Raul Cauduro Girardello, Arran Rumbaugh, , Larry Lerno, Rhonda J. Smith, Charles Brenneman, Anji Perry, Hildegarde Heymann, Pauline Lestringant, Anita Oberholster, Kaan Kurtural, and Cassandra Plank*
*University of California, Davis, 595 Hilgard Lane, Davis, CA 95616 (aoberholster@ucdavis.edu)

The impact of red blotch (RB) disease on grape and wine quality has been of great concern in the United States since its identification in 2011. We studied the impact of RB disease on Cabernet Sauvignon, Chardonnay, and Merlot grape and wine composition over three years. Results from 2014 and 2015 seasons indicated that RB disease can impact grape composition by decreasing sugar concentration and delaying color development, which resulted in lower ethanol and anthocyanin concentration in their respective wines, thus affecting sensory properties. For this reason, in the 2016 season, symptomatic grapevines were harvested sequentially at two time points: (1) at the same time as healthy vines, but at lower Brix, and (2) later, when Brix was similar to that of healthy vines. The aim of this study is to evaluate the impact of RB disease on grape and wine composition and sensory properties. Cabernet Sauvignon, Chardonnay, and Merlot berries from Napa Valley, Sonoma County, and San Luis Obispo, respectively, were collected weekly from veraison until harvest. Brix, pH, titratable acidity (TA), phenolic composition by protein precipitation assay, and RP-HPLC were performed on grapes. Wines were made in triplicate from healthy, RB symptomatic, and second harvest RB symptomatic grapes, and analyzed for residual sugars, % EtOH v/v, volatile acidity, TA, free and bound SO2, phenolic composition by RP-HPLC and protein precipitation, and volatile composition by HS-SPME-GC-MS. Wine sensory characteristics were determined by descriptive analyses. Chemical analysis confirmed that grapes from symptomatic vines had decreased sugar and color accumulation (red varieties) and higher TA. Wines made from second harvest grapes from symptomatic vines showed less impact of the disease, producing wines with chemical, phenolic and volatile profiles, and sensory properties more similar to wines made from healthy fruit than wines made the first harvest of RB-diseased fruit.

Funding Support: CAPES – Science Without Borders (Brazilian Government), the American Vineyard Foundation, Wine X Ray, Jastro Shields Scholarship, and J. Lohr Vineyards and Wines.