The transmission to seeds is a critical step when considering the ecology of numerous phytopathogenic fungi and the epidemiology of diseases caused by these pathogens. This step is also crucial for the survival and the dispersion of fungi. The molecular mechanisms involved in seed colonization and then in seedling infection are until now largely unknown. The studies performed in FungiSem are mainly developed on seed-borne Alternaria species, pathogenic for Brassicaceae (cultivated species in the Brassica and Raphanus genera, Arabidopsis thaliana) and Apiaceae (carrot). The central topic of our research is focused on the identification of pathogenicity factors, particularly those related to fungal adaptation to environmental (chemical and physical) stresses, including the host-plant micro-environment. The seed colonization process is thoroughly examined taking into account both partners of the interaction and the seed microbiome. The applied objectives of these studies are to develop innovative control methods (e.g. application of potentiating agents) and to improve the plant resistance level to fungal diseases.