Context and purpose of the study ‐ Grapevines are an important economic crop grown in temperate climates of both hemispheres characterized by short‐term heat spells and heat waves due to the distinct th st seasonality. However, these events have worsened during the late 20 and early 21 centuries due to accelerated climate change and is expected to exacerbate with even more intensity and frequency in the foreseeable future. This unprecedented speed in climate change has spawned major scientific and viticultural challenges as grape berries particularly exhibit high sensitivities to heat waves during ripening, the key phenophase determining fruit quality, time of harvest, and eventually the economic viability of wine industry. Given that the projections of worsening heat wave events are an immediate concern to the high socio‐economic value of grapes, it is imperative that heat stress be curbed to ensure sustainability of grape production in a challenging environment. Therefore, the objective of this study was to mitigate the impact of heat waves by understanding the response of different grapevine cultivars to heat stress and various protective measures.
Material and methods – The experiment was conducted with field‐grown own‐rooted red and white cultivars. Individual clusters of these cultivars were enclosed using white paper bags and cheese cloth before veraison. Close to harvest, enclosed clusters as well as clusters that developed under ambient growing conditions (heat waves) were sampled and analyzed for primary and secondary metabolites.
Results – The berries of exposed clusters developed typical symptoms of sunburn, which included loss of crystalline structure of epicuticular wax resulting in a shiny surface. Such morphology was due to degradation and transitioning of wax platelets into amorphous masses creating a rough surface with poor development of color. However, the quercetin levels were higher than the enclosed clusters. The juice composition entailing Brix, pH, titratable acidity, content of malic and tartaric acids, sugars, and the levels of predominant mineral nutrient potassium, were compromised in sunburned berries. Furthermore, the response of various secondary metabolites such as tannins, polymeric anthocyanins, methoxypyrazines, guaiacal, and 4‐methylguaiacal varied among exposed (sunburn) and enclosed (protected by bags and cheese cloth) berries. Overall, the enclosed clusters developed with better fruit quality attributes suggesting that cluster enclosure could be an effective strategy to mitigate the ill effects of heat waves.
Author: Bhaskar BONDADA
Washington State University, Richland, WA 99354, USA
Keywords: Climate change, Heat wave, Phenolics, Sugars, Sunburn