Study On Resistance Of Tobacco Bacterial Wilt Induced By Piriformospora Indica

The plant growth promoting fungus Piriformospora indica was isolated from Indian Thar desert by Verma et al in 1988 which provides several benefits to its host plant. It can colonize host plant root efficiently and resultes in plant growth promotion and increase disease resistance. P.indica has broad agricultural applications. Tabacco bacterial wilt, one of the most destructive bacterial diseases of tobacco, is caused by Ralstonia solanacearum and seriously reduces the tobacco production. To explore the possibilities of biological control for this disease by using P. indica, we tested the tobacco resistance induced by P. indica to tobacco bacterial wilt, and then screened bactericides by conducting the antibacterial test. Finally the fungus P. indica and bactericide were applied together to prevent tobacco bacterial wilt. Futhermore, the mechanism of disease resistance was studied in our work. The results were as follows: 1. P. indica improved the resistance of tobacco to Tobacco bacterial wiltThe pot experiments were conducted to identify the impact of P. indica in improving the resistence of tobacco to different concentration of R. solanacearum. The results showed that the disease index of P. indica-colonized N. tobacco was reduced compared with the nagetive control under different concentrations of R. solanacearum,which demonstrates the resistance to tobacco bacterial wilt was improved significantly.Under higher density of pathogen, the tobacco colonized by P.indica had higher resistant level to tobacco bacterial wilt.2. Study of indoor virulence of bactericide towords R. solanacearumIn this study we used the method of bacteriostatic circle to test bacteriostatic efficacy of seven different bactericides on pathogenic bacterial R. solanacearum TB3.0n the basis of inhibition zone and transparency,four effective bactericides were screened out of seven:3% zhongshengjunsu,42% trichloroisocyanuric acid,50% bromochloroisocyanuric acid and PHMB. According to bacteriostatic circle,we screen three efficient bacticides:3% zhongshegjunsu、42% Trichloroisocyanuric acid and PHMB,as efficient and low-toxic and can be applied into the prevention to tobacoo bacterial wilt.3. The resistance of tobacco to tobacco bacterial wilt conferred by the combination of P. indica and bactericides.In order to confirm the control effect of P. indica and bactericide on the tobacco bacterial wilt disease, pot experiments were conducted.The results showed that the combined application of P.indica and bactericide (3% zhongshegjunsu treatment,42% Trichloroisocyanuric acid, and PHMB respectively)has better prevention effect than each alone. It is worthy to mention that the mixture of 3% zhongshegjunsu and P.indica were found to have the best control efficacy up to 80.95%, which is 31.81% higher than 3% zhongshegjunsu treatment, and 33.33% higher than P.indica treatment.And Treatment of 42% Trichloroisocyanuric acid and P. indica together can significantly improve the control efficacy than P.indica colonized tobacco orTrichloroisocyanuric acid treated tobacco. Besides the control efficacy of PHMB and P.indica together was significantly higher than that P. indica and PHMB treated alone.4. The preliminary researches on mechanism of the P indica and bacticideTo study the mechanism of disease resistance, we detected the resistance-related enzymic activities and expression levels of resistance-related genes through qRT-PCR in plants.The results showed that the activities of PAL, POD and PPO in P. indica (PI)-colonized tobacco (PI, PI+zhongshengjunsu, PI+PHMB) were significantly higher than those in non- colonized plants. And the expression levels of disease resistance-related gene PR-Ib,GST,hrs203,GST and P450-I,were significantly increased.Yet the expression of all five genes and enzymic activities in Zhongshengjunsu,PHMB treated (without P.indica) were found having no significant differences with control.This study indicated that the resistance to tobacco bacterial wilt in P.indica coloized N.tobacum was associated with the enzymic activities of PAL,POD,PPO and the expression leval of the disease-related genes.