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

While moderate water deficits advance ripening and improve fruit quality in healthy grapevines, they can potentially amplify negative effects of viral disease in GRBV-infected grapevines. Therefore, a field experiment with two irrigation treatments, wet and dry, and two disease statuses, healthy (RB-) and infected (RB+), was initiated to understand the interaction between GRBV infection and deficit irrigation. Wet vines were irrigated at 100% of crop evapotranspiration (ETc), while dry vines received water at 66% ETc. Healthy and infected vines were confirmed by PCR-based assays. Disease progression and severity were recorded weekly after first symptoms were observed on RB+ vines, and vine water status (Ystem) was regularly monitored throughout the growing season. At harvest, yield and yield components were determined, and berry samples were collected for compositional analyses. There was no significant interaction between irrigation treatment and disease status on disease progression and severity. Preveraison Ystem was not affected by disease status, but was significantly higher in RB+ vines postveraison. The higher Ystem in RB+ vines resulted in larger berries and yield at harvest, but few of the differences in yield and yield components among treatments were significant. Berry flavonoids were more strongly affected by disease status than sugars and acids, with little effect of irrigation treatment. In skins and seeds, significant differences among treatments were observed in the concentration and content of anthocyanins and iron-reactive phenolics (IRPs), but not tannins. Small differences in tannins coupled with large differences in IRPs suggests that GRBV strongly inhibited biosynthesis of non-tannin IRPs, particularly in seeds. Taken together, these results suggest that keeping vines well-watered may mitigate some of the negative effects of GRBV, but ultimate changes in secondary metabolism due to GRBV infection may necessitate using infected fruit for different wine programs or for blending with lots from healthy vineyards.

Funding Support: American Vineyard Foundation