Abstract: In order to screen an antagonistic strain against Fusarium oxysporum f.sp. niveum (Fon), the rhizosphere soil from vegetable crops on Qingxin farm in Qiqihar City was collected and used in this study. The antagonistic strain was screened out using plate confrontation method, and identified by morphological, 16S rDNA, gyrA and gyrB sequence analysis. Pot experiment was conducted to verify the control effect of antagonistic strains on Fusarium wilt of watermelon. Growth rate method was used to study antifungal activities of sterile fermentation filtrate from different growth stages of antagonistic strain and the stability of sterile fermentation filtrate. Fon conidia morphology and cell membrane integrity were analyzed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), respectively. The results showed that the antagonistic strain WD was Bacillus amyloliquefaciens, which could effectively inhibit the occurrence of watermelon wilt, and the inhibition rate reached 57.57%. The sterile fermentation filtrate had higher antifungal ability in the decline period, and the growth inhibition rate of Fon mycelium was 54.32%. Sterile fermentation filtrate from B. amyloliquefaciens WD had high tolerance to temperature and pH. The antifungal activity was the strongest at 30 °C and pH 7, the inhibition rate reached 58.36%; The sterile fermentation filtrate could store at 4 °C for at least 45 days, and UV light for 120 min had no effect on its antifungal activity. The Fon conidia were exposed to the sterile fermentation filtrate from B. amyloliquefaciens WD, the surface of the conidia collapsed and the membrane integrity was destroyed. In conclusion, B. amyloliquefaciens WD had high-efficiency antifungal activity on Fon, the results laid a foundation for development and utilization of biocontrol agent to Fusarium wilt of watermelon.

Key words: Fusarium oxysporum f.sp. niveum, Bacillus amyloliquefaciens, sterile fermentation filtrate, antifungal ability