High Altitude Solar UV-B and Abscisic Acid Sprays Increase Grape Berry Antioxidant Capacity

Abstract

It has been proposed that ultraviolet-B (UV-B) radiation activates grapevines antioxidant defense system and abscisic acid (ABA) acts downstream in the signaling pathway. Effects of solar UV-B perceived by high altitude vineyards and ABA sprays on berry quality indicators and fruit yield were studied on Vitis vinifera L. cv. Malbec at 5 developmental stages during three consecutive growing seasons. Grapevines were exposed to elevated ambient solar UV-B (+UV-B) or to UV-B filtered sunlight ( UV-B) from 15 days before flowering, combined with weekly sprays of 1 mM ABA (+ABA) or H₂O (−ABA) from 27 days before veraison. Berry skin phenols (anthocyanins and total polyphenols) were increased by +UV-B and +ABA, markedly in concentration (UV-B x ABA significant interaction). The increases in antioxidant capacity, measured as oxygen antioxidant capacity (ORAC) and phenols in the berries exposed to +UV-B/+ABA combined treatment were higher compared with UV-B/ ABA, for the same increase in sugar. Also, +UV-B and +ABA interact to lessen the number of berries, possibly due to higher ethylene emissions, and additively reduce clusters weight, without affecting sugar concentration (smaller berries) at harvest. Antioxidant compounds (protective for plants) are triggered in +UV-B/+ABA at the expenses of sugar accumulation, berry retention and growth (fruit yield). UV-B and ABA effects on berry sugar accumulation and growth depend on the stage of development. UV-B perceived by high altitude vineyards and ABA applications interact to increase red grape berry quality indicators, markedly in concentration (important from a winemaking standpoint), while per berry basis their effects are additives.