Confirmation of ancient polyploidy in Dahlia (Asteraceae) species using genomic in situ hybridization

The successful production of interspecific hybrids between members of the d ysploid chromosome series in Dahlia offers a unique opportunity to investig ate chromosome evolution. Analysis of meiotic metaphase I in these hybrids using genomic in situ hybridization (GISH) has shown that pairing occurs bo th between and within parental genomes. These results have provided clear e vidence for the allotetraploid origin of Dahlia species with 2n = 32 and su ggests that species with 2n = 34 and 2n = 36 have also arisen via allopolyp loidy. A bivalent promoting mechanism proposed for species with 2n = 32 als o appears to be present in Dahlia species with 2n = 34 and 2n = 36. (C) 199 9 Annals of Botany Company.