Effects of Bacillus amyloliquefaciens ZM9 on bacterial wilt and rhizosphere microbial communities of tobacco

Ralstonia solanacearum, is a known soil-borne pathogen and causative agent of tobacco (Nicotiana tabacum) bacterial wilt (TBW) worldwide. In this study, we evaluated the effect of different biocontrol agent inoculants on TBW and rhizosphere microbial communities. Bacillus amyloliquefaciens strain ZM9 was selected for its antagonistic characteristics against this pathogen in vitro and its ability to colonize crops in pot-based experiments. ZM9 was effective in the control of TBW, and its effects on the tobacco rhizosphere microbial community were accessed using liquid-state fermentation cultures (LSFC) and solid-state fermentation cultures (SSFC) methods. The biocontrol efficacy of LSFC and SSFC groups was increased by 23.51% and 38.20%, respectively compared to the control group. Sequencing of 16S rRNA gene amplicons from the tobacco rhizosphere revealed the tobacco rhizosphere communities were dominated by Proteobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes and Actinobacteria, and the relative abundance of R. solanacearum decreased in the biocontrol groups relative to the control group, and was negatively correlated with the abundance of ZM9. The dominant OTUs affiliated with Sphingosinicella, Gemmatimonas and Gp1 with a negative correlation to the abundance of Ralstonia, were the beneficial bacteria for TBW control. In addition, the relative abundance of plant growth promoting rhizobacteria increased in both biocontrol groups. These results suggest an antagonistic effect of ZM9 on bacterial wilt pathogen, thereby highlighting the application of this strain and other potential biocontrol agents for controlling TBW in the field. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.