Biological Control Of Bacterial Wilt By Pseudomonas Fluorescens F091

Ralstonia solanacearum is an important soilborne plant bacterial pathogen with a worldwide distribution and a wide host range, which causes severe loss of solanacae, melon, and mulberry crops. In recent years, researchers pay more and more attentions on biological control of the bacterial wilt at home and abroad. To make better use of biological control of the bacterial wilt, at present study 35 antagonistic bacterial strains against R. solanacearum in vitro were screened out of 569 non-pathogenic bacteria. In simultaneity,16 strains with better antagonistic effects were tested on tomato plants. F091 showed a significant inhibitory effect aginst the 4 bivars and the strongest control effect., which was identified as Pseudomonas fluorescens by colony morphology,major bacteriological characteristics, Biolog identification, fatty acid methyl esters analysis(FAMEs) and 16S rDNA sequence analysis.Antagonistic activity of strain F091 were conducted under the condition of bacterial suspension, bacteria-free filtrate, bacterial suspension treated with proteinase K and heat sterilization. The result showed that after proteinase K and heat treatments, bacteriostatic activity of strain F091 decreased significantly which indicated proteins as the main antibacterial substance. The protein from 50% cold ethanol precipitation showed the greatest antibacterial activity, SDS-PAGE derived that molecular weight is about 30-35 kDa. Nowadays, the largescale production of tomato is usually in greenhouse, so it is necessary to know the disease control effect of F091. The disease control effect was evaluated under greenhouse condition. The results showed that the disease incidence was significantly reduced by F091 when tomato seeds were treated with bacterial suspension with the control efficacy of 75.0%; while F091 can increase the biomass of tomato plants, which proved that the strain can induce the tomato plant resistance to the bacterial wilt indirectly; and the population density of R. solanacearum in the soil indicated that the pathogen population was significantly inhibited by F091.