Résumé
Introgression with wild relatives plays a major role in sugarcane breeding. Present sugarcane cultivated clones (#Saccharum# spp. 2n = 100 to 130) are derived from interspecific hybridizations between the sugar producing species, #S. officinarum#, and wild relatives, mainly #S. spontaneum#. We are usina DNA #in situ# hybridization to investigate the complex genome structure of sugarcane cultivars. The rDNA sites have been located by in situ hybridization in the main species of the #Saccharum# genus. The results support a basic chromosome numbers of 10 for #S. Officinarum# and #S. robustum# and 8 for #S. spontaneum# and provide a first bridge between physical and genetic mapping. Using genomic DNA in situ hybridization, we showed the possibility of distinguishing the chromosomes contributed by the species #S. officinarum# and #S. spontaneum# in sugarcane cultivars and, contradicting previous assumptions, demonstrated the occurence of chromosome exchange between these two species. Characterisation of #S. spontaneum# contribution to cultivars from various temperate/sub-tropical and tropical origins is curently in progress. In the cultiver R570 and NCo 376, we identified, about 10% and 22 % of whole chromosomes contributed by #S. spontaneum# respectively and, about 10% of chromosomes derived from exchanges between the two species #S. officinarum# and #S. spontaneum#. Investigating the genome structure of #S. barber#) usina genomic #in situ# hybridization, we could identified two groupe of chromosomes derived from #S. officinarum# and #S. spontaneum# demonstrating the interspecific origin of this taxonomical group. (Texte intégral)