Ecological Control Of Tobacco Bacterial Wilt In Continous-cropping Field And The Microecological Mechanisms

Tobacco bacterial wilt caused by Ralstonia solanacearum is a devastating bacterial disease. It can cause serious loss of tobacco production in the world and more serious in the case of continuous cropping. The disease in the field often breaks out quickly in the hot and humid conditions. Lack of available resistant varieties and efficient chemicals, bacterial wilt control has been mainly depend on agronomic measures and integrated control.In this study, the effect of several mulching modes, calcium fertilizer and rhizosphere-activating additive on preventing bacterial wilt were investigated by field trial test. And the affect of these ecological methods on Ralstonia solanacearum, soil culturable bacteria and fungi were analyzed. Meanwhile, the microbiological diversities were checked by PCR-DGGE. All the aim is to lay the foundation for exploring the repairing technology of soil healthy restoration and developing new pathway to preventing soil-borne diseases. The results are as follows:1. The field trial performed in 2009 showed that both plastic mulch prior to rice straw covering and prior to ryegrass hay covering had significant effect on controlling bacterial wilt, with a relative control effect at 50% about which significant higher than treatment of non-mulch prior to rice straw covering (with a relative control effect at 14%—25%)。Non-mulch combined with calcium fertilizer additive also showed significant disease control (with a relative control effect at 53%), while plastic mulch combined with calcium fertilizer additive had the highest effect (74%). As well, transplanting at end of April without plastic mulch combined with root protectant revealed significant disease control effects.2. By culture-dependent method, the amount of Ralstonia solanacearum, bacteria and fungi in soil sampled in 2009 and 2010 were analyzed. The result suggested that plastic mulch prior to ryegrass hay covering, calcium fertilizer additive and certain root protectant had obvious inhibition on Ralstonia solanacearum, and a significant positive effect on enriching soil bacterium and fungi .3. For soil microbial diversity analysis, the PCR-DGGE detection system was optimized. The results showed that the optimal annealing temperature for bacterial universal primers BacGC-P3/P2 was 57℃in the second nested PCR. And the optimal amplification reaction for the second nested PCR was touch-down PCR. And the optimal denaturing gradient range of DGGE was 40%-80% , and the optimal electrophoresis time was 6h.4. Utilizing the optimal PCR-DGGE method, bacterial diversity of 38 soil samples obtained in 2010 field test were analyzed. The results showed that treatment of plastic mulch with planting ryegrass and treatment of plastic mulch combined with more calcium fertilizer could enrich bacteria during the whole growth stage; adding more calcium fertilizer combined with rice straw covering and certain root protectant (component I: 1g/hole, component II:3g/hole)could enrich soil bacteria in middle and later growth seasons; plastic mulch prior to rice straw covering and certain root protectant ( component I: 0.2g/hole, component II : 8g/hole ) could enrich microorganisms only in the latter growth stage. The molecular ecological results were consistented with the field survey on disease control.