Pentaploid hybrids produced from crosses between hexaploid and tetraploid wheats combine the genetic variation of both parents. Crossing a synthetic hexaploid wheat LM/AT23 with its AB-genome donor, the durum wheat LM, and selfing the pentaploid hybrids to the F₇ generation yielded mostly euploid tetraploids and a few hexaploids. Two special derivatives of tetraploid were isolated, including a 4D(4B) substitution line with large panicles and high resistance to stripe rust and a 2DS.2AL translocation line with non-waxy epidermis. The discovery of small D-genome introgressions in the A and B genomes suggested that pentaploidization can be used to induce homoeologous recombination. The introgression of D genome from Aegilops tauschii to the AB genomes might promote the development of super tetraploid wheat with hexaploid biological characteristics (especially stress resistance) and quality functions and the functional study of the introduced chromosomes or fragments.

Wheat stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a devastating disease threaten food security in China and worldwide. Epidemics of wheat stripe rust have been under control through applying resistant cultivars and crop protection approaches. However, due to climate change, innovation of cropping system, improvement of breeding technology, yield level enhancement of wheat cultivars, variation in structure and frequency of virulence genes in Pst populations in the new era, the current status of stripe rust resistance genes in wheat breeding programs need to be evaluated. The results could provide useful information for applying stripe rust resistance genes to develop new wheat cultivars with broad-spectrum and durable rust resistance. After multiple year’s stripe rust resistance survey, genetic analysis, molecular tagging and mining of stripe rust resistance genes in wheat cultivars and advanced breeding lines, the current status of major stripe rust resistance genes utilization was reviewed. We summarized the present situations of major stripe rust resistance gene discovery and germplasm innovation, the most frequently used stripe rust resistance genes, new strategy for pyramiding adult plant partial resistance and all stage resistance, and molecular marker assisted selection for developing wheat cultivars with broad spectrum and durable resistance in China. This review also proposes the major research areas in wheat stripe rust resistance breeding in the new era.

Genetic recombination produces new allelic combinations, thereby introducing variation for domestication. Allopolyploidization has increased the evolutionary potential of hexaploid common wheat by conferring the advantages of heterosis and gene redundancy, but whether a relationship exists between allopolyploidization and genetic recombination is currently unknown. To study the impact of allopolyploidization on genetic recombination in the ancestral D genome of wheat, we generated new synthetic hexaploid wheats by crossing tetraploid Triticum turgidum with multiple diploid Aegilops tauschii accessions, with subsequent chromosome doubling, to simulate the evolutionary hexaploidization process. Using the DArT-Seq approach, we determined the genotypes of two new synthetic hexaploid wheats with their parents, F₂ plants in a diploid population (2x, D₁D₁ × D₂D₂) and its new synthetic hexaploid wheat-derived population (6x, AABBD₁D₁ × AABBD₂D₂). About 11% of detected SNP loci spanning the D genome of Ae. tauschii were eliminated after allohexaploidization, and the degree of segregation distortion was increased in their hexaploid offspring from the F₂ generation. Based on codominant genotypes, the mean genetic interval length and recombination frequency between pairs of adjacent and linked SNPs on D genome of the hexaploid F₂ population were 2.3 fold greater than those in the diploid F₂ population, and the recombination frequency of Ae. tauschii was increased by their hexaploidization with T. turgidum. In conclusion, allopolyploidization increases genetic recombination of the ancestral diploid D genome of wheat, and DNA elimination and increased segregation distortion also occur after allopolyploidization. Increased genetic recombination could have produced more new allelic combinations subject to natural or artificial selection, helping wheat to spread rapidly to become a major global crop and thereby accelerating the evolution of wheat via hexaploidization.