6 6.4 1.8 0
1,000 38.4 6.2 1.4 0
10,000 35.0 6.8 1.4 0
50,000 34.0 6.2 1.3 0
LSD at 5% 3.2 NS 0.5 NS
C. Exposure for 6 wks
0 70.8 17.4 2.2 0
1,000 66.0 14.6 1.8 0
10,000 67.6 17.6 2.1 0
50,000 65.2 15.2 2.0 0
LSD at 5% 5.1 2.9 NS NS
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Chapter 3
EVALUATION OF LACTUCA SPECIES AND BREEDING LINES OF LACTUCA SATIVA 
FOR RESISTANCE TO ROOT KNOT NEMATODE SPECIES 
(MELOIDOGYNE INCOGNITA, M. JAVANICA, M. HAPLA)
Abstract
Several plant introductions of Lactuca species and breeding lines 
of lettuce were screened for resistance to M. incognita, M. javanica and 
M. hapla. The Lactuca sp. and breeding lines tested were not resistant 
to either M. javanica or M. incognita. Although two of the plant 
introductions (L saligna and L  dregeana) were highly resistant to a 
greenhouse population of M. hapla, they were susceptible upon further 
testing with a field population of M. hapla.
Introduction
Meloidogyne hapla is an important pathogen of lettuce grown in the 
muck soil regions of NY State and Canada. Light green chi orotic leaves 
and a delay of maturity are some of the symptoms associated with root 
knot nematode infected plants. Plants severely infected when young 
often die from the attack (7). Yield losses as high as 87% have been 
reported in Canada (4, 5). Most crops suitable to be grown in 
rotation with lettuce are susceptible to this nematode, making it 
economically unsuitable to reduce the nematode populations by rotation. 
This makes lettuce growers dependent on preplant chemical soil treat­
ments for nematode control. Because of the problems of dispersion 
and adsorption by organic matter, two or three times the normal amount 
of nematicides that are recommended for mineral soils are generally
69
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70
applied to organic soils for economic control (7"). Control of the 
nematode by fumigation is therefore very difficult and expensive.
An effective and more desirable method of control would be the use of 
resistant cultivars.
The objective of this study was to evaluate resistance to root 
knot nematode species in some breeding lines and plant introductions 
of Lactuca species obtained from the Geneva Agricultural Experiment 
Station vegetable breeding program.
Materials and Methods
Three root knot nematode species, M. incognita, M. javanica, and 
M. hapla, were used. The inoculum (eggs) for each species was obtained 
from populations maintained on Rutgers tomato in the greenhouse. The 
eggs were extracted from heavily infested tomato roots with 0.8% NaOCl 
solution, using the method described by Hussey and Barker (2). Approx-
O
imately 2,000 eggs/500 cm of soil were mixed with autoclaved greenhouse 
soil. The seeds of several lettuce breeding lines and plant intro­
ductions were planted 5 per 12.5 cm -d- pots about 1/3" deep in the 
infested soil. Each treatment was replicated four times in pots that 
were kept on a bench in the greenhouse (temperature 21-26°C). Pots were 
watered as necessary and the seedlings were fertilized with soluble 
20-20-20 NPK every ten days after seed emergence. Four weeks after seed 
emergence, the plants were carefully removed from the soil, washed and 
were rated for gall index. An index based on the percent root system 
galled was used: 0 = no galling; 1 = 1-10% galling; 2 = 11-25% galling; 
3 = 26-50% galling; 4 = 51-75% galling and 5 = above 75% galling. 
Breeding lines and plant introductions that had low gall ratings to M.
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hapla obtained from a lettuce field in the summer of 1981.
Rutgers tomato was planted in the infested soil collected from a 
lettuce field near Oswego, New York. Six weeks after planting, roots 
were dug and washed gently in water. Twenty mature females were 
dissected from the roots and put in a petri dish containing 45% lactic 
acid (6). Perineal sections were made and observed under 100X oil 
immersion objective. It was found that 90% of the perineal patterns 
matched those described for M. hapla (1). The population was then increased 
on Rutgers tomato and inoculum for the study was obtained as described 
earlier.
Results and Discussion
Tables 3.1 and 3.2 present results of screening lettuce plant 
introductions and breeding lines for resistance to M. incognita and 
M. javanica. None of the Lactuca species or breeding lines were resistant 
to any of the two root knot nematode species, as determined by the gall 
index rating. Reactions of the breeding lines and plant introductions 
to the original greenhouse population of M. hapla are also presented in 
Tables 3.1 and 3.2. In the preliminary screening, L_. dregeana (PI 
273574), L, augustana (PI 190906), L  virosa (PI 273579) and U  saligna 
(PI 261653) appeared to have some resistance to M. hapla (Table 3.1). 
Breeding lines 80-40, 80-63, 80-438 were intermediate in resistance 
to the greenhouse population of M. hapla (Table 3.2). Breeding lines 
76-503-6, 80-70, 80-39, 80-366, 80-42 and J.. sativa were susceptible.
Except for one plant, all plants of]., saligna were resistant. In 
another experiment, 3 week old seedlings of these plant introductions 
and L.. sativa (cv. Ithaca) were inoculated with 5,000 or 10,000 eggs
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of M. hapla. The experiment was terminated 6 weeks after inoculation.
The wild species of lettuce supported a slower rate of reproduction of 
the nematode (Table 3.2) when compared to the cultivated species, 
k* sativa. L_. saligna and L  dregeana were highly resistant to the high 
inoculum rate of 10,000 eggs/plant. Based on these results, several 
plant introductions of L. saligna, L. dreqena, L_. augustana, L_. virosa 
and U  sativa breeding lines were screened against the field populations 
of M. hapla. Results (Tables 3.2 and 3.4) showed that none of the wild 
species or breeding lines were resistant to this field population. Similar 
results were obtained when the experiment was repeated. Variability in 
pathogenicity of populations of root knot nematodes has been demonstrated 
on several crops (3). Results of these experiments indicate variability 
in pathogenicity of the two populations of M. hapla on lettuce species.
The original greenhouse population had been maintained on Rutgers tomato 
for several years. It is, therefore, probable that there had been a 
change in the population with a loss of virulence for lettuce. The field 
population was collected from a field that had been cropped to lettuce 
for several years. The difference in pathogenicity between the two pop­
ulations may also have been due to the fact that the original greenhouse 
population had been collected from a different host. Since no further 
tests were made with any other plant species or crops, it is difficult 
to conclude that these are two different races. These results, therefore, 
demonstrate the need to test these plant introductions against 
populations of M. hapla collected from other locations.
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Literature Cited
1. Eisenback, J. D., H. Hirschmann, J, N. Sasser and A. C. Triantaphy-
llon. 1981. A guide to four most common species of root-knot 
nematodes (Meloidogyne species), with a pictorial key. Dept, of 
Plant Pathology and Genetics, N.C. State University and USAID. 
Raleigh, N.C. 48 p.
2. Hussey, R. S. and K. R. Barker. 1973. A comparison of methods of
collecting inocula of Meloidogyne spp. including a new technique. 
Plant Dis. Reptr. 57:1025.
3. Netscher, C. and D. P. Taylor. 1979. Physiologic variation with
the genus Meloidogyne and its implication on integrated control.
In Root Knot Nematodes (Meloidogyne species), Systematics, Biology 
and Control. London, U.K. and New York, USA. Academic Press, Inc. 
p. 269-293.
4. Olthof, Th. H. A. and J. W. Potter. 1972. Relating nematode
populations to crop losses. Canada Agriculture 17:18-15.
5. Potter, J. W. and Olthof, Th. H. A. 1974. Yield losses in fall
maturing vegetables relative to population densities of PratyTenchus 
penetrans and Meloidogyne hapla. Phytopathology 64:1072-1075.
6. Taylor, D. P. and C. Netscher. 1974. An improved technique for
preparing perineal patterns of Meloidogyne spp. Nematologica 
20:268-269.
7. Wong, T. K. 1972. The influence of temperature and levels of soil
moisture, oxygen and carbon dioxide on the biology and pathogenicity 
of Meloidogyne hapla, Chitwood 1949, as a pathogen of lettuce 
(Lactuca sativa) in organic soil. Ph.D. Dissertation. Cornell 
University.
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74
Table 3.1. Evaluation of Lactuca sp. for resistance to greenhouse 
populations of M. hapla, M. javanica and M. incognita.
Mean Gall Index
Lactuca so. PI M. hapla M. javanica M. incognita
.. sativa
(cv. Ithaca) 5.0 d 5 a 4.5 a
• augustana 190906 2.8 c 4.5 a 4.3 a
. saliqna 273582 1.0 ab 5.0 a 5.0 a
. saligna 261653 0.5 a 4.8 a 4.0 a
. saliqna 253229 0.3 a 4.5 a 4.7 a
. dregeana 273574 1.2 ab 5.0 a 4.0 a
. virosa 270901 2.1 b 5.0 a 3.5 a
. virosa 273579 1.0 ab 5.0 a 4.5 a
. virosa 271439 1.9 b 4.6 a 5.0 a
. virosa 271939 3.4 c 5.0 a 5.0 a
. virosa 274375 1.0 ab 5.0 a 5.0 a
. serriola 251246 5.0 d 5.0 a 5.0 a
. serriola 204753 4.0 cd - 5.0 a
. serriola 251245 5.0 d - 5.0 a
. 1iv da 273505 3.4 c 5.0 a -
. squarrosa 236396 3.8 c - -
Means followed by the same letter in a column are not significantly 
different at 5% level according to Duncan's Multiple Range Test.
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Table 3.2. Evaluation of lettuce breeding lines for resistance to greenhouse populations of M. hapla, 
M. javanica and M. incognita and a field population of M. hapla.
Mean Gall Index
Breeding Greenhouse Population Field Population
Line (Pedigree) M. hapla M. javanica M. incognita M. napla
80-70 (L. sativa v L. Vanguard 75 A PI
saliqna) r 
261653 4 3.5 cd 3.7 ab 5.0 a 5.0 a
80-39 I II I 3.3 cd 3.6 ab 4.6 a 5.0 a
80-43 I II I 5.0 d - 4.8 a 4.8 a
80-40 I I I 2.7 be 2.7 a 5.0 a 5.0 a
80-42 I II I 4.0 d 2.9 a 5.0 a 4.6
80-63 I U I 2.8 be - - 4.8 a
80-438 I * F5 3,0 c 4.5 cb 5.0 a 4.8 a
80-366 [-/Vanguard 75 F 
l'L. saligna 1
X Vanguard 75)] BG F4 4.5 d 5.0 c 5.0 a 5.0 a
76-503-6 (Vanguard 75 X Ithaca) F2 4.3 d 3.8 ab 5.0 a 5.0 a
L. sali gna (PI 26153) 1.5 a 5.0 c 4.3 a 5.0 a
L. sati va (cv. Ithaca) 4.7 d 4.9 c 5.0 a 5.0 a
Means followed by the same letter in a column are not significantly different at 5% level according to 
Duncan's multiple range test.
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Table 3.3. Reactions of selected Lactuca sp. to two initial inoculum densities (P.)
of a greenhouse population of M. hapla. 1
Gall Index Eqgs & larvae/q root
Lactuca sp. P.= 5,000 P .= 10,000 P ^  5,000 P^=10,000
L. sativa (cv. Ithaca) 5.0 c 5.0 b 15,000 c 24,000 c
L. virosa (PI 274375) 2.1 b 3.2 b 45 a 1,700 b
L. virosa (PI 273579) 2.4 b 4.5 b 300 b 1,500 b
L. saliqna (PI 261653) 0.0 a 1.3 a 15 a 52 a
L. auqustana (PI 190906) 3.8 c 4.8 b 402 b 800 ab
L. dreqeana (PI 274375) 1.2 b 1.8 a 20 a 1.00 a
Means followed by the same letter in a column are not significantly different at 5%
level according to Duncan's Multiple Range Test.
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77
Table 3.4. Reactions of selected Lactuca sp. to a field population 
of M. hapla.
Lactuca sp. Mean Gall Index
L. saliqna (PI 273582) 4.3 a
L. saliqna (PI 3739) 4.5 a
L. saliqna (PI 2615531 4.3 a
L. saliqna (PI 253227) 4.7 a
L. auqustana (PI 190906) 4.8 a
L. virosa (PI 273579) 5.0 a
L. dreqeana (PI 273574) 4.8 a
L. sativa (cv. Ithaca) 5.0 a
Means followed by the same letter in a column are not significantly 
different at 5% level according to Duncan's Multiple Range Test.
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