Overhead spray water treatment as a mitigation strategy to alleviate vine stress and safeguard grape quality during heatwaves

Changes in climate are influencing the quality of wine grapes worldwide. The impact of extreme climate events over short periods is increasingly recognised as a serious risk to grape quality and yield quantity. In this study, the mitigation effects of a pulsed water spray treatment on vine canopy during heatwave (HW) events were evaluated in relation to vine condition during the growing season and grape quality. In the UNCuyo experimental vineyard, vines of the three cultivars Malbec (ML), Bonarda (BO) and Syrah (SY) were treated with an overhead pulsed water spray. Heatwaves were defined as days with a minimum temperature of 21 °C and a maximum temperature of 35 °C. Two heat waves were identified during the growing season. Samples were collected at weekly intervals from veraison to harvest. On five sample dates, Leaf and Stem Water Potential (LWP, SWP), Stomatal Conductance (gs), Leaf Temperature (LT), Berry Temperature (BT), Chlorophyll Content (CC), Fluorescence (Fv/Fm) and Performance Index (PI) were recorded at several time points during the day to evaluate the physiological responses of the vine. Berries were collected on each sample date and at harvest. Berry weight, soluble solid content and pH were recorded. In the treated vines (Trt), LWP, SWP, Fv/Fm, PI and gs were significantly higher and LT was lower than in the control vines (Ctl) during the second heatwave, which was longer and more intense than the first one. One week after the more severe heatwave, LWP, SWP and gs remained significantly higher in Trt than in Ctl, displaying reduced physiological stress in Trt. At harvest, the anthocyanin profile, total polyphenol index (TPI), fruit yield, number of bunches and their average weight, berry weight, soluble solid content and pH were also recorded. Bunch weight was significantly higher in Trt for all cultivars. No differences were found in total anthocyanin concentration. These findings indicate that the vines subjected to targeted overhead water treatment during heatwaves underwent less physiological stress and yielded higher grape production, without increasing the risk of potential fungus diseases, in the Mendoza climate. Consequently, this practice could serve as a valuable strategy for mitigating the adverse effects of heatwaves.