Genome size and chromosome number in Echinops (Asteraceae, Cardueae) in the Aegean and Balkan regions: technical aspects of nuclear DNA amount assessment and genome evolution in a phylogenetic frame

This work focuses on the representatives of genus Echinops (Asteraceae, Cardueae) in the Aegean and Balkan regions, from the perspective of their genome evolution. Chromosome numbers were determined by orcein staining in 14 populations of nine taxa, and DNA contents were assessed by flow cytometry in 24 populations of nine taxa. A molecular phylogeny based on the internal transcribed spacer (ITS) and trnL-trnF and including first sequences for two taxa (Echinops sphaerocephalus subsp. taygeteus and E. spinosissimus subsp. neumayeri) provided a framework for discussing genome changes. From a methodological point of view, similar C-DNA value estimates were obtained when measuring, for a same population, fresh leaves from adult plants collected in the field and from cultivated seedlings. Conversely, despite giving the appearance of being correct (e.g., low coefficient of variation), genome size assessed using silica gel-preserved material differs significantly from values obtained for the same populations with fresh material. Nevertheless, silica gel-preserved material may still provide rough estimates of genome size for, e.g., inferring ploidy level. Suitable-non-silica gel-based-DNA amounts assessed for 23 populations range from 2C = 6.52 pg (E. spinosissimus subsp. neumayeri) to 2C = 9.37 pg (E. bannaticus). Chromosome counts were established for the first time for Echinops graecus (2n = 32), E. sphaerocephalus subsp. albidus (2n = 32), E. sphaerocephalus subsp. taygeteus (2n = ca. 30), and E. spinosissimus subsp. neumayeri (2n = 28). Genome size and chromosome number are confirmed as crucial parameters for deciphering lineage diversification within the genus Echinops.