Corresponding author: Radim J. Vašut ( radim.vasut@upol.cz ) Academic editor: Julio R. Daviña
© 2018 Petra Macháčková, Ľuboš Majeský, Michal Hroneš, Eva Hřibová, Bohumil Trávníček, Radim J. Vašut.
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Citation:
Macháčková P, Majeský Ľ, Hroneš M, Hřibová E, Trávníček B, Vašut RJ (2018) New chromosome counts and genome size estimates for 28 species of Taraxacum sect. Taraxacum. Comparative Cytogenetics 12(3): 403-420. https://doi.org/10.3897/CompCytogen.v12i3.27307
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The species-rich and widespread genus Taraxacum F. H. Wiggers, 1780 (Asteraceae subfamily Cichorioideae) is one of the most taxonomically complex plant genera in the world, mainly due to its combination of different sexual and asexual reproduction strategies. Polyploidy is usually confined to apomictic microspecies, varying from 3x to 6x (rarely 10x). In this study, we focused on Taraxacum sect. Taraxacum (= T. sect. Ruderalia; T. officinale group), i.e., the largest group within the genus. We counted chromosome numbers and measured the DNA content for species sampled in Central Europe, mainly in Czechia. The chromosome number of the 28 species (T. aberrans Hagendijk, Soest & Zevenbergen, 1974, T. atroviride Štěpánek & Trávníček, 2008, T. atrox Kirschner & Štěpánek, 1997, T. baeckiiforme Sahlin, 1971, T. chrysophaenum Railonsala, 1957, T. coartatum G.E. Haglund, 1942, T. corynodes G.E. Haglund, 1943, T. crassum H. Øllgaard & Trávníček, 2003, T. deltoidifrons H. Øllgaard, 2003, T. diastematicum Marklund, 1940, T. gesticulans H. Øllgaard, 1978, T. glossodon Sonck & H. Øllgaard, 1999, T. guttigestans H. Øllgaard in Kirschner & Štěpánek, 1992, T. huelphersianum G.E. Haglund, 1935, T. ingens Palmgren, 1910, T. jugiferum H. Øllgaard, 2003, T. laticordatum Marklund, 1938, T. lojoense H. Lindberg, 1944 (= T. debrayi Hagendijk, Soest & Zevenbergen, 1972, T. lippertianum Sahlin, 1979), T. lucidifrons Trávníček, ineditus, T. obtusifrons Marklund, 1938, T. ochrochlorum G.E. Haglund, 1942, T. ohlsenii G.E. Haglund, 1936, T. perdubium Trávníček, ineditus, T. praestabile Railonsala, 1962, T. sepulcrilobum Trávníček, ineditus, T. sertatum Kirschner, H. Øllgaard & Štěpánek, 1997, T. subhuelphersianum M.P. Christiansen, 1971, T. valens Marklund, 1938) is 2n = 3x = 24. The DNA content ranged from 2C = 2.60 pg (T. atrox) to 2C = 2.86 pg (T. perdubium), with an average value of 2C = 2.72 pg. Chromosome numbers are reported for the first time for 26 species (all but T. diastematicum and T. obtusifrons), and genome size estimates for 26 species are now published for the first time.
Asteraceae, chromosome number, flow cytometry, karyology, Taraxacum officinale
Taraxacum F. H. Wiggers, 1780 (Asteraceae subfamily Cichorioideae) is a species-rich genus of common and widespread perennial grassland herbs growing from the subtropics to subarctic (arctic/alpine) regions across the world. Rough estimates suggest the genus contains approximately 2,800 species in approximately 60 sections (
The basic chromosome number in Taraxacum is x = 8, and it is constant across all the sections. The diploid number (2n = 2x = 16) is confined to only sexually reproducing species, and sexual species are nearly all diploids, with only a few exceptions of sexual tetraploids known in section Piesis (
Genome size estimation (plant genome C-value) (
Taraxacum sect. Taraxacum (formerly known as T. sect. Ruderalia; generally known as Taraxacum officinale group; see
We studied a total of 28 Taraxacum species (25 formally described and three still undescribed, referred to by their working names) belonging to Taraxacum sect. Taraxacum (Table
List of species used in this study, with sampling details. Country codes according to ISO 3166-1 alpha-2 (AT = Austria; CZ = Czechia, DE = Germany, HU = Hungary, IT = Italy, SK = Slovakia); Collectors: BT = Bohumil Trávníček; RJV = Radim Jan Vašut.
Taxon | Country | Locality; GPS; Date; Collector |
---|---|---|
T. aberrans Hagendijk, Soest & Zevenbergen, 1974 | AT | Upper Austria, Obernberg am Inn town, lawn in the street of Therese-Riggle-Strasse; 48°19'14"N; 13°19'52"E; 10.05.2015; BT |
T. atroviride Štěpánek & Trávníček, 2008 | AT | Altaussee village (near Bad Aussee town), lawns and roadsides in the ski resort NNW from the village (valley of Augstbach brook); 47°39'42"N; 13°44'38"E; 08.05.2014; BT |
T. atrox Kirschner & Štěpánek, 1997 | IT | Cave del Predil settlement (S from Tarvisio town), lawns at the road no SP76 (at lake of Lago di Predil); 46°25'11"N; 13°33'42"E; 16.05.2015; BT |
T. baeckiiforme Sahlin, 1971 | HU | Felsöcsatár village (W from the Szombathely town), grassy roadsides at the road towards Vaskeresztes village; 250 m a.s.l.; 47°12'20"N; 16°26'51"E; 26.04.2015; BT |
T. chrysophaenum Railonsala, 1957 | CZ | Bartošovice village (near Nový Jičín town), lawns in park in central part of the village; 49°40'15"N, 18°02'59"E; 23.04.2014; BT |
T. coartatum G. E. Haglund, 1942 | CZ | Lubná village (near Polička town), grassy places at brook in E part of the village; 480 m a.s.l.; 49°46'26"N, 16°13'57"E; 17.05.2016; BT & RJV |
T. corynodes G. E. Haglund, 1943 | CZ | Hanušovice town, lawns at the railway station; 50°04'18"N, 16°55'52"E; 19.05.2015; BT |
T. crassum H. Øllgaard & Trávníček, 2003 | CZ | Nové Město na Moravě town, grassy places at brook in the town, ca 0.6 km ESE from railway station of “Nové Město na Moravě-zastávka”; 600 m a.s.l.; 49°33'45"N, 16°04'04"E; 17.05.2016; BT & RJV |
T. deltoidifrons H. Øllgaard, 2003 | CZ | Jimramov town, grassy places in the park of Bludník in N part of the town; 500 m a.s.l.; 49°38'19"N, 16°13'25"E; 17.05.2016; BT & RJV |
T. diastematicum Marklund, 1940 | CZ | Svratka village, meadows and grassy places at NW margin of the settlement of Česká Cikánka; 630 m a.s.l.; 49°42'35"N, 16°03'01"E; 17.05.2016; BT & RJV |
T. gesticulans H. Øllgaard, 1978 | CZ | Hanušovice town, lawns at the railway station; 50°04'18"N, 16°55'52"E; 19.05.2015; BT |
T. glossodon Sonck & H. Øllgaard, 1999 | CZ | Studnice village (N from Nové Město na Moravě town), meadow at road near the Paseky settlement ca 1 km NNW from the village; 780 m a.s.l.; 49°36'51"N, 16°05'17"E; 17.05.2016; BT & RJV |
T. guttigestans H. Øllgaard in Kirschner & Štěpánek, 1992 | CZ | Nové Město na Moravě town, grassy places at brook in the town, ca 0.6 km ESE from railway station of “Nové Město na Moravě-zastávka”; 600 m a.s.l.; 49°33'45"N, 16°04'04"E; 17.05.2016; BT & RJV |
T. huelphersianum G. E. Haglund, 1935 | CZ | Pekařov settlement (near Hanušovice town), lawns and meadows in the settlement; 50°04'41"N, 17°01'31"E; 19.05.2015; BT |
T. ingens Palmgren, 1910 | CZ | Svratka village, meadows and grassy places at NW margin of the settlement of Česká Cikánka; 630 m a.s.l.; 49°42'35"N, 16°03'01"E; 17.05.2016; BT & RJV |
T. jugiferum H. Øllgaard, 2003 | CZ | Jedlí village (NW from Zábřeh town), lawns and roadsides in central part of the village; 49°55'54"N, 16°47'45"E; 19.05.2015; BT |
T. laticordatum Marklund, 1938 | CZ | C Moravia, Hlinsko pod Hostýnem village, roadside at road towards Prusinovice village; 49°22'34"N; 17°36'47.8"E; 20.05.2016; BT |
T. lojoense H. Lindberg, 1944 † | CZ | Úterý village (near Konstantinovy Lázně town), lawns at the brook on the eastern village margin; 510 m a.s.l.; 49°56'24"N, 13°00'21"E; 25.04.2014; BT |
T. lucidifrons Trávníček, ineditus | CZ | Kunín village (near Nový Jičín town), lawns in chateau park; 49°38'39"N, 17°59'18"E; 23.04.2014; BT |
T. obtusifrons Marklund, 1938 | CZ | Lubná village (near Polička town), grassy places at brook in E part of the village; 480 m a.s.l.; 49°46'26"N, 16°13'57"E; 17.05.2016; BT & RJV |
T. ochrochlorum G. E. Haglund, 1942 | CZ | Svratka village, meadows and grassy places at NW margin of the settlement of Česká Cikánka; 630 m a.s.l.; 49°42'35"N, 16°03'01"E; 17.05.2016; BT & RJV |
T. ohlsenii G. E. Haglund, 1936 | DE | Schönwald village (near Hof town), wet meadow and adjacent roadsides at the road (no. 15) towards Rehau village; 550 m a.s.l.; 50°13'37"N, 12°04'57"E; 27.04.2014; BT |
T. perdubium Trávníček, ineditus | CZ | Záhlinice village (near Hulín town), wet meadow 1.3 km SSW from the railway station; 190 m a.s.l.; 49°16'52"N, 17°28'58"E; 20.04.2016; BT |
T. praestabile Railonsala, 1962 | IT | Sella Nevea settlement (SW from Tarvisio town), lawns near hotel of Canin, road no. SP76; 46°23'19"N, 13°28'25"E; 16.05.2015; BT |
T. sepulcrilobum Trávníček, ineditus | CZ | Záhlinice village (near Hulín town), wet meadow 1.3 km SSW from the railway station; 190 m a.s.l.; 49°16'52"N, 17°28'58"E; 20.04.2016; BT |
T. sertatum Kirschner, H. Øllgaard & Štěpánek, 1997 | CZ | Svratka village, meadows and grassy places at NW margin of the settlement of Česká Cikánka; 630 m a.s.l.; 49°42'35"N, 16°03'01"E; 17.05.2016; BT & RJV |
T. subhuelphersianum M. P. Christiansen, 1971 | SK | Spišské Podhradie village (near Levoča town), lawn at road not far from Sivá brada travertine spring; 49°00'28"N, 20°43'26"E; 01.05.2014; BT |
T. valens Marklund, 1938 | HU | Szombathely town, lawns in the Szent István park (at the street of Jókai Mór); 225 m a.s.l.; 47°13'45"N, 16°36'15"E; 26.04.2015; BT |
For karyological analyses, achenes were sown in Petri dishes containing 1% agar solution and germinated at room temperature. Fresh young leaves for flow cytometric analyses were collected from juvenile plants cultivated in a greenhouse at the Department of Botany, Faculty of Science, Palacký University in Olomouc.
For chromosome counts, we used mitotically active root tip meristems of dandelion seedlings. Seedlings of the investigated species with 1–2 cm long roots were collected in the morning. To obtain the desired metaphase index, the roots were pre-treated in a 2 mM solution of 8-hydroxyquinoline for two hours at room temperature and an additional two hours at 4 °C in the dark. Then, the material was fixed in Carnoy’s fixative (a mixture (3:1, v/v) of absolute ethanol and acetic acid) and stored in a refrigerator (4 °C) until further processing (
The absolute genome size (2C-value;
The chromosome number of all 28 studied species of Taraxacum sect. Taraxacum (T. aberrans, T. atroviride, T. atrox, T. baeckiiforme, T. chrysophaenum, T. coartatum, T. corynodes, T. crassum, T. deltoidifrons, T. diastematicum, T. gesticulans, T. glossodon, T. guttigestans, T. huelphersianum, T. ingens, T. jugiferum, T. laticordatum, T. lojoense, T. lucidifrons, T. obtusifrons, T. ochrochlorum, T. ohlsenii, T. perdubium, T. praestabile, T. sepulcrilobum, T. sertatum, T. subhuelphersianum, T. valens) was counted invariably as 2n = 3x = 24 (Figs
Mitotic metaphase chromosomes of studied triploid species (2n=3x=24) of Taraxacum sect. Taraxacum. A T. aberrans B T. atroviride C T. atrox D T. baeckiiforme E T. chrysophaenum F T. coartatum G T. corynodes H T. crassum I T. deltoidifrons J T. diastematicum K T. gesticulans L T. glossodon M T. guttigestans N T. huelphersianum O T. ingens. Scale Bar: 5µm.
Mitotic metaphase chromosomes of studied triploid species (2n=3x=24) of Taraxacum sect. Taraxacum. A T. jugiferum B T. laticordatum C T. lojoense D T. lucidifrons E T. obtusifrons F T. ochrochlorum G T. ohlsenii H T. perdubium I T. praestabile J T. sepulcrilobum K T. sertatum L T. subhuelphersianum M T. valens. Scale Bar: 5µm.
The DNA content of the twenty-six studied Taraxacum species (two species, i.e., T. chrysophaenum and T. subhuelphersianum, were not analysed due to low-quality fresh material) ranged 1.08-fold from 2C = 2.60 pg in T. atrox to 2C = 2.86 pg in T. perdubium (Table
Nuclear DNA content of studied Taraxacum sect. Taraxacum species (Lyc = Solanum lycopersicon ‘Stupické polní rané’; Gly = Glycine max ‘Polanka’; n.a. = not analysed, N = number of plants analysed; 1Cx = monoploid genome size, 2C = DNA amount/ploidy level).
Species | 2C DNA amount [pg] (mean ± s.d.) | N | Ploidy | 1Cx [pg] | Standard |
---|---|---|---|---|---|
T. aberrans | 2.71 ± 0.010 | 3 | 3x | 0.90 | Lyc |
T. atroviride | 2.70 ± 0.020 | 2 | 3x | 0.90 | Lyc |
T. atrox | 2.60 ± 0.002 | 2 | 3x | 0.87 | Lyc |
T. baeckiiforme | 2.62 ± 0 | 1 | 3x | 0.87 | Lyc |
T. chrysophaenum | n.a. | n.a. | 3x | n.a. | n.a. |
T. coartatum | 2.72 ± 0.070 | 2 | 3x | 0.91 | Lyc |
T. corynodes | 2.67 ± 0.001 | 2 | 3x | 0.89 | Lyc |
T. crassum | 2.62 ± 0.020 | 2 | 3x | 0.87 | Lyc |
T. deltoidifrons | 2.69 ± 0.007 | 3 | 3x | 0.90 | Lyc |
T. diastematicum | 2.67 ± 0 | 1 | 3x | 0.89 | Lyc |
T. gesticulans | 2.83 ± 0.040 | 2 | 3x | 0.94 | Lyc |
T. glossodon | 2.77 ± 0.010 | 2 | 3x | 0.92 | Lyc |
T. guttigestans | 2.74 ± 0.004 | 2 | 3x | 0.91 | Lyc |
T. huelphersianum | 2.79 ± 0.006 | 2 | 3x | 0.93 | Lyc |
T. ingens | 2.68 ± 0.013 | 3 | 3x | 0.89 | Gly + Lyc |
T. jugiferum | 2.71 ± 0.001 | 2 | 3x | 0.90 | Lyc |
T. laticordatum | 2.84 ± 0.008 | 2 | 3x | 0.95 | Lyc |
T. lojoense | 2.62 ± 0.020 | 4 | 3x | 0.87 | Lyc |
T. lucidifrons | 2.81 ± 0 | 1 | 3x | 0.94 | Lyc |
T. obtusifrons | 2.75 ± 0.03 | 2 | 3x | 0.92 | Lyc |
T. ochrochlorum | 2.67 ± 0 | 1 | 3x | 0.95 | Gly |
T. ohlsenii | 2.63 ± 0 | 1 | 3x | 0.88 | Lyc |
T. perdubium | 2.86 ± 0 | 1 | 3x | 0.95 | Lyc |
T. praestabile | 2.73 ± 0.050 | 3 | 3x | 0.91 | Lyc |
T. sepulcrilobum | 2.72 ± 0 | 1 | 3x | 0.91 | Lyc |
T. sertatum | 2.69 ± 0.010 | 2 | 3x | 0.90 | Lyc |
T. subhuelphersianum | n.a. | n.a. | 3x | n.a. | n.a. |
T. valens | 2.70 ± 0 | 1 | 3x | 0.90 | Lyc |
Chromosome number variation differs among sections of the genus Taraxacum and more frequently occurs in sections such as Palustria or Celtica, whereas in section Taraxacum (and also section Hamata), it is nearly unknown. In our study, we aimed to either find variation in ploidy or confirm the prevailing triploid level. Our findings confirmed previously published records of 2n = 3x = 24 for T. diastematicum and T. obtusifrons (
A tetraploid chromosome number (2n = 4x = 32) was counted for only a few species of the 165 species of T. sect. Taraxacum with known chromosome numbers in the Chromosome Counts Database (CDDB, version 1.45;
Our list of species of T. sect. Taraxacum mainly includes typical members of the section, which differ slightly in their eco-geographic preferences. Some species have (in Central Europe) a preference for wet and sub-oceanic regions (such as T. corynodes, T. chrysophaenum, T. lucidifrons and T. ochrochlorum); on the other hand, some occupy more xerothermic regions (e.g., T. atrox, T. baeckiiforme, and T. lojoense). Some species resemble members of T. sect. Celtica (T. lucidifrons) or T. sect. Palustria (T. perdubium and T. sepulcrilobum). However, although the species in our study differ somewhat in ecology and geography, there is no variation in their ploidy levels. This is in agreement with previous studies in which only a triploid level was undoubtedly recorded for Nordic (“Atlantic”) and Pannonian or Mediterranean species.
Genome size estimates in Taraxacum sect. Taraxacum are very limited. Only a few papers dealt with its genome size (
Genome size estimates of T. officinale group in literature record. Values with asterisk (*) indicate re-calculated values according to conversion rate of 1 pg ~ 9.78×108 bp (
Literature | 2C [pg] | 2C [Gbp] |
2.55 | 2.49* | |
|
1.74–2.70 | 1.70–2.64* |
|
2.56* | 2.50 |
|
2.51 | 2.45* |
|
2.67 | 2.61* |
|
1.65–3.09* (2.45–2.76*) | 1.61–3.02 (2.40–2.70) |
this study | 2.60–2.86 | 2.54–2.80* |
Genome size estimates vary in all taxa. Multiple factors can affect the measurement of genome size, e.g., differences in instrument settings among the instruments used (
Our study provided new data for 26 species of T. sect. Taraxacum, which confirmed no variation in chromosome number and ploidy level (2n = 3x = 24) and revealed only minor variation in DNA content that roughly equalled a possible methodological bias. The species sampled cover variation within the section: a sample of typical T. sect. Taraxacum species (most of the studied species) but also species that by morphology or ecology are intermediates of other sections, i.e., T. perdubium and T. sepulcrilobum, which are morphological and ecological intermediates between the studied section and T. sect. Palustria; or T. lucidifrons, which is morphologically similar to T. sect. Celtica or species resembling members of T. sect. Borea (T. ohlsenii, T. lojoense and T. atrox). Two species in our list are apolliniferous (T. atrox and T. subhuelphersianum). Such unusual homogeneity among species in T. sect. Taraxacum rather than great morphological (and ecological) variability might reflect a young evolutionary origin, which is likely in contrast to sections Palustria, Erythrosperma and others that may partly consist of evolutionarily older species (
This study was supported by the Internal Grant Agency of Palacký University (IGA PrF-2018-001), the European Social Fund, Education for Competitiveness Operational Programme (CZ.1.07/2.2.00/28.0158) and by the National Program of Sustainability I (award LO1204).