Studying heat waves effects on berry composition: first outlooks and challenges

Abstract

Extreme climatic events, such as prolonged drought followed by intense flooding, increasingly impact viticulture, affecting vine physiology, productivity, and grape composition. This study examines the effects of long-term late-season flooding on two Vitis vinifera L. cultivars, Montepulciano and Sangiovese, grafted onto 1103 Paulsen rootstock. The experiment was conducted in the summer 2024 at the University of Perugia (central Italy), where six potted vines (60 L), three per cultivar, were submerged in 1000 L of tap water within a controlled flooding system. Plants underwent two treatments: flooded and non-flooded (control) from July 1st (day 0) to July 31st, followed by a one-week recovery. Gas exchange parameters were measured using an ADC-LCA3 system on days 1, 4, 7, 14, 21, 28 (flooding), 35, and 42 (recovery), while leaf water potential was assessed on days 11 and 22. Basic ripening parameters were analyzed, and sugar and starch content quantified in roots, shoots, and leaves immediately after flood removal. Leaf and root samples were collected during flooding and recovery to assess reactive oxygen species (ROS) and carotenoid content as stress indicators and to determine whether intracellular root fermentations occurred due to severe oxygen deprivation. Additionally, an epigenomic approach identified differentially methylated genes (DMGs) potentially linked to flooding stress. Flooding significantly impacted photosynthetic performance from day 15, causing a fivefold decrease in Montepulciano and a threefold decrease in Sangiovese after 20 days. However, Montepulciano recovered more efficiently, whereas Sangiovese did not, suggesting greater sensitivity to prolonged soil saturation. Interestingly, transpiration rates remained unchanged in both cultivars. Regarding phenology and ripening, veraison occurred 17 days earlier in Montepulciano and 15 days earlier in Sangiovese. Montepulciano grapes showed lower soluble solids and pH, along with higher titratable acidity, likely indicating incomplete ripening due to prolonged root hypoxia. These findings underscore the importance of cultivar-specific responses in selecting grapevines for climate-resilient viticulture. Further analyses are ongoing to deepen our understanding of biochemical, genetic, and physiological adaptations to submersion and assess intracellular root fermentations under severe hypoxia.