Gabriela Sinclair*
*University of California Davis, 1 Shields Ave, Davis, CA, 95616 (gcsinclair@ucdavis.edu)

Water-stressed grapevines accumulate solutes in their leaf cells to decrease osmotic potential (i.e., osmotically adjust) and reduce leaf vulnerability to wilting and stomatal closure. The magnitude of osmotic adjustment and types of solutes accumulated varies widely across other plant species and has not been characterized in many grape cultivars. Determining cultivar-specific osmotic adjustment performance could provide insights into stress tolerance and viticultural solutions under continually drier climate conditions. We examined whether cultivars from climatically diverse wine regions vary in osmotic adjustment and leaf biochemistry under hot growing conditions. We compared seven commercially important cultivars from different climate regions (i.e., cool: Riesling and Pinot noir; warm: Chardonnay, Merlot, and Syrah; and hot: Zinfandel and Sangiovese) grafted onto 420A and established in the same experimental vineyard block in a hot region (Davis, California). We measured changes in leaf osmotic potential at full hydration (π_o) and the concentration of major leaf cell solutes (i.e., the sugars glucose, sucrose, and fructose and cations K, Na, Ca, and Mg) from veraison to harvest (monthly from July to Sept) using HPLC and ICP analysis. For all cultivars, π_o significantly decreased over the season. All of the sugar and ion concentrations, except for Na, increased significantly over the season, and all mean concentrations, except for Na and the total ion concentration, were significantly different across cultivars. Interestingly, significant differences in π_o and solute con­centrations between cultivars were not explained by their optimal climate. Together, these findings indicate cultivar variation is a driver of the types of solutes formed in response to osmotic adjustment. A better understanding of the processes plants use to mitigate water stress at the leaf level will improve breeding programs developing more drought-tolerant cultivars.

Funding Support: American Vineyard Foundation