Pertanika 12(1),11-14 (1989)

A Rot of Detached Durian Fruits Caused by Sclerotium rolfsii

T.K. LIM and KAMARUZAMAN SIJAMDepartment of Plant Protection,

Faculty of Agriculture,Universiti Pertanian Malaysia,

43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

Keywords: Dorian; Durio zibethinus; Sclerotium rolftii; fruit rot.

ABSTRAKSatu penyakit reput buah durian yang baru bagi buah-buahan yang gugur telah diperhatikan di ladang buah­buahanUniversiti Pertanian Malaysia, Serdang, Selangor, semasa musim durian masak pada bulan Oktober,1988. Penyebab reput ini membentuk lapisan bebenang miselium kasar yang padat, berwarna putih, ber­bentuk kipas yang tumbuh di atas tompok nekrotik perang berair pada buah yang bersentuhan dengan sisarumpai yang mereput di atas tanah. Penyebab penyakit telah dikenalpasti sebagai kulat Sclerotium rolfsii.Kehadiran pertumbuhan rumpai yang tebal di bawah pokok durian dan sisa daun rumpai yang mereput,serta keadaan lembab dan panas adalah faktorfaktor perangsang yang penting, yang menggalakkan per­kembangan reputan tersebut.

ABSTRACTA new fruit rot of fallen durian fruits was observed in the Uiversiti Pertanian Malaysia fruit orchard inSerdang, Selangor during the fruit ripening month of October, 1988. The rot was characterized by a dense,white, fan-shaped mat ofcoarse mycelial strands ofthe causalfungus growing on a water-soaked, brown necroticpatch on the fruit in contact with decaying weed vegetation on the ground. The causal organism was identifiedas Sclerotium rolfsii. Presence of a thick weed undergrowth and its decaying leaf debris, and warm, moistconditions were shown to be important predisposing factors conducive to the development of the rot.

INTRODUCTIONUp to 1980, forty-five different microorganismshave been listed as associated with multitudi­nous disorders and diseases of durian, Duriozibethinus MUIT. throughout Peninsular MalaysiaUohnston 1960, Singh 1980), Sarawak(Turner 1971) , and Sabah (Williams andLiu 1976). Only one microorganism, thefungus Rhizopus artocmjJi Racib., was listed as as­sociated with a fruit rot of durianOohnston 1960). Recently, a serious fruit rotof durian was reported to be caused by Phytoph­thora palmivora Butler (Lim and Chan 1986).This fruit rot was observed on intact unripe andripe fruits and was particularly severe andrampant in several orchards in Selangor, Pahangand Johore in Peninsular Malaysia.

Lately, during the fruit ripening month ofOctober, 1988, a new and interesting fruit rot

of durian was encountered on fallen durianfruits in one of the University's durian orchards.Fruits which had fallen into the thick, profuseundergrowth of Asystasia intrusa B1. ('RumputBunga Putih') a weed of the family Acantha­ceae, around the base of durian trees and leftuncollected for a few days were found to beinfected by a soil-borne fungus. This paperreports on studies made on the isolation,identification, and pathogenicity of the fungus.Predisposing factors influencing the develop­ment of the fruit rot were also studied.Symptoms of the fruit rot and methods to avoidthe fruit rot are ,also elaborated.

MATERIALS AND METHODS

IsolationDiseased durian fruit tissue (5 x 3 xl mm) weretaken from the advancing edge with a sterilised

T.K. LIM AND K. SIJAM

scalpel after removal of the fruit epidermis andplated on potato dextrose agar (PDA). Mycelialstrands of the fungus growing on the fruitsurface were taken and plated directly on PDA.The PDA plates were incubated in the dark at28° C. Hyphal tip transfers were made to obtainpure cultures from tw<H:lay old PDA culturesand pure cultures were maintained on PDAslants for use in the studies.

Cultural Studies

The following temperature regimes were usedto determine the optimum and cardinal growthtemperatures of the fungus viz. 8, 15, 20, 24,28,32,35, and 40°C. The study was conductedusing a completely randomized design and fourreplicate plates were used for each temperaturelevel. Six mm diameter PDA discs taken fromthree-day old cultures were separately placedcentrally on PDA plates and incubated at theabove temperatures. Colony diameters weremeasured daily for four days and the dataanalysed using analysis of variance. Slides ofthe vegetative hyphae of the fungus were pre­pared for measurement. Sclerotia develop­ment and measurements were recorded after aweek's incubation.

Pathogenicity Studies

Dunan. Mature blemish-free durian fruits(cv. D 8) freshly fallen from the tree the nightbefore were used. The surface of the fruit wassurfaced-sterilised with 95% alcohol and inocu­lated with a 8 mm PDA disc of the test fungustaken from a four-day old culture. Fruits in thecheck treatment were similarly inoculated butwith blank PDA disc without the test fungus.Inoculated fruits were placed in a) humidchamber with relative humidity (R.H.) of>95%,kept in a room of 28°C and b) room with atemperature of 28°C and R.H. of 75%. Eightfruits were used for each of the incubationconditions and the check treatments. Lesiondevelopments were recorded up to six days afterinoculation. Reisolation of the fungus was doneon PDA. .

Three-week-old durian seedlings weretransplanted into sterilised and non-sterilisedsoil which were artificially inoculated withmycelial fragments and sclerotia of the fungus

by incorporation into the medium. Anotherbatch of seedlings transplanted into non­inoculated, sterilised soil served as check treat­ment. The seedlings were kept in a moistchamber at 28°C for three weeks and observedfor development of disease.

Asystasia Intrusa Weeds. Asystasia weedsgrowing beneath the durian tree were uprootedand transplanted into pots filled with sterilisedand non-sterilised soil taken from the durianorchard. Prior to transplanting, the soils wereinoculated with the test fungus as in the caseof the durian fruit above. Some pots were notinoculated and served as the check treatments.All the pots were kept in a humid chamberat 28°C. The trial was carried out in com­pletely randomised design and replicated fourtimes. Disease development was monitored fortwo weeks.

In addition, detached Asystasia plant partswere inoculated with the fungus in moist,covered, plastic containers and observed forcolonisation of plant parts by the fungus.

RESULTS

Isolation and Cultural Studies

Isolation from diseased durian fruit tissues andfungal mycelial strands yielded the same fungus.The fungus was identified as Sclerotium TolfsiiSacCo - sclerotial state of Corticium Tolfsii Curzias it exhibited all characteristics of this fungusas described by Aycock (1966) and Mordue(1974). It grew readily on PDA, 20-25 mm/dayand attained a diameter of 90 mm within fourdays. It produced a white, radiating colony oftough mycelial strands with a white colonyreverse on PDA. The optimum temperature forgrowth was determined to be around 32°C; nosignificant difference in growth was foundbetween 32°C and 28°C (Table 1). No growthwas observed at 8°C and 15°C, and at 40°C thefungus grew sparingly. Abundant sclerotia (1-2mm in diameter) were produced in more thana week old PDA cultures. The sclerotia werewhite at first, turning light brown and subse­quently dark brown, and each had a character­istic thick rind with distinct medulla and cor­tex. Clamp connections were observed in the .primary hyphae. Diameter of primary hyphaevaried from 4-7Ilm, while tertiary branches were

12 PERTANIKA VOL. 12 NO.1, 1989

A ROT OF DETACHED DURlAN FRUITS CAUSED BY SCLEROTIUM ROffSII

much narrower, 2 ~m. The teleomorphic statewas not observed.

TABLE 1Effect of temperature on colony growth of

Sclerotium mlflii

Temperature (0C) Mean colony diameter (em)

8 0 gl

IS 0.39 f20 1.57 d25 1.80 be28 1.86 a

32 1.89 a3S 1.73 e40 0.47 e

dt ~ 14MSE ~ 0.01639LSD ~ 0.07

I Mean values followcd by similar letters denote no sig­nificant diff"rencc at P ~ 0.05 as determined by l.SD

test

Pathogenicity StudiesIn the durian field, this peculiar fruit rot couldeasily be distinguished by the white, fan-shapedtufts of thick mycelial strands of the fungusgrowing on the water-soaked, brown, necroticlesion on the durian fruit (Fig. 1) in contactwith decaying Asystasia weed debris on theground. The weed debris was caused by thedurian fruit falling amongst the thick Asystasiaundergrowth. Internally, necrosis extended intothe seed cavity, rotting the seed and discolou­ring its cotyledons (Fig. 2).

Fig. 1. Tufts of thick, white, Jan-sha/Jed mycelial stmndsof Sclerotium rolfsii covering the bmwn, water­

soaked, necrotic lesion on an ill/eeted durian J11lit.

Fig. 2. Internal necrosis caused fry S. rolfsij extending

inl.o the seed cavit)', rotting the seed and discolour­ing the cot),ledons (arrowed).

The pathogenicity studies demonstratedthat S. rolfsii was able to infect mature durianfruits without prior wounding, producing similarsymptoms as those observed on fallen fruits inthe thick Asystasia undergrowth. Fruits kept atboth levels of relative humidity i.e. 75 and >95%at 28°C developed the rot. However, thoseincubated at the higher R.H. had more exten­sive rotting and more luxuriant growth of thefungus on the fruits. The fungus was easilyisolated from infected fruits, thus satisfYingKoch's postulates. The fungus did not infectthe durian seedlings in both sterilised and non­sterilised soil.

S. rolfsii grew very well on the detachedAsystasia plant parts but did not infect intact,healthy Asystasia plants in both sterilised andnonsterilised soils.

DISCUSSIONS. rolfsii is an ubiquitous fungus, found grow­ing in a diverse array of soil types in thetropics and subtropics (Abeygunawardena andWood 1957; Aycock 1966). In the soil itsurvives by means of its sclerotia and thickmycelial strands, growing saprotrophically ondecaying plant debris and organic matter(Mordue 1974). Aycock (1966) reported thatthe fungus causes root and stem rot and otherdiseases in about 500 plant species from 100families, most of which are dicotyledons com­prising mainly composites and legumes. It is afacultative parasite, but has not been recordedto attack durian or its plant parts before. This

PERTANlKA VOL. 12 NO. I, 1989 13

T.K. LIM AND K. SIJAM

represents the first record of its facultativeparasitism on durian.

The pathogenicity results indicate thatdurian is not a natural host of S. rolfsii. How­ever, once its fruits became detached and fellon the ground where the fungus was present,infection of the fruit occurred especially underwarm and moist conditions as was demonstratedin the pathogenicity tests on the fruits. Such aconducive environment in the orchard couldbe provided by the thick undergrowth ofAs)'stasia weeds around the tree. Empiricalevidence suggests that the falling durian fruitdamaged some of the thick weed undergrowthand the damaged weed debris provided a readyfood source for the luxuriant saprotrophicgrowth of the fungus. The fallen fruit was leftin situ amongst the thick undergrowth, uncol­lected for a few days as it was hidden from thepicker's view. Such a condition predisposed thefruit to infection by the fungus which was alreadyestablished on the weed debris. This was alsoshown by infection studies on the weed: thefungus grew well on the detached Asystasiaplant parts under warm, moist conditionsbut did not infect the healthy Asystasia undersimilar conditions.

To avoid Sclerotium rot of durian fruits,thorough and frequent (once or twice daily)picking of fallen fruits should be carried out.The base of the durian u-ee should be kept freefrom thick weed undergrowth which creates awarm and moist condition for infection of fallenfruits by soil fungi. Also, by having a thickundergrowth of weeds beneath the durian tree,many fallen fruits will remain unpicked as theywill be obscured by the dense undergrowth.Besides, weeds compete wit.h the tree fornutrients. Another way is to erect a strong canvas,nylon or wire netting beneath the durian treeto break the fall of the ripe fruits and to reducefruit damage and mitigat.e the risk of infection

by soil fungi. This can be a practical proposi­tion especially with high priced cultivars like D2, D 24, D 98, D 99 and D 114 where each fruitcan fetch a price of more than $12 ringgit int.he retail market.

ACKNOWLEDGMENTThe authors express their thanks to the DeputyDirector of the University Farm for providingthe fruits used in this study and the MPKSNCouncil for a grant on fruit diseases.

REFERENCES

ABEYGUNAWARDENA, D.v.W. and R.K.S. WOOD. 1957.Factors Affecting the Germination of Sclerotialand Mycelial Growth of Sclerotium rol/sii. Trans.Brit. Mycol. Soc. 40(2): 221-231.

AYCOCK, R. 1966. Stem Rot and Other DiseasesCaused by Sclerotium rolfsii. North Carolina Agric.Expt. Stat. 174, 202 pp.

JOHNSTON, A. 1960. A Supplement to a Host Listof Plant Diseases in Malaya. Mycological Paper No.77. Commonwealth Mycological Institute, Kew,England.

LIM, T.K. and L.G. CHAN. 1986. Fruit Rot ofDurian Caused by Phytophthora pabnivora. Pertanika9(3): 269-276.

MORDUE, J.E.M. 1974. Corticium rolfsii. CMIDescription of Pathogenic Fungi and BacteriaNo. 410.

SINGH, K.G. 1980. A Check List of Host andDiseases in Malaysia. Ministry oj Ag?ic. MalaysiaBull. No. 154.

TURNER, GJ 1971. Fungi and Plant Disease inSarawak. Phytopathological PaperNo. 13, Commmon­wealth Mycological Institute, Kew, England.

WILLIAMS,T.H. and P.S.w. Liu. 1976. A host listof Plant Disease in Sabah. Phytoj)(lthological PaperNo. 19, Commonwealth Mycological Institute, Kew,England.

(Received 29 November, 1988)

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