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 the antioxidant defense system in grapevines and that abscisic acid (ABA) acts downstream in the signaling pathway. Here, we studied the effects of solar UV-B and ABA sprays on berry quality indicators and fruit yield in Vitis vinifera L. cv. Malbec grown in a high-altitude vineyard, for five developmental stages and three 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 water (−ABA) from 27 days before veraison. The concentration of phenols (anthocyanins and total polyphenols) in berry skin was increased by +UV-B and +ABA, and there was a significant interaction between UV-B and ABA. For a given increase in sugar content, antioxidant capacity and phenolic contents were higher in berries in the +UV-B/+ABA treatment than in berries in the −UV-B/−ABA treatment. +UV-B and +ABA interacted to lessen the number of berries, possibly because of higher ethylene emissions, and additively reduced cluster weight without affecting sugar concentration at harvest. Antioxidant compounds, which are protective for plants, were triggered by +UV-B/+ABA at the expense of sugar accumulation, berry retention, and growth (fruit yield). Effects of UV-B and ABA on sugar accumulation and berry growth were dependent on the developmental stage. In high-altitude vineyards, solar UV-B and ABA application interact to increase quality indicators in red grape berries. The effects of UV-B and ABA on berry quality indicators are significant on a concentration basis (important from a winemaking standpoint) and additive on a per-berry basis.