Polyploidy and Evolution in Wild and CultivatedDahliaSpecies

摘要: Observations on the chromosomes of nine species Dahlia Cav. (Asteraceae, Heliantheae—Coreopsidinae) show that some have 2n fl 32, others 64, with a third group having both chromosome numbers in same taxon. Karyotype investigations showed can be divided into groups 14 metacentrics plus two submetacentrics per set 16 chromosomes. In situ hybridization using an rRNA gene probe indicated 32 eight sites whilst 64 sites. Silver nitrate staining these regions not all nucleolar organizers are active. Meiotic analysis at metaphase I and pachytene, by synaptonemal complex spreading, shows exclusive bivalent formation whereas small univalents quadrivalents addition to bivalents. This study proposes allotetraploids those races their autopolyploid derivatives. We suggest bivalent-promoting mechanism may account for meiotic behaviour as component genomes appear so similar, this is also responsible low number taxa. # 1998 Annals Botany Company