Biotechnology applied to the characterisation of the banana germplasm

Cultivated bananas have first been susPected to originate from four different wild species : Musa acuminata (A), M. balbisiana (B), M. schizocarpa (S) and the Australimusa (T) species. Banana germplasm includes di, tri and tetraploid clones. Cultivated clones have been classified in genomic groups by Simmonds and Shepherd according to their chromosome number and morphological traits; the main groups are AA, AAA, AAB, ABB, AS and AAT. Biotechnology now allows a precise and early characterisation of the genomic nature of the accessions. Flow cytometry allows a rapid determination of ploidy level of a clone and in some extend of its genomic group. Analysis of the nuclear genome using only 8 STMS allows the classification of an accession in a genomic group and subgroup. Recently, genomic in situ hybridisation has permitted to determine the specific origin - A, B, S or T- of the chromosomes of some interspecific clones. Molecular markers have also led to a better understanding of the origin of cultivated bananas, particularly through the analysis of the A genome variability. The maternal and paternal origin of the clones may be inferred respectively from the RFLP analysis of the chloroplast and mitochondria genomes. RFLP analysis of the nuclear genome of cultivated bananas reveals all the wild acuminata subspecies at their origin. For instance, this study has shown that fruit quality is related to the nature of the A genome: cooking types with a M a. bankii / errans origin, and dessert types with a M a. malaccensis / zebrina origi