The ascomycete fungus Mycosphaerella fijiensis (anamorph Paracercospora fijiensis) causes black leaf streak disease (BLSD), the most destructive leaf disease of bananas. Knowledge of the extent and distribution of variability within M. fijiensis is necessary for breeding and managment of BLSD resistance. Study of population genetic structure of M. fijiensis at a global scale showed that populations can maintain a high level of genetic diversity and that recombination plays an important role in this pathogen. Thus partial resistance supposed durable is preferentially used in breeding programmes. The objectives of this work was to describe the genetic population structure of M. fijiensis at continental and local scales and to evaluate aggressiveness variability within this pathogen. We analysed with molecular markers (CAPS, STMS) samples collected from plantations in Latin American, Caribbean and African countries and in the Philippines. Within localities, we found that the genetic variability is distributed at a small scale up to the plant scale. Within continents, a high level of genetic differentiation was detected between countries and localities suggesting that the spread of the disease is mainly due to the movement of infected plants. Aggressiveness variability was evaluated from two samples collected in Cameroon and the Philippines by inoculation on 5 partially resistant cultivars. This variability was low and similar for the both countries although the level of genetic diversity observed in the Philippines is much higher. No isolates x cultivars-specific interactions were detected. Since only susceptible hosts are cultivated in these countries, these results might be explained by the absence of host selection. (Author's abstract)