Kaan Kurtural*, Monica Cooper, Rhonda Smith, Deborah Golino, Maher Al-Rwahnih, Johann Martinez-Luscher, and Cassandra Plank
*University of California at Davis, 1380 Oakville Grade Road, Oakville, CA 94562 (skkurtural@ucdavis.edu)

Grapevine red blotch-associated virus (GRBaV) infection can negatively impact primary and secondary metabolism of grapevines, leading to a delay in fruit development. Cabernet Sauvignon/110R vines grown in Oakville, CA, were tested in 2017 using qPCR and primers specific to the GRBaV genome sequence. Vines were classified as GRBaV (-) or GRBaV (+). Experimental vines were free from other common virus infections. Leaf gas exchange and mid-day stem water potential were monitored at two-week intervals from fruit set through harvest. Berry flavonol and anthocyanin composition were monitored from veraison to harvest and characterized with C18 reversed-phase HPLC. Approximately 30 days before onset of symptoms, mid-day SWP was greater in GRBaV (+) vines, which was also observed at harvest. The only reduction of net carbon assimilation due to infection was observed at harvest. Likewise, few differences in leaf stomatal conductance and sub-stomatal CO2 concentration were observed. Despite these observations, TSS and TA of fruit from infected vines were consistently reduced across the season; this response was not observed for pH. At harvest, TSS and TA of GRBaV(+) vines were both reduced by 16% when compared to GRBaV(-). Delayed harvest (by 1.5 weeks) did not allow improvement in TSS, which was 7% lower in fruit from infected vines. Components of yield were not affected by the presence of GRBaV. Development of anthocyanins lagged across the season by up to 8 mg/g SDM, but by harvest no differences in total amount or forms were observed. GRBaV negatively affected secondary metabolism before symptoms were apparent and fruit development was delayed as early as veraison.

Funding Support: American Vineyard Foundation