Screening and Identification of Bacillus subtilis SH7 Strain against Ralstonia solanacearum

The tobacco bacterial wilt disease caused by Ralstonia solanacearum is one of the important diseases of tobacco in China,and influences the field and quantity of tobacco leaves.Six hundred samples of root soil were collected from the serious disease areas in Yunnan and Guizhou,and screened SH7 strain showed strong antagonistic activity against R.solanacearum.The result showed that the inhibition zone width against R.solanacearum was 13.2 mm in the antibacterial test plate of laboratory.The control effect of the sterile fermentation broth of SH7 strain against R.solanacearum was 66.0% by pretreatment of tobacco root.The inhibition of crude protein extraction after precipitation and dialysis by 70%(NH4)2SO4 was strong with 15.7 mm of inhibition zone width and the inhibition determination of supernatant after removing precipitation by 70%(NH4)2SO4 was weak,which indicated that the antifungal substance was possibly protein.The result of phenotypic and general physiological and biochemical determination and 16s rDNA sequence analysis showed that SH7 strain belonged to one strain of B.subtilis.The production availability of B.subtilis SH7 strain was also discussed in this study.