Residiv: Exploring the genetic diversity of rice-blast host-pathogen interactions in China : A tool to improve breeding for resistance to blast disease

The RESIDIV project is supported by the European Community. The project aims at improving our knowledge on resistance diversity in Chinese rice varieties and on the diversity of the pathogen for its ability to attack resistant varieties (avirulence/virulence). Chinese traditional rice varieties have a large biodiversity and characterization of this material will lead to the identification of new genes conferring resistance to the blast disease This knowledge will be of important value for breeders aiming to introduce the appropriate resistance genes by classical methods or by marker assisted selection to obtain durable resistance. The results of the RESIDIV project will be exploited through conventional breeding methods using natural defense systems. Resistance genes are usually characterized by inoculation of different isolates of the rice blast fungus M. grisea. The choice of isolates is a key point for resistance gene characterization. Because resistance is epistatic, two resistance genes in a variety might not be easily distinguished. Our project will use 3 different strategies to improve the identification of resistance genes in rice varieties. First, the most diverse rice varieties and fungal isolates will be identified according to the genetic diversity of the host and of the pathogen in China as determined by molecular markers. The resulting set of varieties will be inoculated with the set of isolates in order to estimate the genetic diversity for resistance. Second, genetic approaches, using the pathogen will be used to obtain progeny with various combinations of avirulence genes. These progeny will be inoculated on Chinese rice varieties to better classify rice varieties sharing the same reaction pattern and therefore the same resistance genes. The third method relies on the mapping of resistance genes by inoculation of Chinese isolates of the rice blast fungus. Genes mapping at different loci should be- distinct. Resistance genes mapping at the same locus will be assessed for allelism using a wide range of isolates either virulent or avirulent to each of the resistance genes studied. At the same time, avirulence of the Chinese populations of the pathogen will be investigated to study frequency of avirulent/virulent alleles. This information will be very useful to estimate the durability of resistance genes or resistance gene combinations. (Résumé d'auteur