Résumé
Modern sugarcane cultivars have a particularly complex genome, being highly polyploid (100-130 chromosomes), aneuploid, and of interspecific origin. Bru1, a major dominant gene conferring resistance to brown rust, has been identified in the cultivar R570. This gene was shown to confer resistance to all eight isolates of Puccinia melanocephala H. & P. Syd. from Brazil, Colombia, Florida (three isolates), Guadeloupe, Réunion, and Zimbabwe that we tested. Bru1 is the focus of a map-based cloning approach that so far resulted in the development of (i) a highresolution genetic map and (ii) a partial physical map of the target haplotype that features an insertion specific to this haplotype. This insertion is associated with a local reduction of the rate of meiotic recombination. Several markers surrounding Bru1 in R570 were surveyed in 380 international sugarcane cultivars that were phenotyped for rust resistance in Réunion Island (Mascarene) or Guadeloupe Island (West Indies). They exhibited strong linkage disequilibrium in the target region. Two PCR markers were found completely associated with Bru1 in the whole population and thus represent efficient molecular diagnostic makers for Bru1 detection. The results suggest that Bru1 is the main source of brown rust resistance in modern cultivars. Only 6.6 % of the resistant cultivars tested did not shown the Bru1 haplotype; they represent alternative sources of resistance to brown rust. These diagnostic markers are used to trace the origin of the chromosome insertion that includes Bru1. Preliminary results suggest that the insertion is old and could have been transmitted to modern cultivars via the Indian canes (barberi) which are natural hybrid between S. officinarum and S. spontaneum. (Résumé d'auteur)