Partial genomic DNA libraries were
constructed in Musa acuminata and M. balbisiana and screened for clones
carrying repeated sequences, and sequences carrying rDNA. Isolated clones were
characterized in terms of copy number, genomic distribution in M. acuminata and
M. balbisiana, and sequence similarity to known DNA sequences. Ribosomal RNA
genes have been the most abundant sequences recovered. FISH with probes for DNA
clones Radkal and Radka7, which carry different fragments of Musa 26S rDNA, and
Radka14, for which no homology with known DNA sequences has been found,
resulted in clear signals at secondary constrictions. Only one clone carrying
5S rDNA, named Radka2, has been recovered. All remaining DNA clones exhibited
more or less pronounced clustering at centromeric regions. The study revealed
small differences in genomic distribution of repetitive DNA sequences between
M. acuminata and M. balbisiana, the only exception being the 5S rDNA where the
two Musa clones under study differed in the number of sites. All repetitive
sequences were more abundant in M. acuminata whose genome is about 12% larger
than that of M. balbisiana. While, for some sequences, the differences in copy
number between the species were relatively small, for some of them, e.g.
Radka5, the difference was almost thirty-fold. These observations suggest that
repetitive DNA sequences contribute to the difference in genome size between
both species, albeit to different extents.
