Irrigation during ripening may reduce sunburn damages on berries of Vitis vinifera L. 'Sangiovese'

In the Mediterranean wine-growing areas, high temperatures often hasten sugar accumulation causing, in black berry varieties, the decoupling between technological and phenolic maturity. Moreover, heat waves, occurring more frequently in the last decades, may cause severe sunburn damages on clusters with serious consequences on yield. Considering these issues, the approach to vineyard management has recently been reconsidered and also irrigation may be applied in an innovative way. The present study aimed to investigate the effects of irrigation during ripening on sunburn berry incidence and yield, and grape composition at harvest. The trial was conducted in 2021 on adult vines of Vitis vinifera L. ‘Sangiovese’, trained to vertical shoot positioned (VSP) spur-pruned cordon. Treatments were laid out in a strip-plot design and the main factors were irrigation and cluster exposure. Irrigation treatments were: a) irrigation from the beginning of veraison to harvest to maintain vines well-watered; b) no irrigation. Cluster exposure treatments were: c) removal of main and lateral leaves from the eight basal nodes of each shoot at the beginning of veraison; d) no leaf removal. From veraison to harvest, berry temperature was continuously measured with thermocouples inserted under berry skin, while the incidence and severity of sunburn damages were recorded weekly on all the cluster of the tagged plant. Midday stem water potential was also measured from the end of July to late August. At harvest, yield parameters were measured and grape composition analyzed, while frozen berries were used for anthocyanin analysis with HPLC. As expected, leaf removal caused berry necrosis and berry shrivel due to the increase of berry temperature, but irrigation halved the severity of those sunburn damages. Sugar and anthocyanin concentrations were slightly affected by leaf removal but decreased significantly with irrigation. This study documented an interesting approach to tackle sunburn damages and to slow down sugar accumulation, which still needs to be modulated to avoid detrimental effects on anthocyanin accumulation.