Investigating the efficacy of Bacillus subtilis SM21 on controlling Rhizopus rot in peach fruit

• Bacillus subtilis SM21 effectively inhibited Rhizopus rot caused by R. stolonifer in peaches.
• B. subtilis SM21 treatment markedly up-regulated the expression of seven defense related genes.
• B. subtilis SM21 showed strong antifungal activities against growth of R. stolonifer.

The efficacy of Bacillus subtilis SM21 on controlling Rhizopus rot caused by Rhizopus stolonifer in postharvest peach fruit and the possible mechanisms were investigated. The results indicated B. subtilis SM21 treatment reduced lesion diameter and disease incidence by 37.2% and 26.7% on the 2nd day of inoculation compared with the control. The in vitro test showed significant inhibitory effect of B. subtilis SM21 on mycelial growth of R. stolonifer with an inhibition rate of 48.9%. B. subtilis SM21 treatment significantly enhanced activities of chitinase and β-1,3-glucanase, and promoted accumulation of H2O2. Total phenolic content and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity were also increased by this treatment. Transcription of seven defense related genes was much stronger in fruit treated with B. subtilis SM21 or those both treated with B. subtilis SM21 and inoculated with R. stolonifer compared with fruit inoculated with R. stolonifer alone. These results suggest that B. subtilis SM21 can effectively inhibit Rhizopus rot caused by R. stolonifer in postharvest peach fruit, possibly by directly inhibiting growth of the pathogen, and indirectly inducing disease resistance in the fruit.