Irrigation Improves Vine Physiology and Fruit Composition in Grapevine Red Blotch Virus-Infected Vitis vinifera L.

Grapevine red blotch virus (GRBV) negatively impacts vine physiology and fruit quality in Vitis vinifera L. by reducing photosynthetic rate, total soluble solids (TSS), and berry anthocyanin concentration. Currently, growers have few management strategies beyond removal of infected vines, which may be particularly costly in vineyards with high disease incidence. The present study was established in 2018 in a GRBV-infected Pinot noir vineyard in southern Oregon to investigate whether reducing vine stress with cultural practices could dampen the impact of the disease on vine physiology and fruit quality. The effects of control and supplemental levels of irrigation and fertilizer on vine growth and physiology, disease severity, and fruit composition were observed over three years. Supplemental irrigation affected vine physiology and fruit composition in 2019 and 2020, but fertilization had no significant effect over three years. Photosynthetic rate, vegetative growth, vine yield, berry weight, TSS, and titratable acidity were increased with supplemental irrigation while disease severity (symptomatic leaves per vine) was reduced. Supplemental irrigation did not have consistent effects on secondary metabolites, though an increase in anthocyanin concentration was observed in 2020 despite an increase in berry size. Irrespective of applied water amounts, maintaining a higher vine water status effectively increased photosynthesis and canopy size, which resulted in greater sugar accumulation. Ultimately, these results suggest that maintaining a high vine water status (Ψstem > -0.8 MPa) may mitigate some of the negative effects of GRBV on vine physiology and fruit composition.