Exploitation of the Leptosphaeria maculans late effector repertoire for diversification of resistances to blackleg in Brassica napus

International audience

English. Leptosphaeria maculans is a phytopathogenic fungus being responsible for a damaging disease of oilseed rape (Brassica napus): stem canker. The disease is mainly controlled by plant genetic resistance: single-gene specific resistance or quantitative, adult-stage resistance. During its particularly complex and long infectious cycle, L. maculans colonizes asymptomatically the stems of oilseed rape, producing late effectors specific to this colonization stage. In the context of a strong need to identify new sources of disease resistance, we exploited the repertoire of ‘late’ effectors to identify genes in the plant that could contribute to quantitative disease resistance. Our hypothesis was that quantitative resistance partly rely on gene-for-gene interactions, with fungal effectors produced during stem infection being recognized by resistance proteins. Using an innovative strategy of early expression of late effector genes, we validated that the interaction between the late effector LmSTEE98 and the resistance RlmSTEE98 obeys a typical gene-for-gene interaction, occurring during the colonization of oilseed rape stems by L. maculans, that contributes partly to quantitative resistance, in controlled conditions. We then used the same strategy to search for new sources of resistance after having established criteria to select the most relevant late effectors, and chosen ten of these for screening. Our screening approach of 130 diversified genotypes representative of the available diversity of B. napus, allowed us to identify new sources of resistance, displaying diversified interaction phenotypes. The next steps of this project now are further validation of the efficacy of the new sources of resistance in the field and of the validity of the quantitative resistance markers. However, as it stands, our results demonstrate the existence of unsuspected sources of resistance that are potentially more durable than the classic major genes expressed early after penetration in plant tissues.