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The application of Bacillus sp. in the biological control of plant soilborne diseases has been shown to be an environmentally friendly alternative to the use of chemical fungicides. In this study, the effects of bioorganic fertilizer (BOF) fortified with Bacillus amyloliquefaciens SQY 162 on the suppression of tomato bacterial wilt were investigated in pot experiments. The disease incidence of tomato wilt after the application of BOF was 65.18% and 41.62% lower at 10 and 20 days after transplantation, respectively, than in the control condition. BOF also promoted the plant growth. The SQY 162 populations efficiently colonized the tomato rhizosphere, which directly suppressed the number of Ralstonia solanacearum in the tomato rhizosphere soil. In the presence of BOF, the activities of defense-related enzymes in tomato were lower than in the presence of the control treatment, but the expression levels of the defense-related genes of the plants in the salicylic acid and jasmonic acid pathways were enhanced. It was also found that strain SQY 162 could secrete antibiotic surfactin, but not volatile organic compounds, to suppress Ralstonia . The strain could also produce plant growth promotion compounds such as siderophores and indole-3-acetic acid. Thus, owing to its innate multiple-functional traits and its broad biocontrol activities, we found that this antagonistic strain isolated from the tobacco rhizosphere could establish itself successfully in the tomato rhizosphere to control soilborne diseases.

Tobacco bacterial wilt (TBW) caused by Ralstonia solanacearum (RS) is one of the most serious tobacco diseases worldwide and no effective control measures are available to date. This study investigated the potential of Trichoderma harzianum SQR-T037 amended bioorganic fertilizer (BOF) and the arbuscular mycorrhizal fungi (AMF) Glomus mosseae 171 (Gm) on the control of TBW and promotion of plant growth in pot experiments. The results showed that the disease incidence in plants treated with integrated application of G. mosseae 171 and T. harzianum SQR-T037 amended bioorganic fertilizer (Gm + BOF) was the lowest, with a control efficacy of 68.2%, which is greater than that of BOF or Gm alone (26.8% and 14.7%, respectively). The application of BOF or Gm alone significantly reduced the abundance of RS in rhizosphere soil, but the integrated treatment (Gm + BOF) showed the strongest inhibitory effect (with a 21.3% increase in inhibition). The root colonization of G. mosseae 171 in samples treated with Gm + BOF was higher than that in samples with solely Gm treatment, indicating that the BOF significantly promoted G. mosseae mycorrhizal colonization. The results showed that the G. mosseae also had a positive effect on SQR-T037 rhizospheric colonization. Denaturing gradient gel electrophoresis (DGGE) results showed that application of BOF and Gm alone or in combination changed the diversity of the rhizospheric microbial community. The integrated application of Gm + BOF to tobacco plants significantly increases the activity of polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD), enzymes associated to systemic resistance. Additionally, the integrated application of Gm with BOF increased the tobacco plant height, shoot dry weight, and root dry weight. In conclusion, a synergistic biological approach integrating application of Gm and BOF for TBW protection seems promising. [ABSTRACT FROM AUTHOR]

Highlights: [•] The application of BOFs delayed wilt development and effectively decreased the disease incidence. [•] Application of BOF7 achieved 58.0% and 56.2% control efficacies in two years field experiments. [•] Application of BOFs could significantly repressed the pathogen in both pot and field experiments. [•] The density of SQR-7 and SQR-29 remained at a high level in later tobacco growth stages. [•] Application of BOFs promoted tobacco growth and increased the tobacco leaf yields. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]