GENE RESOURCES OF PERENNIAL WILD CEREALS INVOLVED IN BREEDING TO IMPROVE WHEAT CROP

The reduction of wheat genetic diversity is an urgent problem in modern wheat breeding, which is primarily due to the limited number of varieties had been used in wheat pedigree. As a result of the depletion of the genetic pool of wheat, its resistance to phytopathogens has dropped, that generally reduces the stability of the agrophytocenosis. One of the ways to expand the genetic diversity of wheat is the transfer of genes of economically valuable traits from closely related genera and species, classified into three genetic pools: primary (varieties of hard and bread wheat), secondary ( Triticum and Aegilops species), tertiary (most distant Triticeae species). The paper presents a review of success in gene transfer of economically valuable traits into the wheat genome from wheat’s wild perennial relatives of the tertiary genetic pool: Thinopyrum , Dasypyrum , Pseudoroegneria , Elymus , and Agropyron . Representatives of these species have different levels of ploidy (di-, tetra, hexa- and even decaploids) and combine the genomes J (= E), St, W, Y, X, V, H, P, as well as their variants. Vari- ous levels of transfer of hereditary material into the wheat genome are considered, i.e. amphidiploids, addition and substitution lines, lines with translocations and small introgressions. Special attention is paid to amphidiploids, namely wheat-wheatgrass hybrids (PPG) combining the wheat genome and a whole or a part of the wheatgrass genome. The wheat-wheatgrass hybrids are considered both as an independent objects of cultivation and as a “breeding bridge”, that is, an intermediate step in the transfer of genes from wheatgrass to wheat. The transfer of large chromatin fragments carrying the target gene is often associated with the additional transfer of undesirable genes which reduce the amount and impair the quality of the final wheat products. Therefore, introgressive lines of wheat are considered the most valuable forms, having a small chromatin insertion of an alien genome carrying a useful gene. Since the genomes of the tertiary genetic pool members are the most distant from the wheat genomes, an important problem considered in the review is the production of introgressions by recombination of homeologous chromosomes. The transfer of useful genes in wheat genome from its wild relatives is illustrated by examples, that consider the introgression of genes for resistance to fungal diseases (leaf and stem rust, powdery mildew, Fusarium blight, Septoria blight), viruses (yellow dwarfism streak mosaic), mite colonization, tolerance to drought, salinity and pre-harvest sprouting, storage proteins (glutenins) and perennial lifestyle of the plant. It is noted that wild relatives can serve as donors not only of genes responsible for resistance to stress factors, but also increase yields by increasing fertility, the number of spikelets and other elements of the yield structure, as well as improving the quality of the final product due to new variants of storage proteins. Special attention is paid to the development and use of molecular and molecular cytogenic markers which allow breeders to transfer target genes or regions of chromatin, as well as to monitor their introgression into the wheat genome in segregating populations. At the same time, in practical selection, different types of markers can be successfully used, i.e. those designed for the whole chromosome or its shoulder, linked to the chromatin region carrying the target gene, as well as the marker developed directly to the nucleotide sequence of the gene itself. Whole genome sequencing and genome editing technologies is noted to play in future a significant role in introduction of genetic material of wild relatives into wheat to improve its breeding programs.