Biocontrol activities of bacteria from cowdung against the rice sheath blight pathogen

To discover bacteria with potential biocontrol activity against the rice sheath blight (RSB) pathogen, Rhizoctonia solani, cowdung (CD) associated bacteria were screened for antifungal activity a dual-culture method. Five potential biocontrol bacteria were identified to species-level based on their colony morphology, physiology, biochemical characteristics, utilization of carbon sources, micromorphology and 16S rRNA sequences. The ability of two selected strains to inhibit RSB was evaluated in vivo and in vitro. The median effective concentration (EC50) of crude extract from Streptomyces cochorusii strain NF0919 (NF0919) culture filtrate was 1.3 μg ml−1, lower than the EC50 of Jinggangmycin (a commercial antifungal agent widely used in China). At a concentration of 25.0 μg ml−1, the crude extract completely inhibited mycelial growth of R. solani. The field biocontrol efficacy after spraying 7 days in 2013 and in 2014 was 78.4 and 98.1% with crude extract from NF0919 culture filtrate and 71.1 and 94.2% with fresh cells of Bacillus amyloliquefaciens strain SB177 (SB177). Results from the 2-year field experiment suggested that the crude extract from NF0919 culture filtrate or fresh cells of SB177 provided better disease control than other fungicides (Jinggangmycin and/or Kresoxim-methyl). S. cochorusii strain NF0919 and B. amyloliquefaciens strain SB177 have good potential for field application and commercial use against the RSB pathogen.