Application of cytoplasmic and nuclear DNA-based marker systems for elucidation of the phylogenetic relationship of Musa acuminate and Musa balbisiana and their hybrids

Musa (Musaceae) is one of the most important staple crops in the tropics and subtropics. The present-day edible bananas originate mostly from the diploid species (2n=22) Musa acuminate and Musa balbisiana. The diploid or polyploid cultivated banana varieties are sterile intra- or interspecific hybrids of these two species and have been fixed through hundreds/thousands of years of human selection. The genetic improvement of banana is slow because knowledge on the putative fertile ancestors is scant. The present study was based on the assumption that the ancestors of the present-day wild types participated in the ancient hybrid formation. These ancient genomes are still analysable in the present-day cultivars because of their limited possibility for recombination in the mostly sterile hybrids. Therefore, in the present work, uniparentally inherited cytoplasmic (maternally inherited chloroplast and paternally inherited mitochondria) as well as biparentally inherited nuclear genome-based marker systems (rDNA) were applied for the identification of putative ancestor genepools of banana. This study was based on a mini core collection of 52 genotypes, including ten M. acuminate and eight M. balbisiana wild types along with ten AAA, ten AAB, eight ABB triploid, three AA, two AB diploid and a single tetraploid cultivar. Genepools featured by present-day wild types could be established with all the three marker systems for M. acuminate, while M. balbisiana yielded no variability for the rDNA locus. Using the cytoplasmic and nuclear marker systems separately, genepools representing the ancient genomes featured by present-day wild types have been established. Using the genepool classification for tracing the maternal lineage by chloroplast and the paternal lineage by mitochondrial genepools in combination with nuclear rDNA genepools allowed the identification of putative family trees suggesting simple ways for the evolution of the present-day hybrid cultivars. In addition, our results indicate that certain wild genotypes are lacking in collections, strengthening the need for more but clearly focused collecting missions.