Effect of gibberellic acid application on berry yield and quality of grapevine cv. Cabernet Sauvignon

Nepal imports vast amounts of fresh and dried grapes every year and the trend is increasing. The massive gap in demand and production shows a great scope to expand the production of quality grapes. Gibberellic Acid (GA3), an important plant growth regulator, is used to cluster (bunch) loosening, thinning berries, and increasing berry sizes for better yield and quality of berries, however, the timing and stages of application are crucial. This study was carried out to assess the effect of GA3 doses and identify the suitable berry stage for its application in cv. Cabernet Sauvignon during 2023 and 2024 in a commercial vineyard at Patleban Vineyard and Winery, Dhading, Nepal. Experiments were carried out in randomized complete block design with two factors i.e., three doses of GA3 (0, 5 and 10 ppm) and three stages of application (post-flowering, 4-5 mm size berry and both post-flowering and 4-5 mm berry stage). The applied GA3 doses along with different stages of its application had no significant effect on the yield and quality attributes of berry. In 2023 and 2024, berry transversal and longitudinal diameters partially influenced berry weight variation. On average, the transversal diameter accounted for 30.56% of the variation, while the longitudinal diameter explained 24.33%. Sizing spray (i.e. post-set berry) of GA₃ after berry set is ineffective for improving yield in Cabernet Sauvignon. However, due to variability among grape cultivars, its application may benefit other wine grapes. Further, cultivar-specific research is recommended to optimize GA₃ use.