Occurrence of Skin Browning according to Cluster Weight and the Gibberellic Acid (GA3) Concentration in ‘Shine Muscat’ Grapes

Abstract

This study aimed to investigate the occurrence of skin browning during the ripening period of ‘Shine Muscat’ grapes to determine the appropriate cluster weight and concentrations of gibberellic acid (GA3), a growth regulator for seedless cultivation, required to achieve optimal fruit production. In the first study year, the yield was adjusted to 2,400 kg per 10 a and the cluster weight was categorized at 500, 700, and 900 g. Weak skin browning and severe external damage were evident from 70 and 91 days after full bloom, respectively, with approximately 20% occurrence in all treatment groups until 105 days after full bloom. In the final investigation (112 days after full bloom), the 500 and 700 g cluster weight groups showed approximately 40% of serious skin browning, while the 900 g cluster weight group showed approximately 20%. The 900 g cluster weight group had a low occurrence of browning but poor fruit quality. Meanwhile, the 700 g cluster weight group had a high occurrence of physiological disorders such as fruit cracking and ripe rot. Therefore, when producing 2,400 kg per 10 a, harvesting approximately 105 days after full bloom with a cluster weight of 500 g would be optimal to obtain high-quality fruits. In the second study year, with a yield of 2,400 kg per 10 a and 500 g cluster weight as the standard, GA3 treatments of 0 (untreated control group), 12.5, 25, and 50 ppm were tested. Weak skin browning occurred from 64 days after full bloom, increasing rapidly in the untreated group. The highest external damage rate was observed in the untreated group, with 51.1% occurrence of skin browning at harvest. In contrast, there was no significant difference between the 12.5 and 50 ppm groups, with the lowest external damage rate in the 25 ppm group. Fruit quality was lowest in the untreated group. At harvest, fruit cracking and ripe rot increased in all groups. Hence, harvesting approximately 110 days after full bloom would be optimal. There were no significant differences among the GA3 treatment groups until 110 days after full bloom. Therefore, based on the two-year experimental results, when producing 2,400 kg per 10 a, the optimal conditions for producing high-quality fruit and reducing skin browning would be a cluster weight of 500 g and GA3 treatment of 25 ppm, with harvesting approximately 110 days after full bloom. © 2023 Korean Society for Horticultural Science.