Résumé
The complex genomic structure of modern cultivars of sugar cane, related to high polyploidy, aneuiploidy and multispecfic origin, was investigated using molecular cytogenetics. lt was demonstrated: i) that the two species involved in modern cultivars, namely S. officinarum (2n=80), the sugar producing species, and S spontaneum (2n=40 to 128), the wild species, have different basic chromosome numbers respectively 10 and 8, ii) that intrachromosomal exchanges occur between these two species and, iii) that the proportion of chromosomes derived front S. spontaneum varies between cultivars (from 1 5 to 25% in the clones studied). It was shown that the taxonomic group, S. barberi, is also derived from interspecific hybridization between S officinarum and S. spontaneum but this kept a much larger proportion of S. spontaneum chromosomes than have modern cultivars. This complex genome structure of cultivars makes the analysis of agronomic trait inheritance difficult However. studying resistance to rust in the self progeny of the clone R 570. it was possible to identify a 3 (Resistant): 1 (Susceptible) segregation indicative of a major dominant resistance gene. These results were obtained through both a field trial and an artificial test in a glass house; they were originally obtained on 150 individuals and have been verified on 700 additional individuals. The rust resistance gene was located on the RFLP map of R 570. The current objective is to produce a fine map around the gene with the ultimate goal of cloning the resistance gene. Two o strategies are currently used to add markers in the vicinity of the gene, one based on the synteny and colinearity demonstrated between sugar cane, sorhum, maize and rice and the other one based on bulk segregant analyses using AFLP markers. (Texte intégral)