Elucidating the genetic basis of adaptive traits is a central issue in evolutionary biology. Plant pathogenic fungi are interesting organisms to address this question since they are able to adapt rapidly to their environment. Through changes in their aggressiveness, they are notably able to erode quantitative host resistances, thereby threatening their durability. This project aims to elucidate the genetic basis of aggressiveness traits involved in the adaptation of a plant pathogenic fungus to this type of resistance. The study model is the fungus Mycosphaerella fijiensis, responsible for a recent and devastating banana pandemic, Black Leaf Streak Disease (BLSD). This model displays biological characteristics which, when combined with available methods and resources, make it possible to take QTL mapping and population genomics approaches in a complementary manner. These methods have seldom been used in fungi. The power of these approaches is greatly increased by new-generation sequencing techniques. During the outgoing phase, I will be joining Stephen Wright's laboratory (University of Toronto, Canada), which is one of the most proficient laboratories in genetics and population genomics on plants using new-generation sequencing techniques. I will thus be able to effectively transfer these approaches to fungi on my return to my research unit (JRU BGPI, Montpellier, France). These new skills will enable me to strengthen the scientific project of my own research group and to become a leader in my scientific field. This stay will also broaden my network for greater international visibility. It will then contribute to the excellence of ERA, enhancing skills in research on plant pathogenic fungi and on banana in Europe. Lastly, the results of this project will serve to define durable strategies for controlling BLSD of banana, a plant grown in the EU outermost regions and important for world food security, and more generally for reduced pesticide use in crops.