Occurrence of Grapevine leafroll associated virus-2, −3 and Grapevine fleck virus in Virginia, U.S.A., and factors affecting virus infected vines

Abstract

A statewide survey of commercial vineyards in Virginia (VA), USA was conducted in 2009–2011 seasons to examine the occurences of Grapevine leafroll-associated virus-2 (GLRaV-2), Grapevine leafroll-associated virus-3 (GLRaV-3), Grapevine fleck virus (GFkV), and mealybugs. Out of 415 samples (comprising 41 wine grape cultivars) from 77 locations (vineyards), GLRaV-2, GLRaV-3 and GFkV were detected by RT-PCR in 8, 25, and 1 %, respectively, and 64 % of vineyards were positive for at least one of the three viruses. Samples from 100 wild Vitis sp. tested negative for the three viruses. Both the grape (Pseudococcus maritimus) and Gill’s (Ferrisia gilli) mealybug were found in VA vineyards. Although regional effect was not significant (P > 0.05), examination of variance showed higher variability of GLRaV-3 incidence at cultivar scale within a vineyard than at a smaller spatial scale (i.e., at sampling site). In addition, the probability of finding a GLRaV-3-infected vine was higher in the presence of mealybugs (P < 0.001) and with increased vine age (P < 0.001). These results also suggest movement of GLRaV-3 by mealybugs in VA vineyards. The high frequency of virus-infected vines emphasizes the importance of clean plant materials as well as management of mealybugs. This is the first study reporting the presence of Ferrisia gilli, GLRaV-2, GLRaV-3, and GFkV in VA vineyards.