Gabriela Sinclair, Megan Bartlett,* Jerry Lin, and Dario Cantu
*UC Davis, 595 Hilgard Ln., Viticulture & Enology Department, Davis, CA 95616 (gcsinclair@ucdavis.edu)

Integrative physiological and molecular approaches to identify traits associated with drought tolerance will be key to developing more tolerant cultivars. Water-stressed grapevines accumulate solutes in their leaf cells, thereby decreasing their osmotic potential, which helps maintain the cell turgor required for leaf structure and gas exchange. Plants use this mechanism of accumulating solutes to help maximize transpiration during drought through stomatal regulation. A greater understanding of the mechanisms used to retain water and dictate water movement (i.e., osmotic adjustment) is needed to predict how grapevines will respond to water stress during drought. We measured solute accumulation from changes in osmotic potential between veraison and harvest in two irrigated experimental vineyards exposed to similar environmental conditions in Northern California on commercially important cultivars (e.g., Chardonnay, Riesling, Pinot noir, Merlot, Zinfandel, Sangiovese, Syrah) and on a population of genotypes resulting from a cross between Riesling and Cabernet Sauvignon. We discovered wide variation in osmotic potential. In comparison to the cultivars, the genotypes displayed more variation in osmotic adjustment, indicating this population may be useful to examine the genetic basis of osmotic potential. Collaborators detected nearly significant quantitative trait loci that suggested a possible correlation between genotypes displaying more negative osmotic potential values and higher rates of transpiration under well-watered conditions. In a future study, we will test a larger sample size to substantiate this genetic component. Collectively, these findings provide a promising starting point to explore the physiological mechanisms and genetic factors that drive cultivar variation and their contrasting responses to water stress in a vineyard setting. Isolating hydraulic traits associated with drought tolerance on the genetic scale, coupled with a better understanding of the strategies plants use to manage their water balance, will further aid breeding programs to develop more drought-tolerant cultivars.

Funding Support: American Vineyard Foundation