Arpa Boghozian, Cristina Medina-Plaza, Reddy Kishorekumar, Hazel Scully, Mysore Sudarshana, and Anita Oberholster*
*University of California, Davis, 595 Hilgard Lane, Davis, CA, 95616 (aoberholster@ucdavis.edu)

Grapevine red blotch virus (GRBV), part of the Geminiviridae family, causes negative impacts on grapes, including a decrease in sugar accumulation, phenolic content, and extractability during winemaking. The impact of GRBV was studied across virus-infected GRBV(+) and non-infected GRBV(-), vines from a commercial vineyard in Paso Robles, CA across two growing seasons: 2021 and 2022. Sixteen GRBV(-) asymptomatic and 20 GRBV(+) symptomatic data vines were confirmed by qPCR test. Exhaustive extractions were conducted in four biological replications of five GRBV(+) and four GRBV(-) data vines, respectively, to characterize grape phenolic composition by high-performance liquid chromatography (HPLC). To evaluate the impact of GRBV on phenolic extractability, grapes were harvested when GRBV(-) reached 27 Brix. Fermentations were conducted in triplicate and the phenolic content of the final wines analyzed by HPLC. Phenolic extractability was calculated as the ratio of wine to grape phenolic content. The 2022 growing season had more growing degree days, days above 35°C, and lower average precipitation than 2021. In 2021, GRBV(-) grapes had similar phenolic content to GRBV(+), while in 2022, GRBV(-) had lower anthocyanin content than GRBV(+), potentially due to degradation as a result of high temperatures. In this study, seasonal impact on grape phenolic content had a greater impact than GRBV. Despite the similarity in phenolic content, the final GRBV(+) wines showed decreases of 3% (v/v) alcohol and lower pH than GRBV(-) wines, suggesting delayed ripening due to GRBV infection. Phenolic extractability was greater in GRBV(-) than GRBV(+) grapes. This is in accordance with previously published studies, which relate greater phenolic extraction with ripening status and lack of GRBV infection. In the next step, cell wall composition of GRBV(-) and GRBV(+) grapes will be characterized to determine if compositional differences are related to phenolic extractability differences.

Funding Support: PD/GWSS Board-CDFA, UC Davis Horticulture and Agronomy Graduate Group, Jastro-Shields Research Award