Pertanika 10(3), 265 - 270(1987)

Occurrence of the Root-knot Nematode Meloidogyne Incognitaon Guava in Malaysia

A.R. RAZAK and T.K. LIMDepartment of Plant Protection,

Faculty of Agriculture,Universiti Pertanian Malaysia,

43400 Serdang, Selangor Oarul Ehsan, Malaysia.

Key words: Root knot nematode; Meloidogyne incognita; guava decline; Psidium guajava

ABSTRAK

Kerosotan tumbesaran pokok jambu batu yang disebabkan oleh nematod, Meloidogyneincognita, di beberapa negeri di Malaysia dilaporkan buat pertama kalinya. Tanda-tanda kerosotaninlah pvmbantutan pertumbuhan, ketiadaan akar-akar halus, perkembangan sistem akar yangkurang baik, daun heat, dan pengurangan mutu serta bilangan buah. Akar-akar yang dikerumuninematod menjadi cacat kerana kehadiran puru-puru kecil dan yang berganda besar. Faktor-faktoryang mempengaruhi perebakan dan kemandirian nematod telahjuga dibincangkan.

ABSTRACT

Incidence oj decline in growth of guava caused by the nematode, Meloidogyne incognita, inseveral states in Malaysia is reported for the first time. The nematode infested plant manifested adrastic reduction in plant growth, small leaves, absence of fine roots, a poorly developed root system,and a decline in yield quality and quantity. Severely infested roots are distorted by small and largemultiple galls. Factors influencing the spread and survival oj the nematode are also discussed.

INTRODUCTION With the rapid expansion of the guavaThe profitability of the Kampuchean guava areas, the incidence of pests and diseases also{Psidium guajava L.) cultivar, has made the increased (Lim & Razak, 1986; Lim et aL,crop popular with fruit growers in Malaysia. 1986). Hitherto, problems of poor plant growthArea of guava cultivation has expanded con- and small fruit size were attributed to soilsiderably both in terms of farm size as well as fertility, and attempts to arrest the problem bygeographical distribution. The cultivar intro- more frequent fertilizer applications were notduced to Bidor, Perak in 1981, has spread to the successful. The growers destroyed infested standsstates of Selangor, Negeri Sembilan, Malacca, by bulldozing and pushing the stubble to oneJohore, Kedah and Pahang. Recently, the crop end of the field but replanted on the same infes-was introduced to Sarawak in East Malaysia. ted area with new seedlings.Likewise, the popularity of the crop among Nematode disease on guava is unknown togrowers has upgraded the farm size from a small- the growers and has not been reported in Asia,holder farm of 0 . 5 - 2 hectares in 1981 to large The incidence of nematode disease in the fieldorchard plantings of more than 20 hectares in was first noted on 6-month old guava plants in1986. Two more new cultivars have since been Semenyih, Selangor in 1985 by the authors. Sub-introduced, namely the apple-shaped, seedless sequently, the nematode decline problem on the"Donrom" and "Glom sali" — a round fruit same cultivar was found to be more severe oncultivar from Thailand. plants cultivated on light soils around Bidor,

A.R. RAZAK AND T.K. LIM

Perak. Diseased plants were found to be associa-ted with disfigured root systems caused by nema-todes. Widespread decline was also found on theKampuchean cultivar in Bentong and in SungaiBaging, Pahang (Chai, T.B., MARDI, Per.Comm.).

This paper reports on the incidence,symptomatology, causal agent, and possiblefactors influencing the spread of disease.

MATERIAL AND METHODSFour guava farms in the Bidor-Sungkai area, 2farms in the Nilai-Semenyih area, a farm inSungai Buloh and a seedless guava farm inSungai Ruang, Raub, were visited to assess theincidence of nematode infected trees. Bothabove-ground and below-ground symptoms ofinfested, bearing trees were recorded. Onehundred and fifty marcotted and bud-graftedpolybag seedlings were also taken from twofarms in Bidor to assess the severity of galling onthe roots. Five soil samples (auger probes) pertree were collected with an auger from a depth of0.3m at a distance of 1 metre from the bases oftrees showing symptoms of poor growth, andcomposited. A total of 100 trees each weresampled from two severely infested orchards inBidor. Nematodes were extracted from the soilsamples using a modified Whitehead Tray'stechnique (Whitehead and Hemming, 1965). A200cc soil volume was used as one subsamplefrom each soil sample. The remaining soil in thesample was bioassayed for nematode incidenceusing tomato seedlings.

Infected roots were washed clean of debrisunder running water and processed for bothlight and scanning electron microscopic exami-nations. For light microscopic studies, the younginfected roots were stained in lactophenol cottonblue and cleared in clear lactophenol, orphloxine B for egg mass assessment. Perinealpatterns from saccate, females and the secondlarvae stages were prepared for species identifi-cation.

Tissues for scanning electron microscopyviewing were prepared by selecting pieces ofmultiple-galled roots and fixed in bufferedaldehyde fixatives according to Eisenback(1985). After washing out the aldehydes, theroots were teased carefully to expose the internal

modified cells of the galled roots; post-fixed inosmium tetroxide, and dehydrated through agraded series of ethanol. Dehydrated specimenswere critical point-dried in CO g. Driedspecimens were mounted on copper stubs,coated with gold and examined under the JEOL-JSM 35C scanning electron microscope at 25kV.

RESULTS

Disease Incidence and SymptomsThe visits showed that the slow decline of guavaplants was rampant and widespread. On all thefarms visited, trees exhibiting poor growthwere found to be infested by nematodes.Symptom manifestation appeared distinct on2\4 year-old plants onwards, on both budgraftedand marcotted plants. The presence of thenematodes was indicated by the heavily galledexposed roots around the base of the plant.Severely stunted 2J/£ year-old plants could beeasily pulled out of the ground, revealing theswollen, disfigured and discoloured root system(Plate 1). This symptom is most indicative of

Plate 1: Severely galled, and discoloured rootsystem of a mature guava tree which isdisfigured by the heavy infestation of root -knot nematode. The roots are devoid offine feeder roots

Meloidogyne spp. The primary and secondarylateral roots, distorted by the large multiplegalls, were dark brown or black in colour withrough corky surfaces and cracks along the longaxes of the roots. There were distinct reductionsin the root systems which were almost devoid offine feeder roots. Young, white roots emerging

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OCCURRENCE OF THE ROOT-KNOT NEMATODE MELOIDOGYNE INCOGNITA ON GUAVA IN MALAYSIA

from the swollen infected tissues were also in-fested by the nematodes. Egg masses on thegalled surfaces could clearly be seen as small redspots when stained in phloxine B (Plate 2).

Plate 2: Egg masses of Meloidogyne (arrowed) onthe guava roots stained with Phloxine Bstain

Roots of seedlings in the polythene bags alsodisplayed a similar corky and distorted rootsystem, with several young white roots sustainingthe infected plant (Plate 3). These young rootswere already showing signs of nematode infec-tion. The roots still retained the white colour,although very heavily galled.

The effect of the nematodes on the rootsresults in stunted and unthrifty growth of theabove-ground parts of the plants. The trees boresmall, pale green to yellowish chlorotic foliage(Plate 4). On severely nematode infested trees,the leaves matured early and were observed todefoliate during dry periods or when underwater stress, leaving a few clusters of pale yellowleaves at the apical end of the branches (Plate 5).The branches became exposed to intense insola-tion and were rendered susceptible to secondaryinfection by Botryodiplodia theobromae.

The quality and quantity of fruits producedby nematode infested trees were also affected.On younger trees (2 years old), the plants tendedto produce a lot of young fruits which abortedreadily. The fruits lacked the smooth, glossy,green appearance. Fruits which developed tomaturity, matured early, were smaller in sizeand became more susceptible to fungal infec-tion. Similar quality fruits were also found onolder bearing trees which survived through the

Plate 3: Roots of an injected guava seedlingobtained from the nursery displaying asimilar corky, galled and distorted rootsystem. Note the few young white rootssupporting the infected plant and whichare already infested by nematodes

heavy infestation of the nematodes. Fruits col-lected from the nematode-infected plantsweighed between 200 to 250gms per fruit (GradeC) instead of the usual average weight ofbetween 450 - 650gms (Grades A & B). This wasobserved in all the farms visited.

The Causal OrganismThe soil extracts showed that at least two generaof plant parasitic nematodes, Meloidogyne spand Pratylenchus sp were present. The popula-tion of Meloidogyne sp (mean 9300 per 200cc ofsoil) was predominant. Pratylenchus sp. waspresent in comparatively smaller numbers (mean33 per 200cc of soil). Roots stained in cotton blue

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A.R. RAZAK AND T.K. LIM

IPI

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4̂ Meloidogyne infested tree characterizedby small, pale, greenish-ye How, chlorotic

foliage and stunted growth

Plate 5: Severely nematode infested trees showingheavy defoliation, with bare branchesbearing clusters of chlorotic leaves at theapices

lactophenoi failed to show the presence ofPratylenchus in the roots. Based on the morpho-

metric measurements of larvae and perinealpattern of saccate females, the Meloidogynespecies was identified as Meloidogyne incognita(Kofoid and White) Chitwood. The species ofthe Pratylenchus was not identified.

All developmental stages of Meloidogyneincognita were present in the tissues of the infec-ted roots, often with different stages present with-in the same locality in the large galls. The electronmicrograph of Plate 6 shows a developing thirdstage larva surrounded by several infectivesecond stage larvae. Likewise, it was not un-common to see several nematodes of the samedevelopmental stage feeding on adjacent tissues(Plate 6). Cells surrounding the nematodes in thegalled tissues appeared to be similar in shapeand size, and assumed a honey-comb pattern.

Plate 6: SEM micrograph showing severalnematodes at the various developmentalstages, feeding on adjacent tissues

The tunnels formed by dislodged saccate femaleswere characterized by the conical-shaped im-

Plate 7: Tunnels formed by dislodged saccatefemales (arrowed) are characterized by theconical-shaped impressions of theanterior part of the body

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OCCURRENCE OF THE ROOT-KNOT NEMATODE MELOIDOGYNE INCOGNITA ON GUAVA IN MALAYSIA

pressions of the anterior part of the body (Plate7). A pea-sized gall could easily sustain 50 to 100nematodes of different developmental stages.The saccate females laid their eggs within themodified root tissues in a gelatinous matrix(Plate 8), numbering about 200 eggs per egg

mass.

Plate 8: Egg mass of the saccate female laid withinthe proliferated cells of the gall instead ofon the surface of the enlarged roots

DISCUSSIONHitherto, nematodes have not been reported asimportant pests of guava in Malaysia or otherAsian countries although Meloidogyne incognitahas been recorded on guava in Hawaii(Martinez, 1973) and Meloidogyne arenaria, inthe Federation of Rhodesia and Nyasaland(Martin, 1959).

This study clearly demonstrates thatMeloidogyne incognita is an important pest ofguava. The presence of the nematode was dis-tinctly manifested by the grotesque root systemof the plant. The discoloured infected roots weregrotesquesly enlarged into galls, almost com-pletely devoid of feeding roots and provided pooranchorage for the plant. Cracks along the longi-tudinal axis of the root as noted on pepper(Razak, 1978b) were observed on the surface ofthe diseased main roots. Consequently, theabove ground parts of the plant developedunthrifty growth, bearing small fruits whichmatured early. It was unlikely that Pratylenchussp contributed to the poor growth, although itwas present in the soil extract, and has beenreported to cause damage to other fruit trees(McElroy, 1972). The failure to detect Praty-lenchus nematode in the stained young rootsfurther supports the statement. Alternatively, the

presence of a high density of M. incognita in theroots as revealed by the electron scanning studiespossibly deprived the Pratylenchus of suitablefeeding sites. Galls or enlargement of the rootsare generally associated with symptoms ofMeloidogyne attack although other nematodegenera can also cause root galling (Taylor andSasser, 1978). Likewise root galling can be in-duced without the nematode actually enteringthe roots (Lowenberge/ al, 1960).

Meloidogyne incognita is the dominantspecies accounting for approximately 64% of thepopulation occurring in the tropical countries(Sasser, 1979) and has a wide host range (Tayloret al., 1982). In Malaysia, the species is ubiqui-tous and associated with several economicallyimportant agricultural crops as well as weeds(Razak, 1978a, 1981; Abdul-Karim, 1985; Lohand Ting, 1970). However, this is the first timethe species is reported to be a significant pest ofguava. Although no direct assessment was made,yield loss in terms of quality and quantity offruits produced could be estimated to be around50%. The eradication of 7-years old infestedstands by some growers further reflected themagnitude of the problem on guava which has aviable life span of more than 20 years. The lossestimated far exceeds the 30% reported inCentral America and Carribean by Sasser(1979).

The extremely high incidence of rootknoton guava in the two farms in Bidor could beattributed to various factors among which arehost susceptibility, soil condition and indigenouspopulation of the nematode in the area. Guavaappears to be a good host of M. incognita.Despite heavy nematode infestation the plantwas still able to survive. Soil structure has a greatinfluence on the host-parasite relationshipinvolving M. incognita, and in light texturedsoils, the nematode could cause considerabledamage to many crops (Lamberti, 1979). Thelight, sandy and sandy-loam soil on which mostof the guava plants are grown in Bidor, Selangorand Pahang thus favour the development of thepopulation of Af. incognita. It was rather diffi-cult to distinguish between the introduced andthe indigenous population of Meloidogyne,especially among the established plants in thefield where the root systems of the trees inter -

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A.R. RAZAK AND T.K. LIM

twined with those of neighbouring plants. Never-theless, the concentration of high numbers ofnematode population on the roots of youngplants (2V& years old) and the absence or verylittle galling on roots of nematode susceptibleweeds in between the planting rows suggest thatthe population was mainly introduced with theplanting materials. The observation was furthersupported by the heavily infested roots of theseedlings in the polythene bags in the nurseries ofthe two farms in Bidor or those put up for sale atthe roadside. Furthermore, most of the planta-tions visited obtained their planting materialsfrom Bidor. Therefore, it was most likely thatthe nematodes in most of the plantings visitedcame with the planting materials from Bidorthrough the soils used to fill the polythene bagswhen the marcotted plants or the stock weretransplanted to the bags. The spread of thenematodes can further be accelerated through-out the country by the farmers who are notaware of the existence of nematodes as pests. It istherefore necessary for the growers to use sterili-zed soil for the rooted marcotted soil bags. Alter-natively, the movement of the planting materialsfrom the infected field should be restricted toprevent further spread of the nematodes. In themeantime, efficacy and residual trials on severalnematicides coupled with selected culturalmeasures to save the existing stands in someinfested orchards are being investigated.

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LAMBERTI, F. (1979): Economic importance of Meloi-dogyne spp. in subtropical and Mediterraneanclimates. In: Root-knot nematodes (Meloidygonespecies) — systematics, biology and control, (eds.F. Lamberti and C.E. Taylor) Academic Press,477 pp.

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LOEWENBERGJ.R., T. SULLIVAN and M.C. SCHUSTER.(1960): Gall induction by Meloidogyne incognitaby surfacing feeding and factors affecting thebehaviour pattern of the second stage larvae.Phytopathology 50: 322.

MARTIN, G.C. (1959): Plants attacked by rootknotnematodes (Meloidogyne) spp., in the Federationof Rhodesia and Nyasaland. Nematologia 4:123-125.

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RAZAK, A.R. (1981): Economic importance and iden-tification of root-knot nematode isolates ofMalaysia. Proc. of 3rd Res. Planning Conf. onRoot-knot Nematodes, Meloidogyne spp. Jakarta1981. pp. 31 -39 .

SASSER, J.N. (1979): Economic importance of Meloi-dogyne in tropical climates. In: Root-knot nema-todes (Meloidogyne species) — systematics,biology and control, (eds. F. Lamberti and C.E.Taylor). Acad. Press, New York. 359 - 374 pp.

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(Received 12 March, 1987)

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