Effects of Lateral or Secondary Induced Shoot Use on Number of Bunches and Fruit Quality in Forcing Cultivation by Current Shoot Cutting and Flower Cluster Removal to Shift Grape Ripening to a Cooler Season

In grapes, the ripening time of bunches on lateral or secondary induced shoots, led by simultaneous treatments of current shoot cutting and flower cluster removal, is typically delayed until the cooler seasons. The aim of this study was to estimate the effects of lateral or secondary induced shoot use in the cultivation of ‘Merlot’ grapevine phenology, including number of bunches and weight, yield, and fruit quality. The timings of flowering, coloration and harvest of lateral and secondary induced shoot grapes were delayed by around one month compared with those of vines grown under standard cultivation, which were used as a control. However, there were substantial differences between treatments in terms of number of bunches and weight, yield, and fruit quality. When lateral shoots grew after the current shoot was cut and the flower clusters were removed, the number of bunches decreased, and yield was significantly reduced. In contrast, when the secondary induced shoot germinated after the current shoot, flower clusters, and growing lateral shoots were removed, a stable number of bunches was observed and there was not a severe decrease in yield. Skin anthocyanin content in both the lateral shoot and secondary induced shoot grape berries was increased compared with control. This effect was comparatively stronger in secondary induced shoot grapes subjected to comparatively lower air temperatures during ripening. The results of this study underscore the importance of discriminating between lateral and secondary induced shoots in the process of shifting grape ripening to a cooler season by removing current shoots and flower clusters.