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Isolation of a novel carlavirus from melon in Brazil

T. Nagataa, E.W. Kitajimab, D.M.T. Alvesa, J.E. Cardosoc, A.K. Inoue-Nagatad M.R.V. de Oliveirae and A.C. de Ávilad*

a Ciências Genômicas e Biotecnologia, Universidade Católica de Brasília, SGAN 916, 70790-160, Brasília, DF, Brazil
b Departamento de Entomologia, Fitopatologia e Zoologia Agrícola, Universidade de São Paulo, Av. Pádua Dias 11, Piracicaba, 13418-900, SP, Brazil
c Embrapa-Agroindústria Tropical, Rua Dra. Sara Mesquita 2270, Planalto Pici Fortaleza, 60511110, CE, Brazil
d Embrapa-Hortaliças, Caixa Postal 218, Brasília, 70359-970, DF, Brazil; eEmbrapa-Recursos Genéticos e Biotecnologia, Caixa Postal 02372, 70770-900, Brasília, DF, Brazil

*avila@cnph.embrapa.br

Accepted for publication 08/04/03

Since 1999, a yellowing disease of melon (Cucumis melo) has been observed, in the Northeast region of Brazil. The symptoms are mainly seen on older leaves and include leaf mottling and yellowing (Fig. 1); symptoms which are similar to those associated with criniviruses (Wisler et al.,1998) or nutritional disorders. Deformation of leaves, stems and fruits was rarely observed, but the low sugar content had a high impact on fruit quality and value. The disease was transmitted from melon to melon (6/24) and to West Indian gherkin (Cucumis anguria) (6/24) by grafting and to melon by whitefly transmission (Bemisia tabaci biotype B) (10/15). It was not mechanically transmitted. Examination of infected tissues by electron microscopy, using leaf dip and partially purified preparations, revealed filamentous particles 600-700 nm in length (Fig. 2) and typical of a carlavirus.


Figure 1: Characteristic symptoms of melon yellowing disease.


Figure 2: Filamentous particles (13 x 600-700 nm) in a leaf dip preparation
from experimentally infected melon with typical yellowing symptoms. Bar = 0.5 µm.

Typical carlavirus-like inclusion bodies were seen in melon leaves with yellowing symptoms, maintained in the glasshouse (Figs. 3 and 4). In a dot-immuno binding assay using antibodies to Cowpea mild mottle virus, no cross reaction was observed. As this is the only carlavirus reported to be whitefly transmitted, this strongly suggests that this is a new carlavirus. Cloning and sequencing of the virus is underway and preliminary comparisons of sequences with those in the GenBank database showed homologies with some carlaviruses. As the possibility of a mixed infection with a crinivirus cannot be ruled out, we suggest the name Melon yellowing-associated virus (MYaV).

Figures 3 and 4. Presumed carlavirus-like particles forming a loose, parallel aggregate in the cytoplasm of a melon leaf mesophyl parenchyma cell. Bar = 1µm.

Acknowledgements

The authors thank Dr. D.R. Lava Kumar and D.V.R. Reddy at ICRISAT, India, for the kind supply of the antibody of Cowpea mild mottle virus.

Reference

Wisler GC, Duffus JE, Liu H-Y, Li RH, 1998. Ecology and epidemiology of whitefly-transmitted closteroviruses. Plant Disease 82, 270-279.

The British Society for Plant Pathology