YIELD AND BERRY COMPOSITION OF 5 VITIS CULTIVARS AS AFFECTED BY RUPESTRIS STEM PITTING VIRUS

Rooted cuttings of Kerner (Vitis vinifera), Michurinetz (V. amurensis X), and Okanagan Riesling (V. labruscana X), either virus-free or infe cted with Rupestris stem pitting virus (RSPV), were planted in 1987 in a randomized block experiment at Summerland, British Columbia (arid c ontinental climate). Also, virus-free and RSPV-infected plants Madelei ne Sylvaner, and Ortega (both V. vinifera) were planted in a completel y randomized experiment at Saanichton Plant Quarantine Station, Sidney , BC (cool maritime climate). Yield components were not affected at th e Summerland site, but weight of cane prunings were reduced in RSPV-in fected Michurinetz vines in 1995-96. RSPV also lowered yield and clust ers per vine of both cultivars in 1994 at Sidney, along with Ortega we ight of cane prunings (1993 and 1994) and berry weight (1994). Berry t itratable acidity (TA) at harvest was reduced at both sites in RSPV-in fected vines, and pH was concomitantly increased. TA was consistently lower and the pH was always higher in the RSPV berries during veraison to harvest at Summerland. No apparent negative impact of RSPV was obs erved except delayed soluble solids (degrees Brix) accumulation in RSP V-infected Kerner and Okanagan Riesling vines at Summerland in 1991, a nd lower degrees Brix in Ortega RSPV berries at Sidney in 1993. in som e seasons, fruit composition differences between virus-free and RSPV v ines disappeared close to commercial maturity, but lower TA and higher pH persisted until harvest at the Summerland site in 1993. RSPV-infec ted vines at Sidney exhibited slightly delayed budburst in 1988-91 and 1994, but not 1993. These results suggest that RSPV has no major impa ct on grapevine growth and yield, and may advance fruit maturity in te rms of TA and pH.