Salicylic acid treatment reduces the rot of postharvest citrus fruit by inducing the accumulation of H2O2, primary metabolites and lipophilic polymethoxylated flavones

To comprehensively analyze the effects of salicylic acid (SA) on the storability of Satsuma mandarin (Citrus unshiu), fruits were treated with 2 mM SA. The disease incidence of control/SA-treated fruit at 50 d and 120 d after treatment was 23.3%/10% and 67.3%/23.3%, respectively, suggesting that SA treatment can significantly reduce the rot rate of postharvest citrus fruit. Fruit quality assays revealed that the treatment can maintain fruit firmness without affecting the inner quality. Furthermore, the contents of H2O2 and some defense-related metabolites, such as ornithine and threonine, in citrus pericarp, were significantly increased by SA treatment. Moreover, it was lipophilic polymethoxylated flavones, rather than flavanone glycosides, that accumulated in SA-treated fruits and these can directly inhibit pathogen development. These results suggest that the effects of SA on postharvest citrus fruit may be attributed to the accumulation of H2O2 and defense-related metabolites.