Optimization of Fermentation Conditions of Lentinula edodes (Berk.) Pegler (Shiitake Mushroom) Mycelia as a Potential Biopesticide

The shiitake mushroom [Lentinula edodes (Berk.) Pegler], is a new source of biopesticide against bacterial spot of tomato having similar efficacy as that of traditional antibiotics in vitro. The culture-filtrates of fifteen commercially available L. edodes strains were screened for antibacterial activity against Erwinia amylovora (Ea) and Xanthomonas campestris pv. vesicatoria (Xcv), based on fermentation time and carbon source for minimum oxalic acid production. Two different carbon sources, glucose and sucrose for fifteen and 30 days were used for fermentation. The detection and quantification of oxalic acid in culture filtrates were performed by using HPLC. Most of the L. edodes strains inhibited the growth of Ea (13 out of 15) and Xcv (14 out of 15) with similar efficacy as that of the control treatment of 100 µg mL–1 streptomycin sulfate. Two of the L. edodes strains, ATCC 38164 and ATCC 28760 released the least amount of oxalic acid in both carbon sources, but did not differ from each other significantly. The concentration of oxalic acid in glucose medium was generally lower than that in sucrose medium, while strains ATCC 20635 and ATCC 38167 released the highest and similar concentrations in both carbon sources. This study provides preliminary evidence that L. edodes strains may be potential alternatives to streptomycin and copper compounds as a source of metabolites against bacterial spot of tomato and fire blight of apple [Malus × domestica (Borkh.)] and merits further investigation.