PERTANlKA 13(3), 357 - 359 (1990)

COMMUNICATION I

Occurrence of a Mosaic Virus in Guava

ABSTRAK

Daun dan satu cabang pokok jambu jenis Burma Red telah didapati menunjukkan simptom mosaik yang selaludikaitkan dengan serangan virus. Kajian mikroskop elektron terhadap sap dan daunyangdiserangmenunjukkanvirus berbentuk isometrik mempunyai garis pusat berukuran 58-64 nm. Virus ini boleh disebarkan secara mekanikdari pokok jenis Burma Red kepada anak pokok jenis Kampuchea. Berdasarkan kepada simptom, virus ini bolehdiberi nama virus mosaik jambu batu.

ABSTRACT

Leaves from a shoot ofguava cv. Burma Red were found to exhibit mosaic symptoms typical of a virus disease.Transmission electron microscopic studies of the sap from infected leaves revealed an isometric virus particle witha diameter of58-64 nm. The virus can be transmitted mechanicallyfrom cv. Burma Red to cv. Kampuchea seedlings.Based on the symptom, the virus can be tentatively designated as guava mosaic virus.

INTRODUCTION

Except for citrus trees, no virus disease has beenreported on other woody perennial fruit trees inMalaysia (Ong and Doon 1988; Lim 1988).However, recently in March 1989, leaves of ashootofthe guava, Psidium guajavacv. BurmaRedin the guava germ-plasm collection of MARDI,Serdang, was found to exhibit mosaic symptomstypical of a virus disease. A thorough scrutinyrevealed that only one shoot from one treedisplayed such symptoms. Old and young leavesof the infected shoot appeared deformed,puckered and rugose with dark and light greenmosaic (Fig. 1). The leaf margins were wavy andirregular, and some leaves were much reduced insize when compared to normal, healthy leaves.Five months later, a new infection with mildersymptoms was detected on the young shoots ofthe same trees (cv. Burma Red) and on a few treesin adjacent rows ofcvs. Kampuchea and MalaysiaSeedless. Symptoms ofrugose and puckered leaveswere observed, but the mosaic symptoms werenot as pronounced as those observed earlier oncv. Burma Red.

This paper reports the result of a study toconfirm its viral identity.

Fig. 1.' Light green with mgosity and leafdeformation symptom onguava'ev. Burma Red (arrow).

MATERIALS AND METHODS

Leaf sap extracted from leaves of cv. Burma Red,Kampuchea and Malaysian' Seedless showingmosaic symptoms were used for electronmicroscopy. The sap was extracted by grinding ina mortar and pestle with 0.01 M Sorensen'sphosphate buffer (pH 7). Formvar-carbon coatedgrids (300 mesh) were dipped in the sap andnegatively stained in 2% aqueous uranyl acetate.The grids were viewed in a Phillips EM 400transmission electron microscope. The diameters

ZAKARIA SIDEK AND LIM TONG KWEE

of the virus particles were compared to adiffraction grating (2,160 lines/mm) andphotographed at the same magnification. Theprocedures were repeated for the infected sap ofthe other cultivars.

For transmission studies, leaves, of each ofthe three cultivars showing mosaic symptoms,were separately ground in mortar and pestle with0.01 M Sorensen's phosphate buffers (pH 7) andCarborundum 600. The leaf extract from eachcultivar was rubbed separately onto young leavesof different healthy guava seedlings cv.Kampuchea. The excess sap was rinsed off theleaves and the seedlings were kept for 4-8 weeksfor observation of symptom development.

RESULTS AND DISCUSSION

Transmission electron microscopic studiesrevealed the occurrence ofiarge viral particles inthe infected leaves ofall three cultivars. The virusparticle had a diameter of 58-64 nm (mean 60nm), was isometric in shape and had an electrondense central area (Fig. 2).

Fig.2: Isometric virus particles from crude leaf sap ofguava cv. Burma Red stained negatively withaqueous acetate. Bar is lOOnm.

The virus from the leaves extract ofcv. BurmaRed was observed to be transmitted mechanicallyby wounding the leaves of cv. Kampucheaseedlings: symptoms appeared 4-6 weeks a~ter

inoculation. No virus-like symptom was seen oncv. Kampuchea seedlings inoculated with extractsfrom leaves of cvs. Malaysian Seedless andKampuchea though virus-like particles wereobserved in the leaf extracts of the inoculum.This might suggest failure of mechanicalinoculation or latent infection.

Based on the mosaic symptoms produced,the virus can be designated as guava mosaic virusand it can be tentatively classified under thecaulimoviruses group as the size and the geometryofthe virus particles subscribed to those describedfor this group by Hull (1984) and Francki et al.(1987). Caulimoviruses have been reported to betransmitted by sap inoculation and by aphids in an on-persistent and semi-persistent manner(Hull1984; Franki et al. 1987). However, confirmationof this still needs further substantiation by nucleicacid analysis, serology, and host indextransmission studies.

To the authors' knowledge, no virus diseasehas been reported on guava in the guava growingcountries of the world. This represents the firstrecord on the occurrence ofvirus infecting guavain the world. Spread of the disease was indicatedby occurrence ofnew infections on plants aroundthe original tree. We also observed that the workersused the same secateur for pruning from tree totree and this could have invariably helped thespread ofthe virus from cv. BurmaRed to adjacen ttrees of cvs. Kampuchea and Malaysian Seedless.This indicated that the virus could have beentransmitted mechanicallyby pruningwoundswithcontaminated implements. This was furthersupported by the mechanical transmission testson cv. Kampuchea seedlings using the extractfrom naturally infected leaves of cv. Burma Red.

The spread ofvirus diseases by contaminatedimplements from an infected tree to other treesconstitute one of the most common means ofvirus disease spread. It follows thus, that thesterilization ofsuch implements should be carriedout by dipping in a detergent solution such assoap, trisodium orthophosphate or Cloroxsolution, or by dipping hands or pruning secateursin milk in between pruning rounds from tree totree as milk inactivates many plant viruses (Lucaset al. 1985) Amore stringent measure would be toremove and destroy any tree showing symptomsof virus infection.

ZAKARIA SIDEKLIM TONG KWEE

Department ofPlant Protection,Universiti Pertanian Malaysia,43400 UPM Serdang, Selangor Darul Ehsan,Malaysia.

358 PERTA lKA VOL. 13, NO.3, 1990

OCCURRENCE OF A MOSAIC VIRUS IN GUAVA

REFERENCES

FR.-\~CKI, R.LB., R.G. MIl.NE and T. HATIA. 1987. Atlaso!Plrllll Virusps. Vol. I, (2nd printing), 222 p. BocaRaton, Florida: CRC Press.

HL"I.l., R. 1984. Caulirnovirus Group. CMIIAABDesrri/Hio/lS ofPlanl Virusf.s, No. 295, 4 p.

LIM. T.K. (1988). Diseases of Selected Perennial FruitTree and Their Control. &/Ilinaron TropicalFmils:Cultivalioll and Pf.sl & Disf.flsf. iV1anagemmt, KotaKinabalu, Sabah, Malaysia, 20-21 Oct., 1988.

LVCAS, G.B., C.L. CAMPBELL and L.T. LUCAS 1985.Introduction to Plant Diseases Identification andManagement, 313 p. Westport, Connecticut: AVlPublishing Co.

ONG, CA. and Y. Dool . 1988. Virus Diseases ofMalaysian Fruit Trees. Seminar on TTOpicalFmits­Cultivation and Pest & Disease Management, KotaKinabalu, Sabah, Malaysia, 20-21 Oct., 1988.

(Received 14 February, 1990;.

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