Yevgen Kovalenko,* Tyler Abbey, Marie Nosten, Bartosz Kozak, 
and Simone Castellarin  
*The University of British Columbia, 330 – 2205 East Mall V6T 1Z4, Vancouver, BC V6T 1Z4, Canada (hophmen@gmail.com)

Crop load management by cluster thinning is a viticultural practice that can improve ripening and the concentrations of secondary metabolites, including volatile organic compounds. Little work has been done on white grapes in the Okanagan Valley. The timing of cluster thinning can alter the efficacy of the treatment. In this study, field-grown Gewürztraminer were cluster-thinned post-fruit set and at veraison at two levels: light (10 tonnes/ha) and moderate (15 tonnes/ha). A control treatment (20 tonnes/ha) was maintained for comparison. The hypothesis is that reducing crop load via cluster thinning will stimulate ripening and syn-thesis of beneficial volatile compounds, with early thinning application having a more positive effect than late application. Treatments were replicated on five plots arranged in a randomized block design. Sampling occurred every seven to 14 days, starting three weeks after fruit set. The effect of these treatments on photosynthesis, vegetative growth, and sugar, acid, and volatile compound concentrations was analyzed. Sugar concentration and vine yield were significantly affected by cluster thinning; however, the timing of cluster thinning seemed to be less important. Previously identified genes involved in central and specialized metabolism were quantified and analyzed for treatment response. Free and bound volatiles were quantified through solid-phase micro-extraction gas chromatography mass spectroscopy. The goal of this project is optimize Gewürztraminer grape quality through targeted crop load management practices, as volatile organic compounds are closely tied to the economic potential of wine grapes.

Funding Support: British Columbia Investment Agriculture Foundation, British Columbia Wine and Grape Council