Characterization of cucurbit yellow stunting disorder virus, a Bemisia tabaci-transmitted Closterovirus.
Symptoms of interveinal chlorosis (yellowing) are commonly observed in melon or cucumber plants grown in greenhouses on the southeastern coast of Spain. The agent of the disease was determined to be cucurbit yellow stunting disorder virus (CYSDV). CYSDV was shown to be transmitted specifically by the tobacco whitefly (Bemisia tabaci), was retained by the vector for at least 7 days and had an experimental host range restricted to members of the family Cucurbitaceae. Filamentous, flexuous virus particles typical of the closteroviruses were observed in infected plants. The length distribution of the virus particles showed 2 peaks at 825 to 850 nm and 875 to 900 nm. Analysis of double-stranded (ds) RNA extracts revealed 2 major dsRNA species of c. 8 and 9 kbp. Random cDNA cloning of viral dsRNA was performed and a virus-specific cDNA clone (p410) of 557 nucleotides that hybridized with the smaller of the 2 viral dsRNA species was identified. Computer-assisted analysis showed that the deduced amino acid sequence of p410 was significantly similar to the HSP70 homologues of the closteroviruses and showed greater similarity to the HSP70 homologue of the B. tabaci-transmitted lettuce infectious yellows closterovirus (LIYV) than to the HSP70 homologues of the aphid-transmitted closteroviruses. The data suggest that CYSDV is a member of a newly recognized subgroup of closteroviruses with bipartite genomes exemplified by LIYV.