Résumé
The cereal pathogen Pyricularia oryzae (syn. Magnaporthe oryzae), the causal agent of rice and wheat blast, is both a threat to global food security and a model for plant pathology. Despite the clear importance of understanding species boundaries and the distribution of intra-specific diversity for molecular plant pathology, disease surveillance and quarantine decisions, many aspects regarding the natural history and population biology of P. oryzae have remained unexplored. Using whole-genome sequence information for 76 M. oryzae isolates sampled from 12 cereal genera, we show that P. oryzae is subdivided into multiple divergent lineages, each preferentially associated with one host genus, suggesting incipient speciation following host shift or host range expansion. The different host-associated lineages have reached an advanced stage of intraspecific divergence, but species recognition by genealogical concordance does not identify cryptic phylogenetic species. Whole genome resequencing and SNP-typing of a global collection of riceinfecting isolates identify six lineages, including two lineages pandemic on japonica and indica rice, respectively, and four lineages with more restricted distributions. We will present our latest findings about the population and genetic characteristics of the lineages within P. oryzae, and about the possible role of extrinsic (e.g. host adaptation) and intrinsic (e.g. prezygotic incompatibility) reproductive barriers in their formation and maintenance in sympatry. Our work contributes to a greater understanding of the eco-evolutionary factors that underlie the diversification of P. oryzae and highlights the practicality of genomic data for epidemiological surveillance in this important multi-host pathogen.