Screening Bacillus species as biological control agents of Gaeumannomyces graminis var. Tritici on wheat

Take-all is one of the most destructive root diseases of wheat, however, effective biological control agents (BCAs) for controlling the causal organism, Gaeumannomyces graminis var. tritici (Ggt), are currently unavailable. In this study, 155 putative Bacillus strains isolated from soil were tested as potential BCAs against Ggt. The most effective was strain YB-57, which was identified as B. subtilis using 16S rDNA, morphology and physiology. Strain YB-57 showed as high as 60.9% growth inhibition of Ggt and also exhibited significantly inhibitory activity against seven other fungal phytopathogens, indicating its broad-spectrum antagonism to fungi. Greenhouse studies showed that YB-57 lowered the incidence of the take-all disease by 56.5%, which was similar to that of the fungicide, silthiofam. The antimicrobial activity of crude extracts from strain YB-57 fermentation liquor was relatively stable under a range of temperature, pH and UV light exposures and was also resistant to protease K digestion. The extract was purified, and five types of lipopeptides, iturin isomers, surfactin isomers, plipastatin isomers, bacillomycin isomers and difficidin, were identified by HPLC/ESI-MS/MS. These results suggested that B. subtilis strain YB-57 could be a useful BCA for take-all management.