The interspecific genome structure of cultivated banana, Musa spp. revealed by genomic DNA in situ hybridization

In cultivated banana, Musa spp., there are four known genomes, A, B, S, and T. These correspond to the genetic constitutions of wild Eumusa species M. acuminata, M. balbisiana. M, schizocarpa and the Australimusa species, res pectively. Most cultivated clones are triploid or diploid, they have been c lassified into genomic groups according to chromosome numbers and morpholog ical traits. Genomic in situ hybridization (GISH) enabled us to differentia te the chromosomes of these four genomes; however, a distal portion of the chromosomes remained unlabelled. GISH was used to determine the exact genom e structure of interspecific cultivated clones. In most cases the results w ere consistent with the chromosome constitution estimated by means of pheno typic descriptors. The one notable exception, the clone 'Pelipita', has the 8 A and 25 B chromosomes instead of the predicted 11 A and 22 B. GISH also enabled us to determine the chromosome complement of a few clones that cou ld not be classified only on the basis of phenotypic descriptors and chromo some counts. The rDNA sites were located in Musa species. They appeared to be often associated with satellites, which can be separated from the chromo somes, representing a potential source of error for chromosome counting usi ng classical techniques.