Prashant Swamy, Sridhar Jarugula, and Naidu Rayapati Naidu* 
*Washington State Unviersity, 24106 N. Bunn Rd, Prosser, WA 99350
(naidu.rayapati@wsu.edu)

Grapevine leafroll (GLD) and red blotch (GRBD) are distinct viral diseases affecting vineyards in many grapegrowing regions in the United States. This study was conducted during several seasons to assess impacts of GLD and GRBD in red-fruited winegrape (Vitis vinifera) cultivars planted in commercial vineyards. Grapevines with and without symptoms were identified for each cultivar and tested for the presence of Grapevine leafroll-associated virus 3 (GLRaV-3) and Grapevine red blotch-associated virus (GRBaV) to ensure symptomatic vines were positive for either GLRaV-3 or GRBaV and non-symptomatic vines were negative for the two viruses. At least 20 vines showing symptoms and testing positive for GLRaV-3 or GRBaV and an equal number of vines without symptoms and testing negative for the two viruses were selected for each cultivar. In each season, data on fruit yield was collected from each cultivar at the time of commercial harvest. Similarly, data on fruit quality attributes (total soluble solids measured as Brix, juice pH, titratable acidity [TA], and total anthocyanins) was compared in grapes harvested from vines with or without symptoms. Both GLD and GRBD affect fruit yield and quality (especially sugars) in red-fruited winegrape cultivars examined during the past two to three vintages. The negative impacts of GRBD on fruit yield and quality appeared to be relatively higher than GLD in cultivars examined in this study. Interestingly, impacts on grape juice pH and TA were not as pronounced as impacts on fruit yield and berry sugars. Mixed results were obtained with berry anthocyanins, depending on the disease and cultivar. The negative impacts of GLD and GRBD on fruit yield and berry sugars were variable among cultivars and across vintages, suggesting cultivar- and season-specific differences to viral infections.

Funding Support: WSU Agricultural Research Center, Wine Research Advisory Committee of the Washington State Wine Commission and Washington State Grape & Wine Research Program, and WSDA-Specialty Crop Block Grant Program (Project # K1275).