Aroma precursors in ‘Grillo’ grape (Vitis vinifera L.): exploit the impact of irrigation regimes

Water stress, applied through regulated deficit irrigation (RDI), is a commonly employed practice to enhance the concentration of secondary metabolites in grapes. However, the impact of RDI on grape aromas has been poorly explored, and metabolic responses to water stress can vary significantly among different cultivars. In the context of warm climate conditions, such as in Sicily, the influence of irrigation strategy on the synthesis of aromatic precursors in the grapes of ‘Grillo’ (Vitis vinifera L.) was investigated in 2022 vintage. Two irrigation regimes were compared: 1) moderate water stress (MWS), maintaining Stem Water Potential (ΨSWP) values > -1.4 MPa and < -1.1 MPa from veraison to harvest; 2) severe water stress (SWS), maintaining stem water potential (ΨSWP) values < -1.4 MPa and > -1.8 MPa from veraison to harvest. Berry sampling was performed at 5% of veraison, full veraison, and at harvest to evaluate the synthesis of aromatic precursors. For each treatment, from veraison to harvest, vegetative growth, bunch and berry weight, ripeness level (total soluble solids, pH, titratable acidity), and the precursors of terpens, norisoprenoids, and thiols were assessed. At harvest, yield per vine was measured while wood weight was measured during pruning time. Although SWS at full veraison showed higher concentrations for most of the aromatic compounds analyzed, the prolonged severe stress conditions triggered degradation processes, resulting in lower levels compared to MWS treatment at harvest. The applied stress conditions had limited effects on primary metabolites and berry weight, indicating that the observed variations of aroma precursors were effectively dependent to the water stress conditions applied. These results suggest that regulated deficit irrigation applied from veraison to harvest with different strategies may improve the aromatic profile of grapes, having a relevant impact in the context of climate change.