Effects of exogenous 24-epibrassinolide treatment on postharvest quality and resistance of Satsuma mandarin (Citrus unshiu)

• Satsuma mandarin fruit were treated with 24-epibrassinolide and stored at 12–16 °C.
• The treatment significantly reduced postharvest rots by more than 78%.
• The treatment induced a rapid weight loss during the first 6 days after treatment.
• The treatment induced the accumulation and expression of some stress-related metabolites and genes.

To elucidate the effects of exogenous brassinosteroids (BRs) treatment on the postharvest behavior of citrus fruit, Satsuma mandarin (Citrus unshiu) fruit were treated with 5 mg L−1 24-epibrassinolide (EBR) and stored at 12–16 °C with a relative humidity of 90–95%. After 50 d treatment, the disease incidence of the control and EBR-treated fruit was 18.7% and 4%, respectively, suggesting that EBR treatment can significantly enhance the postharvest biotic stress tolerance of Satsuma mandarins. Moreover, the fruit quality analysis revealed that EBR treatment induced a rapid weight loss during the first 6 d after treatment, which was similar to the effect of a conditioning treatment, while it exhibited no negative effects on inner quality. Further, we measured the contents of hydrogen peroxide (H2O2) and the primary metabolites as well as the expression of the stress-related genes in the fruit pericarp. The results indicated that H2O2 content was significantly increased by EBR treatment. In addition, analyses on the primary metabolites showed that some stress-related metabolites, such as ornithine, proline, GABA, d-xylose and d-galactose, were increased in the EBR-treated fruit. Expression of the stress-related genes was markedly up-regulated in EBR-treated fruit. These results suggest that the effects of EBR on reducing the postharvest disease incidence of citrus fruit may be associated with the accumulation of H2O2 and stress-related metabolites and the induction of stress-related genes.