Effect of grapevine leafroll virus on vine growth and fruit yield and quality

On the Vinifera variety Mission and the hybrid grapevine Baco 22A, growing on their own roots, spring growth was delayed by grapevine leaf‐roll virus. Cane and root growth of Mission vines was considerably reduced by the virus, but it had little effect on growth of Baco 22A. Leafroll virus reduced fruit yield of Mission vines by an average of 66 percent and sugar content of grapes by 30 percent, corresponding figures for Baco 22A being 44 percent and 9 percent respectively. Tartaric acid content of grapes at harvest was not appreciably affected by the disease. Pigment concentration in wine made from grapes of infected vines of the red‐fruited Mission variety was approximately half that in wine made from grapes of healthy vines.