Biocontrol of green and blue molds in postharvest satsuma mandarin using Bacillus amyloliquefaciens JBC36

Abstract

In order to control postharvest rot of satsuma mandarin (mandarin) fruits, a new strain of Bacillus amyloliquefaciens JBC36 (JBC36) was isolated from rhizosphere of a mandarin orchard and tested for its suppression of decay due to green and blue molds caused by Penicillium digitatum and Penicillium italicum, respectively, and its mode of action was investigated. In addition, carnauba wax-based and paraffin oil-based coating formulations were developed to increase the control efficacy of the antagonist. The strain JBC36 at 108 CFU mL−1 inhibited incidence of green and blue molds on wounded mandarin fruits with control efficacies of 88 and 80.2%, respectively. Mycelial growth and spore germination of P. digitatum and P. italicum were strongly inhibited in the presence of JBC36 or antagonistic metabolites. In order to determine antifungal activity, three kinds of antibiotics were isolated by reverse-phase high performance liquid chromatography (RP-HPLC) and identified as lipopeptide families, iturin A, fengycin and surfactin by RP-HPLC and thin-layer chromatography (TLC) analysis. Fengycin was further identified as C16 fengycin A by liquid chromatography/electrospray ionisation-mass spectrometry (LC/ESI-MS) and mass spectrometry/mass spectrometry (MS/MS) analysis. Volatile organic compounds from the antagonist also reduced the mycelial growth of P. digitatum and P. italicum. Carnauba wax-based and paraffin oil-based coating formulations containing 108 CFU mL−1 of JBC36 efficiently decreased the incidence of green mold with control efficacy of 91 and 80.9%, respectively. Overall, the antagonistic rhizobacterium JBC36 is a promising biocontrol agent for use in preventing postharvest spoilage of mandarin fruits by green and blue molds.