The Impact of Plant Growth Regulators and Floral Cluster Thinning on the Fruit Quality of ‘Shine Muscat’ Grape

Plant growth regulators (PGRs) and floral cluster thinning are commonly used to improve grape yield and quality, but their effects on different fruit quality attributes in the ‘Shine Muscat’ are not well understood. In this study, we investigated the impact of PGRs and floral cluster thinning on various fruit quality parameters such as the cluster weight, berry weight, diameter, shape, sugar and acid content, firmness, and residual feel of peel. Our results indicate that the gibberellic acid 3 (GA3) 25 mg/L + thidiazuron (TDZ) 5 mg/L treatment at full bloom and GA3 25 mg/L treatment at 12 days after full bloom showed the largest cluster weight, berry weight, and diameter, while the forchlorfenuron (CPPU)-treated group, with a more balanced effect on fruit skin and flesh firmness, had the highest proportion of a positive residual feel of the peel. Floral cluster thinning by 4 cm was found to be effective for promoting fruit growth and maintaining an appropriate sugar–acid ratio, while thinning by 5 cm resulted in a higher number of berries but smaller berry size and lower sugar–acid ratio. These findings can be useful for grape growers and researchers in optimizing PGR and floral cluster thinning treatments to improve grape yield and quality.