THE INTERSPECIFIC GENOME STRUCTURE OF CULTIVATED BANANA, Musa spp. REVEALED BY FLOW CYTOMETRY AND GENOMIC DNA IN SITU HYBRIDISATION.

¹ CIRAD, BP 5035, 34032 Montpellier Cedex 1, France

² CIRAD, Neufchâteau 97130 Capesterre B/E, Guadeloupe, French West Indies

The genomes of four different wild Musa species are involved in cultivated bananas : the A, B, S and T genomes related to M. acuminata, M. balbisiana, M. schizocarpa and the Australimusa species, respectively. Most cultivated clones are triploid or diploid. They have been classified into genomic groups according to chromosome numbers and morphological traits. The main groups are AA, AAA, AAB, ABB, AS or AT. Flow cytometry reveals that the sizes of A, B, S and T genomes are significantly different. M. balbisiana has the smallest genome (1.03 pg/2C, 2n=2x=22), followed by M. acuminata (1.11 pg/2C, 2n=2x=22) and M. schizocarpa (1.18 pg/2C, 2n=2x =22). The highest value was obtained for the Australimusa species M. textilis (1.27 pg/2C, 2n=2x=20). Genome size can thus be used to determine the species involved in interspecific diploid clones. Genomic in situ hybridization has been developed to characterize the specific origin of the chromosomes in interspecific clones. This technique enables us to differentiate the chromosomes from the genomes A, B, S and T and is being used to determine the exact genome structure of cultivated clones and synthetic hybrids.