Role of Brassinosteroids in Berry Quality: A Case of Three Table Grape Cultivars

The use of environmentally friendly methods to improve fruit quality and enhance their positive effects on human health has become one of the most important goals of modern fruit production systems. Brassinosteroids (BRs) belong to the sixth group of plant hormones and are used as plant growth regulators in many plant species and cultivars in plant production. This study aimed to determine the effect of applications of BRs on the physicochemical properties of three table grape cultivars (Italia, Michele Palieri, and Royal). The BRs were applied to the grape cultivars in three doses [0, 0.4, and 0.8 mg·L −1 24-epibrassinolide (24-eBL)] during the veraison period and 1 week after the veraison period. The period between treatments and harvest was 45 days for all cultivars. Harvested grapes were analyzed for various parameters, including cluster weight, cluster width, cluster length, 100 berry weight, berry width, berry length, firmness, total soluble solids content (TSS), total acidity, total phenolics, total antioxidant capacity, tartaric acid, citric acid, and malic acid contents. The grape cultivars displayed varying responses to 24-eBL applications. The 0.4 mg·L −1 24-eBL treatment increased the total phenolic content of ‘Italia’ and ‘Michele Palieri’ and tartaric acid and malic acid contents in ‘Italia’. The 0.8 mg·L −1 24-eBL application positively affected berry firmness of ‘Italia’; cluster weight, berry length, tartaric acid, and malic acid of ‘Royal’; and total phenolic content, total antioxidant capacity, tartaric acid, and malic acid of ‘Michele Palieri’. The results of the study showed that BRs applications have the potential to improve the quality of table grapes, but the appropriate dose and phenological period of the cultivars are important factors that ensure its effectiveness.