Résumé
Molecular mechanisms for the specific recognition of fungal pathogens by their host plant remain poorly understood. To date, 12 fungal avirulence genes have been cloned. The peptides encoded by these genes share no structural homology, except for their size which is generally small. Thus, studying more avirulence genes is desirable. Map based cloning remains the best way to clone these genes. The genome sequence of Magnaporthe grisea provided recently a useful tool to rapidly develop microsatellite molecular markers. Among the 1,436 microsatellite sequences identified in the genome, we chose 243 sequences, distributed throughout the genome, to define primers pairs allowing for their amplification by PCR. Eight percent of these primers did not amplify any product. Among the others, 43 % revealed polymorphism between the parents of a reference cross (Guy11 x 2539) as analysed on 3 % agarose gels. One hundred-thirty six microsatellite markers were added to the existing map. These markers are distributed over the seven chromosomes at an average distance of 10 cM. Two crosses between different M. grisea strains allowed to identify 7 avirulence genes. The reference microsatellite map was used to choose markers that allowed us to map them in the new crosses or to increase the density of markers in areas surrounding the avirulence genes. The use of a reference microsatellite map turned out to be very rapid and very efficient for the construction of framework genetic maps and rough mapping of a gene. (Résumé d'auteur)