669 rhizospheric spore-producing bacilli were obtained from healthy tobacco roots. By dual culture on PDA plates and determining inhibition activity of antibiotic substances, it was found that 9 potential biocontrol isolates showed good antagonistic effects to Alternaria alternata, the pathogen of tobacco brown spot, and the diameter of inhibition zone of bacteria and crude antibiotic substances was up to 10 mm. Inoculation of detached leaves of tobacco variety K326 with bacterial suspension and c...