Raul Girardello, Anita Oberhoster,* Larry A. Lerno, Monica L.Y. Cooper, Rhonda J. Smith, Charles Brenneman, and Anji Perry  
*Department of Viticulture and Enology, University of California,
Davis, CA 95616 (aoberholster@ucdavis.edu)

Grapevine red blotch-associated virus (GRBaV) was identified as the causal agent of red blotch disease in 2011. Berries from infected grapevines can present lower sugar concentrations than healthy grapes. For the last 3 years the impacts of red blotch disease on grape and wine composition have been investigated and results indicate that grape berries from symptomatic Cabernet Sauvignon, Chardonnay, and Merlot vines mostly have a decrease in Brix and anthocyanin concentrations, with variable impacts on other phenolic compounds such as flavan-3-ols and their polymers when compared to fruit from healthy vines. The difference in sugar concentration at harvest resulted in significantly higher ethanol concentrations in wines made from fruit from healthy vines in 2014 and 2015, which strongly affected sensory properties. This research compared grape and wine composition of symptomatic and healthy vines harvested on the same date and additional symptomatic vines harvested at a later date at the same Brix as the healthy fruit. Berries from Cabernet Sauvignon, Chardonnay, and Merlot from Napa Valley, Sonoma County, and San Luis Obispo, respectively, were collected weekly from veraison until harvest and analyzed for standard chemical composition (Brix, pH, TA, sugar loading, and malic acid) and phenolic composition by protein precipitation assay and RP-HPLC. Wines made from fruit produced on healthy and symptomatic vines, and fruit harvested from symptomatic vines on a subsequent date, were made in triplicate. Results confirmed that grapes from symptomatic vines had decreased sugar accumulation and increased TA during ripening in all three varieties. Wines made with grapes from symptomatic vines harvested at the same Brix as healthy vines showed less impact of the disease, producing wines more similar in anthocyanin and tannin concentration to wines made from healthy fruit.

Funding Support: Science Without Borders (Brazilian Government), American Vineyard Foundation (AVF)