Biological control of oilseed rape Sclerotinia stem rot by Bacillus subtilis strain Em7

In the present study, the endophytic bacterium Bacillus subtilis strain Em7 (GU258545.1) was evaluated as a biological control agent for Sclerotinia sclerotiorum on oilseed rape. In petri dish, strain Em7 not only strongly inhibited pathogen mycelium growth but also germination of sclerotia at concentrations between 10(9) and 10(11) colony forming unit (CFU)ml(-1). Scanning electron microscopy and transmission electron microscopy studies revealed that in the presence of strain Em7, hyphae of S. sclerotiorum showed leakage and disintegration of hyphal cytoplasm. Furthermore, the strain Em7 showed a broad antifungal spectrum on mycelium growth of numerous important plant pathogenic fungi. Light microscopic observations revealed that strain Em7 caused morphological alterations including increased branching, swelling and collapse of cytoplasm. In the greenhouse, spray treatments of cell suspensions of strain Em7 (1x10(9) CFUml(-1)) reduced leaf and stem rot incidence and severity in the seedling and blossom stage. The control efficacy was higher when strain Em7 cell suspension was applied one day prior to inoculation of the pathogen than after inoculation. Three-year field trials showed that two applications of strain Em7 cell suspension at blossom stage significantly reduced disease incidence and severity by 50-70%. There was no significant difference in control efficacy among treatments with strain Em7 cell suspension and the fungicides containing carbendazim or tebuconazole (P = 0.05). Thus, our results strongly suggest that B. subtilis strain Em7 is a promising biological control agent for control of oilseed rape Sclerotinia stem rot.