Interspecific hybridization and the analysis of meiotic chromosome pairingin Dahlia (Asteraceae-Heliantheae) species with x=6

The successful production of a large number of artificial hybrids between D ahlia species based on x=16 has allowed a detailed study of their genomic r elationships. Chromosome behaviour in these artificial hybrids was extremel y similar to that observed in parental species suggesting that there is a c onsiderable degree of homology between the genomes of these Dahlia species. Using GISH it can be demonstrated that in these hybrids bivalent formation involved pairing only between parental genomes. The ability of GISH to dif ferentiate between parental genomes in artificial hybrids was variable, ind icating that molecular divergence of highly repeated sequences has accompan ied the evolution of these species. However, the extent of chromosome pairi ng and chiasma formation in the hybrids does not reflect the differences th at can be detected by GISH. Several of the new hybrid combinations have res ulted in horticulturally interesting plants.