| Abstract:
The present study bringst the first detailed information
about polyploidy and agamospermy in Hieracium
echioides. The species was used as a model one to contribute to the
solution of general questions about evolutionary processes in polyploid plant
species. In addition, genetic variation, chromosome number and breeding system
were investigated in agamospermous populations of H. echioides subsp. echioidesvar. tauscheri in the Danube Basin
region.
Experimental crossing among diploids, triploids and tetraploids of Hieracium echioides was made to examine mating interactions.
Specifically, cytotype diversity in progeny from experimental crossing,
intercytotype pollen competition as a reproductive barrier among diploids and
tetraploids, differences in seed-set, pollen size and beginning of flowering
periode and differences in genome size among cytotypes were studied. Only
diploids were found in progeny from 2x × 2x crosses. The other types of crosses
yielded more than one cytotype in progeny, however, one cytotype predominated
in each cross type: triploids (93%) in reciprocal crosses between diploids and
tetraploids, diploids (92%) in 2x × 3x crosses, tetraploids (88%) in 3x × 2x,
tetraploids (60%) in 3x × 3x crosses, pentaploids (56%) in 3x × 4x crosses,
triploids (80%) in 4x × 3x crosses and tetraploids (88%) in 4x × 4x crosses. No
aneuploids were detected among karyologically analysed plants. Unreduced egg
cells production was detected in triploids and tetraploids, on the contrary,
formation of unreduced pollen was recorded only in two cases in triploids.
Triploid plants produced x, 2x and 3x gametes, however, in male gametes predominated
x (92%) gametes whereas in female gametes predominated 3x (88%) gametes. No statistically significant difference in seed-set
obtained from intra- and intercytotype crosses between diploids and tetraploids
were observed suggesting absence of post-zygotic reproductive barriers among
cytotypes. Cytotype diversity of
progeny from crossing where diploids and tetraploids were pollinated by mixture
of pollen from diploid and tetraploid plants suggested intercytotype pollen
competition to serve as a prezygotic reproductive barrier. There was no
significant difference in the seed-set of diploids and tetraploids, but they
differed significantly from seed-sets of triploids and pentaploids. No difference among cytotypes in
beginning of flowering periode was found. Values of pollen size were associated
with ploidy level. Genome size of diploids, triploids and tetraploids was found
to be in principle identical. Only pentaploids had lower values of genome size
than the other cytotypes. The origin of polyploidy in H. echioides is discussed based on the knowledge of genome size
pattern in the subgenus.
Detailed flow cytometric analysis of population of co-existing diploid, triploid,
tetraploid and pentaploid cytotypes of Hieracium echioides was carried out at
the model locality (Havranické vřesoviště heathland, Czech Republic, south-west
Moravia). The analysed population is formed by a system of in size restricted
subpopulations. In total, 392 plants from twelve subpopulations were analysed.
Random selection of 25 plants per subpopulation was carried out in nine
subpopulations. Three subpopulationswere analysed in detail (all plants were
analysed). Analysis of 225 randomly selected plants from nine subpopulations revealed
24 (10.67%) diploids, 154 (68.44%) triploids, 42 (18.67%) tetraploids and 5
(2.22%) pentaploids. Detailed analysis of three subpopulations revealed almost
only diploid plants. Analysed subpopulations differed in cytotype structure.
One cytotype predominated in each subpopulation. The subpopulations were
divided into three categories according to the dominant cytotype. In most subpopulations,
triploids predominated. In one subpopulation, the most common cytotype was
represented by tetraploi one. Finally, in four subpopulations (ncluding three
in detail analysed ones), diploids prevailed. Generally, the pattern of
cytotype distribution has striking clump-like character. The dynamic of the
population is discussed with respect to results obtained during previous
hybridization experiments.
Six populations of Hieracium echioides subsp. echioides var. tauscheri from the Danube Basin between Bratislava and Budapest
(locations: Balinka, Čenkov, Devín, Dorog, Győr, Pilis) were analysed using
allozyme and karyological analysis. Five allozyme systems (EST, LAP, 6PGDH,
PGM, and SKDH) were used to analyse the genetic structure of the examined
populations. Analyses revealed low genetic variation both within- and among
populations. Four multilocus allozyme phenotypes were detected; three
populations (Čenkov, Devín, and Győr) possessed phenotype I exclusively, while
phenotype II was found only in the Balinka and Dorog populations. Two different
phenotypes were found in the population of Pilis (phenotypes III and IV).
However, due to the complex banding patterns generated for EST, allelic
interpretation was not possible, and the Balinka and Dorog populations appeared
to possess different phenotypes. All populations proved to be tetraploid (2n =
36) and agamospermous. The geographic distribution pattern of the analysed
populations (one allozyme phenotype at several isolated localities) may reflect
a more common occurrence of the taxon in the past. Landscape changes, caused by
changes in human management of the country, may have resulted in a loss of
suitable localities, mainly open sandy habitats. These changes may have caused
the reduction and fragmentation of H. tauscheri habitat. |
