Stem rot, caused by Sclerotinia sclerotiorum, is a serious disease of rapeseed worldwide. This paper tested
the inhibitory effect of an endophytic bacterial Bacillus subtilis strain, EDR4, on the sclerotial germination
and hyphal growth of S. sclerotiorum. The cell-free filtrate solution and cell suspension of strain EDR4
were sprayed on rapeseed leaves and stems one day before, at the same time and one day after inoculation
in the greenhouse experiments. There was no significant difference in inhibitory efficacy between
the cell-free filtrate solution and cell suspension. The best biocontrol efficacy was achieved by spraying
either the cell-free filtrate solution or cell suspension at the same time as inoculation. In the field trials,
the efficacy of two applications of EDR4 cell suspension at the initial flowering stage and full bloom stage
was the best, but there was no significant difference in efficacy between the one-application and twoapplication
treatments during the initial flowering stage. The efficacy decreased gradually with the
culture suspension dilutions. Scanning electron microscopy revealed that EDR4 cells significantly suppressed
the hyphal growth. The bacterial treatment caused shrink, cytoplasm leakage and irregular tip
swelling of fungal hyphae. The hyphal cells in the treated groups had higher numbers of vacuoles in
the cytoplasm than the non-treated hyphal cells. The hyphal cytoplasm was disintegrated; the hyphal
biomass was reduced; the formation of infection cushions was delayed; and the infection was suppressed
after spraying the bacterial culture on rapeseed leaves. The results showed that the EDR4 bacterial strain
could be used to control stem rot of rapeseed.