Isolation, Identification Of Siderophpre-producting Rhizobacteria And Its Effect On Tobacco Resistance Against Virus

Tobacco viral diseases are important infectious disease in tobacco production. There are many factors to aggravate the viral diseases, called "tobacco cancer", that lead to hard to be controlled and slow progress in disease research.. At present, there are not effective methods to be used. In recent years, the research on tobacco rhizosphere microbiology is becoming more and more attractive. It becomes more and more important that to better tobacco growth by using the beneficial bacteria to improve the eco-environment of tobacco rhizosphere.Many soil bacteria can secret more than one siderophores through non-ribosome pathway. Siderophore is a small molecule which can specifically chelated Fe3+ as a result of bio-adaption to the low ferric environment in the earth. The bacterium can use its siderophore to uptake free Fe3+ in the environment to support its normal life. For a microorganism, its capability to obtain free Fe3+ reflect the capability of competition. As a class of beneficial bacterium, the soderophore-producting rhizobacteria was worth to be researched to help us to control plant diseases.In this study, the main object is the siderophore-producting bacteria living in the tobacco rhizosphere. By biological and molecular biological methods, the siderophore-producting bacteria from the tobacco rhizosphere was isolated and identified. Inoculating their pure culture into tobacco rhizosphore, the development of tobacco seedling, roots and the effect on tobacco resistance to virus disease were investigated, for exploring new pathway to disease control. The main results include:1)19 bacterial isolates were obtained from tobacco field soil samples from Jiaxian, Pingdingshan.8 of them were identified to be siderophore-producting bacteria, their code were JX001, JX002, JX003, JX004, JX005, JX006, JX001, JX0011, respectively. According to the 16S rDNA-based identification, isolate JX004 belongs to Pseudomonas chlorosis, JX003 is Pseudomonas sp., JX006 is Pseudomonas sp. and JX008 is an unknown bacterium. All the 8 isolates come from rhizosphere soil of tobacco with slight mosaic symptom. While no siderophore-producting bacteria be obtained from that of tobacco which infected severe viral disease. The same result reproduced in many repeated testment showed that the siderophore-producting bacteria was related with tobacco health.2) The bioassay suggested that the siderophore-producting bacteria can promote tobacco seedlings growth significantly. All the 4 isolates of siderophore-producting bacteria (JX003, JX004, JX006, JX008) can benefit to seedlings growth and development. Rhizobacteria treated seedlings in the medium plates grew much more vigorous and healthy than the control. 3) The bioassay also showed that siderophore-producting bacteria can improve tobacco to absorb and utilize iron nutrition. Naturally, only the resolvable Fe2+ can be uptake by plants. Seedlings are hard to live when Fe3+ as the sole iron nutrition, because of its very low availability. However, the tobacco seedlings grew vigorously when siderophore-producting bacteria was co-cultured in higher Fe3+ medium. Suggesting that the Fe3+ can be transformed into resolvable by siderophore-producting bacteria, and the necessary iron nutrition for tobacco normal growth and development can be meet.4) The siderophore-producting bacteria can promote tobacco growth and development on aerial parts and root extraordinary. The average height vaccinated siderophore-producting bacteria(JX003) can reach 8.35cm in one month, however the highest average height unvaccinated is 5.85cm;The average height vaccinated siderophore-producting bacteria(JX004) can reach 12.13cm in one month, however the highest average height unvaccinated is 9.48cm; The average height vaccinated siderophore-producting bacteria(JX006) can reach 11.33cm in one month, however the highest average height unvaccinated is 8.7cm; The average height vaccinated siderophore-producting bacteria(JX008) can reach 12.1cm in one month, however the highest average height unvaccinated is 8.8cm. The tobacco plants vaccinated siderophore-producting bacteria all have mature roots.5) The siderophore-producting bacteria can restrain the occurrence of tobacco virus disease significantly. Test results show that the tobacco plants infected siderophore-producting bacteria fall ill in the 18th days after infected, later about 7d than normal process, and disease index is 5-13.8. And the disease index of unvaccinated is 13.9-27.8 which exist significant difference between vaccinated. The vaccinated tobacco plants have a tendency of virus symptom can reduce further in later period of growth..Generally, the siderophore-producting bacteria can improve iron absorption and utilization of tobacco, and then benefit to plant growth and development. And also promote the resistance to virus. Their active substance and action mode were worth to be further investigated.