Cassandra Plank, Monica Cooper, Rhonda Smith, Deborah Golino, Maher Al-Rwahnih, and Kaan Kurtural*
*University of California Davis, 1 Shields Avenue, Davis, CA 95616 (skkurtural@ucdavis.edu)

Grapevine red blotch-associated virus (GRBaV) is a major threat to grape and wine industries in the United States, impacting vine health and berry composition. Cabernet Sauvignon/110R vines grown in Oakville, CA, were grouped as healthy or symptomatic during the 2015 growing season and, using qPCR and primers specific to the GRBaV genome sequence, vines were classified as GRBaV (-) or GRBaV (+) in 2016. We measured leaf gas exchange, midday stem water potential, components of yield, and berry composition at five time points during the 2016 growing season. Berry flavonol and anthocyanin composition was characterized with C18 reversed-phase HPLC. Midday stem leaf water potential was consistently greater in GRBaV(+) vines. Net carbon assimilation was consis-tently lower in GRBaV(+) vines, but recovered postharvest. Likewise, stomatal conductance and evapotranspiration were reduced by 40% from DOY 230 to 265 for GRBaV(+) vines and did not recover until one week postharvest. Conversely, intrinsic water use efficiency of GRBaV(+) vines was similar to GRBaV(-), with the exception that they were 42% greater one week postharvest. Components of yield were not affected by the presence of GRBaV. However, the Brix of GRBaV(+) vines were 18% lower compared to GRBaV(-). Conversely, titratable acidity of GRBaV(+) was 18% greater than GRBaV(-). The glucoside, acetylated, tri-hydroxylated, and coumarated forms of anthocyanidins were reduced by 20% in GRBaV(+) vines. Likewise, the flavonols and their tri-hydroxylated forms were reduced in similar amounts with GRBaV(+). The results provide evidence that GRBaV infection may induce significant reduction in primary metabolism, reducing carbon assimilation and stomatal conductance and altering berry and flavonoid composition.

Funding Support: Harold P. Olmo Department Start-up Funds