Ploidy levels of 8 taxa of the genusHieracium subgenusPilosella collected from the same locality were determined by means of flow cytometric estimation of relative nuclear DNA content. The DNA anaysis of isolated nuclei stained with propidium iodide was performed with a flow cytometer equipped with an argon-ion laser. The diploid speciesH. 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 andH. caespitosum yield relative DNA contents which are the exact multiples of the haploid DNA content ofH. lactucella. In the case ofH. 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 bothH. brachiatum andH. leptophyton range between the value found forH. pilosella and those for the other investigated species, confirming their hybrid origin.
Apomixis AsteraceaeChromosome number CompositaeHybrid origin Nuclear DNA content