Ivana Plačková

Isoenzyme diversity in Reynoutria (Polygonaceae) taxa: escape from sterility by hybridization

The genus Reynoutria is represented by four taxa in the Czech Republic – R. japonica var. japonica and compacta, R. sachalinensis and R. × bohemica. Using isoenzyme analysis, we determined the degree of genotype variability in all taxa and compared clones of R. japonica var. japonica from the Czech Republic with those from Great Britain. While the rarely occurring tetraploid variety R. japonica var. compacta possesses low variability, the octoploid female clone of R. japonica var. japonica is genetically uniform in the 93 clones sampled and belongs to the same genotype that is present in the whole Europe. R. japonica var. japonica can be fertilized by the pollen of tetraploid R. sachalinensis and a hexaploid hybrid R. × bohemica is produced. In R. sachalinensis, 16 genotypes were found in the 50 clones sampled. R. × bohemica is genetically the most diverse taxon in the study area, with 33 genotypes recorded among 88 clones sampled.

How much genetic variation is stored in the seed bank? A study of Atriplex tatarica (Chenopodiaceae)

We investigated to what extent the soil seed bank differed genetically and spatially in comparison to three consecutive life history stages (seedlings, mature plants, and fruiting plants) in a natural population of Atriplex tatarica. Representatives of particular life history stages from twenty subunits within a large population were randomly collected and subjected to allozyme analysis. Comparison of population polymorphism among various life history stages showed significant differences in observed heterozygosity (HO) and F statistics (FIS and FST), but nonsignificant ones in the cases of number of alleles per polymorphic locus (A) and gene diversity (HS). These results indicate an increasing number of heterozygotes, a decreasing level of inbreeding and an increase of the partitioning genetic diversity among populations with increasing population age. Spatial autocorrelation was used to calculate f, the average co‐ancestry coefficient between individuals within distance intervals of two meters along a 39 m long transect. Significant positive fine scale genetic structure was detected in mature and fruiting plants but not in soil seeds and seedlings stages. The results of the presented study on A. tatarica indicated that significant differences exist in genetic differentiation, differentiation in allele frequencies and spatial autocorrelation among early (soil seeds and seedlings) and late (mature and fruiting plants) life history stages but not within early and late ones. This pattern suggests that, rather than storing genetic variability in the soil or germination and establishment success, self‐thinning might be the major microselective force in populations of A. tatarica.

Rare recent natural hybridization in Hieracium s. str. – evidence from morphology, allozymes and chloroplast DNA

The first proven data on natural hybridization in the genus Hieracium s. str. are presented. Plants with intermediate morphological characters between the diploids H. alpinum and H. transsilvanicum were found in the Muntii Rodnei (Romanian Eastern Carpathians) in 2001 and in the Chornohora Mts (Ukrainian Eastern Carpathians) in 2003. While plants of intermediate morphology between usually so called basic species are usually tri- or tetraploid in Hieracium s. str., these plants were diploid (2n=18) like both parental species in this region. The Romanian plant did not produce fertile achenes in free pollination and in control backcrosses with H. transsilvanicum, two hybrids from Ukraine were completly seed sterile in free pollination and reciprocal crosses. Pollen stainability as an indirect measure of male fertility was quite high in the studied Ukrainian hybrid plants and similar to the parental taxa. Evidence from allozyme analysis also confirmed the hybrid origin of the studied plants. Sequencing and PCR-RFLP analyses of the trnT-trnL intergenic spacer revealed that all hybrid plants had the H. transsilvanicum chloroplast DNA haplotype. Maternal inheritance of chloroplast DNA in this particular cross was proved with artificial hybrids from reciprocal experimental crosses between H. alpinum and H. transsilvanicum. In both localities, the natural hybrid plants were found in disturbed habitats, exceptionally allowing contact of the otherwise ecologically vicariate parental species. Morphologically, the hybrid plants belong to H. × krasani Woł.

Enriching Ploidy Level Diversity: the Role of Apomictic and Sexual Biotypes of Hieracium subgen. Pilosella (Asteraceae) that Coexist in Polyploid Populations

The capacity to generate variation in ploidy and reproductive mode was compared in facultatively apomictic versus sexual maternal plants that coexist in two model populations. The population structure was studied in polyploid hybrid swarms comprised of Hieracium pilosella (usually sexual, less commonly apomictic), H. bauhini (apomictic), and their hybrids (sexual, apomictic, or sterile). Relationships among established biotypes were proposed on the basis of their DNA ploidy level/chromosome number, reproductive mode and morphology. Isozyme phenotypes and chloroplast DNA haplotypes were assayed in the population that was richer in hybrids. The reproductive origin of seed progeny was identified in both sexual and apomictic mothers, using alternative methods: the karyological, morphological and reproductive characters of the cultivated progeny were compared with those of respective mothers, or flow cytometric seed screening was used. In both populations, the progeny of sexual mothers mainly retained a rather narrow range of ploidy level/chromosome number, while the progeny of facultatively apomictic mothers was more variable. The high-polyploid hybrids, which had arisen from the fertilization of unreduced egg cells of apomicts, mainly produced aberrant non-maternal progeny (either sexually and/or via haploid parthenogenesis). Apparently, such versatile reproduction resulted in genomic instability of the recently formed high-polyploid hybrids. While the progeny produced by both true apomictic and sexual mothers mostly maintained the maternal reproductive mode, the progeny of those ‘versatile’ mothers was mainly sexual. Herein, we argue that polyploid facultative apomicts can considerably increase population diversity.

Genetic diversity and its effect on fitness in an endangered plant species, Dracocephalum austriacum L.

The aim of this study was to estimate genetic diversity and assess its importance for plant fitness in a species belonging to the most endangered species in Europe, Dracocephalum austriacum L., and to select the most valuable populations for conservation of genetic diversity within the species in the studied regions. We analyzed allozyme variation of 12 populations in three distinct regions (Czech Karst, Moravia and Slovak Karst) in Central Europe. The results showed high genetic diversity within populations (80.14%) and relatively low differentiation among populations within regions (9.42%) and between regions (10.45%). Seed production was significantly higher in larger, genetically more diverse and less inbred populations. The results suggest that genetic diversity has important effect on seed production in this species and thus can be expected to have strong direct consequences for plant fitness and vitality of the whole populations. They also show large variation in genetic diversity between populations and indicate which populations should get a priority in attempts to conserve all the genetic diversity within the region.

Variation in Lamium subg. Galeobdolon (Lamiaceae) – insights from ploidy levels, morphology and isozymes

Abstract.Lamium subg. Galeobdolon was investigated in Central Europe to evaluate karyological, morphological, and isozyme variations. Flow-cytometric analyses revealed three ploidy levels: diploid (corresponding to L. flavidum and L. galeobdolon), tetraploid (corresponding to L. argentatum and L. montanum), and triploid (very rare cytotype most probably of hybrid origin). Mixed samples comprising two or more cytotypes / taxa were repeatedly detected. An existence of hybrid individuals between both tetraploid taxa was also supported. Almost no variation at isozyme level was observed in L. argentatum originating from three European countries thus favouring a hypothesis of a monotopic origin. On the contrary, the pilot study detected high isozyme variability in the other taxa. Morphometric analyses confirmed clear separation between L. galeobdolon and L. montanum; bract characters and maximum number of flowers were selected as quantitative features with the highest discriminant power. Serious discrepancies between the original description of L. endtmannii and both karyological and morphological performance of the plants from localities attributed to this species were found. These results allow us to conclude that any taxonomic status of L. endtmannii is not justified.

Genetic structure of experimental populations and reproductive fitness in a heterocarpic plant Atriplex tatarica (Chenopodiaceae).

Atriplex tatarica is a heterocarpic species of disturbed habitats. Seeds of Atriplex tatarica do not germinate immediately after shedding, but may remain in a dormant but viable state indefinitely. We investigated whether there were genetic and fitness differences between plants derived from seeds of the different fruit types germinated in different temperatures and salinities. Seeds that germinated in optimal and suboptimal conditions differed significantly in their genetic composition due, in part, to their source population. Seeds that germinated in the suboptimal conditions produced more homozygous plants. Plants that were primarily heterozygous were generated from nondormant fruit types as well as from fruits that germinated in the optimal conditions. Moreover, there was a positive correlation between the degree of heterozygosity and plant fitness measured as the mass of the stem and reproductive structures. In conclusion, the genetic variation of natural populations may be at least partly due to the ability of particular seed genotypes to germinate in the specific environmental conditions of a particular locality. In some circumstances, the process of differential germination may select not only for genetic variability but also for higher fitness if heterozygosity-fitness correlations are present.

Allozyme Variation in Diploid, Polyploid and Mixed-Ploidy Populations of the Pilosella alpicola Group (Asteraceae): Relation to Morphology, Origin of Polyploids and Breeding System

The Pilosella alpicola group includes four species (P. alpicola s.str., P. ullepitschii, P. rhodopea and P. serbica) with allopatric distributions (Alps, Balkans, Carpathians) and contrasting cytotype patterns (diploid, diploid-polyploid and polyploid species). Whereas diploid taxa (P. ullepitschii and P. serbica) reproduce sexually, the mode of reproduction of polyploid cytotypes reflects their origin: autopolyploids of P. rhodopea reproduce sexually, while allopolyploid cytotypes of P. alpicola s.str. apomictically. We used allozymes to elucidate overall genetic variation within the group and to test their utility for taxon discrimination, assessment of polyploid origin and possible correlations with breeding systems. Variation of five allozyme systems encoded by eight polymorphic loci and 29 alleles was studied in 20 populations and 298 plants representing all taxa. Allozymes were proved to be only of limited usefulness for the taxonomic classification within the P. alpicola group. The Western Carpathian populations of P. ullepitschii formed the only genetically well-differentiated group. The same allele suite shared by all cytotypes of P. rhodopea and presence of both balanced and unbalanced heterozygotes in tetraploids was consistent with autopolyploid origins of polyploids and provided further evidence for a primary contact zone. An isolated relic population of P. rhodopea from the Southern Carpathians exhibited lowered values of genetic diversity when compared to the core area. Pronounced fixed heterozygosity was found in P. alpicola s.str., supporting its allopolyploid origin. In accordance with assumptions, genotypic variability was significantly higher in sexually reproducing diploid and diploid-polyploid taxa than in apomictic P. alpicola s.str.

Can soil seed banks serve as genetic memory? A study of three species with contrasting life history strategies.

We attempted to confirm that seed banks can be viewed as an important genetic reservoir by testing the hypothesis that standing (aboveground) plants represent a nonrandom sample of the seed bank. We sampled multilocus allozyme genotypes from three species with different life history strategies: Amaranthus retroflexus, Carduus acanthoides, Pastinaca sativa. In four populations of each species we analysed the extent to which allele and genotype frequencies vary in consecutive life history stages including the summer seed bank, which has been overlooked up to now. We compared the winter seed bank (i.e., seeds collected before the spring germination peak), seedlings, rosettes, the summer seed bank (i.e., seeds collected after the spring germination peak) and fruiting plants. We found that: (1) All three species partitioned most of their genetic diversity within life history stages and less among stages within populations and among populations. (2) All genetic diversity parameters, except for allele frequencies, were similar among all life history stages across all populations in different species. (3) There were differences in allele frequencies among life history stages at all localities in Amaranthus retroflexus and at three localities in both Carduus acanthoides and Pastinaca sativa. (4) Allele frequencies did not differ between the winter and summer seed bank in most Carduus acanthoides and Pastinaca sativa populations, but there was a marked difference in Amaranthus retroflexus. In conclusion, we have shown that the summer seed bank is not genetically depleted by spring germination and that a majority of genetic diversity remains in the soil through summer. We suggest that seed banks in the species investigated play an important role by maintaining genetic diversity sufficient for recovery rather than by accumulating new genetic diversity at each locality.