Molecular cytogenetic investigation of chromosome composition and transmission in sugarcane.

Modern sugarcane cultivars (Saccharum spp., 2n = 100-120) are complex polyploids derived from interspecific hybridization performed a century ago between the sugar-producing species S. officinarum L. and the wild species S. spontaneum L. Using genomic in situ hybridization, we revealed that between 15 and 27.5% of the genome of modern cultivars is derived from S. spontaneum, including 10-23% of entire chromosomes from this wild species and 8-13% chromosomes derived from interspecific recombination. We confirmed the occurrence of 2n + n transmission in crosses and first backcrosses between these two species and demonstrated that this also can occur in crosses between S. officinarum and modern cultivars. We analysed five S. officinarum clones with more than 80 chromosomes and demonstrated that they were derived from interspecific hybridization supporting the classical view that this species is characterized by 2n = 80. We also illustrated the complementarities between molecular cytogenetics and genetic mapping approaches for analysing complex genomes.