Natural Infection of Muskmelon by Eggplant Mottled Dwarf Rhabdovirus in Italy

Abstract

Eggplant mottled dwarf rhabdovirus (EMDV) is endemic in the Mediterranean area but within the family Cucurbitaceae has been reported only in cucumber (1). In the spring of 1998 unusual symptoms of stunting, short internodes, fruit deformation, and vein yellowing were observed in about 5% of muskmelon (Cucumis melo L. var. reticulatus Naudin) cv. Hombre F1 grown under plastic in Tuscany (Central Italy). Electron microscopy of negatively stained preparations of crude sap from such melon plants revealed the presence of large numbers of particles resembling rhabdovirus. The virus, sap transmitted to several test plant species, had a host range identical to that of typical EMDV isolates, including the isolate from cucumber. Based on both electron microscopy and test plant reactions, the presence of other viruses was excluded. As with other known isolates, symptoms did not appear until about 30 days after inoculation, except for necrotic local lesions in Gomphrena globosa, which appeared in 10 days. Systemic leaf symptoms of field melon were reproduced by mechanically inoculating glasshouse melon seedlings with sap from infected White Burley tobacco. The virus was identified as EMDV by serology with an antiserum (As-0136) against the type isolate (EMDV-PV-0031), both obtained from the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ), Germany. No differences in protein pattern in Western blots (immunoblots) were observed by coelectrophoresis of the type isolate and our melon isolate. The virus was easily detected in several experimental hosts by antigen-coated plate enzyme-linked immunosorbent assay (ELISA). The vector of EMDV is unknown, but the virus generally infects in low percentage a wide range of plant species belonging to different families. This suggests that a polyphagous insect with low vector efficiency may be involved in transmission. Reference: (1) P. Roggero et al. Plant Dis. 79:321, 1995.