Linkage disequilibrium among modern sugarcane cultivars

Modern sugarcane cultivars are derived from a few interspecific hybrids cre ated early in this century. Linkage disequilibrium was investigated in a po pulation of 59 cultivars representing the most important commercial clones bred in Mauritius as well as a few old cultivars involved in their genealog y. Thirty-eight probes scattered over the sugarcane genome map were used to reveal RFLPs. Forty-two cases of bilocus associations were observed involv ing a total of 33 loci. Most of them are separated by less than 10 cM. All the corresponding allele couples were found in at least 1 of the originally created cultivars, suggesting that they depict ancient associations. This global disequilibrium is interpreted as the result of the foundation bottle neck related to the first interspecific crosses; the preferential allele as sociations thus created have been maintained through subsequent crosses whe n the loci were closely linked. This phenomenon is likely also to apply to genes of agricultural interest. A practical consequence is that markers can be used to track known QTLs in modern breeding materials without the neces sity to repeatedly study segregating progenies. This structure gives high v alue to the correlation between molecular markers and agricultural traits a mong cultivars.