Species of the Genus ×Agrotrigia (Hordeeae, Poaceae)—A Case of a Different Pattern of Parental rDNA Elimination

All taxa of plants have undergone several rounds of whole-genome duplication (WGD), accompanying interspecific and intergeneric crosses; subsequently, some part of one or both parent genomes in hybrid plants can be eliminated. The objective of this study was to evaluate the relationships of the intergeneric hybrid ×Agrotrigia (Poaceae) species with the taxa of parental genera Agropyron and Elytrigia and to determine the distribution as well as conservation or loss of parental genomes in the genomes of hybrid species. Molecular phylogenetic analysis of nuclear (ITS, ETS) and several chloroplast DNA markers confirmed that the most likely parents of this hybrid were really species of Agropyron and Elytrigia. The compositions of ribotypes (sequences of the 18S–ITS1–5.8S rDNA region) assessed by next-generation sequencing (NGS) showed that the genomes of hybrid species of ×Agrotrigia hajastanica and of the sample of ×A. androssovii from Turkmenistan carry ribotypes of both Agropyron and Elytrigia. However, the samples of ×A. kotovii and ×A. androssovii from Pskov Oblast bear ribotypes of the Elytrigia type only, whereas the genome of one sample of the ×Agrotrigia genus collected in Stavropol Krai consists exclusively of two clusters of Agropyron-type ribotypes (P genome) and may represent a new species. Therefore, these two (or three) species may be subject to the elimination of portions of the genome of one of the parents, though the extent of elimination may be different.