Molecular-Cytogenetic Characterization of Spontaneous Fertile Aegilops biuncialis–Wheat Hybrids

In recent years, the task of expanding the genetic diversity of common wheat has become a critical priority due to climate change and the considerable narrowing of the gene pool driven by selection for productivity based on a small number of elite founder varieties. Wild relatives of wheat, in particular species of the genus Aegilops, possess a complex of economically valuable traits and are a valuable source of genes for its improvement. However, the formation of distant hybrids is a technically challenging process that results in the so-called genomic shock, whereby genomes combined in a newly emerged allopolyploid suffer a number of changes that can be observed at the chromosomal level. Spontaneous fertile Ae. biuncialis–wheat hybrids detected in the plantings of the Dagestan branch of VIR can serve as a convenient model to study the processes occurring during the formation of a new allopolyploid species, and their molecular and cytogenetic characterization will allow for the use of these hybrids in directed wheat breeding. Analysis of nine hybrids with fluorescence in situ hybridization (FISH) provided characterization of their karyotypes and determination of the genomic composition. According to the FISH patterns, the accessions were divided into two groups. The first group included six accessions and the second group, three accessions. The chromosome number in accessions from group I were close to the octoploid one (2n = 54–56). These hybrids were characterized by similar marker probes distribution patterns on chromosomes and carried identical T7UbL.3MbL translocation. The three remaining lines were also similar to each other in FISH patterns that differed from those in the previous group and apparently arose from hybridization of other parental forms. They were characterized by high variability of chromosome number (2n = 41–52) with substantially different chromosome elimination rates. The most frequent losses were chromosomes 6A, 3Ub, 2Mb, 4Mb, while some chromosomes of the A, B, Ub, and Mb genomes were present in all examined plants. In two plants, each from two accessions from group II, reduction of the mixed genome (2n = 14) that included representatives of all seven homeologous groups belonging to different parental subgenomes was observed. A suggestion on the influence of genotypes on the formation of hybrid genomes and the prospect of using the resulting forms in breeding was made.