Genetic variability in Grapevine virus A from Vitis vinifera L. x Vitis labrusca L. in Sichuan, China

Grapevine virus A (GVA) has a quasispecies nature and is closely associated with the rugose-wood disease complex of Vitis vinifera L. In the different growing regions of table grape in Sichuan, southwest China, the incidence of GVA infection was found to be 16.9% by ELISA detection among 178 grape plants ( Vitis vinifera L. x Vitis labrusca L.). The results of restriction fragment length polymorphism (RFLP) studies on the polymerase chain reaction (PCR) products of a total of 139 plasmids, cloned from 15 GVA isolates, suggested that the GVA isolates contained highly divergent variants. The plasmids from each GVA isolate that yielded different PCR-RFLP profiles were preferentially chosen for sequencing and were designated as variants. Furthermore, a phylogenetic study based on the analysis of the GVA coat protein genes and RNA silencing suppressor genes showed that the 40 variants obtained from the 15 GVA isolates represented 4 clades, designated as molecular groups I, II, III, and IV, respectively. The variant-specific PCR detection results indicated that the parts of the tested grape plants were specifically infected by mild variants.