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Grapevine interspecific hybrids (PIWIs) represent an interesting alternative to classic cultivars in several wine regions, especially under sustainable and organic production systems. While such gentopyes are well characterised for some agronomic aspects and mainly because their response to biotic stressors such as powdery and downey mildews, little is known about their response to abiotic stressors such as drought. Here we studied the response of three different commercial PIWI genotypes (Donauriesling, Muscaris, and Souvignier gris, all grafted on rootstock Kober 5BB) to drought by monitoring their leaf gas exchange and water potential during dehydration in two seasons (2020 and 2021). We quantified the leaf area development and some leaf hydraulic traits to understand how they relate to the drought response in a pot experiment under controlled conditions. The results showed slight differences between genotypes only during the first days of dehydration, where Souvignier gris exhibited a less tight stomatal control as compared with the other PIWIs and in coordination with a lower (more negative) osmotic potential and turgor loss point. However, after five days under drought, all genotypes exhibited similar stomatal behaviour (gs<0.05 mol m-2 s-1). Our study shows that PIWIs behave and operate within similar ranges of stomatal conductance and water potentials as compared with other V. vinifera cultivars used in this study (Grüner Veltliner and Riesling). Acclimation to long-term water deficit and impacts on fruit composition is needed to better understand PIWIs ability to grow under limited water scenarios. [ABSTRACT FROM AUTHOR]

• Cluster thinning and selective berry thinning significantly increased the accumulation of soluble solids in grapes. • Anthocyanin concentration was increased by both thinning treatments, and a shift in the profile was observed. • As compared to the control, only selective berry thinning promoted a significant reduction of the skin proanthocyanidins. • Both treatments resulted in a reduction of the proanthocyanidins galloylation in skins, but only berry thinning reduced the skin prodelphinidines. 'Refosco dal peduncolo rosso' is a late-ripening and low-yielding red grape variety, mainly cultivated in Northeastern Italy (Veneto and Friuli Venezia Giulia), and characterized by relatively high anthocyanins and average-to-low tannins concentrations. Under Friuli's climatic conditions, it is often challenging to maintain the Refosco dal peduncolo rosso grapes hanging on the vines long enough to match complete berry maturation before the rain season starts. Therefore, winegrowers normally perform cluster thinning in order to enhance or accelerate ripening. This study compared the effects of selective berry thinning (cluster shoulders and tips removal) and classical cluster thinning on fruit technological maturity, anthocyanin profile, and skin and seed proanthocyanidins concentration. Our results revealed that both thinning treatments induced a significant increase in total soluble solids, as well as total anthocyanins through the specific enhancement of OH- and di-substituted monoglucosylated anthocyanins. Additionally, skin high molecular weight proanthocyanidins was reduced by selective berry thinning, while mean degree of polymerization and percentage of galloylation were significantly decreased by both thinning treatments. These results showed that the yield reduction obtained by both methods were profitable to improve the maturation of Refosco dal peduncolo rosso grapes. However, the application of selective berry thinning provided a significant reduction of both skin high molecular weight proanthocyanidins and percentage of prodelphinidins. Therefore, the first evidences on grapes composition favored the cluster thinning technique as less time consuming, but more research on wine and sensory effects is needed to confirm the potential of selective berry thinning. [ABSTRACT FROM AUTHOR]