Effects of Grapevine Red Blotch Disease on Cabernet franc Vine Physiology, Bud Hardiness, and Fruit and Wine Quality

The effects of grapevine red blotch disease (GRBD) on vine performance were studied in a Cabernet franc vineyard in the Okanagan Valley, British Columbia, over two years. Vines with GRBD had lower pruning mass, were less winter hardy than non-GRBD vines, and produced lower yields comprising fewer clusters and larger berries with more seeds. GRBD reduced photosynthesis and stomatal conductance for asymptomatic leaves through the growing season, and more so for symptomatic leaves. Leaf fall was delayed or incomplete for GRBD vines. GRBD reduced berry soluble solids, anthocyanins, yeast assimilable nitrogen, and tannins and increased berry pH and titratable acidity. Wine made from GRBD fruit had reduced anthocyanin and alcohol, lighter color, and more yellow hue. Effects of GRBD on wine sensory characteristics included less body and aftertaste, lower intensity of black and red fruit character, and increased acidity and intensity of vegetal character. Inclusion of low amounts, up to 20%, of GRBD fruit in wine reduced red fruit character in the first year and increased astringency and vegetal character in the second year. The deleterious effects of GRBD on yield, fruit composition for winemaking, and bud hardiness constitute a serious threat to grapegrowing regions in Canada and the United States. The degree of these impacts would be difficult to mitigate through management practices, which underscores the importance of planting virus-tested vines to prevent the introduction and spread of GRBD.