Uncovering the effects of kaolin on balancing berry phytohormones and quality attributes of Vitis vinifera grown in warm-temperate climate regions.

BACKGROUND The application of kaolin particle-film is considered a short-term strategy against several environmental stresses in areas with a Mediterranean-like climate. However, it is known that temperature fluctuations and water availability over the season can jeopardise kaolin efficiency in many Mediterranean crops. Hence, this study aims to evaluate the effects of kaolin foliar application on berry phytohormones, antioxidant defence and oenological parameters at veraison and harvest stages of Touriga-Franca (TF) and Touriga-Nacional (TN) grapevines in two growing seasons (2017 and 2018). The 2017 growing season was considered the driest (-147.1 DI) and the warmest (2705°C GDD) of the study. RESULTS In 2017, TF kaolin-treated berries showed lower salicylic acid (SA) (-26.6% compared with unsprayed vines) and abscisic acid (ABA) (-10.5%) accumulation at veraison, while SA increased up to 28.8% at harvest. In a less hot season, TN and TF kaolin-treated grapevines showed a 2-fold and 3-fold increase in the ABA and indole-3-acetic-acid (IAA) content at veraison, respectively, and lower ABA levels (83.8%) compared with unsprayed vines at harvest. Treated berries showed decreased sugar content without compromising malic and tartaric acid levels, as well as reactive oxygen species (ROS) accumulation throughout berry ripening. CONCLUSION The results suggest kaolin exerts a delaying effect in triggering ripening-related processes under severe summer stress conditions. Treated berries responded with improved antioxidant defence and phytohormone balance, showing significant interactions between kaolin treatment, variety and developmental stage in both assessed years. This article is protected by copyright. All rights reserved.