Preferential Subgenome Elimination and Chromosomal Structural Changes Occurring in Newly Formed Tetraploid Wheat-Aegilops ventricosa Amphiploid (AABBDvDvNvNv)

Genome architecture of the allotetraploid wild grass Aegilops ventricosa reveals its evolutionary history and contributions to wheat improvement

The allotetraploid wild grass Aegilops ventricosa (2n = 4x = 28, genome DvDvNvNv) has been recognized as an important germplasm resource for wheat improvement owing to its ability to tolerate biotic stresses. In particular, the 2NvS segment from Ae. ventricosa, as a stable and effective resistance source, has contributed greatly to wheat improvement. The 2NvS/2AS translocation is a prevalent chromosomal translocation between common wheat and wild relatives, ranking just behind the 1B/1R translocation in importance for modern wheat breeding. Here, we assembled a high-quality chromosome-level reference genome of Ae. ventricosa RM271 with a total length of 8.67 Gb. Phylogenomic analyses revealed that the progenitor of the Dv subgenome of Ae. ventricosa is Ae. tauschii ssp. tauschii (genome DD); by contrast, the progenitor of the D subgenome of bread wheat (Triticum aestivum L.) is Ae. tauschii ssp. strangulata (genome DD). The oldest polyploidization time of Ae. ventricosa occurred ∼0.7 mya. The Dv subgenome of Ae. ventricosa is less conserved than the D subgenome of bread wheat. Construction of a graph-based pangenome of 2AS/6NvL (originally known as 2NvS) segments from Ae. ventricosa and other genomes in the Triticeae enabled us to identify candidate resistance genes sourced from Ae. ventricosa. We identified 12 nonredundant introgressed segments from the Dv and Nv subgenomes using a large winter wheat collection representing the full diversity of the European wheat genetic pool, and 29.40% of European wheat varieties inherit at least one of these segments. The high-quality RM271 reference genome will provide a basis for cloning key genes, including the Yr17-Lr37-Sr38-Cre5 resistance gene cluster in Ae. ventricosa, and facilitate the full use of elite wild genetic resources to accelerate wheat improvement.

Identification of Two Novel QTL for Fusarium Head Blight Resistance in German Wheat Cultivar Centrum

Fusarium head blight (FHB) is a devastating disease that occurs in warm and humid environments. The German wheat 'Centrum' has displayed moderate to high levels of FHB resistance in the field for many years. In this study, an F6:8 recombinant inbred line (RIL) population derived from cross 'Centrum' × 'Xinong 979' was evaluated for FHB response following point inoculation in five environments. The population and parents were genotyped using the GenoBaits Wheat 16 K Panel. Stable quantitative trait loci (QTL) associated with FHB resistance in 'Centrum' were mapped on chromosome arms 2DS and 5BS. The most effective QTL, located in 2DS, was identified as a new chromosome region represented by a 1.4 Mb interval containing 17 candidate genes. Another novel QTL was mapped in chromosome arm 5BS of a 5BS to 7BS translocation chromosome. In addition, two environmentally sensitive QTL were mapped on chromosome arms 2BL from 'Centrum' and 5AS from 'Xinong 979'. Polymorphisms of flanking phenotypic variance explained (PVE) markers (allele-specific quantitative PCR [AQP]) AQP-6 for QFhb.nwafu-2DS and 16K-13073 for QFhb.nwafu-5BS were validated in a panel of 217 cultivars and breeding lines. These markers could be useful for marker-assisted selection (MAS) of FHB resistance and provide a starting point for fine mapping and marker-based cloning of the resistance genes.

Karyotype Reorganization in Wheat-Rye Hybrids Obtained via Unreduced Gametes: Is There a Limit to the Chromosome Number in Triticale?

To date, few data have been accumulated on the contribution of meiotic restitution to the formation of Triticum aestivum hybrid karyotypes. In this study, based on FISH and C-banding, karyotype reorganization was observed in three groups of F₅ wheat–rye hybrids 1R(1A) × R. Aberrations, including aneuploidy, telocentrics, and Robertsonian translocations, were detected in all groups. Some of the Group 1 plants and all of the Group 2 plants only had a 4R4R pair (in addition to 1R1R), which was either added or substituted for its homeolog in ABD subgenomes. In about 82% of meiocytes, 4R4R formed bivalents, which indicates its competitiveness. The rest of the Group 1 plants had 2R and 7R chromosomes in addition to 1R1R. Group 3 retained all their rye chromosomes, with a small aneuploidy on the wheat chromosomes. A feature of the meiosis in the Group 3 plants was asynchronous cell division and omission of the second division. Diploid gametes did not form because of the significant disturbances during gametogenesis. As a result, the frequency of occurrence of the formed dyads was negatively correlated (r = −0.73) with the seed sets. Thus, meiotic restitution in the 8n triticale does not contribute to fertility or increased ploidy in subsequent generations.

Characterization of the Durum Wheat-Aegilops tauschii 4D(4B) Disomic Substitution Line YL-443 With Superior Characteristics of High Yielding and Stripe Rust Resistance

Durum wheat is one of the important food and cash crops. The main goals in current breeding programs are improving its low yield potential, kernel characteristics, and lack of resistance or tolerance to some biotic and abiotic stresses. In this study, a nascent synthesized hexaploid wheat Lanmai/AT23 is used as the female parent in crosses with its AB genome donor Lanmai. A tetraploid line YL-443 with supernumerary spikelets and high resistance to stripe rust was selected out from the pentaploid F₇ progeny. Somatic analysis using multicolor fluorescence in situ hybridization (mc-FISH) revealed that this line is a disomic substitution line with the 4B chromosome pair of Lanmai replaced by the 4D chromosome pair of Aegilops tauschii AT23. Comparing with Lanmai, YL-443 shows an increase in the number of spikelets and florets per spike by 36.3 and 75.9%, respectively. The stripe rust resistance gene Yr28 carried on the 4D chromosome was fully expressed in the tetraploid background. The present 4D(4B) disomic substitution line YL-443 was distinguished from the previously reported 4D(4B) lines with the 4D chromosomes from Chinese Spring (CS). Our study demonstrated that YL-443 can be used as elite germplasm for durum wheat breeding targeting high yield potential and stripe rust resistance. The Yr28-specific PCR marker and the 4D chromosome-specific KASP markers together with its unique features of pubescent leaf sheath and auricles can be utilized for assisting selection in breeding.