Joseph DeShields and Achala KC*
*Oregon State University, 569 Hanley Rd, Central Point, OR, 97501 (joseph.deshields@oregonstate.edu)

Foliar symptoms of grapevine red blotch disease (GRBD) are characterized by interveinal red blotching on the leaf blades of red-fruited cultivars and chlorotic blotching on some white-fruited cultivars. These foliar symptoms are reportedly associated with reduced photosynthesis and carbon translocation in the leaf, resulting in reduced sugars and anthocyanins in the fruit. It is also seldomly reported that asymptomatic grapevines can test positive for grapevine red blotch virus; therefore, it was hypothesized that grapevines that are GRBV-infected, but do not express foliar symptoms, may not exhibit typical fruit quality symptoms of GRBD. In 2021, four 100-vine blocks were selected from a commercial vineyard located in southern Oregon with Vitis vinifera L. cv. Merlot and Cabernet franc. Altogether, 400 vines were recorded for symptoms and dormant canes were tested for GRBV using qPCR. In the 2022 growing season, fruit was sampled from 10 symptomatic and 20 asymptomatic Merlot grapevines to evaluate the effects of GRBV and expression of GRBD symptoms on juice chemistry. Dormant canes from these 30 vines were also tested for GRBV following the growing season in 2022 by qPCR. The incidence of GRBD symptoms was 19.5 and 14.4% in 2021 and 98.5 and 99.8% in 2022 for Merlot and Cabernet franc, respectively. Berry total soluble solids were reduced in symptomatic, GRBV-positive grapevines (22.8 Brix) compared to asymptomatic, GRBV-positive grapevines (25.7 Brix) and asymptomatic, GRBV-negative grapevines (25.8 Brix). Similarly, titratable acidity increased in symptomatic, GRBV-positive grapevines (7.00 g/L) compared to asymptomatic, GRBV-positive grapevines (5.68 g/L) and asymptomatic, GRBV-negative grapevines (5.74 g/L). This study suggests that even with GRBV-infection, the fruit quality of infected vines may not be severely impacted if foliar symptoms are absent. This finding requires further validation and provides an important proof of concept in potentially managing highly infected vineyards by managing foliar symptoms.

Funding Support: OSU-Agriculture Research Foundation and Kandu Ranch, Ashland, OR