Résumé
Clonal expansion has been observed in several invasive fungal plant
pathogens colonizing new areas, raising the question of the origin of
clonal lineages. Using microsatellite markers, we retraced the
evolutionary history of introduction of the chestnut blight fungus,
Cryphonectria parasitica, in North America and western Europe. Combining
discriminant analysis of principal components and approximate Bayesian
computation analysis, it was shown that several introduction events from
genetically differentiated source populations have occurred in both
invaded areas. In addition, a low signal of genetic recombination among
different source populations was suggested in North America. Finally, two
genetic lineages were present in both invaded areas as well as in the
native areas, suggesting the existence of genetic lineages with a high
capacity to establish in diverse environments and host species. This study
confirmed the importance of multiple introductions, but questioned the
role of genetic admixture in the success of introduction of a fungal plant
pathogen.