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

Grapevine cultivars differ in their hydraulic behavior during droughts and are arranged on a continuum of isohydric/anisohydric responses due to varying stomatal regulation. It is unclear how the varying hydraulic responses between grapevine cultivars are reflected in changes to grape yield and composition. The aim of this research was to determine the effect of severe drought on the berry size and composition of two grapevine cultivars with contrasting hydraulic behaviors. Two-year old, own-rooted Semillon and Grenache 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 at postveraison for approximately two weeks, while controls were irrigated daily to maintain the soil water content at 90% of total capacity. Predawn and midday water potentials were measured daily with a Scholander pressure chamber. Stomatal conductance was measured daily with a porometer. Berries were sampled at varying degrees of drought and subjected to HPLC-RID analyses to determine organic sugar and acid content. Semillon maintained a higher stomatal conductance and dropped predawn and midday water potentials more rapidly than Grenache during drought. This coincided with Semillon berries having smaller changes in volume and metabolite concentrations during drought. These results suggest that a more anisohydric behavior might mitigate drought effects on berry volume and sugars postveraison.

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