In the challenging climate of Mississippi, where high heat, rainfall, and humidity pose significant challenges to bunch grape (Vitis spp.) production, identifying resilient cultivars is essential for determining stress adaptation and sustainable agricultural practices. This study assessed the heat tolerance of nine interspecific hybrid bunch grape cultivars/selections (‘Ambulo Blanc’, ‘Black Spanish’, ‘Blanc du Bois’, ‘Lomanto’, ‘MidSouth’, ‘Miss Blanc’, ‘Muench’, OK392, ‘Victoria Red’) grown at the Mississippi Agricultural and Forestry Experiment Station South Mississippi Branch in Poplarville, Mississippi, in 2023. Stomatal density, stomatal conductance, transpiration, vapor pressure deficit, and chlorophyll fluorescence were evaluated both in the field and through leaf disks subjected to a 4-hour heat simulation. ‘Miss Blanc’ and OK392 exhibited the highest stomatal density, while ‘Black Spanish’ had the lowest. Monthly in-field measurements showed no significant differences in physiological measurements. Regarding specific cultivars undergoing the heat simulation, ‘Lomanto’ displayed elevated stomatal conductance and transpiration, contrasting with OK392 with lower values. ‘MidSouth’ showcased high chlorophyll fluorescence, whereas ‘Ambulo Blanc’ consistently displayed lower levels. ‘Miss Blanc’ and OK392 exhibited high vapor pressure deficit, while ‘MidSouth’ showed low values. Further analysis unveiled several correlations: a strong positive correlation between stomatal conductance and transpiration (r=0.9, P
