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.
Sturgeons (Chondrostei: Acipenseriformes) display markedly disjunction distributions with a wide distribution in the northern hemisphere. Their unique benthic specializations and conserved morphology, evolutionary age, the variation in their basic diadromous life history, and the large public interest due to their near extinction or critically endangered status make sturgeons and paddlefishes interesting groups for molecular and cytogenetic studies. From altogether 27 acipenseriform species, seventeen species are supposed to be critically endangered, two species are classified as endangered, four species are vulnerable and other species are near threatened or in low-risk (IUCN Red list 2010). Sturgeons are characteristic by a relatively high number of chromosomes in cell nuclei and differences in ploidy levels. Sturgeons displayed a strong tendency for interspecific and inter-generic hybridization under altered environmental conditions as well as under conditions of artificial propagation. Almost 20 inter-specific sturgeon hybrids were described. The decrease of natural populations and tendencies leading to restocking may result in uncontrolled restocking, production of hybrid specimens (even with non-native species) and decrease of natural genetic diversity of species in their original distribution area. Identification of parental species of natural hybrids by modern methods of molecular biology is still not easy. Here, we attempt to briefly summarize the major aspects of sturgeon genetics and cytogenetics related to ploidy levels and interspecific hybridization.
Four European taxa of the Tortula muralis complex (T. lingulata, T. muralis var. aestiva, T. muralis var. muralis, T. obtusifolia) were evaluated using multivariate analysis of morphological characters, a cultivation experiment and cytological screening (flow cytometry, chromosome counts). This study revealed that only T. lingulata is morphologically well defined within the complex and several new sporophytic characters that can be used to distinguish this taxon from the superficially most similar T. obtusifolia. The traditionally recognized taxa T. muralis var. muralis, T. muralis var. aestiva and T. obtusifolia showed continuous variation, with frequent intermediate plants. However, the main character of the gametophyte used for determination (costa excurrency) proved to be stable in cultivation, indicating that this character is under genetic control. Additionally, rather complex and only partly species-specific patterns of ploidy variation were found within the complex. Tortula lingulata and T. obtusifolia appear to be cytologically homogeneous; plants of T. lingulata were found to be diploid, whereas plants tentatively named as T. obtusifolia were haploid. In contrast, both haploid and diploid cytotypes were found in both varieties of T. muralis, with a marked predominance of diploids in var. aestiva and less marked predominance of diploids in var. muralis. Current varietal level of the evaluated infraspecific taxa of T. muralis was thus found to be warranted. It is suggested that plants previously recognized as T. obtusifolia should be treated as a subspecies of T. muralis.
Perennial grasses belonging to the genus Molinia are widespread in most of Europe and consist of a polyploid complex of closely related taxa with a confusing taxonomy. Based on extensive sampling at 241 localities in Europe, four cytotypes were identified based on chromosome counts and results of flow cytometry: tetraploids (2n = 36), hexaploids (2n = 54), octoploids (2n = 72) and dodecaploids (2n = 108). While tetra- and dodecaploids were commonly recorded, octoploids were less common and only two hexaploid individuals were identified. Previously reported decaploid counts (2n = 90) from central Europe are probably erroneous and refer to 2n = 108. The tetraploid cytotype is distributed throughout Europe and broadly sympatric with other cytotypes. Octo- and dodecaploids were spatially separated with dodecaploids occurring in the western, central and south-central part of Europe and octoploids in the east-central and southeastern part of Europe. All quantitative characters measured (lengths of lemmas, anthers, caryopses and stomata, lengths of the longest hair on the callus and diameter of the culm below the panicle) showed a linear trend across ploidy levels. Tetra-, octo- and dodecaploid cytotypes formed almost non-overlapping groupings in principal component and discriminant analyses of morphological characters. The following taxonomic concept of this complex is proposed: Molinia caerulea (L.) Moench is a predominantly tetraploid taxon incorporating very rarely reported hexaploid and perhaps also diploid plants; higher cytotypes (2n = 8x, 12x) are considered to be M. arundinacea Schrank, consisting of two subspecies: a dodecaploid subspecies occurring in the southern and western part of central Europe and the octoploid Molinia arundinacea subsp. freyi Dančák in east-central and southeastern Europe.
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.