Study On Avirulent Strains Of Ralstonia Solanacearum Against Tobacco Bacterial Wilt

Tobacco bacterial wilt is a fatal disease on tobacco, which is caused by Ralstonia solanacearum. The main method to control tobacco bacterial wilt is chemical control until now, but no miracle drug has been found. At the same time, chemical control is easy to cause "3R" problems, which often bring a great impact on the environment. Biological control is safe to environment and human, so it is favored by more and more plant pathologists. Avirulent strain of Ralstonia solanacearum is isolated from plant and has the same mechanism to enter host with Ralstonia solanacearum, which is regarded as important source of tobacco bacterial wilt biocontrol. It can occupy the sites of colonization and produce bacteriocin to inhibit Ralstonia solanacearum. In this study, avirulent strains of Ralstonia solanacearum were rejuvenated, and the antagonistic of the rejuvenated strains to Ralstonia solanacearum and tobacco bacterial wilt were tested, some trials were carried out to know if Aujd5-2y could colonize in tobacco plants. These strains with better antagonist and the strain Aujd5-2ys were identified finally.1. The avirulent strains of Ralstonia solanacearum conserved in Plant Ecology Institute of Pathology of Southwest University were firstly rejuvenated on the plates, and then the antagonistic of the initial and the rejuvenated strains against Ralstonia solanacearum were tested by plate spray. The results showed that the antagonistic of some rejuvenated strains was better than their initial strains,15 strains with better antagonistic against Ralstonia solanacearum were got after twice screening. The strain FL-9-1 was chosen as the Ralstonia solanacearum for it showed strong pathogenicity to tobacco plants;2. The greenhouse trail on tobacco plant was carried out with 15 strains, which were inoculated by root cutting. It was found that four weeks after the inoculation of FL-9-1, the relative control efficacy of 6 strains were more than 70%, Aujd5-2y, Tbw 1-7-3 and Aujd 11-1-4 could put off the time of tobacco bacterial wilt occurrence and their relative control efficacy was 89.4%, which was much higher than others'. Six strains were chosen for the second greenhouse experiment, for the relative control efficacy of which was higher. Four weeks later, the relative control efficacy of root cutting inoculation was higher than pouring inoculation's except Aujdl 1-1-4, the relative control efficacy of Aujd5-2y and Tbw 1-7-3 was higher than others'clearly.3. The field experiment was carried out with Aujd5-2y and Tbwl-7-3, while agricultural streptomycin was taken as pharmacy control. One month after the diseased control emerging symptom, the relative control efficacy of Aujd5-2y was 35.64%, which was higher than streptomycin treatment obviously.4. The strain Aujd5-2y was tagged with combination of Streptomycin and Rifampicin, the tagged strain was Aujd5-2yk. Then, we tested if Aujd5-2yk can colonize in tobacco by tissue printing and dilution separation. The results showed that, tissue printing detected Aujd5-2yk only on tobacco rhizosphere, and dilution separation detected the tagged strain in tobacco roots, stems and leaves some time later. That showed Aujd5-2yk could colonize on tobacco rhizosphere and in tobacco for a short period, and it could shift in tobacco. The data indicated the number of Aujd5-2yk of root cutting inoculation was higher than pouring inoculation in the same time; the trend of the change of number of Aujd5-2yk by the two inoculation methods was first increased and then decreased.5. The 6 strains used in second greenhouse experiment and the strain Aujd5-2ys recycled in the colonization experiment, were finally identified by morphological, cultural physiological and biochemical characteristics. The results indicated that 6 strains had the same characteristics with Ralstonia solanacearum except Aujdl 1-1-4, so the 6 strains were all identified as Ralstonia solanacearum, and Aujd5-2ys was the strain Aujd5-2yk.