Characterization of a Triticum aestivum-Dasypyrum villosum T2VS·2DL translocation line expressing a longer spike and more kernels traits

Pre-breeding of spontaneous Robertsonian translocations for density planting architecture by transferring Agropyron cristatum chromosome 1P into wheat

KEY MESSAGE

We developed T1AL·1PS and T1AS·1PL Robertsonian translocations by breakage-fusion mechanism based on wheat-A. cristatum 1P(1A) substitution line with smaller leaf area, shorter plant height, and other excellent agronomic traits Agropyron cristatum, a wild relative of wheat, is a valuable germplasm resource for improving wheat genetic diversity and yield. Our previous study confirmed that the A. cristatum chromosome 1P carries alien genes that reduce plant height and leaf size in wheat. Here, we developed T1AL·1PS and T1AS·1PL Robertsonian translocations (RobTs) by breakage-fusion mechanism based on wheat-A. cristatum 1P (1A) substitution line II-3-1c. Combining molecular markers and cytological analysis, we identified 16 spontaneous RobTs from 911 F2 individuals derived from the cross of Jimai22 and II-3-1c. Fluorescence in situ hybridization (FISH) was applied to detect the fusion structures of the centromeres in wheat and A. cristatum chromosomes. Resequencing results indicated that the chromosomal junction point was located at the physical position of Triticum aestivum chromosome 1A (212.5 Mb) and A. cristatum chromosome 1P (230 Mb). Genomic in situ hybridization (GISH) in pollen mother cells showed that the produced translocation lines could form stable ring bivalent. Introducing chromosome 1PS translocation fragment into wheat significantly increased the number of fertile tillers, grain number per spike, and grain weight and reduced the flag leaf area. However, introducing chromosome 1PL translocation fragment into wheat significantly reduced flag leaf area and plant height with a negative effect on yield components. The pre-breeding of two spontaneous RobTs T1AL·1PS and T1AS·1PL was important for wheat architecture improvement.

Chromosome diversity in Dasypyrum villosum, an important genetic and trait resource for hexaploid wheat engineering

BACKGROUND AND AIMS

Dasypyrum villosum (2n = 2x = 14) harbours potentially beneficial genes for hexaploid and tetraploid wheat improvement. Highly diversified chromosome variation exists among and within accessions due to its open-pollination nature. The wheat-D. villosum T6VS·6AL translocation was widely used in breeding mainly because gene Pm21 in the 6VS segment conferred high and lasting powdery mildew resistance. However, the widespread use of this translocation may narrow the genetic base of wheat. A better solution is to utilize diversified D. villosum accessions as the genetic source for wheat breeding. Analysis of cytological and genetic polymorphisms among D. villosum accessions also provides genetic evolution information on the species. Using cytogenetic and molecular tools we analysed genetic polymorphisms among D. villosum accessions and developed consensus karyotypes to assist the introgression of beneficial genes from D. villosum into wheat.

METHODS

A multiplex probe of repeats for FISH, GISH and molecular markers were used to detect chromosome polymorphisms among D. villosum accessions. Polymorphic signal block types, chromosome heterogeneity and heterozygosity, and chromosome polymorphic information content were used in genetic diversity analysis.

KEY RESULTS

Consensus karyotypes of D. villosum were developed, and the homoeologous statuses of individual D. villosum chromosomes relative to wheat were determined. Tandem repeat probes of pSc119.2, (GAA)10 and the AFA family produced high-resolution signals and not only showed different signal patterns in D. villosum chromosomes but also revealed the varied distribution of tandem repeats among chromosomes and accessions. A total of 106 polymorphic chromosomes were identified from 13 D. villosum accessions and high levels of chromosomal heterozygosity and heterogeneity were observed. A subset of 56 polymorphic chromosomes was transferred into durum wheat through wide crosses, and seven polymorphic chromosomes are described in two newly developed durum-D. villosum amphidiploids.

CONCLUSIONS

Consensus karyotypes of D. villosum and oligonucleotide FISH facilitated identification of polymorphic signal blocks and a high level of chromosomal heterozygosity and heterogeneity among D. villosum accessions, seen in newly developed amphiploids. The abundant genetic diversity of D. villosum and range of alleles, exploitable through interploid crosses, backcrosses and recombination (chromosome engineering), allow introduction of biotic and abiotic stress resistances into wheat, translating into increasing yield, end-use quality and crop sustainability.

Transfer of the Resistance to Multiple Diseases from a Triticum-Secale-Thinopyrum Trigeneric Hybrid to Ningmai 13 and Yangmai 23 Wheat Using Specific Molecular Markers and GISH

The middle to lower reaches of the Yangtze River are China's second largest area for wheat production; wheat disease is more serious there than in other areas because of the high humidity and warm weather. However, most cultivated varieties are susceptible to Fusarium head blight (FHB), powdery mildew, and stripe rust, and the lack of disease-resistant germplasm is an obstacle in wheat breeding. Rye and Thinopyrum elongatum, related species of wheat, carry many genes involved in disease resistance. In this study, a trigeneric hybrid, YZU21, with resistance to FHB, powdery mildew, and stripe rust was used to improve two major wheat cultivars, Ningmai 13 (NM13) and Yangmai 23 (YM23). Specific molecular markers and GISH were used to identify hybrid progenies. Five addition or substitution lines and one translocation line of the Triticum-Secale-Thinopyrum trigeneric hybrid were obtained and evaluated for agronomic traits and the resistance to multiple diseases. The results showed that the six trigeneric hybrid lines had desirable agronomic traits and improved resistance to FHB, powdery mildew, and stripe rust; they might be used as parents in wheat breeding for the resistance to multiple disease.

Identification of 5P Chromosomes in Wheat-Agropyron cristatum Addition Line and Analysis of Its Effect on Homologous Pairing of Wheat Chromosomes

As an important wheat wild relative, the P genome of Agropyron cristatum (L.) Gaertn. (2n = 4x = 28) is very valuable for wheat improvement. A complete set of wheat-A. cristatum disomic addition lines is the basis for studying the genetic behavior of alien homoeologous chromosomes and exploring and utilizing the excellent genes. In this study, a wheat-A. cristatum derivative II-11-1 was proven to contain a pair of 5P chromosomes and a pair of 2P chromosomes with 42 wheat chromosomes by analyzing the fluorescence in situ hybridization (FISH) and expressed sequence tag (EST) markers. Additionally, cytological identification and field investigation showed that the 5P chromosome can weaken the homologous pairing of wheat chromosomes and promote the pairing between homoeologous chromosomes. This provides new materials for studying the mechanism of the alien gene affecting the homologous chromosome pairing and promoting the homoeologous pairing of wheat. In addition, chromosomal structural variants have been identified in the progeny of II-11-1. Therefore, the novel 5P addition line might be used as an important genetic material to widen the genetic resources of wheat.

Development and characterization of novel Triticum aestivum-Agropyron cristatum 6P Robertsonian translocation lines

Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP), one of the most important wild relatives of wheat, harbors many desirable genes for wheat genetic improvement. Development of wheat-A. cristatum translocation lines with superior agronomic traits facilitates wheat genetic improvement. In this study, 5106-DS was identified to be a wheat-A. cristatum 6P (6D) disomic substitution line using cytogenetic identification and molecular markers analysis, which displayed higher thousand-grain weight than its wheat parent Triticum aestivum cv. Fukuhokomugi (2n = 6x = 42, AABBDD). Analysis of its backcross populations indicated that there might be genes conferring increased grain weight and width on the chromosome 6P of 5106-DS. In the backcross population, we found three plants as Robertsonian translocation lines, created by chromosome centric breakage-fusion. Among them, there are one T6DS·6PL and two T6PS·6DL Robertsonian translocation lines. Additionally, the centromeres of these three translocation lines were determined to be fused centromeres of 6D and 6P using the probes pAcCR1 and pCCS1. The development of Robertsonian translocation lines would promote the utilization of A. cristatum chromosome 6P in wheat improvement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01251-y.

Development and Molecular Cytogenetic Identification of a New Wheat-Psathyrostachys huashanica Keng Translocation Line Resistant to Powdery Mildew

Psathyrostachys huashanica Keng, a wild relative of common wheat with many desirable traits, is an invaluable source of genetic material for wheat improvement. Few wheat-P. huashanica translocation lines resistant to powdery mildew have been reported. In this study, a wheat-P. huashanica line, E24-3-1-6-2-1, was generated via distant hybridization, ethyl methanesulfonate (EMS) mutagenesis, and backcross breeding. A chromosome karyotype of 2n = 44 was observed at the mitotic stage in E24-3-1-6-2-1. Genomic in situ hybridization (GISH) analysis revealed four translocated chromosomes in E24-3-1-6-2-1, and P. huashanica chromosome-specific marker analysis showed that the alien chromosome fragment was from the P. huashanica 4Ns chromosome. Moreover, fluorescence in situ hybridization (FISH) analysis demonstrated that reciprocal translocation had occurred between the P. huashanica 4Ns chromosome and the wheat 3D chromosome; thus, E24-3-1-6-2-1 carried two translocations: T3DS·3DL-4NsL and T3DL-4NsS. Translocation also occurred between wheat chromosomes 2A and 4A. At the adult stage, E24-3-1-6-2-1 was highly resistant to powdery mildew, caused by prevalent pathotypes in China. Further, the spike length, numbers of fertile spikelets, kernels per spike, thousand-kernel weight, and grain yield of E24-3-1-6-2-1 were significantly higher than those of its wheat parent 7182 and addition line 24-6-3-1. Thus, this translocation line that is highly resistant to powdery mildew and has excellent agronomic traits can be used as a novel promising germplasm for breeding resistant and high-yielding cultivars.

Dissection and physical mapping of wheat chromosome 7B by inducing meiotic recombination with its homoeologues in Aegilops speltoides and Thinopyrum elongatum

We constructed a homoeologous recombination-based bin map of wheat chromosome 7B, providing a unique physical framework for further study of chromosome 7B and its homoeologues in wheat and its relatives. Homoeologous recombination leads to the dissection and diversification of the wheat genome. Advances in genome sequencing and genotyping have dramatically improved the efficacy and throughput of homoeologous recombination-based genome studies and alien introgression in wheat and its relatives. In this study, we aimed to physically dissect and map wheat chromosome 7B by inducing meiotic recombination of chromosome 7B with its homoeologues 7E in Thinopyrum elongatum and 7S in Aegilops speltoides. The special genotypes, which were double monosomic for chromosomes 7B' + 7E' or 7B' + 7S' and homozygous for the ph1b mutant, were produced to enhance 7B - 7E and 7B - 7S recombination. Chromosome-specific DNA markers were developed and used to pre-screen the large recombination populations for 7B - 7E and 7B - 7S recombinants. The DNA marker-mediated preselections were verified by fluorescent genomic in situ hybridization (GISH). In total, 29 7B - 7E and 61 7B - 7S recombinants and multiple chromosome aberrations were recovered and delineated by GISH and the wheat 90 K SNP assay. Integrated GISH and SNP analysis of the recombinants physically mapped the recombination breakpoints and partitioned wheat chromosome 7B into 44 bins with 523 SNPs assigned within. A composite bin map was constructed for chromosome 7B, showing the bin size and physical distribution of SNPs. This provides a unique physical framework for further study of chromosome 7B and its homoeologues. In addition, the 7B - 7E and 7B - 7S recombinants extend the genetic variability of wheat chromosome 7B and represent useful germplasm for wheat breeding. Thereby, this genomics-enabled chromosome engineering approach facilitates wheat genome study and enriches the gene pool of wheat improvement.

Molecular Characterization of the Dwarf53 Gene Homolog in Dasypyrum villosum

The Dwarf53 (D53) gene, first studied in rice, encodes a protein that acts as a repressor of the physiological response of plants to strigolactones—substances that regulate the activity of axillary buds, stem growth, branching of roots and other physiological processes. In this work, we isolated and sequenced the homolog of the D53 gene in several accessions of the wild grass Dasypyrum villosum of different geographical origins, resulting in the discovery of large allelic variety. A molecular marker was also created that allows us to differentiate the D. villosum D53 gene from common wheat genes. Using this marker and monosomic addition, substitution and translocation wheat lines carrying the known D. villosum chromosomes, the D53 gene was localized on the long arm of the 5V chromosome.

Dissection and cytological mapping of chromosome arm 4VS by the development of wheat-Haynaldia villosa structural aberration library

A cytological map of Haynaldia villosa chromosome arm 4VS was constructed to facilitate the identification and utilization of beneficial genes on 4VS. Induction of wheat-alien chromosomal structure aberrations not only provides new germplasm for wheat improvement, but also allows assignment of favorable genes to define physical regions. Especially, the translocation or introgression lines carrying alien chromosomal fragments with different sizes are useful for breeding and alien gene mapping. Chromosome arm 4VS of Haynaldia villosa (L.) Schur (syn. Dasypyrum villosum (L.) P. Candargy) confers resistances to eyespot and wheat yellow mosaic virus (WYMV). In this research, we used both irradiation and the pairing homoeologous gene (Ph) mutant to induce chromosomal aberrations or translocations. By using the two approaches, a structural aberration library of chromosome arm 4VS was constructed. In this library, there are 57 homozygous structural aberrations, in which, 39 were induced by the Triticum aestivum cv. Chinese Spring (CS) ph1b mutant (CS ph1b) and 18 were induced by irradiation. The aberrations included four types, i.e., terminal translocation, interstitial translocation, deletion and complex structural aberration. The 4VS cytological map was constructed by amplification in the developed homozygous aberrations using 199 4VS-specific markers, which could be allocated into 39 bins on 4VS. These bins were further assigned to their corresponding physical regions of chromosome arm 4DS based on BLASTn search of the marker sequences against the reference sequence of Aegilops tauschii Cosson. The developed genetic stocks and cytological map provide genetic stocks for wheat breeding as well as alien gene tagging.

Pairing and Exchanging between Daypyrum villosum Chromosomes 6V#2 and 6V#4 in the Hybrids of Two Different Wheat Alien Substitution Lines

Normal pairing and exchanging is an important basis to evaluate the genetic relationship between homologous chromosomes in a wheat background. The pairing behavior between 6V#2 and 6V#4, two chromosomes from different Dasypyrum villosum accessions, is still not clear. In this study, two wheat alien substitution lines, 6V#2 (6A) and 6V#4 (6D), were crossed to obtain the F₁ hybrids and F₂ segregating populations, and the testcross populations were obtained by using the F₁ as a parent crossed with wheat variety Wan7107. The chromosomal behavior at meiosis in pollen mother cells (PMCs) of the F₁ hybrids was observed using a genomic in situ hybridization (GISH) technique. Exchange events of two alien chromosomes were investigated in the F₂ populations using nine polymerase chain reaction (PCR) markers located on the 6V short arm. The results showed that the two alien chromosomes could pair with each other to form ring- or rod-shaped bivalent chromosomes in 79.76% of the total PMCs, and most were pulled to two poles evenly at anaphase I. Investigation of the F₂ populations showed that the segregation ratios of seven markers were consistent with the theoretical values 3:1 or 1:2:1, and recombinants among markers were detected. A genetic linkage map of nine PCR markers for 6VS was accordingly constructed based on the exchange frequencies and compared with the physical maps of wheat and barley based on homologous sequences of the markers, which showed that conservation of sequence order compared to 6V was 6H and 6B > 6A > 6D. In the testcross populations with 482 plants, seven showed susceptibility to powdery mildew (PM) and lacked amplification of alien chromosomal bands. Six other plants had amplification of specific bands of both the alien chromosomes at multiple sites, which suggested that the alien chromosomes had abnormal separation behavior in about 1.5% of the PMCs in F₁, which resulted in some gametes containing two alien chromosomes. In addition, three new types of chromosome substitution were developed. This study lays a foundation for alien allelism tests and further assessment of the genetic relationship among 6V#2, 6V#4, and their wheat homoeologous chromosomes.

Physical Mapping of Stem Rust Resistance Gene Sr52 from Dasypyrum villosum Based on ph1b-Induced Homoeologous Recombination

Wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt) had been a devastating foliar disease worldwide during the 20th century. With the emergence of Ug99 races, which are virulent to most stem rust resistance genes deployed in wheat varieties and advanced lines, stem rust has once again become a disease threatening global wheat production. Sr52, derived from Dasypyrum villosum and mapped to the long arm of 6V#3, is one of the few effective genes against Ug99 races. In this study, the wheat-D. villosum Robertsonian translocation T6AS·6V#3L, the only stock carrying Sr52 released to experimental and breeding programs so far, was crossed with a CS ph1b mutant to induce recombinants with shortened 6V#3L chromosome segments locating Sr52. Six independent homozygous recombinants with different segment sizes and breakpoints were developed and characterized using in situ hybridization and molecular markers analyses. Stem rust resistance evaluation showed that only three terminal recombinants (1381, 1380, and 1392) containing 8%, 22%, and 30% of the distal segment of 6V#3L, respectively, were resistant to stem rust. Thus, the gene Sr52 was mapped into 6V#3L bin FL 0.92-1.00. In addition, three molecular markers in the Sr52-located interval of 6V#3L were confirmed to be diagnostic markers for selection of Sr52 introgressed into common wheat. The newly developed small segment translocation lines with Sr52 and the identified molecular markers closely linked to Sr52 will be valuable for wheat disease breeding.

Deletion mapping and verification of an enhanced-grain number per spike locus from the 6PL chromosome arm of Agropyron cristatum in common wheat

An enhanced-grain number per spike locus from Agropyron cristatum 6PL was mapped onto 6PL (0.27-0.51) via deletion mapping, and its effect was further verified by evaluating a newly created translocation line. Agropyron cristatum (2n = 4x = 28, PPPP) is an important wild relative of common wheat and carries many desirable yield-related traits. The wheat-A. cristatum 6P disomic addition line 4844-12 exhibited high grain number per spike (GNS), high spikelet number per spike (SNS), and high kernel number per spikelet (KNS). In this study, five A. cristatum 6P deletion lines, five wheat-A. cristatum 6P translocation lines, and genetic populations of these lines were used to map the enhanced-GNS locus from A. cristatum chromosome 6P, which were genotyped via genomic in situ hybridization, fluorescence in situ hybridization, or molecular markers. According to the evaluation of the agronomic traits in four growing seasons (2014-2015, 2015-2016, 2016-2017, and 2017-2018), we found that the deletion lines and the translocation lines carrying the long arm of A. cristatum chromosome 6P (6PL) exhibited high GNS, SNS, and KNS, and the enhanced-GNS locus was ultimately mapped onto 6PL (0.27-0.51). To verify the localization results, we created a new translocation line WAT650a (T5BL•5BS-6PL) that carried 6PL (0.35-0.42); this line exhibited higher GNS and SNS than the recipient parent Fukuhokomugi (Fukuho). Collectively, the enhanced-GNS locus of A. cristatum 6PL can be important for improving yield traits in common wheat; the translocation lines with the enhanced-GNS locus can serve as novel and valuable germplasm resources for wheat breeding.

Diversified Chromosome Rearrangements Detected in a Wheat‒Dasypyrum breviaristatum Substitution Line Induced by Gamma-Ray Irradiation

To determine the composition of chromosome aberrations in a wheat‒Dasypyrum breviaristatum substitution line with seeds treated by a dose of gamma-rays (200 Gy), sequential non-denaturing fluorescence in situ hybridization (ND-FISH) with multiple oligonucleotide probes was used to screen individual plants of the mutagenized progenies. We identified 122 types of chromosome rearrangements, including centromeric, telomeric, and intercalary chromosome translocations from a total of 772 M1 and 872 M2 plants. The frequency of reciprocal translocations between B- and D-chromosomes was higher than that between A- and D-chromosomes. Eight translocations between D. breviaristatum and wheat chromosomes were also detected. The 13 stable plants with multiple chromosome translocations displayed novel agronomic traits. The newly developed materials will enhance wheat breeding programs through wheat‒Dasypyrum introgression and also facilitate future studies on the genetic and epigenetic effects of translocations in wheat genomics.

Development of PCR markers specific to Dasypyrum villosum genome based on transcriptome data and their application in breeding Triticum aestivum-D. villosum#4 alien chromosome lines

Background

Dasypyrum villosum is an important wild species of wheat (Triticum aestivum L.) and harbors many desirable genes that can be used to improve various traits of wheat. Compared with other D. villosum accessions, D. villosum#4 still remains less studied. In particular, chromosomes of D. villosum#4 except 6V#4 have not been introduced into wheat by addition or substitution and translocation, which is an essential step to identify and apply the alien desired genes. RNA-seq technology can generate large amounts of transcriptome sequences and accelerate the development of chromosome-specific molecular markers and assisted selection of alien chromosome line.

Results

We obtained the transcriptome of D. villosum#4 via a high-throughput sequencing technique, and then developed 76 markers specific to each chromosome arm of D. villosum#4 based on the bioinformatic analysis of the transcriptome data. The D. villosum#4 sequences containing the specific DNA markers were expected to be involved in different genes, among which most had functions in metabolic processes. Consequently, we mapped these newly developed molecular markers to the homologous chromosome of barley and obtained the chromosome localization of these markers on barley genome. Then we analyzed the collinearity of these markers among D. villosum, wheat, and barley. In succession, we identified six types of T. aestivum-D. villosum#4 alien chromosome lines which had one or more than one D. villosum#4 chromosome in the cross and backcross BC₃F₅ populations between T. durum–D. villosum#4 amphidiploid TH3 and wheat cv. Wan7107 by employing the selected specific markers, some of which were further confirmed to be translocation or addition lines by genomic in situ hybridization (GISH).

Conclusion

Seventy-six PCR markers specific to chromosomes of D. villosum#4 based on transcriptome data were developed in the current study and their collinearity among D. villosum, wheat, and barley were carried out. Six types of Triticum aestivum-D. villosum#4 alien chromosome lines were identified by using 12 developed markers and some of which were further confirmed by GISH. These novel T. aestivum-D. villosum#4 chromosome lines have great potential to be used for the introduction of desirable genes from D. villosum#4 into wheat by chromosomal translocation to breed new wheat varieties.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5630-4) contains supplementary material, which is available to authorized users.

Pm62, an adult-plant powdery mildew resistance gene introgressed from Dasypyrum villosum chromosome arm 2VL into wheat

Pm62, a novel adult-plant resistance (APR) gene against powdery mildew, was transferred from D. villosum into common wheat in the form of Robertsonian translocation T2BS.2VL#5. Powdery mildew, which is caused by the fungus Blumeria graminis f. sp. tritici, is a major disease of wheat resulting in substantial yield and quality losses in many wheat production regions of the world. Introgression of resistance from wild species into common wheat has application for controlling this disease. A Triticum durum-Dasypyrum villosum chromosome 2V#5 disomic addition line, N59B-1 (2n = 30), improved resistance to powdery mildew at the adult-plant stage, which was attributable to chromosome 2V#5. To transfer this resistance into bread wheat, a total of 298 BC₁F₁ plants derived from the crossing between N59B-1 and Chinese Spring were screened by combined genomic in situ hybridization and fluorescent in situ hybridization, 2V-specific marker analysis, and reaction to powdery mildew to confirm that a dominant adult-plant resistance gene, designated as Pm62, was located on chromosome 2VL#5. Subsequently, the 2VL#5 (2D) disomic substitution line (NAU1825) and the homozygous T2BS.2VL#5 Robertsonian translocation line (NAU1823), with normal plant vigor and full fertility, were identified by molecular and cytogenetic analyses of the BC₁F₂ generation. The effects of the T2BS.2VL#5 recombinant chromosome on agronomic traits were also evaluated in the F₂ segregation population. The results suggest that the translocated chromosome may have no distinct effect on plant height, 1000-kernel weight or flowering period, but a slight effect on spike length and seeds per spike. The translocation line NAU1823 has being utilized as a novel germplasm in breeding for powdery mildew resistance, and the effects of the T2BS.2VL#5 recombinant chromosome on yield-related and flour quality characters will be further assessed.

Characterization of New Wheat-Dasypyrum breviaristatum Introgression Lines with Superior Gene(s) for Spike Length and Stripe Rust Resistance

Dasypyrum breviaristatum (genome VbVb) contains potentially important traits for commercial wheat production. Chromosome 2Vb of D. breviaristatum carries several desirable agronomic characters, including long spike length as well as enhanced resistance to stripe rust, which are expressed in a common wheat background. In this study, wheat-D. breviaristatum 2Vb deletion lines were produced and identified by fluorescence in situ hybridization (FISH), and 74 molecular markers specific to D. breviaristatum chromosome 2Vb were physically localized in 4 distinct chromosomal regions. New wheat-D. breviaristatum 2Vb translocation lines were also characterized by FISH. The breakpoint of the translocation T3AS.3AL-2VbS was determined by physically mapped molecular markers. Field evaluation revealed that genes affecting plant height and spike length are located on fraction length (FL) 0.65-1.00 of 2VbS, while the stripe rust resistance gene(s) are located on FL 0.40-1.00 of D. breviaristatum chromosome 2VbL. The newly characterized wheat-Dasypyrum chromosomal introgressions are of potential value for the improvement of the yield and disease resistance of wheat.

Molecular markers and cytogenetics to characterize a wheat-Dasypyrum villosum 3V (3D) substitution line conferring resistance to stripe rust

Dasypyrum villosum has been used as a valuable gene resource for disease resistances, yield increase and quality improvement in wheat. A novel wheat-D. villosum alien introgression line CD-3 was generated through hybridization between the common wheat Chinese Spring (CS) and a CS- D. villosum 3V addition line having considerably high stripe rust resistance, which enable the characterization of a potential new stripe rust resistance gene (s) derived from D. villosum. The results of non-denaturing fluorescent in situ hybridization (ND-FISH) showed that CD-3 contained 42 chromosomes, including a 3V chromosome pair, and the absence of both of the 3D chromosomes. PCR-based Landmark Unique Gene (PLUG) molecular marker analysis supported results from the FISH analysis, revealing CD-3 was a wheat-D. villosum 3V (3D) disomic substitution line. Resistant test of stripe rust on 52 plants of F2 generation (CD-3/CS), CD-3, CS and D.villosum have been conducted at seedling stage. 7 plants of F2 generation possessing two 3V chromosomes exhibited high resistance to stripe rust as CD-3 and D.villosum, 10 plants carrying one 3V chromosome and 35 plants without 3V chromosome were susceptive to stripe rust as CS. The result implied the high stripe rust resistance of CD-3 should be controlled by recessive gene(s) originating from D.villosum. To rapidly detect chromosome 3V in the genetic background of wheat, we developed a novel Sequence Characterized Amplified Region (SCAR) marker specific for 3V chromosome based on the sequence of a grain size-related gene DvGS5 in D. villosum, an orthologue of TaGS5 from wheat. The SCAR marker was designated DvGS5-1443, which could successfully amplify a unique 3V-specific fragment in CD-3 and D. villosum, suggesting that this SCAR marker could facilitate targeting the chromosome 3V in the genetic background of wheat for wheat improvement.

Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement

The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality. Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.

Chromosome Pairing in Hybrid Progeny between Triticum aestivum and Elytrigia elongata

In this study, the intergeneric hybrids F₁, F₂, BC₁F₁, BC₁F₂, and BC₂F₁ from Elytrigia elongata and Triticum aestivum crosses were produced to study their chromosome pairing behavior. The average E. elongata chromosome configuration of the two F₁ hybrids agreed with the theoretical chromosome configuration of 21I+7II, indicating that the genomic constitution of this F₁ hybrid was ABDStStE^eE^bE^x. Compared with the BC₁F₁ generation, the BC₂F₁ generation showed a rapid decrease in the number of E. elongata chromosomes and the BC₁F₂ generation showed a more extensive distribution of E. elongata chromosomes. In addition, pairing between wheat and E. elongata chromosomes was detected in each of the wheat-E. elongata hybrid progenies, albeit rarely. Our results demonstrated that genomic in situ hybridization (GISH) using an E. elongata genomic DNA probe offers a reliable approach for characterizing chromosome pairing in wheat and E. elongata hybrid progenies.

Isolation of two new retrotransposon sequences and development of molecular and cytological markers for Dasypyrum villosum (L.)

Dasypyrum villosum is a valuable genetic resource for wheat improvement. With the aim to efficiently monitor the D. villosum chromatin introduced into common wheat, two novel retrotransposon sequences were isolated by RAPD, and were successfully converted to D. villosum-specific SCAR markers. In addition, we constructed a chromosomal karyotype of D. villosum. Our results revealed that different accessions of D. villosum showed slightly different signal patterns, indicating that distribution of repeats did not diverge significantly among D. villosum accessions. The two SCAR markers and FISH karyotype of D. villosum could be used for efficient and precise identification of D. villosum chromatin in wheat breeding.

Mapping of novel powdery mildew resistance gene(s) from Agropyron cristatum chromosome 2P

A physical map of Agropyron cristatum 2P chromosome was constructed for the first time and the novel powdery mildew resistance gene(s) from chromosome 2P was(were) also mapped. Agropyron cristatum (L.) Gaertn. (2n = 28, PPPP), a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies showed that wheat-A. cristatum 2P disomic addition line II-9-3 displayed high resistance to powdery mildew, and the resistance was attributable to A. cristatum chromosome 2P. To utilize and physically map the powdery mildew resistance gene(s), 15 wheat-A. cristatum 2P translocation lines and three A. cristatum 2P deletion lines with different chromosomal segment sizes, obtained from II-9-3 using ⁶⁰Co-γ ray irradiation, were characterized using cytogenetic and molecular marker analysis. A. cristatum 2P chromosomal segments in the translocations were translocated to different wheat chromosomes, including 1A, 4A, 5A, 6A, 7A, 1B, 2B, 3B, 7B, 3D, 4D, and 6D. A physical map of the 2P chromosome was constructed with 82 STS markers, consisting of nine bins with 34 markers on 2PS and eight bins with 48 markers on 2PL. The BC₁F₂ populations of seven wheat-A. cristatum 2P translocation lines (2PT-3, 2PT-4, 2PT-5, 2PT-6, 2PT-8, 2PT-9, and 2PT-10) were developed by self-pollination, tested with powdery mildew and genotyped with 2P-specific STS markers. From these results, the gene(s) conferring powdery mildew resistance was(were) located on 2PL bin FL 0.66-0.86 and 19 2P-specific markers were identified in this bin. Moreover, two new powdery mildew-resistant translocation lines (2PT-4 and 2PT-5) with small 2PL chromosome segments were obtained. The newly developed wheat lines with powdery mildew resistance and the closely linked molecular markers will be valuable for wheat disease breeding in the future.

Chromosomal Localization of Genes Conferring Desirable Agronomic Traits from Wheat-Agropyron cristatum Disomic Addition Line 5113

Creation of wheat-alien disomic addition lines and localization of desirable genes on alien chromosomes are important for utilization of these genes in genetic improvement of common wheat. In this study, wheat-Agropyron cristatum derivative line 5113 was characterized by genomic in situ hybridization (GISH) and specific-locus amplified fragment sequencing (SLAF-seq), and was demonstrated to be a novel wheat-A. cristatum disomic 6P addition line. Compared with its parent Fukuhokomugi (Fukuho), 5113 displayed multiple elite agronomic traits, including higher uppermost internode/plant height ratio, larger flag leaf, longer spike length, elevated grain number per spike and spikelet number per spike, more kernel number in the middle spikelet, more fertile tiller number per plant, and enhanced resistance to powdery mildew and leaf rust. Genes conferring these elite traits were localized on the A. cristatum 6P chromosome by using SLAF-seq markers and biparental populations (F1, BC1F1 and BC1F2 populations) produced from the crosses between Fukuho and 5113. Taken together, chromosomal localization of these desirable genes will facilitate transferring of high-yield and high-resistance genes from A. cristatum into common wheat, and serve as the foundation for the utilization of 5113 in wheat breeding.

De novo balanced complex chromosome rearrangements involving chromosomes 1B and 3B of wheat and 1R of rye

Complex chromosome rearrangements (CCRs) are defined as structural abnormalities involving more than two chromosome breaks, coupled with exchanges of chromosomal segments. Information on CCRs in plants is limited. In the present study, a plant (26-4) harboring translocation chromosomes 1RS.1BL and 4RS.4DL was selected from a double monosomic (1R and 4R) addition line, which was derived from the hybrid between wheat cultivar MY11 and a Chinese local rye variety. The genome of the plant with double alien translocation chromosomes in the monosomic form showed more instability than that harboring a single translocation. The CCRs involving chromosomes 1RS.1BL and 3B, which were generated de novo in this plant, showed double monosomic translocation chromosomes. A new CCR line with balanced reciprocal translocations 1RS.3BL and 3BS.1BL was developed, which presented normal morphological traits of wheat and underwent rapid growth in the field. A new 1RS.1BL translocation line was also selected from the progeny of plant 26-4. The CCRs and simple 1RS.1BL translocation lines showed significant improvement in grain yield, number of spikes per square meter, kernel number per spike, and resistance to stripe rust and powdery mildew. The CCR line exhibited better agronomic traits and adult plant resistance in the field than its sister line, which harbored a simple 1RS.1BL translocation. The CCRs are remarkable genetic resources for crop improvement.

An intercalary translocation from Agropyron cristatum 6P chromosome into common wheat confers enhanced kernel number per spike

This study explored 6P chromosomal translocations in wheat, and determined the effects of 6P intercalary chromosome segments on kernel number per wheat spike. Exploiting and utilising gene(s) from wild relative species has become an essential strategy for wheat crop improvement. In the translocation line Pubing2978, the intercalary 6P chromosome segment from Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP) carried valuable multi-kernel gene(s) and was selected from the offspring of the common wheat plant Fukuho and the irradiated wheat-A. cristatum 6P disomic substitution line 4844-8. Genomic in situ hybridisation (GISH), dual-colour fluorescence in situ hybridisation (FISH), and molecular markers were used to detect the small segmental 6P chromosome in the wheat background and its translocation breakpoint. Cytological studies demonstrated that Pubing2978 was a T1AS-6PL-1AS·1AL intercalary translocation with 42 chromosomes. The breakpoint was located near the centromeric region on the wheat chromosome 1AS and was flanked by the markers SSR12 and SSR283 based on an F2 linkage map. The genotypic data, combined with the phenotypic information, implied that A. cristatum 6P chromosomal segment plays an important role in regulating the kernel number per spike (KPS). By comparison, the mean value of KPS in plants with translocations was approximately 10 higher than that in plants without translocations in three segregated populations. Moreover, the improvement in KPS was likely achieved by increasing both the spikelet number per spike (SNS) and the kernel number per spikelet. These excellent agronomic traits laid the foundation for further investigation of valuable genes and make the Pubing2978 line a promising germplasm for wheat breeding.

Pm55, a developmental-stage and tissue-specific powdery mildew resistance gene introgressed from Dasypyrum villosum into common wheat

Powdery mildew resistance gene Pm55 was physically mapped to chromosome arm 5VS FL 0.60-0.80 of Dasypyrum villosum . Pm55 is present in T5VS·5AL and T5VS·5DL translocations, which should be valuable resources for wheat improvement. Powdery mildew caused by Blumeria graminis f. sp. tritici is a major wheat disease worldwide. Exploiting novel genes effective against powdery mildew from wild relatives of wheat is a promising strategy for controlling this disease. To identify novel resistance genes for powdery mildew from Dasypyrum villosum, a wild wheat relative, we evaluated a set of Chinese Spring-D. villosum disomic addition and whole-arm translocation lines for reactions to powdery mildew. Based on the evaluation data, we concluded that the D. villosum chromosome 5V controls post-seedling resistance to powdery mildew. Subsequently, three introgression lines were developed and confirmed by molecular and cytogenetic analysis following ionizing radiation of the pollen of a Chinese Spring-D. villosum 5V disomic addition line. A homozygous T5VS·5AL translocation line (NAU421) with good plant vigor and full fertility was further characterized using sequential genomic in situ hybridization, C-banding, and EST-STS marker analysis. A dominant gene permanently named Pm55 was located in chromosome bin 5VS 0.60-0.80 based on the responses to powdery mildew of all wheat-D. villosum 5V introgression lines evaluated at both seeding and adult stages. This study demonstrated that Pm55 conferred growth-stage and tissue-specific dependent resistance; therefore, it provides a novel resistance type for powdery mildew. The T5VS·5AL translocation line with additional softness loci Dina/Dinb of D. villosum provides a possibility of extending the range of grain textures to a super-soft category. Accordingly, this stock is a new source of resistance to powdery mildew and may be useful in both resistance mechanism studies and soft wheat improvement.

Molecular cytogenetic characterization of a new wheat-rye 1BL•1RS translocation line expressing superior stripe rust resistance and enhanced grain yield

A new wheat-rye 1BL•1RS translocation line, with the characteristics of superior stripe rust resistance and high thousand-kernel weight and grain number per spike, was developed and identified from progenies of wheat-rye- Psathyrostachys huashanica trigeneric hybrids. The wheat-rye 1BL•1RS translocation line from Petkus rye has contributed substantially to the world wheat production. However, due to extensive growing of cultivars with disease resistance genes from short arm of rye chromosome 1R and coevolution of pathogen virulence and host resistance, these cultivars successively lost resistance to pathogens. In this study, a new wheat-rye line K13-868, derived from the progenies of wheat-rye-Psathyrostachys huashanica trigeneric hybrids, was identified and analyzed using fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH), acid polyacrylamide gel electrophoresis (A-PAGE), and molecular markers. Cytological studies indicated that the mean chromosome configuration of K13-868 at meiosis was 2n = 42 = 0.14 I + 18.78 II (ring) + 2.15 II (rod). Sequential FISH and GISH results demonstrated that K13-868 was a compensating wheat-rye 1BL•1RS Robertsonian translocation line. Acid PAGE analysis revealed that clear specific bands of rye 1RS were expressed in K13-868. Simple sequence repeat (SSR) and rye 1RS-specific markers ω-sec-p1/ω-sec-p2 and O-SEC5'-A/O-SEC3'-R suggested that the 1BS arm of wheat had been substituted by the 1RS arm of rye. At the seedling and adult growth stage, compared with its recurrent wheat parent SM51 and six other wheat cultivars containing the 1RS arm in southwestern China, K13-868 showed high levels of resistance to stripe rust (Puccinia striiformis f. sp. tritici, Pst) pathogens prevalent in China, which are virulent to Yr10 and Yr24/Yr26. In addition, K13-868 expresses higher thousand-kernel weight and more grain number per spike than these controls in two growing seasons, suggesting that this line may carry yield-related genes of rye. This translocation line, with significant characteristics of resistance to stripe rust and high thousand-kernel weight and grain number per spike, could be utilized as a valuable germplasm for wheat improvement.

Cytological and molecular analysis of wheat - Agropyron cristatum translocation lines with 6P chromosome fragments conferring superior agronomic traits in common wheat

Agropyron cristatum (2n = 4x = 28, PPPP) is a wild relative of common wheat and confers several desirable agronomic traits to wheat, such as high grain number per spike and enhanced resistance to certain diseases. Development of wheat - A. cristatum 6P translocation lines facilitates its utilization in wheat improvement. In this study, 26 wheat - A. cristatum 6P translocation lines were characterized by in situ hybridization (ISH) and 6P-specific sequence-tagged-site (STS) markers. These translocation lines carried different 6P chromosomal segments, which covered the whole 6P chromosome. FISH results showed that 15, 5, and 6 lines were translocated onto wheat A, B, and D genomes, respectively. Compared with the previous reports, a fine physical map of 6P chromosome was constructed, consisting of 31 chromosomal bins with 255 STS markers. Twelve translocation lines containing 6PS13∼14 chromosomal bins were highly resistant to leaf rust. Two lines showed high grain number per spike, and three lines displayed both enhanced grain number per spike and thousand-grain weight. Development of wheat - A. cristatum 6P translocation lines will not only provide novel wheat germplasm for wheat breeding but also be helpful to broaden the genetic basis of common wheat.

Transferring Desirable Genes from Agropyron cristatum 7P Chromosome into Common Wheat

Wheat-Agropyron cristatum 7P disomic addition line Ⅱ-5-1, derived from the distant hybridization between A. cristatum (2n = 4x = 28, PPPP) and the common wheat cv. Fukuhokomugi (Fukuho), displays numerous desirable agronomic traits, including enhanced thousand-grain weight, smaller flag leaf, and enhanced tolerance to drought. In order to transfer these traits into common wheat, Ⅱ-5-1 was induced by ⁶⁰Co-γ ray, leading to the creation of 18 translocation lines and three deletion lines. Genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) indicated that multiple wheat chromosomes were involved in the translocation events, including chromosome 2A, 3A, 5A, 7A, 3B, 5B, 7B, 3D and 7D. A. cristatum 7P chromosome was divided into 15 chromosomal bins with fifty-five sequence-tagged site (STS) markers specific to A. cristatum 7P chromosome. Seven and eight chromosomal bins were located on 7PS and 7PL, respectively. The above-mentioned translocation and deletion lines each contained different, yet overlapping 7P chromosomal fragments, covering the entire A. cristatum 7P chromosome. Three translocation lines (7PT-13, 7PT-14 and 7PT-17) and three deletion lines (del-1, del-2 and del-3), which contained the common chromosomal bins 7PS1-3, displayed higher thousand-grain weigh than Fukuho, suggesting that potential genes conferring high thousand-grain weigh might be located on these chromosomal bins. Therefore, wheat-A. cristatum 7P translocation lines with elite traits will be useful as novel germplasms for wheat genetic improvement.

Characterization of wheat – Psathyrostachys huashanica small segment translocation line with enhanced kernels per spike and stripe rust resistance

Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs), a distant wild relative of common wheat, possesses rich potentially valuable traits, such as disease resistance and more spikelets and kernels per spike, that could be useful for wheat genetic improvement. Development of wheat – P. huashanica translocation lines will facilitate its practical utilization in wheat breeding. In the present study, a wheat – P. huashanica small segmental translocation line, K-13-835-3, was isolated and characterized from the BC1F5 population of a cross between wheat – P. huashanica amphiploid PHW-SA and wheat cultivar CN16. Cytological studies showed that the mean chromosome configuration of K-13-835-3 at meiosis was 2n = 42 = 0.10 I + 19.43 II (ring) + 1.52 II (rod). GISH analyses indicated that chromosome composition of K-13-835-3 included 40 wheat chromosomes and a pair of wheat – P. huashanica translocation chromosomes. FISH results demonstrated that the small segment from an unidentified P. huashanica chromosome was translocated into wheat chromosome arm 5DS, proximal to the centromere region of 5DS. Compared with the cultivar wheat parent CN16, K-13-835-3 was highly resistant to stripe rust pathogens prevalent in China. Furthermore, spikelets and kernels per spike in K-13-835-3 were significantly higher than those of CN16 in two growing seasons. These results suggest that the desirable genes from P. huashanica were successfully transferred into CN16 background. This translocation line could be used as novel germplasm for high-yield and, eventually, resistant cultivar breeding.