Streptomyces rochei A-1 induces resistance and defense-related responses against Botryosphaeria dothidea in apple fruit during storage

• S. rochei A-1 induced resistance against B. dothidea in apple fruit.
• A-1 increased activities of POD, CAT, SOD, PAL, β-1,3-glucanase and chitinase.
• S. rochei A-1 promoted H2O2 generation, decreased lipid peroxidation in apple fruit.
• S. rochei A-1 markedly up-regulated the expression of three defense-related genes.

Apple ring rot caused by Botryosphaeria dothidea is an important disease in most apple-growing regions in China. It results in severe losses during fruit storage. Induced resistance against plant pathogens is a promising alternative to traditional control strategies. In the present study, a potential biocontrol agent, Streptomyces rochei A-1, was evaluated for its induction of resistance against B. dothidea in postharvest apple fruit, and the defense mechanisms involved were investigated. The results indicated that S. rochei A-1 treatment could effectively induce the resistance of apple fruit to ring rot caused by B. dothidea. The lesion area and disease incidence were 65.4% and 27.1% lower than those of the control fruit after storage at 25 °C for 7 d. S. rochei A-1 treatment significantly increased the activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) and phenylalanine ammonia-lyase (PAL) and highly inhibited lipid peroxidation. β-1,3-glucanase and chitinase activities and H2O2 generation were also markedly promoted by the biocontrol agent. Moreover, the expression levels of three pathogenesis-related proteins genes (PR-8, GLU and CHI) were enhanced. The most significant increase was observed in apple fruit pretreated with S. rochei A-1 and inoculated with B. dothidea. Therefore, our results suggest that S. rochei A-1 treatment induces resistance against B. dothidea in apple fruit by stimulating a series of defense responses.