Chromosome numbers are given for 16 taxa (and one interspecific hybrid) of Hieracium subgen. Pilosella originating from Central Europe: H. apatelium Nägeli et Peter (2n = 45), H. aurantiacum L. (2n = 36), H. bauhini Besser (2n = 36, 45, 54), H. brachiatum Bertol. ex DC. (2n = 45, 48, 63, 72), H. densiflorum Tausch (2n = 36), H. echioides Lumn. (2n = 18, 27, 36), H. floribundum Wimm. et Grab. (2n = 36, 45), H. glomeratum Froel. (2n = 36, 45), H. guthnickianum Hegetschw. (2n = 54), H. lactucella Wallr. (2n = 18), H. onegense (Norrl.) Norrl. (2n = 18), H. pilosella L. (2n = 36, 45, 54), H. piloselliflorum Nägeli et Peter (2n = 36, 45), H. piloselloides Vill. (2n = 36), H. rothianum Wallr. (2n = 36), H. schultesii F. W. Schultz (2n = 45), and the hybrid H. floribundum × H. aurantiacum (2n = 36). New chromosome numbers are reported for H. brachiatum and H. floribundum. The octoploid cytotype (2n = 72), recorded in H. brachiatum, is the highest ploidy level ever found in plants from the subgen. Pilosella originating from the field. Aneuploidy, rare in this subgenus in Europe, occurs in this hybridogenous species as well: it was recorded in one plant (2n = 48) collected in a hybrid swarm H. pilosella × H. bauhini. The breeding system in H. bauhini, H. brachiatum, H. densiflorum, H. echioides, H. pilosella, H. piloselloides, and H. rothianum was studied. The sexual reproduction of pentaploid H. pilosella is a new observation: it means an increase of diversity in possible reproduction modes of those cytotypes having odd chromosome numbers.
The annotated chromosome numbers of 25 species from 6 families of monocotyledons, most of them (14) belonging to Poaceae family, are presented here. The data, except three chromosome counts (Allium oleraceum from Hungary and Calamagrostis villosa from Slovakia), are all based on plants collected in the Czech Republic. The karyological data of 21 species represents new information. While the majority of species presented here originated from one or two localities each, the species Calamagrostis villosa has been studied more extensively: all plants, collected altogether at 13 localities (mountain and lower altitudes), are characterized by an invariable decaploid level (2n = 70). The record of triploid Allium oleraceum is only the second reference to this rare ploidy level in this species. All original karyological data are compared with literature references to particular species, preferentially from Europe.
Gymnadenia densiflora was recently either misinterpreted or not accepted as a distinct taxon by several authors. To resolve its taxonomic position and differentiation from the related G. conopsea, a detailed study of the morphology, chromosome numbers and distribution of these two taxa in the Czech Republic, Slovakia and neighbouring areas was carried out. Chromosome counts showed an invariable diploid chromosome number (2n = 40) for G. densiflora, while G. conopsea is diploid, tetraploid and rarely also pentaploid (2n = 40, 80, 100). Results of morphometric analyses (principal component analysis, cluster analysis, classificatory and canonical discriminant analysis) confirmed a good morphological separation between G. densiflora and G. conopsea. Characters such as the width of the second lowermost leaf, height of the plant, number of flowers in the inflorescence, number of leaves, and the ratio of height of the plant and distance from the stem base to the base of the uppermost sheathed leaf contributed most to this separation. Our study supports the recognition of G. densiflora as a distinct species.
Populations of Pilosella (Hieracium subgenus Pilosella) at ruderal localities were investigated in an urban area (Prague City) with respect to their distribution, variation in DNA ploidy level/chromosome number and mode of reproduction. The following species, hybridogenous species or hybrids (with ploidy level/chromosome number and mode of reproduction) were found: P. aurantiaca, P. caespitosa (4x, 5x), P. cymosa subsp. vaillantii (5x), P. officinarum (2n = 36, sexual; 2n = 54, sexual; 2n = 63), P. piloselloides subsp. bauhinii (2n = 45, 54; both apomictic), P. piloselloides subsp. praealta (5x; apomictic), P. brachiata (4x; sterile), P. densiflora, P. flagellaris, P. floribunda, P. erythrochrista, P. glomerata (5x; apomictic), P. leptophyton (5x; apomictic), P. rothiana (4x, apomictic), P. setigera, P. visianii (4x; apomictic), P. ziziana (4x, apomictic) and the previously undescribed hybridogenous type P. piloselloides × P. setigera (5x, apomictic). Pilosella visianii is reported from the Czech Republic for the first time. New habitats resulting from highway construction are suitable for Pilosella species. Many previously rare types, such as P. rothiana, can colonize these habitats and spread, not only locally, but also throughout the whole country.
Haploid parthenogenesis in facultatively apomictic Pilosella generated polyhaploid progeny (with half the maternal chromosome set) both in natural populations and garden experiments. Production of polyhaploids varied considerably among different species, hybridogenous species and hybrids. In the field (14 localities), the highest frequency of polyhaploids exceeded 80% of the total seed progeny produced by some recent hybrids. A similar diversity in the production of polyhaploids was also recorded in garden experiments. A two-step process by which new genotypes of both P. aurantiaca (tetraploid) and P. rubra (hexaploid) were formed under garden conditions during a polyploid–polyhaploid–polyploid cycle is described. In the first step, the maternal plants generated dihaploid and trihaploid F1 progeny, respectively. Although a substantive part of this polyhaploid progeny was either non-viable or sterile, the apomictic polyhaploids occasionally doubled their genome. Consequently, the F2 progeny resulting from the second step had a double ploidy level, identical to that of the original maternal parent. The complete process was autonomous, without contribution of pollen from parent genotype. This cycle necessarily implicates increasing homozygosity in F2 progeny compared to the original maternal polyploid plant. The probabilities of particular steps of this process occurring in Pilosella and the variation in polyhaploids are estimated and described, and the ability of polyhaploid plants to survive under field conditions discussed. Probability of the complete cycle (haploid parthenogenesis followed by doubling of the genome), which occurred under garden conditions in P. rubra, is estimated to be in the order of hundredths of percent. Despite this low probability, it can result in the production of new homozygous genotypes in populations of apomicts, especially in those occurring in disturbed habitats with little competition.
We studied the agamic complex of Hieracium subgen. Pilosella in the Šumava/Böhmerwald, the borderland between the Czech Republic and Germany. Their DNA ploidy levels/chromosome numbers, breeding systems, chloroplast haplotypes as well as the clonal structure of apomicts were determined. The complex consists of the following basic and intermediate species and recent hybrids. Basic species: H. aurantiacum L. (tetraploid and pentaploid, both apomictic), H. caespitosum Dumort. (tetraploid, apomictic), H. lactucella Wallr. (diploid, sexual), H. pilosella L. (tetraploid, sexual); intermediate species: H. floribundum Wimm. et Grab. (tetraploid, apomictic), H. glomeratum Froel. (tetraploid and pentaploid, both apomictic), H. scandinavicum Dahlst. (tetraploid, apomictic); recent hybrids: H. floribundum × H. pilosella (partly corresponding to H. piloselliflorum – tetraploid and hexaploid; tetraploid sexual or apomictic), H. glomeratum × H.pilosella (aneuploid, 2n = 38), H. aurantiacum × H. floribundum (tetraploid, almost sterile or apomictic), H. lactucella × H. pilosella (H. schultesii, triploid sterile, tetraploid sexual), H. aurantiacum × H. pilosella (H. stoloniflorum, tetraploid, sexual), H. aurantiacum > H. pilosella (H. rubrum, hexaploid). The hexaploid hybrids between H. pilosella and H. floribundum or H. aurantiacum produced mainly polyhaploid progeny. Two trihaploid plants were found growing in the neighbourhood of their putative hexaploid maternal parent H. rubrum, which is the first record of polyhaploids of this subgenus in the field. Comparison with other mountain ranges (especially the Krušné hory/Erzgebirge, and Krkonoše) with an almost identical composition of basic species, revealed that the structure of the agamic complexes differ.
This paper reviews recent use of flow cytometry in studies on apomictic plant taxa. The most of apomictic angiosperms are polyploid, often differing in ploidy level from their sexual counterparts within the agamic complex. Flow cytometry is widely used for screening the ploidy levels of mature plants and their seed generated both in the field and in experiments. Routine ploidy screening often accompanied by molecular markers distinguishing individual genotypes are used to reveal novel insights into the biosystematics and population biology of apomictic taxa. Apomixis (asexual seed formation) is mostly facultative, operating together with other less frequent reproductive pathways within the same individual. The diversity in modes of reproduction in apomicts is commonly reflected in the ploidy structure of their progeny in mixed-cytotype populations. Thus, flow cytometry facilitates the detection and quantification of particular progeny classes generated by different reproductive pathways. The specific embryo/endosperm ploidy ratios, typical of the different reproductive pathways, result from modifications of double fertilization in sexual/apomictic angiosperms.Thus, the reproductive origin of seed can be identified, including autonomous or pseudogamous apomixis, haploid parthenogenesis and sexual reproduction, involving either reduced or unreduced gametes. Collectively, flow cytometry has been used to address the following research topics: (i) assessing the variation in ploidy levels and genome sizes in agamic complexes, (ii) detection and quantification of different reproductive modes in facultative apomicts, (iii) elucidation of processes in populations with coexisting sexual and apomictic biotypes, (iv) evolution of agamic complexes, and (v) genetic basis of apomixis. The last topic is of paramount importance to crop breeding: the search for candidate gene(s) responsible for apomixis is the main objective of many research programmes. A list of the angiosperm taxa that could provide model systems for such research is provided.