Determination of the ploidy level in the genus Hieracium subgenus Pilosella (Hill) S.F. Gray by flow cytometric DNA analysis

Ploidy levels of 8 taxa of the genus Hieracium subgenus Pilosella collected from the same locality were determined by means of flow cytometric estimation of relative nuclear DNA content. The DNA analysis of isolated nuclei stained with propidium iodide was performed with a flow cytometer equipped with an argon-ion laser. The diploid species H. lactucella (2n=18) was used as internal standard. As a rule 20 individuals per taxon were analysed. The flow cytometric analysis proved to be a rapid, accurate and sensitive method for screening of ploidy levels. Considering the known cytological data, the following ploidy levels were determined: H. aurantiacum 4x, H. pilosella 4x, H. piloselloides 4x, H. bauhini 5x, H. caespitosum 5x, H. stoloniflorum 4x, H. brachiatum 4x and 6x, H. leptophyton 7x. H. piloselloides, H. bauhini and H. caespitosum yield relative DNA contents which are the exact multiples of the haploid DNA content of H. lactucella. In the case of H. pilosella the haploid DNA content is lower than that predicted from the diploid, namely 0.43 instead of the expected 0.5. The haploid 1x DNA contents of both H. brachiatum and H. leptophyton range between the value found for H. pilosella and those for the other investigated species, confirming their hybrid origin.