Sugarcane cultivars are interspecific hybrids between Saccharum officinarum (S.o., 2n=80, x=10) and Saccharum spontaneum (S.s., 2n=40-128, x=8). They are derived from a few interspecific crosses a century ago, followed by recurrent intercrossing among the progeny. Partial genome mapping studies suggest that the mode of chromosome assortment in S.s. is essentially polysomic, whereas S.o. exhibits some preferential pairing in part of its genome. Our model cultivar (R570, 2n=Ca115) has approximately 80: 10: 10% chromosomes derived from S.o., S.s. and interspecific recombination, respectively, as visualized by GISH. Molecular markers covering about half of the genome (more than 1000 markers) detect 12 cases of strong preferential chromosomal pairing, even possibly exclusive pairing in 6 cases; several instances illustrate possibilities for interspecific intrachromosomal recombination. The rest of the genome seems little affected by preferential pairing. We investigated the mutual affinities between homo- or homoeologous chromosomes for a particular linkage group by surveying one locus for which we could resolve all 10 alleles. The result is an atypical picture, with occasional lack of pairing, leading to more than two chromosomes left impaired per meiosis, and with pairing frequencies between homo(eo)logues ranging from 0 to 40%. Sugarcane, as exemplified by this cultivar, thus displays a continuous range of pairing affinities between chromosomes. (Texte intégral)