Nikolas Wilson,* Thorsten Knipfer, and Simone Castellarin
*University of British Columbia, 2205 E Mall, V6T 1Z4, Canada (nikolas.wilson@ubc.ca

Physiological stress thresholds such as stomatal closure and turgor loss can give insights into the performance of grapevine cultivars during drought. Recent studies have shown that predawn versus midday water potential curves accurately predict stomatal closure in a variety of species and predict turgor loss point in walnut. The water potential curve is a promising approach to classify the hydraulic behavior of grapevine (Vitis vinifera L.) cultivars under drought; however, it is unknown whether it accurately predicts turgor loss point in this species. The objective of this research was to determine the accuracy of water potential curves in predicting turgor loss points in different grapevine cultivars, and to confirm the accuracy of stomatal closure prediction. Two-year-old, own-rooted Grenache, Semillon, Cabernet franc, and Riesling vines were grown in 11.3-L pots in a greenhouse at the University of British Columbia. Vines were exposed to progressive drought by withholding irrigation for approximately two weeks, while well-irrigated vines were watered daily to maintain soil water content at 90% of capacity. Predawn and midday water potentials were measured daily with a Scholander pressure chamber. Stomatal conductance was measured daily using a porometer. Prior to withholding irrigation, pressure-volume curves were performed on hydrated leaves from each cultivar. Significant three-phase water potential curves were generated for each cultivar. These curves accurately predicted the turgor loss points determined via pressure-volume curves. Stomatal closure was not as accurately predicted, but differences in stomatal regulation between varieties were reflected by water potential curves. These results highlight that the water potential curve is a promising approach to characterize the performance of different grapevine cultivars under drought.

Funding Support: NSERC Discovery Program (AWD-000128 NSERC 2020); American Society for Enology and Viticulture – Traditional Scholarship; BC Hospitality Foundation – BC WISE Scholarship