Leptosphaeria maculans is a plant-pathogenic fungus that infects Brassica species, including Brassica napus (rapeseed). Breeding for rapeseed varieties with genetic resistance is efficient to control the disease, nevertheless, L. maculans can adapt and evolve to bypass these resistances. Deciphering the mechanisms that enable L. maculans to adapt is essential to manage emergence of new and better adapted isolates. Brassica carinata (Ethiopian mustard, closely related to B. napus) is considered a nonhost species of L. maculans as this fungus cannot infect this plant species. Despite the extreme resistance of Ethiopian mustard, one natural isolate of L. maculans has been identified as causing moderate and atypical symptoms on B. carinata, but unable to infect B. napus. A cross was performed between this isolate (the ″carinata″ isolate) and an isolate adapted to B. napus (the ″napus″ isolate). A progeny of a hundred individuals was obtained. With this ″carinata″ isolate and the progeny, the aim is to identify genes involved in the adaptation of L. maculans toward B. carinata and B. napus. A genetic approach (QTL analysis), a transcriptomic and a genomic analysis will be combined, using the ″carinata″ and the ″napus″ isolates, in order to identify L. maculans candidate genes potentially involved in its adaptation to the two Brassica species. Functional analyses on candidate genes identified through these approaches will be performed to confirm their implication in adaptation of L. maculans to its hosts. Here, we focus on the genomic regions identified through the QTL analyses and on functional analyses of a few candidate genes. These first results will provide opportunities to study L. maculans adaptive capacities as well as data to initiate analysis of the extreme resistance of B. carinata.