Control Of Bacterial Wilt In Eucalyptus Urophylla By Endophytic Bacteria And Genetically Modified Strains Of Pseudomonas Fluorescens

Endophytic bacteria were isolated from different plant tissues, and their antagonistic activities to Ralstonia solanacearum were screened. The suppressive effects of 12 genetically modified strains of Pseudomonas fluorescens WCS417r carried the phl gene against Ralstonia solanacearum was tested as well. Bioassays were performed to control bacterial wilt in E. urophylla by antagonistic endophytic bacteria, and genetically modified strains, L3d6 and L2c9 of WCS417r. Based on these, two kinds of experiments, endophytic bacteria CN015r with WCS417r or L3d6, and CN017r with WCS417r or L3d6, were performed to suppress eucalypt bacterial wilt by combinations of endophytic bacteria and genetically modified strains of WCS417r. Finally, the colonization ability within E. urophylla of endophytic bacterial strains CN015r and CN017r were studied. The main results of this research are as follows:1. All the 13 endophytic bacteria strains isolated from eucalyptus, tomato and grape had inhibitive abilities against R. solanacearum, but CN015,CN017, CN078 and CN081 are the strongest. Suppression of CN080,CN084 and CN085 against R. solanacearum affected by the quantity of iron in environment. All the strains that had transparent circle on medium made from the cells of R. solanacearum suppressed R. solanacearum on KB, but the size of transparent circle was not related to the inhibitive ability.2. In biocontrol assays in vivo, strains CN078, CN015r and CN017r reduced the percentages of wilted seedlings by 23.2 %, 30.0 % and 3 1.7 %, respectively, when 10⁹ CFU·mL^-1 suspension were applied by root dipping for 10-12 h, and the percentages of wilted seedlings were significant compared with that of the control(a=0.05).3. The 12 genetically modified strains of P. fluorescens WCS417r carried the phl gene had strong inhibitive abilities against Ralstonia solanacearum, but L3d6 is the strongest. The percentage of wilted seedlings of L3d6 was significantly decreased when 10⁹ CFU·mL^-1 suspension were applied by root dipping in vivo, and L2c9 reduced the percentages of wilted...