Origin of the Rare Hybrid Genus ×Trisetokoeleria Tzvelev (Poaceae) According to Molecular Phylogenetic Data

In our article, we analyzed new data on the origin of the hybrid genus ×Trisetokoeleria. According to the morphological criteria ×T. jurtzevii is a hybrid between Koeleria asiatica s. l. and Trisetum spicatum, ×T. taimyrica, and originated from Koeleria asiatica s. l. and Trisetum subalpestre, ×T. gorodkowii, a hybrid between Koeleria asiatica and Trisetum ruprechtianum. Later ×T. taimyrica was transferred to Koeleria. Parental taxa are prone to active hybridization themselves, thus, new methods of next-generation sequencing (NGS) were needed to clarify the relationships of these genera. For NGS we used the fragment 18S rDNA (part)–ITS1–5.8S rDNA (totally 441 accessions). We analyzed ITS1–5.8S rDNA–ITS2 region, trnL–trnF and trnK–rps16 from eight samples of the five species, using the Sanger method: ×Trisetokoeleria jurtzevii, ×T. taimyrica, Koeleria asiatica, Sibirotrisetum sibiricum (=Trisetum sibiricum), and Trisetum spicatum. We also studied the pollen fertility of ×Trisetokoeleria and its possible progenitors. Our data partly contradicted previous assumptions, based on morphological grounds, and showed us a picture of developed introgression within and between Koeleria and Trisetum. ×T. jurtzevii, a totally sterile hybrid formed rather recently. We can suppose that ×T. jurtzevii is a hybrid between K. asiatica and some Trisetum s. str. Species, but not T. spicatum. ×T. gorodkowii, a hybrid in the stage of primary stabilization; it has one unique ribotype related to T. spicatum s. l. The second parental species is unrelated to Trisetum ruprechtianum. ×T. taimyrica and is a stabilized hybrid species; it shares major ribotypes with the T. spicatum/T. wrangelense group and has a minor fraction of rDNA related to genus Deyeuxia s. l.