Carl Bogdanoff,* Pat Bowen, Brad Estergaard, and Steve Marsh 
*Agriculture and Agri-Food Canada, Summerland Research and Development Centre, 4200 Hwy 97, Summerland, BC, V2A 8V4, Canada (carl.bogdanoff@agr.gc.ca)

The effects of irrigation deficit timing on yield, fruit quality, and winter hardiness of Merlot in the Okanagan Valley of British Columbia were studied to explore the relationship between seasonal photosynthetic rates and bud hardiness. The irrigation treatments were full irrigation (FI), which was a sustained, mild-deficit regime, and three treatments with a severe irrigation deficit period: prebloom-to-harvest (PBH), fruit set-to-veraison (FSV), and fruit set-to-harvest (FSH). Leaf gas exchange and stomatal conductance were less in vines undergoing severe deficit irrigation. Yield was greater for FI than PBH vines, which had fewer and smaller berries per cluster. Compared with all severe deficit treatments, FI produced larger berries, lower juice pH, and higher juice TA, but similar juice soluble solids. Bud hardiness in early November was improved by FSV over FI, but sustaining the severe deficit period beyond veraison (FSH and PBH) did not improve hardiness compared with FI. Enhanced bud hardiness associated with higher photosynthesis rates found previously was not observed in this study, indicating that in Merlot, vine water stress and carbon balance less-consistently influence bud winter hardiness than yield components and fruit quality.

Funding Support: British Columbia Wine Grape Council and Agriculture and Agri-Food Canada