Biocontrol activity of Bacillus nakamurai BDI-IS1 and investigation of its mechanisms against Northern corn leaf blight byGaspard Nihorimbere

Chemical pesticides are widely used to control plant diseases and pests, despite their adverse effects on human health and the environment. In Burundi, chemical pesticides are primarily applied to cash crops, while diseases and pests affecting staple crops receive limited or no control. This thesis focused on the biocontrol activity of Bacillus nakamurai BDI-IS1 isolated from Burundi against major fungal diseases impacting crop production in this country. Multiple approaches, including in vitro and in planta trials, combining the use of wild type and mutants of BDI-IS1, dynamic of gene expression and microscopy were used to assess the biocontrol efficacy and mechanisms of action of the bacterium. BDI-IS1is antagonistic against a broad range of bacterial and fungal phytopathogens. It consistently reduced the severity of tomato early blight and Northern corn leaf blight. This bacterium produces several bioactive metabolites that act either directly against Exserohilum turcicum or by stimulating maize defenses. Its direct activity is mediated by iturin, a metabolite with fungicidal properties, whilst its indirect activity is partly mediated by surfactin. BDI-IS1 induced systemic resistance in maize, as evidenced by the increased expression of defense-related genes. This study demonstrated the biocontrol potential of BDI-IS1, which can be attributed to multiple modes of action. We developed in this study a process to multiply and produce active spores of BDI-IS1 on lignocellulosic substrates. This work thus demonstrated that BDI-IS1 exhibits interesting biocontrol activity. Further research is needed to improve the formulation and storability of BDI-IS1 and to explore its biocontrol efficacy against other pathogens.