Résumé
Magnaporthe species cause serious diseases on grasses. Magnaporthe oryzae (previously named Pyricularia oryzae by Cavara in 1891, Pyricularia grisea and Magnaporthe grisea by Rossman in 1990) is responsible for rice blast disease and foliar diseases of wheat, barley, Panicum, Eleusine and Setaria. Magnaporthe grisea is responsible for foliar diseases of Digitaria. Magnaporthe poae causes summer patch of turf grass. The asexual genus Pyricularia encompasses species isolated from various monocots that produce pyriform, tri-cellular conidia from conidiophores. Pyricularia higginsii was isolated from infected Cyperus, while P. zingiberi was isolated from ginger, P. penniseti from Pennisetum, P. zizaniicola from Zizania, P. juncicola from Juncus and P. commelinicola from Commelina. Here we present the phylogenetic relationships among isolates from a wide range of Magnaporthe/Pyricularia species based on partial DNA sequences of multiple genes including LSU, ITS, RPB1, actin and calmodulin. Our extensive analysis reveals a large diversity within the genus Pyricularia. Almost all Pyricularia species belong to a clade that includes all Magnaporthe oryzae/M. grisea isolates tested. This clade is clearly distinct from Gaeumannomyces/Magnaporthiopsis clades for all the sequences tested. A few Pyricularia species (e.g. P. parasitica, P. lauri) are unrelated to the Magnaporthaceae. This strongly suggests that the conidium morphology defining this genus is polyphyletic and cannot be used as taxonomical criterion without phylogenetic data. Magnaporthe oryzae/M. grisea isolates cluster in numerous related clades, one of which corresponds to M. oryzae. This clade includes isolates from rice (specific to this clade), wheat (specific), Setaria (specific) and Eleusine (specific) as well as isolates from other plants found as hosts also represented in other clades such as Echinocloa, Cenchrus or Lolium. Another clade corresponds to M. grisea and consists of isolates from Digitaria (specific to this clade). In addition, we identified four clades that could correspond to novel species, two of which were already described as distinct clades in previous phylogenetic analyses of this genus. These novel species are more related to M. oryzae/M. grisea clades than Pyricularia species clades. A re-evaluation of generic and species concepts within the Magnaporthe/Pyricularia clade is suggested and potential novel names will be proposed for discussion. (Texte intégral)