RFLP MAPPING IN CULTIVATED SUGARCANE (SACCHARUM SPP) - GENOME ORGANIZATION IN A HIGHLY POLYPLOID AND ANEUPLOID INTERSPECIFIC HYBRID

Sugarcane cultivars are polyploid, aneuploid, interspecific hybrids be tween the domesticated species Saccharum officinarum and the wild rela tive S. spontaneum. Cultivar chromosome numbers range from 100 to 130 with similar to 10% contributed by S. spontaneum. We have undertaken a mapping study on the progeny of a selfed cultivar, R570, to analyze t his complex genome structure. A set of 128 restriction fragment length polymorphism probes and one isozyme was used. Four hundred and eight markers were placed onto 96 cosegregation groups, based on linkages in coupling only. These groups could tentatively be assembled into 10 ba sic linkage groups on the basis of common probes. Origin of markers wa s investigated for 61 probes and the isozyme, leading to the identific ation of 80 S. officinarum and 66 S. spontaneum derived markers, respe ctively. Their distribution in cosegregation groups showed better map coverage for the S. spontaneum than for the S. officinarum genome frac tion and occasional recombination between the two genomes. The study o f repulsions between markers suggested the prevalence of random pairin g between chromosomes, typical of autopolyploids. However, cases of pr eferential pairing between S. spontaneum chromosomes were also detecte d. A tentative Saccharum map was constructed by pooling linkage inform ation for each linkage group.