Résumé
Host specialization has important consequences for the diversification and
ecological interactions of obligate pathogens. The anther-smut disease of
natural plant populations, caused by Microbotryum fungi, has been
characterized by specialized host-pathogen interactions, which contribute
in part to the isolation among these numerous fungal species. This study
investigated the molecular variation of Microbotryum pathogens within the
geographic and host-specific distributions on wild Dianthus species in
southern European Alps. In contrast to prior studies on this pathogen
genus, a range of overlapping host specificities was observed for four
delineated Microbotryum lineages on Dianthus hosts, and their frequent
co-occurrence within single-host populations was quantified at local and
regional scales. In addition to potential consequences for direct pathogen
competition, the sympatry of Microbotryum lineages led to hybridization
between them in many populations, and these admixed genotypes suffered
significant meiotic sterility. Therefore, this investigation of the
anther-smut fungi reveals how variation in the degrees of host specificity
can have major implications for ecological interactions and genetic
integrity of differentiated pathogen lineages.