Comparative effect of bacterial cultures and cell-free supernatants on the development of Sclerotinia sclerotiorum

International audience

Inglés. Oilseed rape (Brassica napus), one of the main oil-producing crops worldwide is susceptible to white mold caused by the fungal pathogen Sclerotinia sclerotiorum. Control of this necrotrophic, polyphagous fungal pathogen still mainly relies on chemicals. Therefore, the development of new biocontrol agents appears to be a promising option for contributing to more sustainable oilseed rape production. Previous work carried out in our laboratories has identified two bacteria with particularly interesting activities under controlled conditions and in the field. An analysis of the entire genome of these bacteria shows that they have the genes to produce metabolites having antifungal activity. This result suggests that antibiosis is a possible mode of action explaining the protective efficacy of these bacteria against S. sclerotiorum on oilseed rape. The objective of this study is to validate this hypothesis through biological experiments.<p>To this end, dual culture plate assays were performed to evaluate the inhibitory effect on S. sclerotiorum of the bacterial strains and of their cell-free supernatants. In addition, tests on detached oilseed rape leaves were carried out to assess the protective efficacy of the cellfree supernatants compared with the living bacteria.</p><p>Results show that the bacterial strains exhibit antibiosis against S. sclerotiorum, reducing its mycelial growth and forming a zone of inhibition. This direct effect can be attributed to the synthesis by the bacteria of antifungal metabolites, present in the cell-free supernatant. Additional results showed that the cell-free supernatant could significantly enhance the efficacy of protection provided by both bacteria. Understanding the underlying mechanism should help guide the development of a future biocontrol product with stable efficacy.</p>