# Elucidate the modes of action of biocontrol agents against Sclerotinia sclerotiorum on rapeseed

Margot Grimonpont, Estelle Turc, Adrien Lies, Noadya Monnier, Philippe C. Nicot, Marc Bardin

► To cite this version:

Margot Grimonpont, Estelle Turc, Adrien Lies, Noadya Monnier, Philippe C. Nicot, et al. Elucidate the modes of action of biocontrol agents against Sclerotinia sclerotiorum on rapeseed. 17. IOBC-WPRS meeting of the working group "Biological and Integrated Control of Plant Pathogens". From single microbes to microbiome targeting One Health, International organisation for Biological Control, Jun 2025, Turin, Italy. [hal-05122362](https://hal.inrae.fr/hal-05122362v1)

HAL Id: hal-05122362

https://hal.inrae.fr/hal-05122362v1

Submitted on 20 Jun 2025

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# Elucidate the modes of action of biocontrol agents against *Sclerotinia sclerotiorum* on rapeseed

Grimonpont M. (1), Turc E. (2), Lies A. (2), Monnier N. (2), Nicot P. (1), Bardin M. (1)

(1) INRAE, Pathologie Végétale, F-84140, Montfavet, France

(2) Groupe Elephant Vert France, 77700 Serris, France

**Abstract** : Rapeseed (*Brassica napus*), one of the most widely grown rapeseed crops in the world, is highly susceptible to white mold caused by the fungal pathogen *Sclerotinia sclerotiorum*. The management of this necrotrophic and polyphagous pathogen primarily relies on chemical treatments. Consequently, the development of novel biocontrol agents offers a promising alternative for promoting the sustainable cultivation of this crop. However, microbial biocontrol products are often perceived by farmers as lacking in efficacy and reliability when used in the field. This issue is generally attributed to a lack of knowledge of the factors that modulate their efficacy, including their mode of action.

In previous work, two bacteria have shown particularly promising activity under controlled conditions and in the field to protect rapeseed against *S. sclerotiorum*, and are currently being developed by a company. Antibiosis and resistance induction have been demonstrated as two possible modes of action implemented by these bacteria, with variation depending on the strain. Studies are therefore needed to decipher in detail the mechanisms underlying the protective efficacy of each bacterial strain. In this context, our first objective was to identify, among the various elements present in the by-products of bacterial fermentations, those that play a key role in rapeseed protection. A second objective was to characterize the active metabolites produced by these bacteria that may explain the effects observed.

To address the first objective, we investigated the contribution of washed bacterial cells, killed bacterial cells and cell-free supernatant produced in two culture media to the development of *S. sclerotiorum* on rapeseed, for each antagonistic bacterium. Detached leaves of rapeseed were treated with the various constituent derived from bacterial fermentation either 1, 3 or 7 days prior to pathogen inoculation. Inoculated leaves are then incubated at 21°C, a temperature conducive to pathogen development, until lesion size measurements were conducted. Preliminary results indicate that cell-free supernatant has a prominent role in reducing the development of *S. sclerotiorum* and, for one of the two strains, in inducing defense-related genes in rapeseed.

To further characterize the active compounds within the cell-free supernatant, a 'candidate metabolite' approach and a non-targeted metabolomics approach have been implemented. The first approach focused on evaluating the effect on *S. sclerotiorum* of combinations of purified metabolites present in the cell-free supernatant and known to be associated with biocontrol activity. The second approach was to fractionate the cell-free supernatant and perform LC-MS analyses for further characterization. The main results of these approaches will be presented.

**Key words** : *Sclerotinia sclerotiorum*, biocontrol, mode of action, fermentation constituent, metabolomics