Résumé
The level of linkage disequilibrium (LD) in a crop germplasm collection determines the scale at which associations studies will resolve the localisation of favourable variation in the genome. Among grasses, LD estimates range from several-cM segments in sugarcane, where modern cultivars form a very recent interpsecific population, to the nucleotide level in maize, an old annual outbreeder. In rice, a selfpollinating species, LD spans over segments larger than 100 kb in the germplasm sample surveyed. Sorghum (Sorghum bicolor L.) provides another example of predominantly selfing crop. We used RFLP among 205 representative accessions to assess LD between 12 loci within a 4cM/600kb segment of a distal chromosomal region, with reference to a genome-wide RFLP survey at 74 loci. In the target segment, LD commonly extends beyond 2 cM and decays within 4 cM. Use of the genome-wide survey for selecting a less structured subsample of accession improves the significance of the results. This opens the door to genome-wide association studies and supports the identification of reference collections to integrate phenotypic and molecular characterisation efforts. (Texte intégral)