Maximum stomatal conductance rather than stomatal sensitivity to drought differentiates the PIWI grapevine cultivar Souvignier gris from Muscaris and Donauriesling

Pioneering grapevines also referred to as “PIWIs” (after the German expression “pilzwiderstandsfähig” = fungus resistant), represent an interesting alternative to classic cultivars in several wine regions. Their resistance to some fungal diseases places them among the potential solutions for sustainability, especially under organic production systems. However, little is known about their response to abiotic stressors, such as water stress under drought conditions. Here we studied the response of three PIWI cultivars (Donauriesling, Muscaris, Souvignier gris, and Riesling or Grüner Veltliner Vitis vinifera cultivars as comparison; all plants without fruit) to drought under semi-controlled conditions over two consecutive seasons. While in season 2020, we imposed a single dry-down and re-watering cycle inside a glasshouse, during season 2021, we subjected the vines to three cycles of dehydration and re-watering under field conditions with the aid of a rain shelter. Along the experiments, we monitored leaf gas exchange and water potential during soil dehydration and characterised leaf area development and some key leaf hydraulic traits. Despite different conditions in our two study seasons, we found connective significances in some key parameters. Under well-watered conditions, Souvignier gris had the highest rates of stomatal conductance, whereas Muscaris exhibited the most conservative water use behaviour. When under drought, Souvignier gris showed an apparent less tight stomatal control than the other PIWIs in coordination with a lower (more negative) osmotic potential and turgor loss point. Our results suggest that Muscaris (and Donauriesling showed similar behaviour) might be more suitable for non-irrigated conditions than Souvignier gris. However, further research on berry composition and open field is needed to upscale our results and address the water management of PIWI vineyards.