Effects of late winter pruning at different phenological stages on vine yield components and berry composition in la Rioja, north-central Spain

Abstract

[Aims] Under global warming, the desynchrony between technological maturity and phenolic maturity of wine grapes is a worthy concern. Late winter pruning (LWP) has proven to be an effective way to delay grape phenology. The aim of this study was to evaluate the effects of LWP at different phenological stages (based on the Baillod & Baggiolini system) on grape ripening delay, vine yield components, berry composition, and anthocyanin to sugar ratio. [Methods and results] The two-year (2015 and 2016) trial was conducted in the Rioja wine region (north of Spain) on Maturana vines and in each year, four pruning treatments were carried out taking apical buds/shoots as reference: (1) winter pruning at stage A (WPA; dormant bud); (2) LWP at stage C (LWPC; green shoot tip) in 2015 and at stage F (LWPF; inflorescence clearly visible) in 2016; (3) LWP at stage G (LWPG; inflorescences separated); and (4) LWP at stage H (LWPH; flowers separated). LWPC failed to delay the late phenological stages and did not exert an important influence on vine yield and berry composition. LWPG and LWPH succeeded to delay all the phenological stages of grapes, shifting development to a considerably cooler and longer ripening period compared to WPA. Vine yield was not affected by LWPF and was significantly reduced (by 41% on average) by LWPG. LWPH led to greater losses in yield (by 67% on average), especially in 2015. LWPG did not change the fruit composition, while LWPH increased the anthocyanin to sugar ratio and helped to maintain a relatively high level of acidity in berries. [Conclusions] The primary cause of the decline in yield seems to be the reduced berry number per cluster, most likely associated with a loss of flowers and/or a reduction in fruit set percentage in the current season, than losses in inflorescences within buds during the previous season. For Maturana grapes, LWP after stage F could reduce vine yield and be applied as an alternative to the time consuming cluster thinning to meet the needs of yield control. Delaying winter pruning to stage H could improve fruit quality, though the risk of botrytis and yield loss would be greater. [Significance and impact of the study] The outcomes of this research open a door for winegrowers to perform yield control in an alternative way. For those who aim for top quality wines (regardless of yield), a very late winter pruning might provide grapes with more desirable attributes. Moreover, winegrowers could postpone the budburst date to some extent, thus reducing the risk of spring frost injury to zero, though this point is not the focus of our study.