Genome Size Variation In Hieracium Subgenus Pilosella

J Suda1,2, A Krahulcová2, F Krahulec2, R Rosenbaumová2 and T Peckert1

1 Department of Botany, Charles University, Benátská 2, Prague, CZ-128 01, Czech Republic
2 Institute of Botany, Academy of Sciences of the Czech Republic, Pruhonice 1, CZ-252 43, Czech Republic

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    Hieracium subg. Pilosella (hawkweed) is a typical example of a taxonomically intricate polyploid complex whose structure is substantially influenced by hybridization. The group consists of two types of taxa: the "basic" species and the "intermediate" species of hybridogenous origin. A continuous variation connecting the intermediate species with the basic ones is common. Flow cytometry was employed to test whether the genome size reflects the species relationships established on the basis of the morphological traits. The genome size (DNA content of the monoploid chromosome set) of the basic species varied from 1.70 pg in hexaploid H. pilosella to 2.11 pg in diploid H. onegense (about 1.24-fold difference). A tendency towards a reduction of the genome size was detected in higher ploidy levels of multiploid species. Nevertheless, these differences were small with a maximum value of 4.5% between the diploid and tetraploid cytotypes of H. cymosum. A low variation in nuclear DNA content within the cytotypes supports a theory of stable genome size. Preliminary results indicate that the location of genome size of the intermediate taxa is in the range between the values of their putative parents, although closer to the parental species with the lower DNA content.