Overhead spray water treatment as a mitigation strategy for reducing vine stress and preserving grape quality during heatwaves

Abstract

Changes in climate have been influencing the quality of wine grapes worldwide. The impact of extreme climate events over short periods is increasingly recognized as a serious risk to grape quality and yield quantity. In this study the mitigation effects of a pulsed water spray on vine canopy during heatwave events has been evaluated for maintaining vine condition during the growing season and grape quality. Vines of three varieties (Malbec, Bonarda, and Syrah) under drip irrigation in the UNCuyo experimental vineyard were treated with an overhead pulsed water spray. The spray was applied to the top of the vine canopy for 15 minutes per hour during 12 daylight hours over the course of heat waves occurring between veraison and harvest. Heatwaves were defined as days with a minimum temperature of no less than 21 ⁰C and a maximum temperature of no less than 34 ⁰C. Two heat waves were identified over the course of the growing season. Temperature was measured at the canopy level (CT) while a weather station provided multiple climate parameters of the vineyard (VT). Samples were collected at weekly intervals from veraison to harvest. During 5 sample dates Leaf and Stem Water Potential (LWP, SWP), Stomatal Conductance (SC), Leaf Temperature (LT), Berry Temperature (BT), Chlorophyll Content (CC), Fluorescence (FV/FM), and Performance Index (PI) were collected at several intervals during the day to evaluate physiological responses. Berries were collected at each sample date as well as at harvest. Berry weights, soluble solids content, and pH were measured. At harvest, anthocyanin profile, kg/plant, number of bunches and their average weight were also evaluated. LWP, SWP, FV/FM, PI, SC, CC, Kg/plant, and BW, were significantly higher while LT, BT, and CT were lower in treated vines as compared to the control during the second heatwave, which was longer and more intense than the first one. One week after the more severe heatwave, LWP, SWP and SC were still significantly different between treatment and control, displaying reduced physiological stress in the treated vines. No differences were identified in the sum of total anthocyanins. However, some individual anthocyanins were higher in treated vines. These results suggest that vines with the overhead water treatment during heat waves had reduced physiological stress and increased yield. As a consequence, this practice could be used as a mitigating tool to reduce the impact of heat waves.