Effect of delayed winter pruning of Portugieser grapevine on grape primary and phenolic composition

Elevated temperatures in spring and summer often advance flowering, veraison and harvest, resulting in grapes with higher sugar content, lower acidity and poor color development. Late winter pruning is an effective tool to delay fruit ripening and improve the chemical composition of grapes. A one- year study (2021) was carried out on the Portugieser grape variety grown in a vineyard in north-western Croatia, to study the effects of late winter pruning on berry primary and phenolic composition. Late winter pruning was performed at the time of basal budburst and when 2 to 3 leaves were separated, while winter pruning was a control treatment. Samples of grapes obtained in all three treatments were harvested at the same time. The treatments with late winter pruning reduced the sugar content of the grapes. Late winter pruning performed at budburst resulted in grapes with the highest total phenolic and anthocyanin content and the lowest flavonol content at harvest, while late winter pruning performed when 2 to 3 leaves were separated had the highest titratable acidity and the lowest total phenolic content. This study suggests that the method has rather positive effects on grape quality compared to standard winter pruning.