Competitive use of root exudates by Bacillus amyloliquefaciens with Ralstonia solanacearum decreases the pathogenic population density and effectively controls tomato bacterial wilt

•Root exudates affect chemotaxis of Ralstonia and SQYUV 162.•Organic acids induced the chemotaxis and pathogenicity of Ralstonia.•Citric acids induced the population density of Ralstonia resulting in higher disease incidence.•Competitive use of citric acid by SQYUV 162 decrease pathogenicity of Ralstonia.•Competitive use of citric acid decreases population density of Ralstonia in rhizosphere.

Understanding the interactions between beneficial bacteria, plant pathogens, and root exudates is necessary for the optimization of the bio-control strategies targeted toward plant soil-borne diseases. In this study, we showed that the competitive use of root exudates by the antagonistic bacterial strain SQYUV 162 along with the pathogenic strain Ralstonia solanacearum affected the pathogenic population density and the pathogenicity of R. solanacearum. All of the tested organic acids induced chemotaxis in both SQYUV 162 and R. solanacearum. In addition, the growth of both SQYUV 162 and R. solanacearum was affected by the addition of organic acids. Strong chemotactic responses in SQYUV 162 and R. solanacearum were induced by malic acid and citric acid respectively. It was also observed that the addition of organic acids significantly induced the expression of several virulence-related genes and increased the population density of the pathogen on the roots, resulting in higher disease incidences in hydroponic experiments in comparison to a control. When SQYUV 162 was inoculated, however, both the expression of virulence-related genes and the population density of the pathogen decreased. The population density of SQYUV 162 also increased when roots were placed in contact with organic acids. The improved colonization density of SQYUV 162, as well as the decreased pathogenicity and population density of the pathogen, efficiently suppressed the incidence of bacterial wilt. The present results indicate that certain components of root exudates could suppress soil-borne diseases: by applying bacteria whose resource consumption profile overlaps that of plant pathogens, plant diseases may be better controlled.