Confirmation of Ancient Polyploidy in Dahlia (Asteraceae) Species using Genomic In Situ Hybridization

The successful production of interspecific hybrids between members of the dysploid chromosome series in Dahlia offers a unique opportunity to investigate chromosome evolution. Analysis of meiotic metaphase I in these hybrids using genomic in situ hybridization (GISH) has shown that pairing occurs both between and within parental genomes. These results have provided clear evidence for the allotetraploid origin of Dahlia species with 2n=32 and suggests that species with 2n=34 and 2n=36 have also arisen via allopolyploidy. A bivalent promoting mechanism proposed for species with 2n=32 also appears to be present in Dahlia species with 2n=34 and 2n=36 .