Pathozone Dynamics of Meloidogyne Incognita in the Rhizosphere of Tomato Plants in the Presence and Absence of the Nemat

8/6/2019 Pathozone Dynamics of Meloidogyne Incognita in the Rhizosphere of Tomato Plants in the Presence and Absence of the Nemat

1/9

Plant Pathology (2008) 57, 354362 Doi: 10.1111/j.1365-3059.2007.01776.x

2007 The Authors

354 Journal compilation 2007 BSPP

BlackwellPublishingLtd

Pathozone dynamics of Meloidogyne incognita

in the

rhizosphere of tomato plants in the presence and absence of

the nematophagous fungus, Pochonia chlamydosporia

D. J. Bailey

a

*, G. L. Biran

a

, B. R. Kerry

b

and C. A. Gilligan

a

a

Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA; andb

Rothamsted Research, Harpenden,

AL5 2JQ, UK

Pathozone dynamics were derived for approx. 50 Meloidogyne incognita

juveniles infecting a single root of tomato under

controlled conditions from a point source of inoculum and described using simple, non-linear models. The pathozone

decayed sigmoidally with distance, but increased over time as progressively more nematodes were able to infect the root.

Despite the reported ability ofM. incognita

juveniles to travel up to 50 cm in some conditions, the maximum width of

the pathozone for a single tomato root was estimated as 181 mm. It is conjectured that this was because of (i) diffusionfrom a point source of inoculum, (ii) a small infection court (a single root tip) and (iii) the limited life span of the

nematode. A second experiment was used to assess the effect of the nematophagous fungus Pochonia chlamydosporia

on the pathozone dynamics of the nematode. This fungus is known to produce nematicidal products in vitro

, which may

affect invasion of roots by the free-living nematode. To examine the possibility of a change in the position of the site

of infection, changes in the probability of gall formation along the root length were also examined. In the absence

ofP. chlamydosporia

, the pathozone dynamics ofM. incognita

were very similar to those of the first experiment. It was

shown that P. chlamydosporia

did not significantly affect the pathozone dynamics ofM. incognita

nor the site of gall

formation, which appear to have little importance for the role of the fungus as a biological control agent.

Keywords

: biocontrol, epidemiology, Lycopersicon esculentum

, root-knot nematode, soilborne parasite

Introduction

The nematode Meloidogyne incognita

is a root-infectingparasite that attacks a wide range of cultivated plants andcauses extensive economic damage, worldwide(Whitehead, 1998). The epidemiology of root-knotdisease is well known. Epidemics are initiated by primaryinfection from egg masses that persist in soil followinginfection of a previous crop and from which second-stagejuvenile (J2) nematodes hatch, migrate and infect nearbyroots. Within the roots, further nematode developmentdepends upon the formation of giant multinucleate

feeding cells. Swelling of cortical cells around the giantcells gives rise to galls on the roots of infected plants thatare characteristic of parasitism by root-knot nematodes.Female nematodes obtain nutrients from the plant via thegiant cells and eventually produce egg masses from which

a new generation of J2s hatch and spread to fresh roots,thus initiating the secondary phase of the epidemic (Bridge& Starr, 2007).

For soilborne parasites, the distance over which theycan migrate and infect a susceptible host root is a criticalfactor affecting the outcome of an epidemic. Thesecharacteristics are defined within the concept of thepathozone (Gilligan, 1985). The pathozone is the regionof soil surrounding the root in which inoculum must bepresent if it is to have any chance of infecting the root. Theprobability of infection is not constant when inoculum islocated at any site within the pathozone, but depends on

the distance between inoculum and host. Changes in theprobability of infection with distance can be derivedexperimentally by challenging replicate hosts with singleunits of inoculum placed at different distances fromthe host and then recording the proportion of successfulinfections at each distance after a given period of time.The resulting data can be described by a curve known asthe pathozone profile, which typically decays as thedistance between inoculum and host increases, butevolves over time, as progressively more inoculum issuccessful in causing infection. In combination with

*E-mail: [email protected]

Current address: INRA Agrocampus Rennes, UMR BiO3P

BP 35327, F-35653 Le Rheu Cedex, France.

Accepted 15 July 2007


2/9

Plant Pathology

(2008) 57

, 354362

Pathozone dynamics ofMeloidogyne incognita 355

simple non-linear models, the dynamics of the pathozoneare defined by a three-dimensional surface for change inthe probability of infection over distance and time (Bailey& Gilligan, 1997; Kleczkowski et al

., 1997).Pathozone dynamics have been carefully quantified for

particulate inoculum of certain soilborne oomycetes andfungi, but not for nematodes. For example, the pathozone

ranges from 5 mm for Phytophthora

spp. (Reynolds et al

.,1985) and Sclerotium rolfsii

on Phaseolus

spp. (Punja &Grogan, 1981) to 50 mm for Rhizoctonia solani

on sugarbeet petioles (Henis & Ben-Yephet, 1970). Nematodes arecapable of moving much faster and further than fungi, andProt (1978) reported Meloidogyne

populations migrating50 cm vertically in 9 days. Thus, one might expect a pro-portional increase in the magnitude and dynamics of thepathozone for nematodes compared to that for fungi.Moreover, the ability of nematodes to detect the presence ofa host from distances of up to 45 mm (Wallace, 1963) furtherincreases the probability of locating a susceptible root.

The potential for reducing the spread of disease canbe quantified using the pathozone bioassay (Bailey &

Gilligan, 1997), where disease control may be associatedwith either the inoculum (a reduction in infectivity) or thehost (increase in resistance via protection of the infectioncourt). For the root-knot nematode, M. incognita

, thesoilborne fungus Pochonia chlamydosporia

(Zare et al

.,2001) is a well-known parasite (Kerry, 2000) andstrategies for its exploitation as a biological control agenthave been developed (Atkins et al

., 2003). The fungus is afacultative parasite and develops saprotrophically inthe rhizosphere of many healthy and nematode-infectedplant species. The egg masses of root-knot nematodesproduced on the surface of infected roots may be colonizedby the fungus and the eggs containing infective juvenile

nematodes destroyed (Segers et al

., 1996; Kerry, 2000).Importantly, P. chlamydosporia

also produces bioactivecompounds in vitro

(Lopez-Llorca & Boag, 1993;Khambay et al

., 2000) that may act to protect the rootfrom infection, thus augmenting the hosts own resistance.Phomalactone was produced by P. chlamydosporia

during in vitro

culture and this weakly nematicidalmetabolite significantly reduced M. incognita

invasion oftomato roots when applied as a soil drench (Khambay

et al

., 2000). However, the importance of this mode ofaction in the regulation of Meloidogyne

populations inthe rhizosphere is not known.

In this paper a simple experimental bioassay combinedwith non-linear modelling was used to quantify the

pathozone dynamics for the infection of tomato plantsby the root-knot nematode, M. incognita

. The bioassaywas then used to test for any nematicidal effect of

P. chlamydosporia

in the rhizosphere of tomato plantscolonized by the fungal antagonist. A further level ofanalysis was also included involving the effect of P.chlamydosporia

on the distribution of galls producedalong a root (defined as the probability of gall formationat a given position). The potential of the methodology foranalysis and interpretation of nematode dynamics andtheir control are briefly discussed.

Materials and methods

Inoculum

Second-stage juveniles (J2) of the nematode Meloidogyneincognita

, race 2, population 1135, supplied as a gift fromNorth Carolina State University, USA and maintained

under quarantine at Rothamsted Research, were hatchedfrom egg masses produced on roots of infected aubergine(

Solanum melongena

) cv. Purple Ruby plants (grown inglasshouses at 27

C with a day length of 16 h) using themethod of de Leij & Kerry (1991) to provide an inoculumsuspension of 500 juveniles mL

1

water.An inoculum ofP. chlamydosporia isolate Vc-10 was

prepared from 21-day-old cultivars on cornmeal agarcontaining 50 mg each of streptomycin sulphate, chlortet-racycline and chloramphenicol (Sigma, USA) L

1

in Petridishes, incubated in the dark at 23

C. Aliquots of 1 mLsterile reverse-osmosis (RO) water were pipetted onto thecentre of each agar plate and the surface of each colonylightly agitated with a surface-sterilized spatula to

dislodge chlamydospores. The spore suspension waspipetted into a sterile universal tube and the concentrationadjusted to 500 chlamydospores mL

1

with sterile RO water.

Sand microcosms

Sand packs were prepared by adding approximately330 g of sand (acid-washed, quartz sand grade 16/30;Hepworth Minerals & Chemicals), moistened (10% v/w)with Hoaglands solution (Hoagland & Arnon, 1950), to20-cm lengths of 10-cm-wide Layflat tubing (1000-gauge). Each end of the tubing was partially sealed withstaples to allow for drainage.

A small hole was cut 10 mm from the top of each sandpack and a tomato seed (

Lycopersicon esculentum

cv.Tiny Tim; E. W. King & Co. Ltd) planted beneath the sandsurface at a depth of approximately 3 mm. The sandpacks were incubated in humid chambers at 23

C with16 h light (1828

moles m

2

s

1

) on a slope (30

fromvertical) to force the roots to grow towards the rear of thepacks.

Experiments

Two experiments were performed. Experiment 1 was usedto examine the pathozone dynamics ofM. incognita

andto identify the form of non-linear model with which to

describe changes in the probability of gall formation withdistance and time. The second experiment, whilstdemonstrating reproducibility of the pathozone bioassay,examined the effect of root colonization by P. chlamy-dosporia

on the pathozone dynamics of M. incognita

inoculum and on the precise location at which gallsdeveloped along the root. This latter experiment wasdesigned to demonstrate whether nematicidal metabolitesproduced by the fungus in vitro

were important for theinteractions between the nematode and the fungus in therhizosphere. Additional tests (results not shown) were


3/9

Plant Pathology

(2008) 57

, 354362

356

D. J. Bailey et al.

performed to show that the fungus had no effect on thegrowth of tomato roots and that it could be re-isolatedafter the experiment had finished.

Experiment 1: pathozone dynamics ofM. incognitaTomato plants grown in sand packs were inoculatedslowly with 100

L of nematode inoculum (approx. 50

J2s) injected 0, 5, 10, 15, 20 or 25 mm from the tip of aroot (the target root) to prevent spread of inoculumduring the injection process. The packs were completelyrandomized and incubated for 8 days in humid chambersat 23

C with 16 h light per day. The experiment included16 replicates for all inoculation distances except 20 mm,for which there were 15 replicates. Roots were examinedfor the presence of galls with the aid of a dissectingmicroscope (

20 magnification) each day for 8 daysfollowing inoculation.

Experiment 2: effect of root colonization byP. chlamydosporia

on the pathozone dynamics ofM. incognita

Tomato plants grown in sand packs were inoculated with100

L nematode inoculum injected 0, 5, 10, 15, 20 or25 mm from the tip of the target root. Half of the packsfor each distance were also inoculated with P. chlamydosporia

on the target root tip (

+

Pc). The remaining packs wereinoculated with 100

L tap water on the target roottip (Pc). The numbers of replicates per treatment were:16 for 0, 5 and 20 mm Pc; 17 for 10, 15 and 25 mm Pc;17 for 0, 5, 10 and 20 mm +

Pc; 15 for 15 mm +

Pc; and16 for 25 mm +

Pc. The packs were completely randomizedand incubated in humid chambers for 8 days at 23

C with16 h light.

Roots were examined for the presence and precise

location (with respect to the site of inoculation withnematodes) of galls with the aid of a dissecting microscope(

20 magnification) each day for 8 days after inoculation.

Modelling and statistical analyses

Experiment 1

Data for the probability of infection (gall formation), P

g

with distance, r

, were described by a sigmoidal curve:

(1)

at each time of observation, where

was the maximumprobability of infection when inoculum was placed at thesurface of the root and

was a measure of the rate at

which the probability of infection decayed as the distancebetween inoculum and the root increased. Changes in theparameters and

over time, t

, were described bymonomolecular and sigmoidal functions, respectively:

(2)

and

(3)

Note that the power on t

,

4

, was introduced to avoid verylarge values for

as t approached

3

. Incorporating

Eqns 2 and 3 into Eqn 1, the probability of infection overdistance and time was described by the surface

(4)

The furthest extent of the pathozone over time was

estimated from P

g

005 as t

approached infinity.

Experiment 2

Equation 4 was used as the basis for a statistical compar-ison of parameters estimated from data describing changein the probability of gall formation with distance and overtime (Gilligan, 1990) in the presence and absence of

P. chlamydosporia

.A distribution of the probability of gall formation with

distance below the point of inoculation was obtainedfrom data (pooled for all distances between inoculum androot) describing the position of galls along the root 8 daysafter incubation. Data were divided into 10 classescorresponding to contiguous 5-mm lengths of root

extending 45 mm below the point of inoculation anddescribed by a gamma function. Distributions for gallproduction in the presence and absence ofP. chlamydosporia

were compared using Kolmogorov-Smirnov tests (Kanji,1995). All curves were fitted using genstat

(V42, VSNInternational Ltd) assuming a binomial distribution oferrors (Anonymous, 1993).

Results

Experiment 1: pathozone dynamics ofM. incognita

on tomato

After 2 days incubation, the probability of infectiondecayed from 025 when inoculum was placed at the rootsurface to zero when inoculum was placed 10 mm fromthe root surface (Fig. 1). The probability of infectionincreased for a further 3 days so that, after 5 daysincubation, the probability of infection for inoculumplaced at the root surface was 075 and decayed to zerowhen inoculum was placed at a distance of 25 mm fromthe root surface.

Equation 1 provided a good description of thepathozone data at each time of observation. The param-eters and both changed significantly over time (Fig. 2).Parameter , describing change in the probability ofinfection when inoculum was placed at the surface of a

root, increased monotonically and was described by amonomolecular curve rising from zero after 175 days to082 after 8 days (Fig. 2a, Eqn 2). Parameterwas describedby an exponential decay over time (Fig. 2b, Eqn 3).

Using Eqns 2 and 3, a single surface:

(5)

was used to describe the evolution of the pathozoneover time (Fig. 3, Table 1). Change in the furthest

P r rg( ) exp( )= 2

( ) ( exp( ( ))),t t= 1 2 31

( ) ( exp( )).t t= + 1 2 34

P r t t

t rg( , ) ( exp( ( )))

exp ( ( exp( )) )

=

+

1 2 3

1 2 32

14

P r t t

t rg( , ) ( exp( ( )))

exp ( ( exp( )) )

=

+

0 79 1 1 29 1 69

0 009 6 41 3 41 0 61 2


4/9

Plant Pathology(2008) 57, 354362


extent of the pathozone was estimated at Pg= 005.

Pathozone width increased monotonically from 62 mmafter 2 days to a maximum of 1811 mm after 8 days(Fig. 4).

Experiment 2: effect of root colonization byP. chlamydosporia on pathozone dynamics ofM. incognita

In the absence of P. chlamydosporia, data describingchange in the probability of gall formation with distancebetween inoculum and root were similar to those

Figure 1 Pathozone profiles describing change in the probability of infection (gall formation) by the nematode Meloidogyne incognita with distance

from roots of tomato after 2, 3, 4, 5, 6 and 8 days of incubation. Profiles were described by Eqn 1: exp(r2).

Figure 2 (a) Change in the probability of gall formation for Meloidogyne incognita inoculum placed at the surface of the root () over time (t)

described by the monomolecular function 1(1 exp(2(t 3))); and (b) change in the rate of decay () with time (t) described by an exponential

decay: 1+ (2 exp(3t4)).

Table 1 Parameter estimates for the pathozone dynamics (change in

the probability of gall formation with distance and over time) ofMeloidogyne

incognita on tomato described using the pathozone model (Eqn 4):

Parameter Value ( SE)

1 079 005

2 129 073

3 169 024

1 0009 0002

2 641 (fixed)

3 341 125

4 061 035

P r t t t r g( , ) ( exp( ))) exp ( ( exp( )) )( .= +

1 2 3 1 2 3

4 21


5/9


358 D. J. Bailey et al.

obtained from experiment 1. After 2 days incubation, the

probability of gall formation when inoculum waspositioned at the root surface was 02 and decayed to zerowhen inoculum was placed at a distance of 5 mm.However, in contrast to the first experiment, after 7 daysincubation the maximum probability of gall formationPg= 068 occurred from inoculum placed 5 mm from theroot surface and declined to zero at a distance of 20 mm.

In the presence ofP. chlamydosporia, the probability ofgall formation was marginally increased during the first5 days when inoculum was positioned at or 5 mm fromthe root surface and marginally decreased when placed

10 mm from the root surface. After 8 days, the probabilityof gall formation in the presence of P. chlamydosporia

was slightly higher when inoculum was placed 15 mmfrom the root surface, but lower when it was placed at adistance of 5 or 10 mm.

Using the pathozone model (Eqn 4) to describe surfacesfor change in the pathozone over time (Table 2, Fig. 5), nosignificant effect ofP. chlamydosporia was detected on thepathozone dynamics of M. incognita. The pathozoneincreased monotonically from 28 mm after 2 days to amaximum of 20 mm after 8 days in the absence of the fungalantagonist and from 395 mm after 2 days to a maximumof 192 mm in the presence of the fungal antagonist.

Figure 3 Pathozone dynamics describing change

in the probability of gall formation over distance

and time for the infection of tomato by Meloidogyne

incognita. Data were fitted with the model

P r t t

t rg( , ) ( exp( ( ))) exp (

( exp( )) )

.

= +

1 2 3 1

2 3

4 2

1

Figure 4 Change in width of the Meloidogyne incognita pathozone

over time, estimated from pathozone dynamics (Eqn 4), where

pathozone width was estimated at Pg= 005.

Table 2 Parameter estimates for the pathozone dynamics (change in

the probability of gall formation with distance and over time) of Meloidogyne

incognita on tomato described using the pathozone model (Eqn 4):

in the

presence (+Pc) or absence (Pc) of Pochonia chlamydosporia

Parameter

Treatment

Pc ( SE) +Pc ( SE)

1 05769 011 06123 005

2 05020 045 22100 248

3 12350 085 18540 018

1 00061 0001 00068 0001

2 641 (Fixed) 641 (Fixed)

3 17100 122 27900 115

4 11100 062 06780 034

P r t t t r g( , ) ( exp( ( ))) exp ( ( exp( )) ).= +

1 2 3 1 2 3

4 21


6/9



Eight days after inoculation with the nematode, a totalof 55 galls had been produced on roots in the presence and52 galls in the absence ofP. chlamydosporia. The probabilityof gall formation rose from zero, at the point of inoculationwith the nematode, to a maximum of 033, 1620 mmbelow the height of inoculation. The probabilitythen decreased again to zero, 45 mm below the height

of inoculation (Fig. 6). A gamma distribution describedthe change in the probability of gall formation withdistance, x, from the height of inoculation with thenematode. No significant difference was detectedfor distributions describing change in the probabilityof gall formation with distance from the point ofinoculation.

Figure 5 Pathozone dynamics describing

change in the probability of gall formation over

distance and time for the infection of tomato by

Meloidogyne incognita in (a) the absence

and (b) the presence of Pochonia

chlamydosporia. Data were fitted with the model

P r t t t r

g( , ) ( exp( ( ))) exp (( exp( )) )

.

= +

1 2 3 1

2 3

4 21


7/9



Discussion

The pathozone dynamics ofM. incognita on single rootsof tomato plants were quantified. Despite the potential ofnematodes to spread by several cm each day, the furthestextent of the pathozone in the absence ofP. chlamydosporiawas estimated to be between 181 mm (experiment 1) and200 mm (experiment 2). Others estimates of the furth-est extent from which nematodes can infect a host

ranged from 5 mm (Wieser, 1955) to 100 cm (Johnson &McKeen, 1973) and were based on the infection of aroot system by individuals from a large population ofnematodes. The measurements in the present studyestimated the probability of infection of a single root andshowed that, although infection from distance is possible,the probability of infection decays very rapidly as thedistance between inoculum and root increases. The reasonfor this may result from a combination of three factors: (i)the concentration of nematodes decreases rapidly as theymove away from the site of inoculation, a process which

is most likely related to simple diffusion or a randomwalk (Feltham et al., 2002); (ii) the life expectancy ofnematodes in this system was less than 10 days (results notshown); and (iii) the susceptible portion of the root doesnot include the entire root, but may well be restricted tothe zone of elongation just behind the root tip. This meansthat, whilst the nematodes in this system may be capable

of travelling significantly greater distances than denotedby the furthest extent of the pathozone detected here,when placed only a small distance from the root surface,few will actually make contact with the susceptibleportion of a target root during the course of theirmigration. Observations were not made on other roots todetermine if they had been invaded elsewhere.

The variability between reported estimates of pathozonewidth undoubtedly results from differences in the inoculumsource, the host target and the soil environment throughwhich the nematodes migrate. For example, some studiesinvolved inoculum composed of over 300 juvenilenematodes (Wieser, 1955; Prot & Netscher, 1979;Stephan & Estey, 1982; Pinkerton et al., 1987; Pline &

Dusenbery, 1987; Diez & Dusenbery, 1989). In contrast,the present study used only 50. Others have includedlarger or multiple targets for infection (Bird, 1959;

Johnson & McKeen, 1973; Prot & Netscher, 1979;Stephan & Estey, 1982; Pinkerton et al., 1987), therebyincreasing the probability of infection. Moreover, forstudies involving incubation periods of over 50 days (e.g.Wallace, 1963; Johnson & McKeen, 1973; Stephan &Estey, 1982) resulting in estimates for infection over largedistances, secondary, root-to-root, infection cannot bediscounted. A wide range of abiotic and biotic factors,such as pH, temperature, moisture, redox potential,presence of a mate and root diffusates, affect nematode

movement in soil or in sand columns in controlled conditions(Prot, 1980). The present experiments to measure thepathozone used sand-based soil packs combined with ahighly controlled environment providing relativelyhomogeneous and repeatable growth conditions for theplant, nematode and fungus. This had the advantage ofreproducibility within (between replicates) and betweenexperiments, and forms the mechanistic platform fromwhich variability in other factors (inoculum size, hostnumber, soil type, the presence of an antagonist, etc.) canbe investigated.

Equation 4 accurately described the pathozone dynamicsfor M. incognita. Changes in the probability of infectionfor inoculum placed at the root surface, , increased

monotonically over time and the rate at which the prob-ability of infection decreased with distance, , decreasedexponentially over time. This is consistent with a profile(probability of infection with distance) that increasesdisproportionately more over time for inoculum placed atthe root surface than for inoculum placed away from theroot surface. It suggests that nematodes located on theroot surface remain more efficient at infecting the root andforming galls and may be related to a more favourablebalance between energies invested in foraging versusinfection.

Figure 6 Probability distributions of galls below the point of inoculation

along a Meloidogyne incognita-infested tomato root in (a) the absence

or (b) the presence of Pochonia chlamydosporia 8 days after

inoculation with M. incognita. Data were summarized using a gamma

distribution (solid lines).


8/9



By inoculating P. chlamydosporia directly onto the rootsurface, and despite the presence of actively growingfungus for the duration of the experiment, no significanteffects of fungal presence on pathozone dynamics(parameters 1, 2, 3, 1 and 2 of Eqn 4) ofM. incognitawere detected. Either the fungus had no direct effect oninfection of the nematode or the nematode was able to

avoid the fungus by infecting at another location. Yet,distributions describing change in the probability ofinfection along the root in the presence and absence ofP. chlamydosporia were identical and there was no significanteffect of the fungus on the site of gall formation. SinceP. chlamydosporia is a poor saprotroph with a slow rateof mycelial growth (Kerry, 1989), the nematode probablyenters the root ahead of extensive colonization by thefungus and the fungus is incapable of providing controlduring this phase of the nematode infection cycle.Therefore, the role ofP. chlamydosporia in the biologicalcontrol of M. incognita presumably depends on thereduction of secondary inoculum through the parasitismof nematode eggs and not the protection of the root from

nematode attack.To date, the development of biological control strategies

for nematodes is hampered by the lack of general descriptivemodels for the complex interactions between pest speciesand their microbial natural enemies. Scaling up fromsmall experimental plots to field crops will increase thevariation in the system and require such knowledge aspresented here to identify the key factors that affect theefficacy of biological control and so help provide con-sistent and practical levels of nematode management. Thispaper begins to address this need.

Acknowledgements

This work was funded by the award of a ResearchStudentship from the Biotechnology and BiologicalSciences Research Council (BBSRC), which we gratefullyacknowledge. Rothamsted Research receives grant-aidedsupport from the BBSRC and CAG also acknowledgesBBSRC support. We are also grateful to Dr D. Hall fortechnical assistance during the experiments. The workwas conducted in accordance with Defra Plant HealthLicence No. 174A/4485.

References

Anonymous 1993. Genstat 5: Reference Manual. Oxford, UK:Oxford University Press.

Atkins SD, Hidaldo-Diaz L, Kalisz H, Mauchline TH, Hirsch

PR, Kerry BR, 2003. Development of a new management

strategy for the control of root-knot nematodes (Meloidogyne

spp.) in organic vegetable production. Pest Management

Science59, 1839.

Bailey DJ, Gilligan CA, 1997. Biological control of

pathozone behaviour and disease dynamics of

Rhizoctonia solani by Trichoderma viride.New Phytologist

136, 35967.

Bird AF, 1959. The attractiveness of roots to the plant parasitic

nematodes Meloidogyne javanica and M. hapla.

Nematologica4, 32235.

Bridge J, Starr JL, 2007. Plant Nematodes of Agricultural

Importance. London, UK: Manson Publishing Ltd.

de Leij FAAM, Kerry BR, 1991. The nematophagous fungus

Verticillium chlamydosporium as a potential biological

control agent for Meloidogyne arenaria. Rvue de

Nmatologie14, 15764.

Diez JA, Dusenbery DB, 1989. Repellent of root-knot

nematodes from exudate of host roots.Journal of Chemical

Ecology15, 244555.

Feltham DL, Chaplain MAJ, Young IM, Crawford JW, 2002.

A mathematical analysis of a minimal model of nematode

migration in soil.Journal of Biological Systems10,

1532.

Gilligan CA, 1985. Probability models for host infection by

soilborne fungi. Phytopathology 75, 617.

Gilligan CA, 1990. Comparison of disease progress curves. New

Phytologist115, 22342.

Henis Y, Ben-Yephet Y, 1970. Effect of propagule size of

Rhizoctonia solani on saprophytic growth, infectivity and

virulence on bean seedlings. Phytopathology 60, 13516.

Hoagland DR, Arnon DI, 1950. The Water Culture Method forGrowing Plants Without Soil. Berkeley, CA, USA: California

Agricultural Experiment Station: Circular 347.

Johnson PW, McKeen CD, 1973. Vertical movement and

distribution ofMeloidogyne incognita (Nematoda) under

tomato in a sandy loam greenhouse soil. Canadian Journal of

Plant Science53, 83741.

Kanji GK, 1995. 100 Statistical Tests. London, UK: SAGE

Publications.

Kerry BR, 1989. Fungi as biological control agents for plant

parasitic nematodes. In: Whipps JM, Lumsden RD, eds.

Biotechnology of Fungi for Improving Plant Growth.

Cambridge, UK: University of Cambridge Press Syndicate,

15370.

Kerry BR, 2000. Rhizosphere interactions and the exploitationof microbial agents for the biological control of nematodes.

Annual Review of Phytopathology38, 42341.

Khambay BPS, Bourne JM, Cameron S, Kerry BR, Zaki MJ,

2000. Communication to the editor. A nematicidal metabolite

from Verticillium chlamydosporium. Pest Management

Science56, 10989.

Kleczkowski A, Gilligan CA, Bailey DJ, 1997. Scaling and

spatial dynamics in plant-pathogen systems: from individuals

to populations. Proceedings of the Royal Society Series B264,

97984.

Lopez-Llorca LV, Boag B, 1993. Biological properties of a red

pigment produced by the nematophagous fungus Verticillium

suchlasporium. Nematologia Mediterranea21, 1439.

Pinkerton JN, Mojtahedi H, Santo GS, OBannon JH, 1987.Vertical migration ofMeloidogyne chitwoodi and M. hapla

under controlled temperature.Journal of Nematology19,

1527.

Pline M, Dusenbery DB, 1987. Responses of plant-parasitic

nematode Meloidogyne incognita to carbon dioxide

determined by video camera-computer tracking.Journal of

Chemical Ecology13, 87388.

Prot J-C, 1978. Vertical migration of four natural populations of

Meloidogyne. Revue de Nmatologie1, 10912.

Prot J-C, 1980. Migration of plant parasitic nematodes towards

plant roots. Revue de Nmatologie3, 30518.


9/9



Prot J-C, Netscher C, 1979. Influence of movement of juveniles

on detection of fields infested with Meloidogyne. In: Lamberti

F, Taylor CE, eds. Root-knot Nematodes (Meloidogyne spp.)

Systematics, Biology and Control. London, UK: Academic

Press, 193203.

Punja ZK, Grogan RG, 1981. Mycelial growth and infection

without a food base by eruptively germinating sclerotia of

Sclerotium rolfsii. Phytopathology 71, 1099103.

Reynolds KM, Benson DM, Bruck RI, 1985. Epidemiology

ofPhytophthora root rot of Fraser fir: estimates of

rhizosphere width and inoculum efficiency. Phytopathology

75, 10104.

Segers R, Butt T, Kerry BR, Beckett A, Peberdy JF, 1996. The

role of the proteinase VCP1 produced by the nematophagous

Verticillium chlamydosporium in the infection process of

nematode eggs. Mycological Research100, 4218.

Stephan ZA, Estey RH, 1982. Effect of soil texture, moisture

and temperature on the migration ofMeloidogyne hapla

larvae and their invasion of tomato roots. Phytoprotection

63, 69.

Wallace HR, 1963. The Biology of Plant Parasitic Nematodes.

London, UK: Edward Arnold Publishers.

Whitehead AG, 1998. Plant Nematode Control. Wallingford,

UK: CAB International.

Wieser W, 1955. The attractiveness of plants to larvae of

root-knot nematodes. I. The effect of tomato seedlings and

excised roots on Meloidogyne hapla Chitwoodi. Proceedings

of the Helminthological Society of Washington22, 106

12.

Zare R, Gams W, Evans HC, 2001. A revision ofVerticillium

section Prostrata. V. The genus Pochonia, with notes on

Rotiferophthora. Nova Hedwigia73, 5186.

Documents

Pathozone Dynamics of Meloidogyne Incognita in the Rhizosphere of Tomato Plants in the Presence and Absence of the Nemat