Molecular markers in the genetic analysis of crossability of bread wheat with rye

Bread wheat (Triticum aestivum L.), the varieties of which are widely used for the grain production, is difficultly crossable with related species of Triticeae Dum. This factor limits the chance of introduction of alien genetic material into the wheat gene pool and the possibility of new varieties breeding with good adaptation to adverse environmental factors. The crossability between wheat and related species is controlled by Kr1-Kr4 genes (Crossability with Rye, Hordeum and Aegilops spp.) and the SKr gene (Suppressor of crossability). SKr and Kr1 have the largest influence on the trait. In the case of the recessive alleles, these genes do not function and the quantity of hybrid seeds after pollination with alien species can achieve more than 50 %. SKr is located on 5BS between the GBR0233 and Xgwm234 markers, closely linked with the markers Xcfb341, TGlc2 and gene12. Kr1 was mapped on 5BL, proximally to the Ph1 gene, between the EST-SSR markers Xw5145 and Xw9340. The markers of SKr were used to control the transfer of its recessive allele into other wheat genotypes, which made it possible to obtain highly crossable forms. However, the advantages of using the SKr and Kr1 markers in marker-assisted selection and in the screening of ex situ collections are not sufficiently studied. The published Kr1 sequence for varieties with different crossability offers great prospects, because it will be possible to create allele-specific markers. In this review, the following issues are considered: genetic resources created by wheat and rye hybridization, the geographical distribution of easy-to-cross forms of wheat, genetic control of the wheat and rye compatibility, advances of the use of molecular markers in the mapping of Kr-genes and their transmission control.

Homoeologous Recombination: A Novel and Efficient System for Broadening the Genetic Variability in Wheat

Gene transfer from wild wheat relatives to bread wheat is restricted to homologous recombination. The presence of the Pairing homoeologous 1 (Ph1) gene in the long arm of wheat chromosome 5B allows only homologous chromosomes to pair and recombine, resulting in diploid inheritance of polyploid wheat. Previously, we identified a potent homoeologous pairing promotor gene(s) (Hpp-5Mg); its carrier chromosome 5Mg derived from Aegilops geniculata and its wheat homoeologous chromosome 5D freely recombined in the presence of the Ph1 gene. In this study, we investigated the effect of Hpp-5Mg on homoeologous recombination in the absence of Ph1. In Hpp-5Mg/ph1bph1b plants, we observed a vast genome-wide increase in homoeologous recombination and multiple crossovers (CO), including CO breakpoints in proximal regions of the chromosomes where recombination is known to be suppressed. We tested the efficacy of Hpp-5Mg/ph1bph1b-induced homoeologous recombination by producing new recombinants for the wheat streak mosaic virus resistance gene, Wsm3, present in the wheat-Thinopyrum intermedium Robertsonian translocation (RobT T7BS.7S#3L). A recombination frequency of 6.5% was detected by screening the progenies double monosomic for T7BS.7S#3L and 7B by genomic in situ hybridization. This recombination frequency was about 100-fold higher compared with the recombinant frequency of 0.06% observed by using ph1b-induced homoeologous recombination alone. Our results indicate that chromosome 5Mg promotes homoeologous recombination between wheat and wild wheat relative chromosomes, which helps in the generation of pre-breeding materials thereby accelerating wheat crop improvement.

Attempts to induce homoeologous pairing between wheat and Agropyron cristatum genomes

Agropyron cristatum (2n = 4x = 28, PPPP) possesses potentially valuable traits that could be used in wheat (Triticum aestivum) improvement through interspecific hybridization. Homoeologous pairing between wheat chromosomes and P chromosomes added to wheat in a set of wheat – A. cristatum addition lines was assessed. First, the Ph-suppressing effect of P chromosomes (except 7P) was analyzed. It was concluded that this system is polygenic with no major gene, and consequently, has no prospect in the transfer of alien genes from wild relatives. In a second step, the potential of the deletion ph1b of the Ph1 gene for inducing P–ABD pairing was evaluated. Allosyndetic associations between P and ABD genomes are very rare. This very low level of pairing is likely due to divergence in the repeated sequences between Agropyron and wheat genomes. Development of translocation lines using ionizing radiation seems to be a more suitable technique than homoeologous recombination to exploit the A. cristatum genome in wheat improvement.Key words: Triticum aestivum, Agropyron cristatum, addition line, GISH, Ph1 gene.