Biocontrol of Rhizoctonia solani: complex interaction of biocontrol strains, pathogen and indigenous microbial community in the rhizosphere of lettuce shown by molecular methods
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Background and aims
Co-inoculation of biocontrol agents with different modes of action is assumed to improve biocontrol activity. The present study aimed to investigate the effects of single or co-inoculation of Trichoderma viride strain GB7 and Serratia plymuthica strain 3Re4-18 on microbial communities in the rhizosphere of lettuce and their ability to suppress Rhizoctonia solani AG1-IB.
Growth chamber experiments with two different application modes were performed with single or co-inoculation of GB7 and 3Re4-18 in the presence or absence of R. solani. Biocontrol efficacy and plant growth parameters were assessed. Bacterial and fungal communities were analyzed by 16S rRNA gene and ITS fragments PCR-amplified from total community DNA of rhizosphere samples and analyzed by denaturing gradient gel electrophoresis.
Compared to the single application, the co-inoculation of 3Re4-18 and GB7 resulted in an improved biocontrol efficacy. DGGE analysis revealed more pronounced effect on microbial community in co-inoculation treatment. The abundance of 3Re4-18 in the rhizosphere seemed to be increased in the presence of R. solani.
The applied cultivation-independent methods provided insights into the complex interaction in response to the pathogen and the antagonists. Co-inoculation resulted in an improved biocontrol efficacy and an increased evenness of the microbial communities.
KeywordsBiocontrol Co-inoculation Rhizosphere community 16S rRNA gene and ITS-based fingerprints
The authors acknowledge the bilateral project between Brazil and Germany funded by the BMBF BRA 05/021 and the DFG SM59/11-1/GR568121. We would also like to thank Angelika Fandrey for her skilled technical assistance and Christin Zachow for her helpful comments.
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