PARTIAL CHARACTERISATION OF A GRAPEVINE LEAFROLL- ASSOCIATED VIRUS ISOLATED FROM AN INFECTED CYPRIOT VINE OF cv. MAVRO

Abstract

A grapevine accession of cv. Mavro from Cyprus showing mild leafroll symptoms and containing closterovirus- like virus particles failed to react with commercial antisera to Grapevine leafroll-associated virus 1, - 2, -3, -5 and -7. The virus, denoted GLRaV-Cyp1, was not mechanically transmissible to herbaceous hosts but was successfully transferred by chip-bud grafting and through Planococcus ficus to healthy rooted cutting of cv. Cabernet sauvignon in which it induced leafroll symptoms as mild as those seen in the mother vine. Three different fragments of the viral genome, corresponding to the heat shock protein 70 homologue (HSP70h), major coat protein (CP) and p23 genes were amplified using degenerate and specific primers, cloned and sequenced. In a comparative analysis, GLRaV-Cyp1 showed amino acid sequence identity never higher than 86% with the HSP70h and 70% with CP and p23 genes of other GLRaVs species and strains, with the exception of a GLRaV isolate from a Greek grapevine, with which it showed 94% identity. In phylogenetic trees constructed with sequences of HSP70h, CP and p23 genes, GLRaV-Cyp1 consistently grouped in a cluster comprising sequences of the “type strains” of GLRaV-4, -5, -6, and -9 and of several other viral isolates regarded as molecular variants of one or more of the above species. This supports the notion that GLRaV-Cyp1 may not be a new ampelovirus species. In a small-scale survey carried out by PCR on a collection of vines from ten Mediterranean countries, GLRaVCyp1 was detected in 5 out of 121 vines tested.