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Triticum boeoticum(2n = 2x = 14, AbAb) contains beneficial traits for common wheat improvement. The discrimination of Ab-genome chromosomes from A-genome chromosomes is an important step in gene transfer from T. boeoticumto common wheat. In this study, fluorescence in situ hybridization (FISH) analysis using nine oligonucleotide probes revealed high divergence between chromosomes of the common wheat germplasm Crocus and T. boeoticumaccession G52. The combination of Oligo-pTa535-HM and Oligo-pSc119.2-HM can differentiate Aband A chromosomes within homologous groups 2, 4, 5, and 6; chromosomes 2Aband 6Abcan be identified by using (ACT)7, (CTT)7, and (GAA)7. The probes Oligo-pTa713 and (ACT)7can be utilized for the identification of chromosomes 1Aband 3Ab, respectively. Probes (CAG)7and (CAC)7can be applied in the identification of 7Ab. Moreover, probe combinations consisting of Oligo-pTa535-HM and (AAC)7with (ACT)7or (CTT)7and of Oligo-pTa535-HM and Oligo-pTa713 with (CAC)7or (CTT)7will help discriminate the Ab-genome chromosomes of T. boeoticum. These probes are being used as potential markers to select common wheat Crocus-T. boeoticumG52 alien chromosome lines. Moreover, FISH patterns are highly divergent between Ab- and A-genome chromosomes, indicating that obvious chromosome structural variations arose during wheat evolution.

Diploid wild einkorn wheat, Triticum boeoticumBoiss (AbAb, 2n= 2x= 14), is a wheat-related species with a blue aleurone layer. In this study, six blue-grained wheat lines were developed from F8progeny of crosses between common wheat and T. boeoticum. The chromosome constitutions of these lines were characterized by fluorescence in situ hybridization (FISH) using the oligonucleotide probes Oligo-pTa535-1, Oligo-pSc119.2-1, Oligo-pTa71-2, and (AAC)7. Multicolor FISH using Oligo-pTa535-1, Oligo-pSc119.2-1, and Oligo-pTa71-2 identified all 42 common wheat chromosomes, while Oligo-pTa535-1 and (AAC)7discriminated the 14 chromosomes of T. boeoticum. FISH revealed that all six blue-grained lines were wheat-T. boeoticum4Ab(4B) disomic substitution lines. The substitution lines were validated by genotyping using the wheat 55 K single nucleotide polymorphism (SNP) array containing 53,063 markers. These 4Ab(4B) substitution lines represent novel germplasm for blue-grained wheat breeding. The FISH probes and SNP markers used here can be applied in the development of blue-grained wheat-Triticum boeoticumtranslocation lines.

The spikelet number per spike (SNS) and spike length (SL) are key traits of interest for improving grain yields. Photoperiod-1(Ppd-1) is a key regulator of inflorescence architecture and paired spikelet development in wheat. In this study, 170 recombinant inbred lines (RILs) derived by crossing synthetic hexaploid wheat (SHW-L1) with a commercial cultivar (Chuanmai 32) were evaluated for the number of days to heading (DTH), SNS and SL in four different years. Eight PPD1combination homoeologs were also identified in the RILs by using genetic marker analysis. DTH had highly significant or significant positive correlations with SNS and SL, while SL also had a highly significant positive correlation with SNS. As a single factor, the photoperiod-sensitive ppd-D1balleles had the largest effect on delaying heading, and these results showed that SL and SNS can eventually be increased. These findings confirmed that photoperiod-sensitive ppd-D1bis a potential means of increasing wheat yields.

The Chinese wheat landrace Kaixianluohanmai (KL) expresses the ph-like phenotype. A major QTL, QPh.sicau-3A(syn. phKL), responsible for this effect has been mapped to chromosome arm 3AL. This study presents some characteristics of homoeologous pairing and recombination induced by phKL. In KL haploids, the level of homoeologous pairing was elevated relative to Ph1Chinese Spring (CS) haploids. There was a clear preference for A–D pairing and less frequent for A–B and B–D, reflecting the higher levels of affinity between genomes A and D in wheat. The characteristics of pairing were affected by temperature and magnesium ion supplementation. The suitability of phKLfor chromosome engineering was tested on three pairs of homoeologues: 2Sv-2B, 2Sv-2D, and 2RL-2BL. The recombination rates were 1.68%, 0.17%, and 0%, respectively. The phKLlocus in KL induced a moderate level of homoeologous chromosome pairing and recombination when the Ph1locus of wheat was present, both in wheat haploids and hexaploids. The Ph1-imposed criteria for chromosome pairing and crossing over were relaxed to some degree, permitting homoeologous crossing over but only between closely related chromosomes; there was no crossing over between more differentiated chromosomes. Therefore, the phKLsystem (QPh.sicau-3A) can be a useful tool in chromosome engineering of wheat to transfer genes from closely related species with the benefit of reduced genomic chaos generated by the ph1bmutation.

Aegilops comosa(2n= 2x= 14, MM) contains many excellent genes/traits for wheat breeding. Wheat–Ae. comosaintrogression lines have potential value in the genetic improvement of wheat quality. A disomic 1M (1B) Triticum aestivum–Ae. comosasubstitution line NAL-35 was identified by fluorescence in situ hybridization and genomic in situ hybridization analysis from a hybridization cross between a disomic 1M (1D) substitution line NB 4-8-5-9 with CS N1BT1D. The observation of pollen mother cells showed that NAL-35 had normal chromosome pairing, suggesting that NAL-35 could be used for the quality test. NAL-35 with alien Mx and My subunits showed positive effects on some protein-related parameters including high protein content and high ratios of high-molecular-weight glutenin subunits (HMW-GSs)/glutenin and HMW-GS/low-molecular-weight glutenin subunits. The changes in gluten composition improved the rheological properties of the dough of NAL-35, resulting in a tighter and more uniform microstructure. NAL-35 is a potential material for wheat quality improvement that transferred quality-related genes from Ae. comosa.

Diploid wild einkorn wheat, Triticum boeoticumBoiss (AbAb, 2n= 2x= 14), provides a resource of blue aleurone layers for wheat breeding. The anthocyanin composition and nutritional quality of the blue-grained wheat-Triticum boeoticumintrogression line Z18-1244 were compared with those of its T. boeoticumparent G52 and bread wheat parent Crocus. The results showed that the content of all four anthocyanins averaged 67.24 μg/g in the whole meal of the blue-grained wheat Z18-1244, which was slightly lower than that in G52 (72.31 μg/g) but significantly higher than that in Crocus. The total essential amino acid content in Z18-1244 was 48.03% higher than that in Crocus. Compared with Crocus, the protein nutritional quality of Z18-1244 was improved, including an SRC increased by 5.31% and an EAAI increased by 22.70%. The contents of zinc (Zn) and iron (Fe) in the mineral elements were 74.5 mg/kg and 109.7 mg/kg with increases of 39.34% and 109.65%, respectively. The nutritional quality of Z18-1244 has been considerably improved in comparison with its common wheat parent Crocus. Therefore, Z18-1244 could be used as a potential germplasm for wheat breeding to improve the nutritional value of wheat-based end-products.

The common wheat landrace Chinese Spring (CS) was made famous by the work of Ernie Sears, a great cytogenetist, who developed a number of CS-based aneuploid series that were used to identify individual wheat chromosomes. Based on this, a standard karyotype and nomenclature system was developed for wheat chromosomes that allowed wheat researchers to analyze and manipulate the wheat genome with unprecedented precision and efficiency. Nevertheless, not much is known about the utilization of CS at its hometown, Chengdu in Sichuan province, during early wheat breeding activity. In this review, we follow the speculation that CS is a selection from the Cheng-du-guang-tou (CDGT) landrace. We provide a description of how CDGT became a founder landrace for wheat breeding activities in early times. We show that CDGT-derived varieties were reinforced genetically by crosses to six more exotic parents. These varieties remained the major elite cultivar for several decades. Later, synthetic hexaploid wheats were introduced into the breeding program, firstly using those from CIMMYT and later using materials produced with local tetraploid wheat and goat grass. Finally, we discuss the strategies and future directions to improve wheat yield and resistance through an expanded genetic basis, especially by recapturing lost genetic variations from landraces and related wild species, a process that may set an example for wheat breeders in China and elsewhere.

Hexaploid wheat has triplicated homoeologs for most of the genes that are located in subgenomes A, B, and D. GASR7, a member of the Snakin/GASA gene family, has been associated with grain length development in wheat. However, little is known about divergence of its homoeolog expression in wheat polyploids. We studied the expression patterns of the GASR7homoeologs in immature seeds in a synthetic hexaploid wheat line whose kernels are slender like those of its maternal parent (Triticum turgidum, AABB, PI 94655) in contrast to the round seed shape of its paternal progenitor (Aegilops tauschii, DD, AS2404). We found that the B homoeolog of GASR7was the main contributor to the total expression level of this gene in both the maternal tetraploid progenitor and the hexaploid progeny, whereas the expression levels of the A and D homoeologs were much lower. To understand possible mechanisms regulating different GASR7homoeologs, we firstly analyzed the promoter sequences of three homoeologous genes and found that all of them contained gibberellic acid (GA) response elements, with the TaGASR7Bpromoter (pTaGASR7B) uniquely characterized by an additional predicted transcriptional enhancer. This was confirmed by the GA treatment of spikes where all three homoeologs were induced, with a much stronger response for TaGASR7B. McrBC enzyme assays showed that the methylation status at pTaGASR7Dwas increased during allohexaploidization, consistent with the repressed expression of TaGASR7D. For pTaGASR7A, the distribution of repetitive sequence-derived 24-nucleotide (nt) small interfering RNAs (siRNAs) were found which suggests possible epigenetic regulation because 24-nt siRNAs are known to mediate RNA-dependent DNA methylation. Our results thus indicate that both genetic and epigenetic mechanisms may be involved in the divergence of GASR7homoeolog expression in polyploid wheat.

Aegilops tauschiiCoss., the D‐genome progenitor of hexaploid wheat (Triticum aestivumL.), is an important source of useful genes for wheat improvement. We characterized a germplasm collection of 118 Ae. tauschiiaccessions for response to stripe rust, a devastating disease caused by the fungus Puccinia striiformisf. sp. tritici(Pst). We evaluated tillering stage and adult‐plant resistance to stripe rust using prevalent Pstraces from the United States and China. Resistant accessions predominated in Ae. tauschiisubsp. strangulataand Ae. tauschiisubsp. tauschiifrom the Caspian Sea region. We further analyzed the inheritance of stripe rust resistance by inoculating F2plants of 60 crosses with a mixture of Chinese Pstraces. Crosses between resistant and susceptible lines indicated both dominant and recessive inheritance. Tests of allelism among 14 highly resistant accessions indicated the common presence of YrAS2388, previously mapped on chromosome arm 4DS, in all accessions. In conclusion, the study presented valuable data on stripe rust resistance in Ae. tauschii, which assist with informed introgression of the D‐genome trait for stripe rust resistance in common wheat.

Abstract: By colchicine treatment of hybrids betweenTriticum turgidum andAegilops tauschii (as seedlings), a fertile wheat plant (SHW-L2) carrying 56 chromosomes was artificially synthesized. At metaphase I of 50 pollen mother cells, the 56 chromosomes of the new wheat SHW-L2 showed a mean pairing configuration of 2.82 univalents, 6.18 rod bivalents, 19.39 ring bivalents, 0.5 trivalents, and 0.14 quadrivalents. Cytological analyses suggested that SHW-L2 had additional 7 pairs of chromosomes from the A and D genome besides the 42 chromosomes of common wheat. The special chromosome constitution of SHW-L2 may be derived from the chromosome doubling by the colchicine treatment of seedlings and then spontaneous doubling of gametes.