Pat Bowen,* Carl Bogdanoff, José Ramón Úrbez Torres, Sudarsana Poojari, Kevin Usher, and Tom Lowery
*Summerland Research and Development Centre, 4200 Highway 97, PO Box 5000, Summerland, BC, V0H 1Z0, Canada (pat.bowen@agr.gc.ca)

Grapevine leafroll-associated virus 3 (GLRaV-3) infections are spreading within and among vineyards in the southern Okanagan Valley, British Columbia. Understanding the epidemiology and economic impacts of GLRaV-3 infection will help producers make decisions regarding vineyard management, replant scheduling, and winemaking.  The effects of GLRaV-3 infection on vine performance were determined in a Cabernet franc vineyard near Osoyoos, BC, over four years beginning in 2013. Symptomatic vines were verified as GLRaV-3 infected, and flanking asymptomatic vines, as non-infected, each year using reverse-transcriptase PCR test. Twenty infected vines and their two flanking non-infected vines were evaluated for growth and fruiting performance. Fruit was harvested from all vines on the same day each year. There were no effects of GLRaV-3 infection on pruning mass or yield, and effects on yield components were small and inconsistent among years. Averaged over years, infection reduced berry soluble solids (SS) at harvest by 1.2 Brix, increased TA by 0.38 g/L, and reduced the anthocyanin concentration in berry skin by 5%. In 2014 and 2015, single-vine wines were made from 10 randomly selected sets of infected and flanking non-infected vines. In 2014, when berry soluble solids averaged 26.8 and 27.6 Brix for infected and non-infected vines, respectively, infection led to wines with lower total phenolics, less black fruit flavor, more vegetative flavor, and less body and aftertaste. In comparison, in 2015, when the harvested fruit was more mature, with SS averaging 28.2 and 29.0 Brix for infected and non-infected vines, respectively, infection had less influence on wine quality, causing only reduced red fruit aroma. These results indicate that GLRaV-3 infection effects on wine quality may depend on fruit maturity at harvest. In a year when harvested fruit was very mature, infection had little influence on wine sensory quality.

Funding Support: BC Wine Grape Council; and Agriculture and Agri-Food Canada