| Verticillium wilt, caused by the soil inhabiting fungus Verticillium dahliae (Kleb.) is a widespread soil-borne fungus, and is one of the most important diseases responsible for great economic losses in many crops. It is difficult to control Verticillium wilt, because the pathogen had a broad host and the resting structures (microsclerotia) can survive in soil for many years. In practice, the control of diseases caused by Verticillium wilt relies mainly on fungicides. As we all know, chemical pesticides can cause seriously environment pollution. At present, with increasing concern about the health and environmental, we search for viable alternatives such as biological control agents (BAC) and biological control had been considered as a substitute or a supplement to reduce the use of chemical pesticides.The two most promising bacterial isolates, Bacillus amyloliquefaciens41B-land Pseudomonas aeruginosa841P-3had strong inhibitory on Verticillium dahliae (Kleb.) was isolated from the endosphere of cotton plants. In our reasreach, spontaneous rifampicin-resistant mutants of biological control agents (41B-1and841P-3) were generated to facilitate reisolation of the bacteria inoculants. Rifampicin-resistant mutant41B-1R and841P-3R showed effective colonization in root of weat, maize, soybean and rice with seed soaking inoculation and41B-1R showed good colonization ability than841P-3R. But the two biological control agent had different colonization ability in different corps.V107was inoculated into soil and inoculated with41B-1R or841P-3R in order to assess its impact to soil microbial community the survival of these two strans and also biocontrol effect. Changes in microorganism populations and bacterial and fungal community structures in rhizosphere soil of cotton were investigated using a plate culture method and PCR-DGGE analysis.Through plate supplemented with rifampicin revealed that41B-1R and841P-3R also have effective colonization in root of cotton and in the rhizosphere of cotton plants. During the following days after inoculation, the survival of BAC decreased, but41B-1R was not sharply in contrast to841P-3R. As the same as in other crops,41B-1R also showed good colonization ability than841P-3R.Plate culture showed that populations of culturable bacteria were decreased by841P-3R and V107with a shot effect, but the fungi population had the opposite pattern.41B-1R did not have any effect. But as the time flows, the impant of all this treatments to microorganism populations had almost vanished. Furthermore, one week after inoculation, the bacterial DGGE results indicating that V107inoculation severely affected the bacterial community structure and that these effects were much less pronounced in the presence of841P-3R, while this effect did not change with the presence of41B-1R. Three weeks after inoculation, this effect was almost vanished. In contrast to the bacterial fingerprints, one week after inoculation, the presence of V107and the inoculation with41B-1R or841P-3R had the the similar effect to V107in contrast to control treatment, and in five weeks the presence of V107and the inoculation with41B-1R or841P-3R had strong effect than V107. While, the effect of Bacillus and Pseudomonas DGGE profiles was similar to bacterial DGGE profiles.As we can see from disease index of Verticillium wilt,41B-1R and841P-3R can efficiently control the pathogen in the growth chamber experiment. And our QRT-PCR results also revealed that the population of V.dahlia in the rhizosphere of the cotton plants was significantly decreased by41B-1R and841P-3R, as same as the biocontrol effect showed. |
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