Evaluation of the Bacillus-based biological control of potato late blight

Although scientists have demonstrated that many beneficial microorganisms are able to contribute to crop protection, true alternatives to pesticides are still limited. Nowadays, the management of late blight in potato crop resorts on massive use of fungicides while farmers and industries have to cope with an increasing demand for a more sustainable agriculture. In line with these environmental concerns, this work aims at selecting indigenous field efficient Bacillus spp. that could be used to biologically control potato pathogens and especially late blight. The first part of this work establishes a methodology to find out Bacillus spp. with a high biocontrol potential. Their selection relies on characterizations conducted in vitro and at a genomic level. Biocontrol of late blight is assessed in vitro, in greenhouse and in field assays. It allows the selection of the B. subtilis 30B-B6 which is able to significantly decrease late blight in field. In order to identify the metabolites synthesized by Bacillus spp. and which are responsible for the anti-oomycete activity, the second part of this study establishes an experimental procedure to isolate, purify and identify the antimicrobial compounds produced by two B. pumilus strongly effective against P. infestans. Analyses reveal the putative involvement of bacilysin and chlorotetaine that might be the substances active against P. infestans. Even though microbial biopesticides sound environmental-friendly, a large-scale use of metabolites they synthesized could impact the agro-ecosystems. Therefore, the third part of this work explores the potential effects of both chemical and biological control of potato late blight using the soil microbiota as an ecological indicator.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201