Screening for antagonistic bacteria against Fusarium oxysporum and their influence on the consecutive monoculture problem of Rehmannia glutinosa

Rehmannia glutinosa is an important Chinese medicinal plant with a severe consecutive monoculture problem which might be caused by Fusarium oxysporum . In this work, we isolated a bacterial strain DU-1 from the rhizosphere soil of R. glutinosa . The strain was identified as belonging to the genus Bacillus through 16S rDNA sequencing, and showed an antagonistic effect against F. oxysporum , indicating that it can inhibit the growth of F. oxysporum . Field experiments showed that the two bacterial agents (grown in bran and straw) consisting of DU-1 increased both biomass and effective compounds (catalpol and polysaccharide) of the monocropping R. glutinosa . Moreover, soil total nitrogen content was increased by 24.0% and 39.1%, respectively, indicating that the bacteria are involved in nitrogen fixation. Analysis of rhizosphere microbial communities also indicated that the agents significantly increased the abundance of genus Bacillus in R. glutinosa rhizosphere, suggesting the bacteria can successfully colonize the rhizosphere soil and might play a positive role in improving R. glutinosa growth. Furthermore, application of the agents reduced the diversity of soil rhizosphere microorganisms to a certain extent; however, it did not induce alterations in the predominant species. These results strongly indicate that the application of this bacterial strain may alleviate the consecutive monoculture problem of R. glutinosa .