Endomycorrhizae produced by non-septatefungi are commonly known as "VesicularArbuscuJar Mycorrhiza" (VAM) belonging to theFamily - Endogonaceae of the class ­Zygomycetes.

VAM fungi have a mutualisticsymbiotic relationship with most agriculturalcrops and enhance plant growth. Interactionsbetween fungal antagonists and nematodeshave been known to occur in aBricultUral soilsfor many years. Mycorrhizal fungi and plantparasitic nematodes are commonly foundinhabiting the rhizosphere and colonizing theroots of their host plants. exert an oppositeeffect on plant health. VAM supplies nutrientsto crop, where as, nematode takes out vitalnutrients from the roots resulting in reducedplant growth.

2.1. Habitat: On a global scale, VAMfungi are virtually ubiquitous, being present intropical, temperate and arctic regions. Withinthe different global regions VAM fungi have abroad ecological range. They are found in mostecosystems including dense rain forests, openwoodlands, scrub, savanna, grasslands, heaths,sand dunes and semi-deserts. VAM populationsof cultivated lands are affected by the varioussoil, plant and environmental factors in naturalecosystems plus various agricultural practiceslike fertilizer amendments, pesticideapplications and crop rotations.

Agric. Rev., 26 (4) : 249 - 260. 2005

BIOMANAGEMENT OF NEMATODES BYMYCORRHIZA - A REVIEW

G. Jothi, Rajeswari Sundara Babu and G. RajendrenDepartment of Nematology.

Tamil Nadu Agricultural University. Coimbatore - 641003. India

ABSTRACTVesicular - Arbuscular mycorrhizal associations with plants are attributed to the growth promoting

ac;pects. Plant growth is mainly due to nutrient acquisition from soil, water uptake, growth promotingsubstance and biological control of soil borne pathogens. The nematode control may be throughimproved vigour, physiological alteration of root exudates or through direct role of mycorrhiza inretarding the development and reproduction of nematode within root tissues. In an integratedmanagement of nematodes the compatibility of VAM with other biocides and nematicides are alsodiscussed.

1. Plant parasitic nematodes haveemerged as a serious limiting factor, hinderingcrop productivity. Nematicides of chemicalorigin are widely used and are effective incontaining the nematode menace worldwide.Large scale, indiscriminate use of suchchemical nematicides poses environmentalhazards, besides being costly anduneconomical. Hence, it is imperative to searchfor safer and economic alternativemanagement strategy against plant parasiticnematodes. On these lines, a tremendousbreak through in research efforts on use ofbiD-control agents for management of plantnematodes has been made in the recent past.Though more than 200 microorganisms havebeen identified as nematode antagonists, veryfew of them are commercialized and arepresently in use for farming community.Besides Vesicular Arbuscular Mycorrhizal(VAM) fungi in vermiculite formulation,Pseudomonas fJuorescens (PFI strain) andTrichoderma viride are available in commercialformulation for use and are highly effectiveagainst plant parasitic nematodes.

2. Vesicular Arbuscular Mycorrhizal (VAM)fungi

Mycorrhiza, a symbiotic association offungi and plant roots, is a universalphenomenon throughout the plant kingdomand is beneficial and even indispensable ,forhealthy growth of the host plants.

..

250 AGRICULTURAL REVIEWS

VAM colonization in the roots includesintra cellular unbranched hyphae, intercellularhyphae, arbuscules and vesicles. In the outercortical ceils, hyphae spread intracellular andform characteristic hyphal coils. When thehyphae come to inner cortex they becomeintercellular. Here the hyphae spreads inbetween cells and do not penetrate host cells.They grow in the same direction of the root.They form 'H' connections and 'Y' joints, asseveral hyphae pass through intercellularspaces. The intercellular hyphae again becomeintracellular, penetrate the host cells, andbecome highly branched forming a structurecalled arbuscule. It is the site of exchange ofnutrients between the host and the fungus.Essentially this transfer involves carbohydratesfrom plants to fungus and minerals especiallyphosphate from fungus to plants. Life span ofarbuscules is generally 4-5 days. The formationof arbuscules was visible after 17 th day ofsowing and the vesicles were seen after 25days as round structures in the beginning andbecame oval shaped later on. The hyphae werenoticed sticking outside the roots from 31St dayon wards indicating that the hyphae, vesiclesand arbuscules occupy the space inside theroots (Jothi and Rajeswari Sundara Babu,1997b)'vesicles are globose structures, eitherterminal or intercalary. Size varies from 30­100 pm. They are formed between the corticalcells or occasionally inside them. They containoil, sometime as a large single globule as inGlomus and are believed to function as storageorgans. In older roots they develop a thick walland presumably function as resting spore whenthe roots decay. Fungi belonging to Gigasporaand ScuteJIospora do not form vesicles.AcauJospora forms irregular vesicles. Vesiclesact as storage structures and as reproductiveorgans.

2.2. Function: The mycorrhizae arevital for uptake and accumulation of ions fromsoil and translocation to hosts because of their

high metabolic rate and strategically diffusedistribution in the upper soil layers. In fact,the fungus serves as a highly efficient extensionof the host root system. Minerals like N, P, K,Ca, S, Zn, Cu and S absorbed from soils bymycorrhizal fungi are translocated to the hostplant (Smith, 1987). Ions such as P, Zn, Cu donot diffuse readily through soil. Because of thispoor diffusion, roots deplete the immobile soilnutrients from a zone immediately surroundingthe root. Mycorrhizal fungal hyphae extend intothe soil, penetrating the zone of nutrientdepletion and can increase the effectivenessof absorption of immobile elements by as muchas 60 times.

Along with other mineral nutrients,phosphate enters the plant both directly fromthe soil and through the fungus. VAM is notonly used as biofertilizer, but have also beenshown to enhance water transport in plants(Safir et a/., 1971), decrease transplant injury(Menge et a/., 1978), help plants withstandhigh temperature (Marx and Bryan, 1971),promote establishment of plants in wastelandand in soil polluted with heavy metals (Chandraand Kheri, 1994) and reduce the wlnerabilityto disease caused by plant parasitic nematodes.(Hasan and Jain, 1992; Jain and Hassan,1995).

2.3. Assessment of spore density:A quantity of one ml of water was pipettedout into a nematode counting dish and thenumber of spores was counted. Based on thisthe total number of spores in the extract fromthe seives were calculated by multiplying thenumber of spores/ml. Thus total number ofspores present in the soil can be calculated.

2.4. Assessment of rootcolonization: VAM fungi inoculated roots areto be examined for colonization and presenceof VAM hypae, arbuscules and vesicles aftercleaning and staining as suggested by Philipsand Hayman (1970). Per cent colonization onroot segment can be computed as suggested

by Nicholson (1955).

Per cent colonization =

Vol. 26, No.4, 2005

Number of root segments colonized

Total number of segments examinedx 100

251

3. VAM Fungi for bio control of plantparasitic nematodes

Nematodes and VAM Fungi oftenoccur together in the rhizosphere and roots ofplants and therefore frequently encounter eachother. This is especially true for VAM andendoparasitic nematodes, since both theorganisms co-habit same locality In the rootsystem. Since mycorrhizae and nematodes areactive dUring the same periods, they overlaptemporally as well as spatially, Increasing theprobability of biological Interactions betweenthem.

Early evidence of possible interactionsbetween VAM and nematodes was obtainedfrom· surveys In which spores and mycelia ofVAM were found to be more abundant In fieldsfree of cyst (Heterodera spp.) or root-knot(Meloidogyne spp.) nematodes than In fieldswhere these nematodes were present (SchenckandKlnloch. 1974). In addition, several studiesrevealed Increased numbers of spores,arbuscules or vesicles when densities of certainroot- parasitic nematodes were reduced bynematicide treatments (Bird et a/., 1974; Richand Bird, 1974; Germani et aI., 1980; Richand Schenck, 1981).

Many workers have demonstrated areduction in nematode population densities(Sikora and Schonbeck, 1975; Bagyaraj et al.,1979; Cooper and Grandison, 1986;Grandison and Cooper, 1986; Jain and Hasan,1994; Kassab and Taha, 1990; Sharma andTrivedi, 1994; Sadasivan Nageswari andRajeswari Sundara Babu, 1998) but caseswhere nematode population remain unaffected(O'Bannon et aI., 1974; Cason et al.,1983;Hasan and Jain,1987 and 1992) or even

increased under the influence of mycorrhlza(Atilano et aI., 1981 j Kassab and Taha, 1990)are not uncommon. The majority of interactionstudies have showed that VAM decreasedpopulations of endoparasltic nematodes. Foxand Spasoff (1972) were among the first todiscover that these two organisms may bemutually Inhibitory and observed decrease of25 - 35% In populations of H. so/ancearumwhen co-Inoculated on tobacco with Endogonegigantea. Similarly, Sikora .and Schonbeck(1975) found that significantly fewer (75%) M.incognita and M. hap/a juveniles developed intoadults In tobacco, oats and tomatoes pre­Inoculated with G. mosseae. Bagyaraj et al.(1979) and Suresh and Bagyaraj (1984)observed that significantly fewer galls of M...incognita or M. javanica developed whentomato roots were colonized with G.fasciculatum. Galls that did develop weresmaller In size than in plants without VAM.The number of galls of M. incognita on soybeanwas also reduced by G. macrocarpus, eventhough rootsystems of VAM plants were larger(Kellam and Schenck, 1980). Sikora (1979)observed that the prior presence of VAM fungi,G. mosseae has resulted Inan.lncrease In plantresistance against· Meloidogyne sp. andsuggested that fungal symbiont may haveexerted its Influence of the nematode by:

1. Altering root attractiveness2. RedUcing larval penetration and larval

development3. Increased root growth and function4. Alteration in root exudation5. Competition for host photosynthesis,

space and nutrition6. Production of nematostatic compounds7. Parasitism of eggs

252 AGRICULTURAL REVIEWS

Table 1. Possible effects of interactions between,plant parasitic nematodes and VA Mycorrhizae(After Hussey and Roncadori, 1982)

Type of interaction

Neutral

Positive

Negative

Component

FungusHost

Nematode

FungusHostNematode

FungusHostNematode

Effect on component

Root infection or sporulation not altered.Mycorrhizal stimulation of vegetative growth or yield notaltered, nematode suppression of vegetative growth or yieldnot offset.Attraction to roots, penetration, development andreproduction not altered.Root infection or sporulation increased.Nematode suppression of vegetative growth or yield offset.Attraction to roots, penetration, development andreproduction suppressed.Root infection or sporulation suppressed.Vegetative growth or yield response to mycorrhizae suppressed.Attraction to roots, penetration, development andreproduction increased.

•

The nature of interaction betweennematode and mycorrhizae may beantagonistic, neutral or synergistic (Table 1).

In tomato plants, development ofsecond stage juvenile was retarded in wellcolonized roots. The mycorrhizal tomato plantsbecame resistant to root-knot nematode(Sikora, 1979). In the case of maize inoculatedwith VAM, the plants recorded higher yield andreduced nematode, (Pratylenchus zeae)population compared to control both in potculture and field studies (Jothi and RajeswariSundara Babu, 1996 and 1997a). G. mosseaewas effective in reducing the nematodepopulation especially M. incognita and R.simi/is infecting banana besides enhancinggrowth and bunch weight under field condition.There was an increase in number of hands andincreased in fingers (Sosamma, et a/., 1998).Significantly fewer juveniles of R. reniformispenetrated tomato roots pre-inoculated withG. fasciculatum, regardless of the number ofnematodes inoculated (Sitaramaiah and Sikora,1982). Pre-inoculation of tomato, tobacco.oats, brinjal and carrot with G. mosseae toallow this slow-growing symbiont to becomeestablished in the roots before introducing ofM. incognita resulted in fewer juvenilespenetrating and developing to maturity in roots

of mycorrhizal plants than in roots of non­mycorrhizal controls. (Krishna Prasad, 1991,Jain and Gupta, 1991; Rao et a/., 1998).

Earlier introduction of G. fasciculatumby 15 days adversely affected H. cajani rootpenetration to a greater extent in cowpea thansimultaneous inoculations. Over 60 per centcolonization of root system by VAMconsiderably hampered root invasion (Jain andSethi, 1988). Umesh et al. (1988) studied theinteraction of R. similis with G. fasciculatumin banana and found that mycorrhizal plantscontained fewer nematodes, supported lowernumber of nematodes in soil and had fewernematode induced root lesions than non­mycorrhizal plants if G. fasciculatum was addedsimultaneously with or seven days before R.simi/is. Inoculation of G. fasciculatum 15 and20 days earlier than the nematode hadcontrolled the root - knot nematode populationand also increased the biomass production inblackgram. VAM sporulation was affectedwhen the nematodes were inoculated earlier(Sankaranarayanan and Rajeswari SundaraBabu, 1997i. When the VAM fungus, G.fasciculatum was inoculated 15 days earlierthan M. javanica on tomato, VAM preventedthe multiplication of nematode and offset thedeleterious effects of nematode on the plant

Vol. 26, No.4, 2005 253

growth (Rajeswari Sundara Babu et aJ., 1993).Prior inoculation of VAM was found to be moreeffective against R. similis than simultaneousinoculation of VAM and nematode in coconutseedlings (Koshy et al., 1998).

Cooper and Grandison (1987)reported that M. incognita infection anddevelopment were less in the plants, (TamariJIo)pre-infected with mycorrhizal fungi and inplants inoculated simultaneously with both theorganisms. Glomus mosseae inoculationstimulated growth of Citrus jambhiri seedlingswhile the nematode decreased growth in potexperiment. When the two organisms wereinoculated simultaneously the adverse effectsof the nematode was partly neutralized andthe fungus limited the development of thenematode (O'Bannon et aL, 1979a).

""Glomus intraradices decreasednematode development and egg productionmore when inoculated 28 days beforenematodes than when both organisms wereadded at the same time. When pre-inoculated,VAM reduced total eggs produced and numberof eggs g-l of root but numbers of eggs perfemale was not affected (Smith et al., 1986a).Cooper and Grandison (1986) also found thatthe numbers of M. hapla on tomato or cloverwas decreased appreciably more when VAMfungi were Inoculated 4 weeks before thenematode. Presence of the fungal symbiontssubstantially reduced or completely suppressedadult development. Similarly, G. mosseaereduced the number of adult female R.reniformis by 87 and 63% on two cottoncultivars (Sikora and Sitaramaiah, 1980).

Suresh et al. (1985) found thatsignificantly fewer giant cells developed in eachgall of M. incognita. Average cell size was alsoless than in non-mycorrhizal roots but this resultwas not statistically significant. Kellam andSchenck (1980) also suggested that VAMdecreased giant-cell development.

Rajeswari Sundara Babu andSankaranarayanan, 1995) incorporated VAMinto nursery beds of tomato allowing the fungusto colonize the root before it was transplantedto main field thereby preventing thepenetration and development of the nematodein the VAM infected plants. Thus the VAM wasable to offset the adverse effect of nematodesand increase the yield by 91 per cent overcontrol. Rajeswari Sundara Babu et aJ. (1996)and Jothi and Rajeswari Sundara Babu (1998)observed that with VAM application containedthe ill-effects induced by the nematode, R.reniformis and gave higher yield compared tocontrol. Different doses of G. fasciculatuminoculum viz., 5, 10, 15 and 20 g/kg of soilwere tried on tomato and bhendl for controlof M. incognita. All the doses were effective insuppressing nematode population, but 10g/kg soil was found to be the effective optimumdose for the management of the nematode(Rajeswari Sundara Babu et al., 1998 and Jothiand Rajeswarl Sundara Babu, 2001 a).

4. Mechanism involved in nematodemanagement through VAM fungi

Many mechanisms operatesimultaneously during interaction of VAM andplant parasitic nematode on a particular host.Following factors play significant role inreducing nematode population and inenhancing plant growth.

1. VAM fungi may increase root growth,expand the absorptive capacity of the rootsystem for nutrient and water and enhancecellular processes in roots (Hayman, 1982).

2. VAM fungi improve plant nutrition andby doing so may aid the host In compensatingfor damage caused by parasitic nematodes,thereby increasing plant tolerance to thesepathogens.

3. Mycorrhizal root colonization has beenshown to affect root exudation (Gerdemann,1968; Hayman, 1982). These changes couldalter chemotactic attraction of nematodes to

254 AGRICULTURAL REVIEWS

roots or directly retarded nematodedevelopment within root tissues.

4. VAM fungi have reduced nematodeinfection and development on several hosts inspite of larger root systems on mycorrhizalplants (Cooper and Grandison, 1986;Grandison and Cooper, 1986; Smith et a/.,1986a; Sharma, 1992, 1993, 1994). It maybe due to unfavourable conditions fornematodes developed on root system due toVAM colonization. Changes in hormones,amino acids and cell permeability in roots havebeen attributed to mycorrhizal symbiosis(Hayman, 1982).

5. VAM fungi may cause change in the post­infectional nematode - host interaction byaltering nematode reproduction anddevelopment.

6. Direct competition for space may accountfor reduced nematode infection on mycorrhizalroot system since endoparasitic nematodesoccupy similar root tissues as VAM fungi.However, results of several studies do notsupport this hypothesis.

In addition to above given factors,increased tolerance or resistance to nematodesby VAM fungi may be due to competition forhost photosynthates, production ofnematostatic compound and parasitism ofeggs. It may be concluded from observationsthat VAM fungi do not directly interact withplant parasitic nematodes in spite of theirproximity in root tissue. More likely, VAM fungialter the host either physical~ orphysiologically, and thus indirectly affect thehost nematode relationship (Smith, 1987).

5. Bio chemical basis for nematodemanagement though VAM fungi

Disease incidence was observed to begreater when the level of sugars in host plantswas low. It was noted that resistant plants hadhigher total and reducing sugar content.Compared to uninoculated control plants,those inoculated with mycorrhiza or with

mycorrhiza and nematodes simultaneouslyshowed increases in the reducing sugar contentlower amounts reducing sugar were recordedfrom plants with nematode only. Total sugarswere highest in plants inoculated withnematodes first followed by mycorrhiza (Sureshand Bagyaraj, 1984; Jothi, 1999). Mycorrhizalplants had high concentrations ofphenylalanine and serine which are known toreduce the growth and reproduction of theroot-knot nematode (Krishnaprasad, 1991;Parvatha Reddy et a/., 1975). Graham et aJ.(1981) reported that amino acids and reducingsugars were greater from root exudation ofmycorrhizal sudan grass grown in phosphorusdeficient soils than from non-mycorrhizalplants. Mycorrhizal plants had increasedquantities of phosphorus, potassium, calcium,amino acid, phenylalanine and serine than non­mycorrhizal plants (Suresh and Bagyaraj,1984). Total phenols, total free ami:1o acidsand acid phosphates activity were found to behigher in VAM inoculated plants (O'Bannonand Nemec, 1979).

Plants inoculated with mycorrhizacontained larger amounts of amino acidsspecifically phenylalanine, isoleucine, threonineand serine than in uninoculated plants. Plantsinoculated with mycorrhiza plus nematodesgenerally showed an increase in amino acids,especially glutamic acid and aspartic acidscompared with plants inoculated withnematodes only. Plants with nematodes onlyhad more tyrosine and phenylalanine and lessproline, aspartic acid and histidine than diduninoculated control plants (Nemec andMeredith, 1981). Further, the mycorrhizalplants had higher concentration ofphenylalanine and serine which are known toreduce the growth and reproduction of rootknot nematodes (Krishnaprasad, 1991;Parvatha Reddy et a/., 1975). The presenceof increased quantities of aminoacids likephenylalanine and serine play a role in

Vol. 26, No.4, 2005 255

suppressing the development of M. incognitain mycorrhizal tomato plants (Suresh andBagyaraj, 1984).

Studies conducted at Pant Universityindicated that preoccupation of tomato cv.Pusa Ruby roots with G. fascicu/atum coupledwith biochemical changes such as increase inlignins and phenols made Pusa Ruby resistantto root-knot nematode, M. incognita (Singhet a/., 1990). Various biochemical changesoccur due to the presence of VAM, like increasein the contents of lignins, total phenolics,protein, total sugars, reducing suga~ andaminoacids like arginin and phenylalanine.Reproduction of nematode or recovery ofsecond stage juveniles from soil supportingmycorrhizal plants were significantly less thansoil containing non-mycorrhizal plants. Thisdifference could be justified on the basis ofhigher counts of females without eggs or lessnumber of eggs per egg-sac in mycorrhizalroots. Lignin and phenols were foundsignificantly more in the mycorrhizal roots.Both the chemicals are known for their role inhost resistance (Bhatia et a/., 1972; Krishnaand Bagyaraj, 1984). Suresh and Bagyaraj(1984) noted that elevated levels of amino acidsand sugars observed in VAM roots areassociated with increased plant resistance, eachsingly or collectively playing a role insuppressing nematode development.Significant difference was observed in totalphenol contents in mycorrhizal and nonmycorrhizal plants. In nematode infested plantsthe phenolic content was less. The phenolicsare associated with disease resistingcompounds responsible for hypersensitivity ofplants and increased percentage was observedin resistant cultivar (Suresh and Bagyaraj,1984; Umesh et aJ., 1988; Sharma, 1994).Some phenols are known to form complexesof amino acid, chlorogenic acid complex whichis highly toxic to the parasite. The phenolicsstimulate IAA oxidase which favours auxin

decomposition and formation of necrosis inplants resisting sedentary parasites. Thephenols in mycorrhizal roots are associated inthe reduced reproduction of nematodes, M.javanica reproduction in tomato (Singh et a/.•1990). Suresh et aJ. (1985) found that 50% ofM. incognita juveniles exposed to extracts ofmycorrhizal tomato roots died after 4 days.Only 32% of juveniles exposed to either cleantap water or extracts of non-mycorrhizal plantsdied during the same period. Suresh andBagyaraj (1984) suggested that the presenceof nematicidal substances in VAM roots mayresult from improved plant vigor owing toenhanced P uptake or increased concentrationsof phenylalanine and/or serine which areknown to be nematicidal. Thickening of thecell walls through lignification and productionof their polysaccharides in mycorrhizal plantsprevented the penetration by the nematodes(Dehne and Schonbeck, 1979; Jothi, 1999).This phenomenon was the result of increasedphenol synthesis in the plants brought aboutby an increase in phenyl propanes which is alignin precursors.

6. Histopathological changes in plants dueto VAM fungi mediated nematodesuppression

VAM hyphae penetrated theepidermis and invaded the cortex whichresulted in the formation of vesicles andarbuscules. In the citrus seedling infested byTylenchu/us semipenetrans, G. mosseae wasfound in 50 per cent of the cortical cells. Inthe cortex, vesicles, were formed along thepericycle. The fungus rapidly invaded the rootsand produced vesicles as well as arbusclesbefore nematode invasion (O'Bannan et a/.,1979a, Sankaranarayanan, 1995).

VAM infected roots gave rise tovesicles and arbuscules. The cytoplasmicgranules and nuclei were condensed in thecentre leaving clear space in the giant cells.The xylem and phloem vessels were pushed

256 AGRICULTURAL REVIEWS

Table 2. VAM fungi in r:ematode management

Host plant Nematode VAM fungus Reference

M incognita G. fascicu/atusTomato

Tomato

TomatoEgg plantCitrusBananaGrapePeachCotton

Soybean

ChickpeaPigeonpeaPhaseolus

vulgarisCowpeaOnionTobaccoPepper

Coffee

Beachgrass

M. incognita

Rotylenchu/us reniformisM. incognitaTylenchu/us semipenetransRadopholus simi/isM. arenariaM. incognitaM. incognitaM. incognitaPratylenchus brachyurusM. incognitaM. incognitaH. glycinesH. glycinesM. javanicaH. cajaniPratylenchus penetrans

H. cajaniM. haplaM. incognitaM. incognita

Pratylenchus coffeae

Pratylenchus spHeterodera spp.

G. mosseae

G. fascicuJatumG. fasciculatumGlomus mosseaeG. fascicu/atumG. fasciculatumG.margari~.G.&unkatus

G intraradicesGigaspora margaritaG. margaritaG. margaritaG. mosseaeG. intraradicesMixed speciesEntrophospora colombianaG. MargaritaG. fascicuJatum

G. fasciculatumG. fascicuJatumG. mosseaeG. fasiculatumG. etunicatumG. darum,AcauJospora melJeaMixed species

Bagyaraj et al., 1979;Suresh et al., 198.5;Suresh and Bagyaraj, 1984;Rajeswari Sundara Babu et al., 1996;Rajeswari Sundara Babu andSankaranarayanan, 1998Rao et a/., 1995; Sikora, 1979;Thomas Cason et al., 1983Sitaramaiah and Sikora, 1982Rao et al., 1998O'Bannon eta/., 1979Umesh et al., 1988Atilano et al.. 1981Strobel et a/., 1982Smith et al., 1986Roncadori and Hussay, 1977Hussey and Roncadori, 1978Carling et al., 1989Kellam and Schenck, 1980Price et al.. 1995Winkler et aI., 1994Diederichs, 1987Siddiqi and Mahmood, 1995Elliot et al.. 1984

Jain and Sethi, 1987MacGuicfwin et al., 1985Krishnaprasad, 1991Sivaprasad and Sheela, 1998

Vaast et al., 1998

Uttle and Maun, 1996

to one side of the root cortex and the spacewas occupied by the giant cells. In VAMinoculated plants, the wall thickening in thecortex cells of root prevented the penetrationof pathogen. Increased Iignins in mycorrhizalroots were associated with reducedreproduction of M. javanica on tomato (Singhet ai., 1990).

7. Compatibility of VAM with othermanagement practices

7.1. Organic amendments: Theorganic amendments like saw dust, neem cake,poultry manure effectively reduced the galls,final nematode population and increased the

yield (Devi and Das, 1998), The neem cakeextract is found to trigger the resistancemechanism in plants (Siddiqi and Alam, 1988).Release of certain fatty acids during thedecomposition of botanicals (Sitaramaiah,1990) and development of antagonistic fungiby application of botanicals (Bhattacharya andGoswami, 1987) were responsible for thereduced nematode infestation.

Integrating eco-friendly compoundssuch as oil cakes with endo-mycorrhizaeffectively reduced the nematode populationboth in soil and roots. Integrating G. mosseaewith karanj cake was most effective in

Vol. 26. No.4. 2005 257

increasing plant growth parameters andbanana yield, while G. mosseae in combinationwith neem cake was highly effective in reducingthe burrowing nematode population andincreased the root colonization and the numberof chlamydospores in soil (Parvatha Reddyet aI., 1997).

When brinjal seedlings weretransplanted in castor cake amended soil, thenematode population densities both in soil androot significantly reduced and plant growthparameters were increased. Favourable effectwas observed by castor cake amendment onthe growth of G. fascicuIatum in therhizosphere of brinjal plant. The combinedeffect of colonization of G. fascicuIatum onroots and castor cake amendment in the soilwas responsible for the significant reductionof M. incognita infestation on transplantedbrinjal plants (Rao et aI., 1998). SimilarlySanthi and Rajeswari Sundara Babu (1998)reported that soil amendment with choppedleaves of Prosopis julif/ora, Catharanthusroseus, Ca/otropis procera and Azadirachtaindica in combination with G. fasciculatum gavethe highest growth of plants and high degreeM. incognita control.

Application of oilcakes asamendments to the soil increased the rootcolonization of G. mosseae and the additiveeffects of both oil cakes and mycorrhizasignificantly reduced R. similis population.Colonization was increased in citrus andtomato by G. mosseae and G. fascicuIatum inneem cake/CaIotropis procera leaf amendedsoil which resulted in the reduction ofTyIenchuIus semipenetrans and M. incognitapopulation respectively (Pal vatha Reddy et a/.,1995; Rao et al., 1995 and 1996).

7.2. Bio-control agents: Pasteuriapenetrans (Thorne) Sayre and Starr is apotential biocontrol agent of root knotnematodes as it parasitizes females andprevents their reproduction (Sayre, 1980).

Integration of P penetrans and G. mosseaefor the management of M. incognita infectingtomato revealed significant increase in plantgrowth parameters and reduction in rootgalling, nematode population in roots, eggmass production and fecundity of thenematodes. Combination of these eco-friendlycomponents has also significantly increased theparasitisation of nematode female by P.penetrans. Bacterial bioagents had not affectedthe root colonization of endomycorrhiza aftertransplanting (Rao et a/., 1999).

PaeciIomyces lilacinus (Thorn) Samsonis an effective parasite on eggs of plant parasiticnematodes. The combinat:on effect of P.lilacinus and VAM is one of the bestopportunities for integrated nematodemanagement (Widhi Sharma and Trivedi,1997). Integration of these two componentshad an additive effect in reducing the nematodeinfestation by reducing the root-knot index,final nematode population density and numberof eggs per egg mass of M. incognita on brinjalwhen both the components were integrated.Mycorrhizal presence had not affected thecolonization of P. Ii/acinus on the roots of brinjalor the densities of P. IiIacinus. Similarly, thepresence of P. lilacinus did not affect thecolonization of G. mosseae indicating that theintegration of these components did not affecteach other (Rao et al., 1998).

7.3. Nematicides: Chemicals bothfumigants and non-volatile granularnematicides give -;ontrol of nematodes andhigher yield. Nematicides and insecticidesdecrease mycorrhizal infection and sporenumbers (Tommerup and Briggs, 1981).Majority of the pesticides, adversely affectedthe plant mycorrhizal symbiosis (Menge,1982).In black gram, the management of root-knotnematode was tested with leaf extracts andnematicides. There was a greatest reductionin mycorrhizal spore population andmycorrhizal colonization in nematicidal

258 AGRICULTURAL REVIEWS

treatments. Mycelium and spores of Glomussp., were decreased in citrus seedlings withincreased dose of 1-3-dichloropropene (Baineset al., 1977).

CONCLUSIONThe VAM exploitation in the

management of plant nematodes Is a non­chemical method with the concept of healthhazards due to nematicides, there is a growinginterest in VAM with-in the field of biocontrol.This interest in VAM fungi was more in thelast three decades, where a number of researchpapers focused their studies on the utilizationof species of Glomus in laboratory and in field.

VAM fungi can be the applied to plants toaccomplish the dual purpose of increased plantgrowth and health. VAM fungi is a commonand natural components in our agro­ecosystem. We can no longer ignore them inthe search for better crop managementmethods, particularly at a time when we arefaced with simultaneous energy andenvironmental pollution problems. The futurethrust of work should be on the organism whichis already present and readily available in thefield. This should be recognized as a symbioticorganism and find ways to trigger its biocontrolpotential by manipulation of Its environment.

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