Isolation and evaluation of Bacillus subtilis RSS-1 as a potential biocontrol agent against Sclerotinia sclerotiorum on oilseed rape

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most important diseases of oilseed rape in the world. Because of the absence of resistant varieties and the disadvantages of chemical control, application of antifungal microbes has become an eco-friendly and effective measure to control this disease. In this study, Bacillus subtilis strain RSS-1, isolated from soil samples, was identified based on morphological, physiological and biochemical tests, and DNA gyrase subunit A ( gyrA ), gyrB , DNA-directed RNA polymerase subunit beta ( rpoB ) and rpoC gene sequence analysis. It significantly inhibited mycelial growth and sclerotial production of S. sclerotiorum in vitro . In greenhouse experiments, all three tested concentrations (10 6 , 10 7 , 10 8 cfu mL −1 ) of cell fermentation broth and culture filtrate significantly reduced the severity of sclerotinia stem rot on oilseed rape ( P < 0.05). RSS-1 was more effective at reducing disease severity when applied 24 h before inoculation with S. sclerotiorum than at 24 h post inoculation, suggesting that RSS-1 should be applied as a prophylactic rather than a curative biological agent. Colonization tests indicated that the population density of RSS-1 on rapeseed leaves significantly decreased ( P < 0.05) over 6 days. However, RSS-1 could stably colonize in rhizospheric soil of rapeseed over 30 days. Challenge inoculation tests showed that RSS-1 significantly inhibited the activities of polygalacturonase and cellulase and accumulation of oxalic acid during the S. sclerotiorum infection. These results suggest that RSS-1 was a potential biological agent for controlling sclerotinia stem rot caused by S. sclerotiorum on oilseed rape.