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Bacillus subtilis strain SB1 isolated from tomato roots was evaluated for its ability to control tomato bacterial wilt under greenhouse conditions.Application of strain SB1 culture suspension suppressed tomato wilt disease both in sterilized and non-sterilized soil,providing 76.03% and 77.78% protection,respectively.Wilt symptom was significantly reduced when strain SB1 was applied before pathogen inoculation,while less suppression was conferred by strain SB1 application after pathogen inoculation.The result implied that strain SB1 exhibited both preventive and therapeutic effects on tomato wilt disease.Inhibition abilities of different fractions of strain SB1 suspension were examined as well.Results indicated that treatments with whole cell suspension and culture filtrate gave 71.77% and 65.88% protection,respectively,which were significantly higher than those of the washed cell.This experiment indicated that suppression by strain SB1 was mainly the consequence of activity of the culture filtrate.The possible action mechanisms of the culture filtrate on Ralstonia solanacearum were investigated.The pathogen′s cell shape was greatly altered by the culture filtrate,and the protein expression profiles of R.solanacearum were also affected.