PARTIAL CHARACTERIZATION OF A NEW AMPELOVIRUS ASSOCIATED WITH GRAPEVINE LEAFROLL DISEASE

A virus associated with leafroll symptoms in Vitis vinifera was selected for further analysis because it was undetectable in all reverse-transcriptase polymerase chain reaction (RT-PCR) tests available for Grapevine leafroll associated viruses (GLRaVs). Extracts of infected plant material were also negative in all enzyme-linked immunosorbent assays available for GLRaVs. Nonetheless, the unknown virus caused typical grapevine leafroll symptoms in the indicator host, V. vinifera cv Cabernet Franc. High molecular weight double-stranded RNA (dsRNA) purified from an infected vine appeared typical of the dsRNA recovered from plants infected by viruses in family Closteroviridae. RT-PCR was performed using this purified dsRNA with degenerate oligonucleotide primers designed to amplify a fragment from the heat shock protein 70 homologue (HSP70) from any closterovirus. Sequence information from the resulting RT-PCR products allowed the determination of a full length HSP70 sequence from the unknown virus for comparison with those of other GLRaVs. A specific RT-PCR assay based on primers developed from this sequence was negative for all GLRaVs tested, other than the unknown virus. The name Grapevine leafroll associated virus 9 (GLRaV-9) is tentatively proposed for the novel pathogen.