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Annals of Botany 81: 647-656, 1998
© 1998 Annals of Botany Company

Polyploidy and Evolution in Wild and CultivatedDahliaSpecies

MELANIE GATT, HONG DING, KEITH HAMMETT and BRIAN MURRAY+,

School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand 488C Don Buck Road, Massey, Auckland, 8, New Zealand

Received: November 4, 1997 ; Accepted: January 29, 1998 .

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

Chromosome pairing,Dahlia, in situhybridization, karyotype analysis, polyploidy, synaptonemal complex analysis


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