Origin, structure and migration of Magnaporthe oryzae populations pathogenic on rice : DP-2

Inferring invasion routes and identifying reservoirs of diversity of plant pathogens are essential to propose new strategies for their control. Magnaporthe oryzae, the fungus responsible for rice blast disease, has invaded all rice growing areas. Virulent genotypes regularly (re)emerge, causing rapid resistance breakdowns. However, the worldwide genetic subdivision of M. oryzae populations on rice and its past history of invasion have never been elucidated. To investigate the centers of diversity, of origin and of migration of M. oryzae on rice, we analyzed the genetic diversity of fifty-five samples from fifteen countries. Three genetic clusters were identified worldwide. Asia was the center of diversity and the origin of most migrations to other continents. In Asia, two centers of diversity were revealed in the Himalayan foothills: South China-Laos-North Thailand, and Western Nepal. Sexual reproduction persisted only in the South China-Laos-North Thailand region, which was identified as the putative center of origin of all M. oryzae populations on rice. Our results suggest a scenario of early evolution of M. oryzae on rice that matches the past history of rice domestication. This study confirms that crop domestication may have considerable influence on the pestification process of natural enemies. (Texte intégral)