Translocation Lines Research Articles

1RS arm of Secale cereanum \u2018Kriszta\u2019 confers resistance to stripe rust, improved yield components and high arabinoxylan content in wheat

Wheat-rye T1BL.1RS translocation is widespread worldwide as the genes on 1RS arm have positive effect on stress resistance, grain yield and adaptation ability of wheat. Nowadays, the T1BL.1RS wheat cultivars have become susceptible to rust diseases because of the monophyletic (‘Petkus’) origin of 1RS. Here we report and discuss the production and detailed investigation of a new T1BL.1RS translocation line carrying 1RS with widened genetic base originating from Secale cereanum. Line ‘179’ exhibited improved spike morphology traits, resistance against stripe rust and leaf rust, as well as higher tillering capacity, fertility and dietary fiber (arabynoxylan) content than the parental wheat genotype. Comparative analyses based on molecular cytogenetic methods and molecular (SSR and DArTseq) makers indicate that the 1RS arm of line ‘179’ is a recombinant of S. cereale and S. strictum homologues, and approximately 16% of its loci were different from that of ‘Petkus’ origin. 162 (69.5%) 1RS-specific markers were associated with genes, including 10 markers with putative disease resistance functions and LRR domains found on the subtelomeric or pericentromeric regions of 1RS. Line ‘179’ will facilitate the map-based cloning of the resistance genes, and it can contribute to healthy eating and a more cost-efficient wheat production.

Development and application of oligonucleotide-based chromosome painting for chromosome 4D of Triticum aestivum L.

Chromosome painting is a useful technique for distinguishing specific chromosomes (fragments), elucidating the genetic relationships of different genomes or chromosomes, and identifying chromosomal rearrangements. The development of chromosome- or genome-specific probes is fundamental for chromosome painting. The possibility for developing such probes specifically painting homoeologous chromosomes in allopolyploid species has been questioned since that chromosomes belonging to the same homoeologous group share highly conserved sequences. In the present study, we attempted to construct a wheat chromosome 4D-specific oligo probe library by selecting 4D-specific sequences in reference genome of common wheat cv. Chinese Spring (CS, 2n = 6x = 42, AABBDD). The synthesized library contains 27,392 oligos. Oligo painting using the probe library confirmed its specificity, shown by that only chromosome 4D could be painted in three wheat genotypes and CS nulli-tetrasomic line N4AT4D. Oligo painting was successfully used to define the 4D breakpoints in CS deletion lines involving 4D and two wheat-Haynaldia villosa 4D-4V translocation lines. Thirteen wheat relatives and a Triticum durum-H. villosa amphiploid were used for oligo painting. Except the 4D in two Aegilops tauschii accessions, the 4M in Ae. comosa and 4U in Ae. umbellulata could be painted. In tetraploid Ae. ventricosa, both 4D and 4M could be painted; however, the signal intensity of 4M was less compared with 4D. No painted chromosome was observed for the other alien species. This indicated that the relationship among D/M/U was closer than that among D/A/B as well as D with genomes H/R/Ss/Sc/Y/P/N/J. Our successful development of 4D-specific oligo probe library may serve as a model for developing oligo probes specific for other homoeologous chromosomes.

Identification and characterization of a new stripe rust resistance gene Yr83 on rye chromosome 6R in wheat.

A physical map of Secale cereale chromosome 6R was constructed using deletion mapping, and a new stripe rust resistance gene Yr83 was mapped to the deletion bin of FL 0.73-1.00 of 6RL. Rye (Secale cereale L., RR) possesses valuable genes for wheat improvement. In the current study, we report a resistance gene conferring stripe rust resistance effective from seedling to adult plant stages located on chromosome 6R. This chromosome was derived from triticale line T-701 and also carries highly effective resistance to the cereal cyst nematode species Heterodera avenae Woll. A wheat-rye 6R(6D) disomic substitution line exhibited high levels of seedling resistance to Australian pathotypes of the stripe rust (Puccinia striiformis f. sp. tritici; Pst) pathogen and showed an even greater resistance to the Chinese Pst pathotypes in the field. Ten chromosome 6R deletion lines and five wheat-rye 6R translocation lines were developed earlier in the attempt to transfer the nematode resistance gene to wheat and used herein to map the stripe rust resistance gene. These lines were subsequently characterized by sequential multicolor fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), mc-GISH, PCR-based landmark unique gene (PLUG), and chromosome 6R-specific length amplified fragment sequencing (SLAF-Seq) marker analyses to physically map the stripe rust resistance gene. The new stripe rust resistance locus was located in a chromosomal bin with fraction length (FL) 0.73-1.00 on 6RL and was named Yr83. A wheat-rye translocation line T6RL (#5) carrying the stripe rust resistance gene will be useful as a new germplasm in breeding for resistance.

Genetic stability of wheat-rye 6RS/6AL translocation chromosome and its transmission through gametes

<p indent="0mm">The wheat-rye 6RS/6AL translocation line HM812-41 harbors the powdery mildew resistance gene <italic>Pm56</italic>. In order to evaluate the potential utilization in breeding, the translocation line was crossed to common wheat varieties Shumai 580, Shumai 830, and Shumai 969. The F₁ hybrids were then reciprocally crossed with Chinese spring to estimate the genetic stability of 6RS/6AL and its transmission rate through male and female gametes in different genetic backgrounds. Double-top crossing (DTC) strategy was used to improve the agronomic traits of the translocation line. Genome <italic>in situ</italic> hybridization analysis indicated that the 6RS/6AL translocation was very stable during transmission. The 6RS/6AL translocation was transmitted to offsprings with a high frequency, which was 45.05%–53.33% for female gametes and 43.94%–53.04% for male gametes. Based on the agronomical performances of DTC F₂ populations, we found that the 6RS/6AL translocation was not linked to obvious defects for major agronomic traits, such as plant height, spike length, spikelet number and seed-setting ratio in selfing. The agronomic traits of the translocation line can be obviously improved through DTC strategy.

Identification, Characterization, and Evaluation of Novel Stripe Rust-Resistant Wheat-Thinopyrum intermedium Chromosome Translocation Lines.

Stripe rust is an important disease in wheat, and development of genetic resistance in cultivars is an effective approach to control the disease. Wild species of wheat, such as Thinopyrum intermedium, are an excellent gene source for wheat improvement. In this study, two stripe rust-resistant wheat-Th. intermedium chromosome translocation lines, CH4131 and CH4132, were characterized by cytogenetic and pathological methods. The introgressed chromosome fragment was tagged using amplified fragment-length polymorphism-derived sequence-characterized amplified region (SCAR) markers and intron targeting markers, indicating that CH4131 and CH4132 both possess a homologous group 3 chromatin of Th. intermedium. Genomic in situ hybridization results suggested that a very small Th. intermedium chromosome segment was translocated to the terminal region of wheat 1BS for both lines, forming a configuration of T3Ai-1BS.1BL. The two translocation lines were resistant to stripe rust, and the resistance gene, temporarily designated YrCH-1BS, was likely derived from Th. intermedium. The translocated chromosome fragments have no genetic linkage drag to agronomic performance. The grain quality indexes of these two translocations were higher than local wheat varieties. Therefore, CH4131 and CH4132 could be used as potential gene sources in wheat improvement programs. The SCAR markers are useful to select stripe rust resistance from Th. intermedium.

Identification of stress defensive proteins in common wheat-Thinopyron intermedium translocation line YW642 developing grains via comparative proteome analysis.

Thinopyrum intermedium (2n = 6x = 42, E1E1E2E2XX) serves as an important gene source of desirable traits for genetic improvement of wheat cultivars resistant to stresses. This study used the comparative proteomic approach to identify stress defense related proteins in the developing grains of common wheat (Zhongmai 8601)-Thinopyron intermedium 7XL/7DS translocation line YW642 and to explore their potential values for improving wheat stress resistance. Two-dimensional electrophoresis identified 124 differentially accumulated protein spots representing 100 unique proteins, which mainly participated in stress defense, energy metabolism, protein metabolism and folding and storage protein synthesis. Among these, 16 were unique and 35 were upregulated in YW642. The upregulated DAPs were mainly involved in biotic and abiotic stress defense. Further cis-elements analysis of these stress-related DAP genes revealed that phytohormone responsive elements such as ABREs, G-box, CGTCA-motif and TGACG-motif, and environment responsive element As-1 were particularly abundant, which could play important roles in response to various stressors. Transcription expression analysis by RNA-seq and qRT-PCR demonstrated a large part of the stress-related DAP genes showed an upregulated expression in the early-to-middle stages of grain development. Our results proved that Thinopyron intermedium contains abundant stress responsive proteins that have potential values for the genetic improvement of wheat stress resistance.

The production of wheat – Aegilops sharonensis 1Ssh chromosome substitution lines harboring alien novel high-molecular-weight glutenin subunits

In our previous work, a novel high-molecular-weight glutenin subunit (HMW-GS) with an extremely large molecular weight from Aegilops sharonensis was identified that may contribute to excellent wheat (Triticum aestivum) processing quality and increased dough strength, and we further generated HMW-GS homozygous lines by crossing. In this study, we crossed the HMW-GS homozygous line 66-17-52 with 'Chinese Spring' Ph1 mutant CS ph1b to induce chromosome recombination between wheat and Ae. sharonensis. SDS-PAGE was used to identify 19 derived F2 lines with the HMW-GSs of Ae sharonensis. The results of non-denaturing fluorescence in situ hybridization (ND-FISH) indicated that lines 6-1 and 6-7 possessed a substitution of both 5D chromosomes by a pair of 1Ssh chromosomes. Further verification by newly developed 1Ssh-specific chromosome markers showed that these two lines amplified the expected fragment. Thus, it was concluded that lines 6-1 and 6-7 are 1Ssh(5D) chromosome substitution lines. The 1Ssh(5D) chromosome substitution lines, possessing alien subunits with satisfactory quality-associated structural features of large repetitive domains and increased number of subunits, may have great potential in strengthening the viscosity and elasticity of dough made from wheat flour. Therefore, these substitution lines can be used for wheat quality improvement and further production of 1Ssh translocation lines.

Molecular cytogenetic characterization of wheat\u2013Elymus repens chromosomal translocation lines with resistance to Fusarium head blight and stripe rust

BackgroundFusarium head blight (FHB) caused by the fungus Fusarium graminearum Schwabe and stripe rust caused by Puccinia striiformis f. sp. tritici are devastating diseases that affect wheat production worldwide. The use of disease-resistant genes and cultivars is the most effective means of reducing fungicide applications to combat these diseases. Elymus repens (2n = 6x = 42, StStStStHH) is a potentially useful germplasm of FHB and stripe rust resistance for wheat improvement.ResultsHere, we report the development and characterization of two wheat–E. repens lines derived from the progeny of common wheat–E. repens hybrids. Cytological studies indicated that the mean chromosome configuration of K15–1192-2 and K15–1194-2 at meiosis were 2n = 42 = 0.86 I + 17.46 II (ring) + 3.11 II (rod) and 2n = 42 = 2.45 I + 14.17 II (ring) + 5.50 II (rod) + 0.07 III, respectively. Genomic and fluorescence in situ hybridization karyotyping and simple sequence repeats markers revealed that K15–1192-2 was a wheat–E. repens 3D/?St double terminal chromosomal translocation line. Line K15–1194-2 was identified as harboring a pair of 7DS/?StL Robertsonian translocations and one 3D/?St double terminal translocational chromosome. Further analyses using specific expressed sequence tag-SSR markers confirmed that the wheat–E. repens translocations involved the 3St chromatin in both lines. Furthermore, compared with the wheat parent Chuannong16, K15–1192-2 and K15–1194-2 expressed high levels of resistance to FHB and stripe rust pathogens prevalent in China.ConclusionsThus, this study has determined that the chromosome 3St of E. repens harbors gene(s) highly resistant to FHB and stripe rust, and chromatin of 3St introgressed into wheat chromosomes completely presented the resistance, indicating the feasibility of using these translocation lines as novel material for breeding resistant wheat cultivars and alien gene mining.

Full-length transcriptome sequences of Agropyron cristatum facilitate the prediction of putative genes for thousand-grain weight in a wheat-A. cristatum translocation line

BackgroundAgropyron cristatum (L.) Gaertn. (2n = 4x = 28; genomes PPPP) is a wild relative of common wheat (Triticum aestivum L.) and provides many desirable genetic resources for wheat improvement. However, there is still a lack of reference genome and transcriptome information for A. cristatum, which severely impedes functional and molecular breeding studies.ResultsSingle-molecule long-read sequencing technology from Pacific Biosciences (PacBio) was used to sequence full-length cDNA from a mixture of leaves, roots, stems and caryopses and constructed the first full-length transcriptome dataset of A. cristatum, which comprised 44,372 transcripts. As expected, the PacBio transcripts were generally longer and more complete than the transcripts assembled via the Illumina sequencing platform in previous studies. By analyzing RNA-Seq data, we identified tissue-enriched transcripts and assessed their GO term enrichment; the results indicated that tissue-enriched transcripts were enriched for particular molecular functions that varied by tissue. We identified 3398 novel and 1352 A. cristatum-specific transcripts compared with the wheat gene model set. To better apply this A. cristatum transcriptome, the A. cristatum transcripts were integrated with the wheat genome as a reference sequence to try to identify candidate A. cristatum transcripts associated with thousand-grain weight in a wheat-A. cristatum translocation line, Pubing 3035.ConclusionsFull-length transcriptome sequences were used in our study. The present study not only provides comprehensive transcriptomic insights and information for A. cristatum but also proposes a new method for exploring the functional genes of wheat relatives under a wheat genetic background. The sequence data have been deposited in the NCBI under BioProject accession number PRJNA534411.

Identification of univalent chromosomes in monosomic lines of cotton (Gossypium hirsutum L.) by means of cytogenetic markers

The lack of clear morphological markers of cotton chromosomes contributed to the development of an unconventional method for marking chromosomes using translocations. Today, tester translocation cotton lines represent the most complete set of cytological markers. The results of cytogenetic analysis of F1 hybrids obtained from crosses of monosomic cotton lines with translocation lines with identified chromosomes are presented. Cytogenetic identification and numbering of univalent chromosomes in 25 monosomic lines of the cytogenetic collection of the National University of Uzbekistan allowed us to establish the following univalent occurrences: chromosome 2 in four monosomic lines, chromosome 4 in 15 lines, chromosome 6 in four lines, chromosome 7 of the At-subgenome in one line and chromosome 18 of the Dt-subgenome in one line. The remaining 21 lines were duplicates of three non-homologous chromosomes. All monosomic lines identified were characterized by differences in univalent sizes, meiotic index, number of tetrads with micronuclei, pollen fertility, frequency of monosomy in the progeny, and a complex of morphological characters associated with the monosomy of the chromosome identified. Despite differences in the genotypic environment and methods for producing monosomics in the two cotton collections, there is a surprising coincidence of data suggesting a higher frequency of chromosomes 2, 4 and 6 occurring as monosomics, while the other chromosomes of the set occur as monosomics at a much lower frequency, and eight nonhomologous chromosomes (5, 8, 13 of the At-subgenome and 14, 15, 19, 22 and 24 of the Dt-subgenome of cotton) never do.

The creation and characterization of the bread wheat line with a centric translocation T2DL.2RL

The development of bread wheat introgressions with alien genetic material from cultural and wild Triticeae species is an effective method for expanding the wheat gene pool necessary for breeding. To date, numerous collections of introgressions as substitutions and chromosome modifications have been obtained; however, the creation and study of wheat with new valuable traits still remain an important line of research. Rye Secale cereale L., whose chromosomes carry genes that control valuable economic and biological characteristics and properties, is widely used to produce new wheat forms. In this study, a wheat-rye translocation obtained by backcrossing the wheat-rye disomic-substitution line 2R(2D)1 with the variety Novosibirskaya 67 was characterized. The chromosomal composition of karyotypes was studied using fluorescent in situ hybridization and C-banding. Two centric translocations, derived from two long arms of chromosomes 2D and 2R, T2DL.2RL, were identified, the remaining 40 wheat chromosomes did not undergo modifications. Meiosis in the lines was stable. Chromosomes T2DL.2RL formed bivalents in all meiocytes, which confirmed their homology. The morphological characteristics of the spike in the T2DL.2RL line and Novosibirskaya 67 did not differ. A comparative analysis of productivity between the T2DL.2RL translocation line and the parental forms, Novosibirskaya 67 and the 2R(2D)1 line, was carried out. The T2DL.2RL line is inferior to Novosibirskaya 67 in all characters with different confidence levels. The productivity characters of the 2R(2D)1 line exceeded or did not differ from those of T2DL.2RL, however, the mass of 1000 grains was significantly lower. The results showed the effect of the T2DL.2RL translocation on the trait “plant height”. This character was significantly lower than that of Novosibirskaya 67 in two vegetation periods. Consequently, the T2DL.2RL translocation reduces plant height and productivity.

Development of Novel Wheat-Rye Chromosome 4R Translocations and Assignment of Their Powdery Mildew Resistance.

Rye (Secale cereale L.) is an important gene donor for wheat improvement because of its many valuable traits, especially disease resistance. Development of novel wheat-rye translocations with disease resistance can contribute to transferring resistance into common wheat. In a previous study, a wheat-rye T4BL·4RL and T7AS·4RS translocation line (WR41-1) was developed by distant hybridization, and it was speculated that its resistance to powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), was derived from rye based on pedigree analysis. To make accurate use of chromosome 4R in wheat improvement, a set of new 4R translocations involving different arm translocations (e.g., 4RS monosomic, 4RL monosomic, 4RL disomic, 4RS monosomic plus 4RL monosomic, 4RS monosomic plus 4RL disomic, and 4RS disomic plus 4RL disomic translocations) was developed from crosses with common wheat. Those translocations were characterized by genomic in situ hybridization and expressed sequence tag simple sequence repeat marker analysis. To confirm the source of powdery mildew resistance, the translocation plants were tested against Bgt isolate E09. The results indicated that all translocations with 4RL were resistant at all tested growth stages, whereas those with only 4RS translocation or no alien translocation were susceptible. This further indicated that the powdery mildew resistance of WR41-1 was derived from the alien chromosome arm 4RL. To effectively use 4RL resistance in wheat improvement, two competitive allele-specific PCR markers specific for chromosome arm 4RL were developed to detect the alien chromosome in the wheat genome. These new translocation lines with diagnostic markers can efficiently serve as important bridges for wheat improvement.

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.

Plasticity in Triticeae centromere DNA sequences: a wheat × tall wheatgrass (decaploid) model.

Centromeres mediate chromosome attachment to microtubules and maintain the integrity of chromosomes for proper segregation of the sister chromatids during cell division. Advances in the assembly of Triticeae genome sequences combined with the capacity to recover hybrid species derived from very distantly related species provides potential experimental systems for linking retrotransposon amplification and repositioning of centromeres via non-mendelian inheritance in partial amphiploid breeds. The decaploid tall wheatgrass (Thinopyrum ponticum) is one of the most successfully used perennial species in wheat breeding for generating translocation lines with valuable agronomic traits. We found that wheat centromere retrotransposons CRW and Quinta widely occur within the tall wheatgrass genome. In addition, one of the genome donors to Th. ponticum, Pseudoroegneria stipifolia (StSt), has been shown to have Abigail and a satellite repeat, CentSt. We also found two other centromeric retrotransposons, Abia and CL135 in Th. ponticum by ChIP-seq. Examination of partial amphiploid lines that were generated in the 1970s demonstrated extensive modification in centromere sequences using CentSt, Abigail and Abia as probes. We also detected that St-genome chromosomes were more enriched with Abigail and CentSt, whereas E-genome chromosomes were enriched with CRW and Quinta in tall wheatgrass and its closer relatives. It can be concluded that bursts of transposition of retrotransposons and repositioning of centromeres via non-mendelian segregation are common in partial amphiploids derived from interspecific hybrids. Practically speaking, our study reveals that the existence of homologous centromere functional sequences in both a donor and its receptor can substantially contribute to the successful transfer of alien genes into crop species. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://www.ncbi.nlm.nih.gov/sra/SRR9089557; https://www.ncbi.nlm.nih.gov/sra/SRR9089558; https://www.ncbi.nlm.nih.gov/sra/SRR9089559; https://www.ncbi.nlm.nih.gov/sra/SRR9089560; https://www.ncbi.nlm.nih.gov/sra/SRR9089561; https://www.ncbi.nlm.nih.gov/sra/SRR9089562; https://www.ncbi.nlm.nih.gov/sra/SRR9089563; https://www.ncbi.nlm.nih.gov/sra/SRR9089564; https://www.ncbi.nlm.nih.gov/nuccore/MK999394; https://www.ncbi.nlm.nih.gov/nuccore/MK999395; https://www.ncbi.nlm.nih.gov/nuccore/MK999396.

Pedigree and development of wheat varieties in Sichuan Province

Variety pedigree contains a lot of information, including parental origin, breeding methods, genetic relationship, and so on. Studying them could reveal the evolution characteristics and rules of breeding and ultimately guide practice. The pedigrees of 326 wheat varieties from 1936 to 2017 in the history of the Sichuan Province was collected and analyzed in terms of breeding methods, parental composition, changes of high frequency parents and backbone parents, genetic contribution, distribution of translocation lines and synthetic germplasms. Over the past 80 years since 1930s, breeders have selected 387 direct parents from a large number of materials, made 256 combinations by means of cross breeding, and have released 314 varieties from them, which contributed directly to wheat breeding and production in Sichuan. Wheat breeding experienced a process from utilizing landraces, introducing foreign germplasm to creating breeding materials independently; high-frequency parents and backbone parents used for breeding gradually changed in different stage of the breeding history. Synthetic germplasms contributed greatly to wheat breeding in recent years. The consistency of breeding objectives will inevitably lead to the loss of genetic diversity and the fragility of genetic basis. In the future, the protection and utilization of genetic resources should be strengthened. In this review, the development of wheat breeding in Sichuan was summarized through pedigree analysis, in order to provide a reference for future research.

Improvement of three commercial spring wheat varieties for powdery mildew resistance by marker-assisted selection

Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici is one of the most economically important wheat diseases in China. Almost all commercially cultivated wheat varieties are susceptible to PM disease, especially the commercial spring wheat varieties grown in the Northwestern region of China. Pm21 was identified as one of the most effective resistance gene to PM in China, and many wheat varieties carrying Pm21 have been developed and released in different areas since 2010. In this study, 3 PM susceptible spring wheat varieties (Ningchun4, Ningchun47, and Ningchun50) were crossed with a PM resistant line CB037 (carrying Pm21) which is a wheat-Dasypyrum villosum T6AL·6V#2S translocation line, and were then backcrossed with the three spring varieties as recurrent parents, combining the disease test with molecular marker selection. After five times of backcrossing and four generations of selfing, nine advanced lines with strong PM resistance and good agronomic traits (plant height, grains per spike, one thousand kernels weight, and yield) were developed. These lines were further evaluated using the analyses of Pm21-specific markers and genomic in situ hybridization (GISH), and tested in a field trial for agronomic traits including grain yield. Results indicated that all the improved lines were similar to their corresponding recurrent varieties except an obvious difference in plant height. Lines NZ39, NZ42, and NZ46 showed an increase in grain yield (by 1.70–9.38%) and one thousand kernel weight (by 0.4–7.3 g). Compared to their respective recurrent parents, lines NZ41 and NZ46 showed improved bread-making quality, displaying optimal application potential in wheat production.

Comparative FISH and molecular identification of new stripe rust resistant wheat-Thinopyrum intermedium ssp. trichophorum introgression lines

Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt) has been hybridized extensively with common wheat and has proven to be a valuable germplasm source for improving disease resistance, quality attributes, and yield potential in wheat. We characterized new disease resistant wheat-Th. intermedium derivatives A1082 and A5-5 using sequential multi-color fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A1082 was identified as a wheat-Th. intermedium 3J disomic addition line, and A5-5 was a T4BS·5JsL homozygous Robertsonian translocation line. Seventy-one and 106 pairs of primers amplified Th. intermedium-specific bands allowing chromosomes 3J and 5Js to be tracked, respectively. A new oligonucleotide probe, Oligo-6H-2-100, was developed for FISH labeling of the subterminal region of the long arm of chromosome 5Js. Both lines were highly resistant to stripe rust pathogen races prevalent in Chinese field screening nurseries. A5-5 also displayed a significant increase in tiller number compared to its wheat parent. The new lines can be exploited as useful germplasms for wheat improvement.

Uncovering homeologous relationships between tetraploid Agropyron cristatum and bread wheat genomes using COS markers

Key messageUsing COS markers, the study reveals homeologous relationships between tetraploid Agropyron cristatum and bread wheat to support alien introgression breeding of wheat.Crested wheatgrass (Agropyron cristatum L. Gaertn.) is a wild relative of wheat that possesses many genes that are potentially useful in wheat improvement. The species comprises a complex of diploid, tetraploid and hexaploid forms. In this study, wheat–A. cristatum chromosome, telosome and translocation lines were used to characterize syntenic relationships between tetraploid A. cristatum and bread wheat. Prior to mapping COS markers, the cytogenetic stock lines were characterized for fertility and by FISH and GISH for karyotype stability. Out of 328 COS markers selected for the study, 279 consistently amplified products in tetraploid A. cristatum, and, out of these, 139 were polymorphic between tetraploid crested wheatgrass and wheat. Sixty-nine markers were found to be suitable for the detection of tetraploid A. cristatum chromosomes 1P–6P in wheat, ranging from 6 to 17 markers per chromosome. BLASTn of the source ESTs resulted in significant hits for 67 markers on the wheat pseudomolecules. Generally, COS markers of the same homeologous group were detected on similar arms in both Agropyron and wheat. However, some intragenomic duplications and chromosome rearrangements were detected in tetraploid A. cristatum. These results provide new insights into the structure and evolution of the tetraploid A. cristatum genome and will facilitate the exploitation of the wild species for introgression breeding of bread wheat.

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.

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

BackgroundDasypyrum 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.ResultsWe 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).ConclusionSeventy-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.