Screening of Antagonistic Bacteria in Soil Against Main Tobacco Diseases in Chongqing

752 bacterial strains were isolated from 85 soil samples collected from tobacco rhizospheres in Shizhu,Qianjiang and Fengjie of Chongqing,among them,499 strains were Bacillus spp.and other 253 strains were Pseudomonas fluorescent.348 strains primarily isolated showed antagonistic effects on Alternaria alternata,Phytophthora parasitica var.nicotianae and Ralstonia solanacearum after duel culturing on PDA or plate spraying on NA,which accounted for 46.3% of the total isolated strains.The results of further screening showed that the width of inhibition zone of 29 strains against A.alternata ranged from 8.0 to 12.0mm,of which 12 strains were Bacillus spp.and 17 strains were P.fluorescent,the width of inhibition zone of 26 strains against P.nicotianae ranged from 9.0 to 14.0mm,of which 2 strains were Bacillus spp.and 24 strains were P.fluorescent;the inhibition diameter of 31 strains against R.solanacearum ranged from 30.0 to 42.0mm,of which 9 strains were Bacillus spp.,and 22 strains were P.fluorescent.