Abstract: The study aimed to clarify the antagonistic effect of strain gfj-4 on plant pathogens and its potential in biological control of plant diseases. The traditional morphology, physiological-biochemical properties as well as 16S rDNA gene sequence analysis were applied to the bacteria classification. The pathogen of maize sheath blight worked as the indicator, the fermentation supernatant with different dilution times, and the culture time, inoculation amount and pH value on the antifungal activity of Rhizoctonia solani were determined by mycelial growth rate method. The inhibition of lipopeptides extracted from fermentation supernatant on the other 16 plant pathogens were determined by oxford cup method. It showed that the strain gfj-4 was identified as Bacillus amyloliquefaciens. The fermentation supernatant of strain gfj-4 had significant inhibitory activity on the mycelial growth, and the inhibition rate was from 31.1% to 92.4% within the dilution factor expanded from 8 to 25 times. The EC₅₀ of fermentation supernatant to R. solani was 53.1 μL·mL^-1. The highest inhibition rate of 12-fold dilution of fermentation supernatant was 82.0% when incubation time was 96 h, and the inhibition rate to R. solani was 83.2% when the inoculation amount was 0.5% (V/V), the inhibitory rate reached 82.6% when the pH value was 7.0. The inhibition ratio of the crude lipopeptides diluted from 60 to 180 times extracted from the fermentation broth was from 43.8% to 92.0%. The EC₅₀ of lipopeptides to R. solani was 5.90 μL·mL^-1. Compared with the control group, it was found that the mycelia growth of R. solani was reduced and the growth of mycelium was sparse, and the aerial mycelium was also inhibited significantly. The inhibitory effects of lipopeptides on the other 16 plant pathogens were also investigated and the inhibition zones were from 16.7 to 31.0 mm, and the inhibitory effect on the Bipolaris maydis was the strongest, while it had the weakest inhibitory activity against Sclerotinia sclerotiorum.

Key words: maize sheath blight, antagonistic bacteria, fermentation supernatant, antifungal property