Abstract: In order to clarify the control effect of antifungal protein of strain ML-3 on potato early blight and to provide reference for biological control of potato early blight,the methods of ammonium sulfate fractionation,agar diffusion,orthogonal test,field test and 16S rDNA sequence analysis were used to study the optimal carbon source,nitrogen source,fermentation conditions,optimal ammonium sulfate precipitation concentration,bacteriostatic stability,field control effect and taxonomic status of strain ML-3. The results showed that the optimal composition of fermentation broth was 2% potato,1% peptone and 0.5% NaCl. The optimal fermentation conditions were initial pH 7.0,temperature 30℃,and fermentation liquid 400 mL in 500 mL Erlenmeyer flasks,inoculation volume 5 mL,and fermentation 48 h. In addition,the antifungal protein presented fine stability,when temperature ≤ 60℃,pH value from 5 to 8,and UV irradiation 36 h. The antifungal protein also had favorable stability to K⁺,Fe²⁺,Zn²⁺,and Na⁺. Besides,the concentration of antifungal protein should be ≥10 mg/L when it was used to control potato early blight in field. Strain ML-3 was identified as Bacillus subtilis subsp. inaquosorum based on 16S rRNA sequence analysis. All results indicate that the antifungal protein of strain ML-3 demonstrates obvious application potential in controlling potato early blight and the development bio-pesticide.

Key words: potato early blight, antifungal protein, optimization of fermentation, bio-control bacterium ML-3, field control effect