Screening of Antagonistic Bacterium Strains against Verticillium dahliae and Identification of the Antifungal Substance

Thirty spore-forming bacterium strains were isolated from several samples of soil in cotton field.Antagonistic tests of all these strains against Verticillium dahliae were carried out on PDA medium by pairing culture method.The results showed that there were six strains which had antagonistic activity against Verticillium dahliae and of the six strains,there were three strains whose metabolite had the antagonistic activity.After treated with(NH4)2SO4 fractional precipitation,the liquid fermentation production of S4-3 strain showed antagonistic activity against Verticillium dahliae.And the antagonistic activity was lost after treated with heat(100℃,30 min)and CHCl3.It is suggested that the antifungal substance of the S4-3 strain should be protein.The antagonistic activity of liquid fermentation production of the S4-5 strain remained relatively high after treated with heat(100℃,30 min),and the chloroform extracts of liquid fermentation production of the S4-5 strain showed the antagonistic activity too.But after treated with(NH4)2SO4 fractional precipitation,the liquid fermentation production of strain S4-5 did not show the antagonistic activity to Verticillium dahliae.The antagonistic activity of liquid fermentation production of the S5-6 strain was lost after treated with heat(100℃,30 min),but the chloroform extracts of liquid fermentation production of the S5-6 strain still had the antagonistic activity.In addition,after treated with(NH4)2SO4 fractional precipitation,the S5-6 strain did not show the antagonistic activity,either.All these results indicated that the antifungal substance of S4-5 strain and S5-6 strain must not be protein.