Résumé
In Madagascar, rice is the staple food of the population. With the increase in population, rice cultivation in lowlands has become insufficient. Therefore, rainfed upland rice farming has gained importance. Since the 1990s, different varieties of rainfed upland rice have been made available to farmers. Unfortunately, their resistance to blast disease was overcome by Pyricularia oryzae populations after a few years of cultivation. But since 2006, a Nepalese variety called Chhomrong Dhan (ChD), which was first tested at the FOFIFA Antsirabe research station in the mid-1990s, has been massively deployed. Thanks to its resistance to blast disease, it was quickly adopted by farmers and covers 85% of the land dedicated to rainfed upland rice in 2017. Studies conducted by Raveloson et al. from 2014-2017 suggest that ChD displays resistance to P. oryzae, that the strains attacking ChD panicles come from neighboring varieties by spillover at late stage, but no pathogen population has yet adapted to ChD. The resistance of ChD reduces the pressure of the disease on rainfed upland rice cultivation in the Vakinankaratra region. Rice blast incidence survey on ChD and neighboring varieties will be continued. The genetic diversity of P. oryzae will be characterized to monitor the evolution of its population structure over the years, on ChD and neighboring varieties. Finally, the genetics of resistance of ChD will be characterized by crossing with susceptible varieties and genetic mapping.