Identification and epidemic distribution of two flavescence doree-related phytoplasmas in Veneto (Italy)

Grapevine yellows associated with phytoplasmas of the elm yellows group (16SrV), better known as flavescence doree (FD), is a serious quarantine problem in some important grapevine growing regions in the European Union. A survey was carried out in 1997 to 1998 in Veneto region (Italy) where a serious outbreak of FD was in progress. Phytoplasma identification by nested polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) analyses on 275 grapevine samples and on batches of Scaphoideus titanus was carried out. RFLP analyses of the 16S rDNA/spacer region with TaqI detected the presence of two distinct elm yellows phytoplasma subgroups designated 16SrV-C and 16SrV-D in 77 FD-infected grapevine samples. Only phytoplasmas of the 16SrV-D subgroup were detected in S. titanus. In 1997, the two phytoplasma subgroups appeared to be located in two diverse geographic areas; but in 1998, the 16SrV-D type also was detected in the provinces where in 1997 only 16SrV-C type was identified. The sequencing of a 400-bp fragment at the 3' end of 16S rDNA plus spacer region allowed a specific primer construction that was successfully employed for detection of both FD types in grapevine by direct PCR.