rDNA-FISH pattern in selected <i>Hieracium</i> species representing different ploidy levels

Abstract

Polyploid species of <i>Hieracium</i> s.str. are near-obligatory apomicts capable of producing non-reduced pollen grains and intrageneric crossing with sexual diploid species. Most probably, such a mating system leads to the emergence of separate lineages of apomictic plants with increased ploidy levels, each of which has a complete set of genomes of its putative (most probably triploid) apomictic parent. The correct identification of such lineages could facilitate taxonomic and phylogenetic research in <i>Hieracium</i>. In this paper, we analyzed the distribution of the 5S and 45S rDNA segments in the karyotypes of six selected <i>Hieracium</i> taxa, representing all ploidy levels reported in the genus: <i>H. alpinum</i> 2x, <i>H. alpinum</i> 3x, <i>H. schustleri</i> 4x, <i>H. chrysostyloides</i> 5x (<i>H</i>. sect. <i>Alpina</i>) and <i>H. bifidum</i> 3x, <i>H. levicaule</i> 3x (<i>H</i>. sect. <i>Bifida</i>). The analyzed rDNA markers suggest that two taxa of the higher ploidy level (4x and 5x) belonging to <i>H</i>. sect. <i>Alpina</i> inherited three genomes from the triploid <i>H. alpinum</i>, which has 2:1 genomic composition with two genomes from diploid <i>H. alpinum</i> and one genome with an untypical 5S rDNA-bearing chromosome of unknown origin. <i>H. bifidum</i> and <i>H. levicaule</i> differ from each other in the rDNA distribution pattern, which suggests that <i>H</i>. sect. <i>Bifida</i> may be a less homogenous group of species.