Effects of delayed winter pruning on vine performance and grape composition in cv. Merlot

Abstract

Delaying winter pruning until after budburst is a technique that can retard vine phenological phases and reduce grape sugar concentration at harvest. Given these characteristics, many studies have recently been conducted to verify the ability of pruning after budburst to contrast the negative effects of climate change. In our trial, vines of the cv. Merlot, trained to a VSP spur pruned cordon, were pre-pruned leaving 8 nodes per shoot and hand finished when the shoots sprouted by the apical nodes were at BBCH13 (treatment LP) and BBCH18 stage (treatment VLP). Vines refinished during winter were used as control (WP). Anthocyanins and tannins of skin and seeds were analysed after both exhaustive extraction (total content) and extraction conducted with a hydroalcoholic solution (extractable portion). Vines refinished after budburst showed reduced leaf area, yield, cluster and berry weights; technological maturity of these vines was delayed as lower sugar concentration and pH were observed at harvest. Treatment VLP had a stronger effect than LP on these parameters. Considering phenolic compounds, the skin and seed tannin concentration increased only in VLP, while no effect was found on anthocyanins. In conclusion, delaying pruning until after budburst revealed interesting prospects for contrasting the negative effects of climate change.