Study On Biocontrol Potential Of Bacteria Carried By Pine Wood Nematode

Pine wilt disease is one of the important forest diseases of pine trees,previous study found that pine wood nematodes from different sources have different virulence and the cause is the different bacteria carried by nematodes. In this study, we collect U.S. pine wood nematodes and study its carrying bacteria. We hope to screen out some bacteria which have strong viability and lower toxicity, then released into the wild to replace virulent bacteria, in order to reduce the strong pathogenicity of Chinese pine wood nematodes.The major research results are as following:1. We isolated ten bacterial strains from two U.S. pine wood nematodes. Through statistical ratio of bacterial colonies, we identified MG3,MG4 and MG5 as dominant bacteria of Am-Bx1, and MG8 and MG9 as Dominant bacteria of Am-Bx2.2. The confrontation experiments between dominant bacteria carried by American pine wood nematode and pseudomonas fluorescents is carried out for selecting strong viability bacterial strains. We screen MG4, MG5, MG8 and MG9 four bacteria as strong viability bacteria in Chinese nematode. But in ordinary liquid medium, they cannot inhibit the growth of pseudomonas fluorescents.3. We measure the toxicity of MG4.etc four strains bacteria, and choose pseudomonas fluorescents as the comparison. The results show that pine seedlings treated with MG4, MG5, MG8 and MG9 wither slower than that treated with pseudomonas fluorescents. In addition, either using bacterial cell-free culture medium treat with pine seedlings, or mixture of bacteria and nematodes treat with pine seedlings, the results are the same.4. In order to measure the viability of bacteria on wild pine wood nematode, we spray bacteria marked with rifampicin on wild nematode. The result shows that MG4.etc four bacteria can grow on wild nematode, and the viability of MG5 and MG8 are stronger than the others.5. According to the methods of observing bacterial morphology and analyzeing bacterial 16S rDNA sequence, we identify MG4 as Delftia tsuruhatensis, identify MG5 as Pseudomonas putida, identify MG8 asStenotrophomonas maltophilia and identify MG9 as Pantoea sp.