The Study On Differentiation Of Pathogenicity Of Ralstonia Solanacearum

Ralstonia solanacearum were isolated from different parts of tomato, peanut and ginger in the different stages of bacterial wilt disease. The isolated strains included not only virulent strains but also avirulent strains in the root of tomoto in the early stage of bacterial wilt disease and the stem of tomoto in the late stage of bacterial wilt disease. The strains isolated from the stem of ginger both were avirulent strains.The inhibition rates of the biocontrol bacterium strain BC-0711 (Bacillus cereus) against ten Ralstonia solanacearum virulent strains were investigated.But the inhibition rates were diverse in different Ralstonia solanacearum virulent strains. The inhibition rate of BC-0711 against Rs466 was only 4.6%,and was significantly different from against Rs91 and Rs1447,which respectively was 78.3% and 79.9%, and the others were between 43.5% to 59.6%. After subculturing 5 generations , differentiation of pathogenicity didn't appeare in Rs91, but appeared in Rs1100 when it was subcultured to the fifth generation. BC-0711 and Rs91 were co-clutured for three generations, and its differentiation of pathogenicity still didn't appear. But Rs1100's differentiation of pathogenicity appeared after co-clutured with BC-0711 at the first generation.This study constructed avirulent mutants of Ralstonia solanacearum(strain Rs91) using Tn5 transposon mutagenesis and obtained 1004 mutants. There are 13 avirulent mutants were identified by TTC medium. And among which there were 5 avirulent mutants'insertion site flanking sequences were amplified by IPCR and sequenced. The insertion sites of this 5 avirulent mutants were located in phcA gene and phcS gene. The 5 avirulent mutants were finally identified by bioassay of potted tomato. The growth curve and the relative content of EPSI of this 5 mutants are significantly lower than strain Rs91,but their optimum temperature and optimum pH for growing changed a few. The supernatants of this 5 mutants in TTC Liquid medium were scanned by UV-spectrophotometer in the wavelength of 400-450nm.The result of scanning were analysed by UPGMA dendrogram.We detected that this 5 avirulent mutants and Rs91 can be separated into 3 groups, it was that Rs91 was in group I,the phcA- mutants were in group II, and the phcS- mutant was in group III.