The management of disease resistant varieties requires an epidemiosurveillance of pathogen genotypes that breakdown or erode them. This is the case of black leaf streak disease, a serious leaf disease caused by the fungus Pseudocercospora fijiensis which was recently introduced into the French West lndies (FWI). Very aggressive strains that breakdown the resistance of genitors and new resistant hybrids from breeding programs have been isolated in Guadeloupe. The mains goals of this work are to 1) elucidate the origin of these aggressive strains and 2) identify genes involved in adaptation to varietal resistances. Multiple introductions into the FWI from different Caribbean islands have been shown from population history study of the P. fijiensis in the geographic area and erosion of quantitative resistances have been observed in some Caribbean countries such as Cuba and Dominican Republic. These observations lead us to suspect introduction in the FWI of genotypes previously adapted to varietal resistance. To test this hypothesis, we have first confirmed using cross inoculations that P.fijiensis populations have adapted to resistant cultivars in Cuba and Dominican Republic, countries where resistant cultivars have been first deployed in the Caribbean. Isolates from FWI will be tested the same way to compare their aggressiveness with Cuban and Dominican strains. A previous genome scan study showed that genomic region implicated in P. fijiensis adaptation to quantitative resistances can be identified using a genome scan approach based on genome sequencing from pools of isolates (pool seq). Such an approach will be broadened to more than 20 populations representing the genetic diversity in the Caribbean and including samples from the FWI. Genomic regions putatively implicated in adaptation to cultivars resistance will be then compared between samples of P. fijiensis to test whether adaptation genes have been introduced in the FWI.