Since 2011, when Grapevine Red Blotch Associated Virus (GRBaV) was identified as the causal agent of red blotch disease (RB), the disease has been found in several white and red winegrape growing regions in California. Vines with RB show symptoms like red veins on the leaf undersides and no rolling. In white varieties, RB symptoms include chlorotic regions within leaf blades. Currently, little is known about the impact of RB on grape composition. What is known is that in infected grapes, there is decreased sugar accumulation and delay in fruit maturation. Only anecdotal evidence exists regarding phenolics. The impact of RB on the chemical and phenolic composition of Cabernet Sauvignon and Chardonnay grapes, two important winegrape varieties, was investigated. During the 2014 and 2015 harvests, Cabernet Sauvignon and Chardonnay berries were sampled from healthy and symptomatic, RB-infected grapevines. Samples were collected every two weeks from veraison to harvest from vineyards in Napa and Sonoma counties. Standard grape chemistries were determined during ripening and harvest (Brix, pH, titratable acidity, malic acid, tartaric acid, total anthocyanins, and tannins). Selected samples were also analyzed by RP-HPLC and phloroglucinolysis to determine the phenolic and tannin profiles of the grapes. Grapes harvested from RB-infected grapevines had less sugar accumulation (0 to 9% in Chardonnay and 4 to 20% in Cabernet Sauvignon), less total anthocyanins (0 to 16% in Cabernet Sauvignon), higher titratable acidity (0 to 3% in Cabernet Sauvignon and 11 to 16% in Chardonnay), and greater catechin concentration (46% in Cabernet Sauvignon) than noninfected vines.

Funding Support: American Vineyard Foundation Science Without Borders (Brazil)