Krista Shellie* 
*USDA-ARS HCRL Parma, ID worksite, USDA-ARS, 29603 U of I Lane, Parma, ID 83660 (krista.shellie@ars.usda.gov)

Deficit irrigation reduces seasonal carbohydrate supply and decreases starch concentrations in vegetative tissues. The specific role of starch metabolism in conferring tolerance to cold is still poorly understood. A decrease in cold tolerance after sequential years of deficit irrigation could limit sustainable productivity in arid, high-latitude production regions; however, the topic has received little research attention. In this study, multiple Vitis vinifera cultivars grown at two locations in replicated trial plots were visually rated for cold injury severity after six or more sequential years of deficit irrigation. Cold injury severity was estimated after budbreak by determining the percentage of total spur positions per vine without live shoots. The Merlot trial site was evaluated in spring 2007 after vines were exposed to sequential seasons of deficit irrigation at amounts that supplied 90, 70, or 35% of estimated vine water demand (ETc). The second trial location contained 15 cultivars that were evaluated in spring 2014 and 2015 after sequential seasons of deficit irrigation at 70 or 35% ETc. In the Merlot trial, the spring injury rating of vines irrigated at 35% ETc was significantly greater (74%) than vines irrigated at 70 or 90% ETc (35 and 6%, respectively). Greater injury was also observed in vines irrigated at 35 relative to 70% ETc in four out of 15 cultivars in 2014 and in all cultivars in 2015. Results from this research suggest that sequential years of exposure to deficit amounts of water during the growing season may influence subsequent tolerance to cold. Understanding the underlying mechanisms by which water deficit may influence subsequent cold tolerance is required before deficit irrigation strategies can be customized to avoid undesirable influences on cold tolerance. The empirical observations reported here demonstrate that this topic warrants further investigation.

Funding Support: U.S. Department of Agriculture, Agricultural Research Service