Alexander Levin,* Daniel Dalton, Vaughn Walton, and Achala KC
*Oregon State University, Southern Oregon Research and Extension Center, 569 Hanley Rd., Central Point, OR 97502 (alexander.levin@oregonstate.edu)

Plant growth regulators are commonly used to improve ripening and berry composition in healthy grapevines. Recently, it has been suggested that grapevine red blotch virus (GRBV) disrupts the normal hormonal signaling involved in ripening onset in berries. Since endogenously produced abscisic acid (s-ABA) plays a large role in berry ripening, it is possible that exogenous applications of s-ABA could mitigate the deleterious effects of GRBV. Therefore, the effects of exogenous s-ABA application on fruit ripening in GRBV-infected grapevines were tested in two Oregon AVAs characterized by different climates: the Willamette Valley (WV; cool and wet) and the Rogue Valley (RV; warm and dry). At each site, candidate vines were identified based on previous symptoms and confirmed for GRBV infection with PCR-based assays. Cluster-directed spray applications of s-ABA were made at 50% veraison and 10 to 14 days later at a rate of 300 mg/L. Experimental treatments were a 2 × 2 factorial combination of disease condition – healthy (RB-) and infected (RB+) – and s-ABA application – spray (ABA+) or no spray (ABA-). At harvest, there were no significant effects of s-ABA on berry fresh weight, total soluble solids (TSS), pH, or titratable acidity within RB+ or RB- vines. There were also no significant effects of disease status on the aforementioned parameters in WV vines, and in RV vines, only TSS was significantly higher in RB- vines. There were no significant interactions between s-ABA application and disease status with respect to polyphenolic composition in skins and seeds. Surprisingly, ABA+ vines had lower concentrations of tannins and iron-reactive phenolics across either disease status in the skins, but since there were minimal effects in the seeds, there were non-significant treatment effects in total concentration. Overall, exogenous application of s-ABA at veraison did not improve fruit composition across two distinct growing regions.

Funding Support: Oregon Department of Agriculture, Oregon Wine Research Institute, Agricultural Research Foundation, Oregon Wine Board