Effects of Late Pruning and Elevated Temperature on Phenology, Yield Components, and Berry Traits in Shiraz

Abstract

Recent warming has shortened and compressed vintages and has altered enologically relevant berry traits. Late pruning can decompress harvest and preserve fruit quality. Here, we were interested in exploring the interactive effects of late pruning and heating on Shiraz development and composition. We established a factorial experiment that combined two thermal regimes (ambient versus heated) with open-top chambers, and three pruning times (late pruning at budbreak and at two to three leaves, a winter control) in Shiraz vines over three seasons in the Barossa Valley. Late pruning delayed budbreak by up to 23 days, flowering by up to 17 days, and veraison by up to 16 days. Heating advanced flowering in late-pruned vines by up to seven days, with a minor effect in winter-pruned controls. Heating advanced veraison by up to seven days, with greater advances in years with warmer springs. Pruning weights were unaffected by late pruning and were increased by heating. Yield was increased in a single season by late pruning and heating, but it remained unchanged for the pooled three-year data. Late pruning delayed maturity in four of six cases; the largest delay was 17 days in unheated vines pruned when two to three leaves had emerged. Late pruning maintained the anthocyanin-to-sugar ratio, which decreased with heating in two seasons. There was an interaction between the timing of pruning and heating, whereby late pruning enhanced the berry tannin-to-sugar ratio in heated but not in unheated control vines. Late pruning delayed the harvest by shifting the onset and rate of ripening, with a higher degree of response in the warmest season in both ambient and heated treatments.