CONSTRUCTION OF A COMPOSITE SORGHUM GENOME MAP AND COMPARISON WITH SUGARCANE, A RELATED COMPLEX POLYPLOID

A sorghum composite linkage map was constructed with two recombinant i nbred line populations using heterologous probes already mapped on mai ze and sugarcane. This map includes 199 loci revealed by 188 probes an d distributed on 13 linkage groups. A comparison based on 84 common pr obes was performed between the sorghum composite map and a map of a su garcane (Saccharum spp.) cultivar being developed and presently compri sing 10 tentative Linkage groups. A straight synteny was observed for 2 pairs of linkage groups; in two cases, 1 sorghum linkage group corre sponded to 2 or 3 sugarcane linkage groups, respectively; in two cases 1 sugarcane linkage group corresponded to 2 separate sorghum linkage groups; for 2 sorghum linkage groups, no complete correspondance was f ound in the sugarcane genome. In most cases loci appeared to be coline ar between homoeologous chromosomal segments in sorghum and sugarcane. These results are discussed in relation to published data on sorghum genomic maps, with specific reference to the genetic organization of s ugarcane cultivars, and they, illustrate how investigations on relativ ely simple diploid genomes as sorghum will facilitate the mapping of r elated polyploid species such as sugarcane.