Synthetic Hexaploid Wheat Research Articles

Analysis of the Genome D Polymorphism of Synthetic Wheat Obtained on the Basis of Ae. tauschii L.

An SNP analysis is performed using the iSelect90K SNP array to identify the genetic diversity of synthetic hexaploid wheat lines of Kyoto University (Japan) bred by crossing durum wheat variety Langdon (Triticum durum, 2n = 4x = 28, BBAA) with accessions of Aegilops tauschii (2n = 2x = 14, DD) of different ecological origin. The level of genomic variability is calculated by using the Emma approach (Efficient Mixed-Model Association) and genomic relationship matrix (G). The genetic diversity of the genome D of synthetic lines is greater than that of genomes A and B by 50%. The greatest genetic polymorphism is observed in the line Langdon/Ku-2105 from Pahlavi province on the southern coast of Caspian Sea and the line Langdon/Ig 131606 from Kyrgyzstan. Lines from India (Langdon/Ig 48042), Iranian provinces Sari and Babolsar (Langdon/Ku-2088, Langdon/Ku-2093, Langdon/Ku-2096), and Turkmenistan (Langdon/Ig 26387) are characterized by a lower genetic diversity of the genome D. Thus, the involvement of synthetic hexaploid wheat on the basis of Ae. tauschii accessions from the Caspian basin into hybridization will extend the genetic diversity of wheat varieties and increase the efficiency of genetic resources.

Multi-Parental Populations Suitable for Identifying Sources of Resistance to Powdery Mildew in Winter Wheat.

Wheat (Triticum aestivum L.) is one of the world’s staple food crops and one of the most devastating foliar diseases attacking wheat is powdery mildew (PM). In Denmark only a few specific fungicides are available for controlling PM and the use of resistant cultivars is often recommended. In this study, two Chinese wheat landraces and two synthetic hexaploid wheat lines were used as donors for creating four multi-parental populations with a total of 717 individual lines to identify new PM resistance genetic variants. These lines and the nine parental lines (including the elite cultivars used to create the populations) were genotyped using a 20 K Illumina SNP chip, which resulted in 8,902 segregating single nucleotide polymorphisms for assessment of the population structure and whole genome association study. The largest genetic difference among the lines was between the donors and the elite cultivars, the second largest genetic difference was between the different donors; a difference that was also reflected in differences between the four multi-parental populations. The 726 lines were phenotyped for PM resistance in 2017 and 2018. A high PM disease pressure was observed in both seasons, with severities ranging from 0 to >50%. Whole genome association studies for genetic variation in PM resistance in the populations revealed significant markers mapped to either chromosome 2A, B, or D in each of the four populations. However, linkage disequilibrium between these putative quantitative trait loci (QTL) were all above 0.80, probably representing a single QTL. A combined analysis of all the populations confirmed this result and the most associated marker explained 42% of the variation in PM resistance. This study gives both knowledge about the resistance as well as molecular tools and plant material that can be utilised in marker-assisted selection. Additionally, the four populations produced in this study are highly suitable for association studies of other traits than PM resistance.

Additive genetic variance and covariance between relatives in synthetic wheat crosses with variable parental ploidy levels.

Cultivated bread wheat (Triticum aestivum L.) is an allohexaploid species resulting from the natural hybridization and chromosome doubling of allotetraploid durum wheat (T. turgidum) and a diploid goatgrass Aegilops tauschii Coss (Ae. tauschii). Synthetic hexaploid wheat (SHW) was developed through the interspecific hybridization of Ae. tauschii and T. turgidum, and then crossed to T. aestivum to produce synthetic hexaploid wheat derivatives (SHWDs). Owing to this founding variability, one may infer that the genetic variances of native wild populations vs improved wheat may vary due to their differential origin and evolutionary history. In this study, we partitioned the additive variance of SHW and SHWD with respect to their breed origin by fitting a hierarchical Bayesian model with heterogeneous covariance structure for breeding values to estimate variance components for each breed category, and segregation variance. Two data sets were used to test the proposed hierarchical Bayesian model, one from a multi-year multi-location field trial of SHWD and the other comprising the two species of SHW. For the SHWD, the Bayesian estimates of additive variances of grain yield from each breed category were similar for T. turgidum and Ae. tauschii, but smaller for T. aestivum. Segregation variances between Ae. tauschii—T. aestivum and T. turgidum—T. aestivum populations explained a sizable proportion of the phenotypic variance. Bayesian additive variance components and the Best Linear Unbiased Predictors (BLUPs) estimated by two well-known software programs were similar for multi-breed origin and for the sum of the breeding values by origin for both data sets. Our results support the suitability of models with heterogeneous additive genetic variances to predict breeding values in wheat crosses with variable ploidy levels.

Modeling multiple phenotypes in wheat using data-driven genomic exploratory factor analysis and Bayesian network learning.

Inferring trait networks from a large volume of genetically correlated diverse phenotypes such as yield, architecture, and disease resistance can provide information on the manner in which complex phenotypes are interrelated. However, studies on statistical methods tailored to multidimensional phenotypes are limited, whereas numerous methods are available for evaluating the massive number of genetic markers. Factor analysis operates at the level of latent variables predicted to generate observed responses. The objectives of this study were to illustrate the manner in which data‐driven exploratory factor analysis can map observed phenotypes into a smaller number of latent variables and infer a genomic latent factor network using 45 agro‐morphological, disease, and grain mineral phenotypes measured in synthetic hexaploid wheat lines (Triticum aestivum L.). In total, eight latent factors including grain yield, architecture, flag leaf‐related traits, grain minerals, yellow rust, two types of stem rust, and leaf rust were identified as common sources of the observed phenotypes. The genetic component of the factor scores for each latent variable was fed into a Bayesian network to obtain a trait structure reflecting the genetic interdependency among traits. Three directed paths were consistently identified by two Bayesian network algorithms. Flag leaf‐related traits influenced leaf rust, and yellow rust and stem rust influenced grain yield. Additional paths that were identified included flag leaf‐related traits to minerals and minerals to architecture. This study shows that data‐driven exploratory factor analysis can reveal smaller dimensional common latent phenotypes that are likely to give rise to numerous observed field phenotypes without relying on prior biological knowledge. The inferred genomic latent factor structure from the Bayesian network provides insights for plant breeding to simultaneously improve multiple traits, as an intervention on one trait will affect the values of focal phenotypes in an interrelated complex trait system.

Development and Characterization of Synthetic Hexaploid Wheat for Improving the Resistance of Common Wheat to Leaf Rust and Heat Stress

Synthetic hexaploid wheat (SHW) is a valuable resource for breeding because it possesses more desirable traits, such as better yield and abiotic and biotic stress tolerance than common wheat. In this study, our group developed a SHW line, named ‘SynDT’, which has markedly better characteristics than Korean bread wheat ‘Keumkang’. The SynDT line is thermotolerant as it rapidly expresses heat shock proteins under heat stress. In addition, this line exhibits resistance to leaf rust by inducing the expression of antifungal enzymes, mainly chitinase, along with the rapid and high expression of pathogen-related genes. Moreover, it possesses the favorable traits of its parent wheat lines Triticum durum #24 and Aegilops tauschii #52. Therefore, the SynDT wheat line can be used as a breeding material for improving local common wheat cultivars.

Expression profiling of DREB1 and evaluation of vegetation indices in contrasting wheat genotypes exposed to drought stress

DREBs, the Dehydration Responsive Element binding proteins belonging to the superfamily of AP2/ERF plant transcription factors regulate diverse processes of plant development and stress responses. The expression level of DREB1 transcription factor gene was examined under drought in wheat genotypes of Azerbaijani origin differing in drought resistance: two tetraploid wheat (Triticum durum Desf.), cultivars Barakatli 95 (tolerant), Garagylchyg 2 (sensitive) and two hexaploid wheat (Triticum aestivum L.), cultivars Azamatli 95 (less sensitive), Giymatli 2/17 (sensitive), as well as German hexaploid winter wheat cultivar Batis and the synthetic hexaploid wheat accession Syn022L. The seeds were sown in pots in control and drought blocks inside the growth chamber and 12-day-old seedlings were exposed to drought stress. These genotypes were thoroughly phenotyped for variability of vegetation indices like NDVI, SR, OSAVI, ARI1, GM2 and PRI using spectro-radiometer PolyPen RP400 & RP410 under control and drought stress. In tetraploid genotypes and synthetic wheat accession, the vegetation indices were less affected by drought than in hexaploids and the response to stress recovery was faster. Drought sensitive genotypes experienced lower vegetation indices as compared to the tolerant ones. The expression of DREB1 gene was analyzed at 7 days after stress, when the visible stress-related traits were observed. The transcript level was determined by qRT-PCR using the elongation factor 1 alpha (Elf1-α) gene as an internal control. There was no genotypic difference in the basal expression of DREB1 under control conditions. Overall, the transcript levels were significantly increased among all genotypes exposed to drought stress. Futher, under drought stress the expression level of DREB1 in tolerant genotypes increased more than in drought sensitive ones. The German wheat cultivar Batis revealed the highest up-regulation of DREB1 under drought stress conditions. These data will help to screen drought stress tolerance at large scale among the diverse wheat gene pool non-invasively using digital phenotyping.

Genetic mapping of the three-pistil gene Pis1 in an F2 population derived from a synthetic hexaploid wheat using multiple molecular marker systems

The wheat spike mutant 'three-pistil' (TP) exhibits normal external morphology but produces two additional pistils per floret. Much attention has been paid to this natural mutation because elucidation of its genetic foundation potentially paves a way to increase the number of grains per spike for breeding. Our previous studies roughly mapped the causal locus of TP on chromosome 2D. In this study, we performed genetic mapping of the three-pistil gene Pis1 in an F2 population derived from a cross of TP and synthetic hexaploid wheat of which chromosome 2D was from Aegilops tauschii. Segregation analysis in the F2 population confirmed the dominance of the Pis1 locus. Bulked segregant analysis with three DNA marker systems revealed a total of 18 markers genetically linked with Pis1. Successive genetic linkage analysis of the F2 individuals using the 18 markers identified two sequence-related amplified polymorphisms markers, Me5-eM33 and Me26-eM33, flanked the Pis1 locus at distances of 0.6 and 1.7 cM, respectively. Integration of the genetic linkage and previously discovered DNA markers associated with Pis1 revealed a potential location of the Pis1 locus between Me5-eM33 and a KASP marker M75. Thus, the constructed partial genetic linkage map is useful for the isolation of Pis1 and marker-assisted breeding in wheat.

QTL mapping for adult-plant resistance to powdery mildew in Chinese elite common wheat Chuanmai104

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major fungal disease of wheat worldwide. The economic and environmentally friendly strategy is developing the wheat varieties with resistance to powdery mildew in wheat-breeding program. Chuanmai104 (CM104, Triticum aestivum L.), derived from synthetic hexaploid wheat, was an elite wheat variety with high adult-plant resistance to powdery mildew. The phenotype of powdery mildew resistance was conducted on a set of 234 recombinant inbred lines (RIL, F8) derived from the cross of CM104 and high susceptible wheat landrace Baimaomai (BMM) in five environments in this study. Three QTLs were identified on chromosomes 7D and 4A by the high-density wheat 50 K single-nucleotide polymorphism array, designed as QPm.saas-7DS, QPm.saas-4AL and QPm.saas-4AS, respectively. Of the three QTLs, QPm.saas-7DS derived from BMM and QPm.saas-4AL derived from CM104 were minor locus, QPm.saas-4AS derived from CM104 was detected as a new major locus for adult-plant resistance to powdery mildew in all environments and localized in a 1.06 Mb interval of the genomic region on chromosome arm 4AS referenced to Chinese Spring genome explained up to 26.5% of the phenotypic variances. The newly major locus QPm.saas-4AS would be supplied as a resistant source in wheat-breeding program.

Insights into the resistance of a synthetically-derived wheat to Septoria tritici blotch disease: less is more

BackgroundLittle is known about the initial, symptomless (latent) phase of the devastating wheat disease Septoria tritici blotch. However, speculations as to its impact on fungal success and disease severity in the field have suggested that a long latent phase is beneficial to the host and can reduce inoculum build up in the field over a growing season. The winter wheat cultivar Stigg is derived from a synthetic hexaploid wheat and contains introgressions from wild tetraploid wheat Triticum turgidum subsp. dicoccoides, which contribute to cv. Stigg’s exceptional STB resistance, hallmarked by a long latent phase. We compared the early transcriptomic response to Zymoseptoria tritici of cv. Stigg to a susceptible wheat cultivar, to elucidate the mechanisms of and differences in pathogen recognition and disease response in these two hosts.ResultsThe STB-susceptible cultivar Longbow responds to Z. tritici infection with a stress response, including activation of hormone-responsive transcription factors, post translational modifications, and response to oxidative stress. The activation of key genes associated with these pathways in cv. Longbow was independently observed in a second susceptible wheat cultivar based on an independent gene expression study. By comparison, cv. Stigg is apathetic in response to STB, and appears to fail to activate a range of defence pathways that cv. Longbow employs. Stigg also displays some evidence of sub-genome bias in its response to Z. tritici infection, whereas the susceptible cv. Longbow shows even distribution of Z. tritici responsive genes across the three wheat sub-genomes.ConclusionsWe identify a suite of disease response genes that are involved in early pathogen response in susceptible wheat cultivars that may ultimately lead to susceptibility. In comparison, we hypothesise that rather than an active defence response to stave off disease progression, cv. Stigg’s defence strategy is molecular lethargy, or a lower-amplitude of pathogen recognition that may stem from cv. Stigg’s wild wheat-derived ancestry. Overall, we present insights into cv. Stigg’s exceptional resistance to STB, and present key biological processes for further characterisation in this pathosystem.

Synthetic hexaploid wheat as a source of novel genetic loci for aluminium tolerance

Aluminium (Al3+) tolerance is second only to drought tolerance for its importance as an agronomic trait in many parts of the world. In wheat (Triticum aestivum L.), Al3+ tolerance is largely conditioned by a single gene, TaALMT1, but given the diverse origins of tolerant genotypes, it is possible that other chromosomes may harbour genes that confer Al3+ tolerance. The large genetic diversity present in synthetic hexaploid wheat (SHW) prompted the objective in this study, which was to evaluate SHW as a source of novel genetic loci linked to Al3+ tolerance. We evaluated 300 SHW accessions using the haematoxylin staining method, and a genome-wide association analysis (GWAS) using 6575 markers generated from traditional diversity-arrays and genotyping-by-sequencing genotyping platforms and from TaALMT1 gene specific simple sequence repeat polymorphisms. The GWAS detected a set of 24 loci located to chromosomes 1B, 1D, 2A, 2B, 4A, 4D, 5A, 5B, 6A, 6D and 7A that showed statistically significant association with Al3+ tolerance. We leveraged the available high-quality annotation data of the wheat genome to identify candidate genes localised to within 1.6 Kb of the identified markers. Besides markers for TaALMT1, MATE and NRAMP, identified markers were located close to known transcription factors (C2H2 zinc finger protein) and novel candidate genes that encode ABC transporter-like protein, glutathione synthetase, Blue copper protein and expansin proteins. In summary, our results showed that Al3+ tolerance is present in SHW but is genetically complex and appeared to involve interactions between the major TaALMT1 gene and other gene loci.

Balanced Genome Triplication in Wheat Causes Premature Growth Arrest and an Upheaval of Genome-Wide Gene Regulation.

Polyploidy, or whole genome duplication (WGD), is a driving evolutionary force across the tree of life and has played a pervasive role in the evolution of the plant kingdom. It is generally believed that a major genetic attribute contributing to the success of polyploidy is increased gene and genome dosage. The evolution of polyploid wheat has lent support to this scenario. Wheat has evolved at three ploidal levels: diploidy, tetraploidy, and hexaploidy. Ample evidence testifies that the evolutionary success, be it with respect to evolvability, natural adaptability, or domestication has dramatically increased with each elevation of the ploidal levels. A long-standing question is what would be the outcome if a further elevation of ploidy is superimposed on hexaploid wheat? Here, we characterized a spontaneously occurring nonaploid wheat individual in selfed progenies of synthetic hexaploid wheat and compared it with its isogenic hexaploid siblings at the phenotypic, cytological, and genome-wide gene-expression levels. The nonaploid manifested severe defects in growth and development, albeit with a balanced triplication of the three wheat subgenomes. Transcriptomic profiling of the second leaf of nonaploid, taken at a stage when phenotypic abnormality was not yet discernible, already revealed significant dysregulation in global-scale gene expression with ca. 25.2% of the 49,436 expressed genes being differentially expressed genes (DEGs) at a twofold change cutoff relative to the hexaploid counterpart. Both up- and downregulated DEGs were identified in the nonaploid vs. hexaploid, including 457 genes showing qualitative alteration, i.e., silencing or activation. Impaired functionality at both cellular and organismal levels was inferred from gene ontology analysis of the DEGs. Homoeologous expression analysis of 9,574 sets of syntenic triads indicated that, compared with hexaploid, the proportions showing various homeologous expression patterns were highly conserved in the nonaploid although gene identity showed moderate reshuffling among some of the patterns in the nonaploid. Together, our results suggest hexaploidy is likely the upper limit of ploidy level in wheat; crossing this threshold incurs severe ploidy syndrome that is preceded by disruptive dysregulation of global gene expression.

Mapping QTLs for enhancing early biomass derived from Aegilops tauschii in synthetic hexaploid wheat

Strong early vigour plays a crucial role in wheat yield improvement by enhancing resource utilization efficiency. Synthetic hexaploid wheat (SHW) combines the elite genes of tetraploid wheat with Aegilops tauschii and has been widely used in wheat genetic improvement for its abundant genetic variation. The two SHWs Syn79 and Syn80 were derived from the crossing of the same tetraploid wheat DOY1 with two different Ae. tauschii accessions, AT333 and AT428, respectively. The Syn80 possessed better early vigour traits than Syn79, theretically caused by their D genome from Ae. tauschii. To dissect their genetic basis in a hexaploid background, 203 recombinant inbred lines (RILs) derived from the cross of Syn79 x Syn80 were developed to detect quantitative trait loci (QTL) for four early biomass related traits: plant height (PH), tiller number (TN), shoot fresh weight (SFW) and shoot dry weight (SDW) per plant, under five different environmental conditions. Determined from the data of SNP markers, two genome regions on 1DS and 7D were stably associated with the four early biomass related traits showing pleiotropic effects. Four stable QTLs QPh.saas-1DS, QTn.saas-1DS, QSfw.saas-1DS and QSdw.saas-1DS explaining 7.92, 15.34, 9.64 and 10.15% of the phenotypic variation, respectively, were clustered in the region of 1DS from AX-94812958 to AX-110910133. Meanwhile, QPh.saas-7D, QTn.saas-7D, QSfw.saas-7D and QSdw.saas-7D were flanked by AX-109917900 and AX-110605376 on 7D, explaining 16.12, 24.35, 15.25 and 13.37% of the phenotypic variation on average, respectively. Moreover, these genomic QTLs on 1DS and 7D enhancing biomass in the parent Syn80 were from Ae. tauschii AT428. These findings suggest that these two QTLs from Ae. tauschii can be expressed stably in a hexaploid background at the jointing stage and be used for wheat improvement.

Quantitative trait loci analysis for root traits in synthetic hexaploid wheat under drought stress conditions

Synthetic hexaploid wheat (SHW), possesses numerous genes for drought that can help breeding for drought-tolerant wheat varieties. We evaluated 10 root traits at seedling stage in 111 F9 recombinant inbred lines derived from a F2 population of a SHW line (SHW-L1) and a common wheat line, under normal (NC) and polyethylene glycol-simulated drought stress conditions (DC). We mapped quantitative trait loci (QTLs) for root traits using an enriched high-density genetic map containing 120370 single nucleotide polymorphisms (SNPs), 733 diversity arrays technology markers (DArT) and 119 simple sequence repeats (SSRs). With four replicates per treatment, we identified 19 QTLs for root traits under NC and DC, and 12 of them could be consistently detected with three or four replicates. Two novel QTLs for root fresh weight and root diameter under NC explained 9 and 15.7% of the phenotypic variation respectively, and six novel QTLs for root fresh weight, the ratio of root water loss, total root surface area, number of root tips, and number of root forks under DC explained 8.5–14% of the phenotypic variation. Here seven of eight novel QTLs could be consistently detected with more than three replicates. Results provide essential information for fine-mapping QTLs related to drought tolerance that will facilitate breeding drought-tolerant wheat cultivars.

Transferring diversity of goat grass to farmers\u2019 fields through the development of synthetic hexaploid wheat

Genetic variation in wheat is needed to address global food security challenges, particularly as climates change. Crop wild relatives are unique reservoirs of useful alleles for crop improvement and are important components of genebank collections. We analyzed how the derivatives of ‘goat grass’ (Aegilops tauschii) have been used to widen the genetic base for wheat breeding and surveyed wheat breeders to elicit adoption estimates. Synthetic hexaploid wheat (SHW) is derived by crossing goat grass with durum wheat, serving as a bridge to transfer desirable traits into modern varieties of bread wheat. Our data show that wheat scientists used 629 unique accessions from 15 countries for pre-breeding, producing 1577 primary SHWs. These derivatives represented 21% of the germplasm distributed by the genebank of the International Maize and Wheat Improvement Center between 2000 and 2018. Over the period, more than 10,000 samples of SHW were sent to 110 institutions in 40 countries, with rising numbers of synthetic hexaploid-derived lines (SHDL) included in international nurseries. Lines were screened for major diseases of wheat. At least 86 varieties have been selected from SHDL and released in 20 countries. Survey estimates indicate the highest scale of adoption in southwest China and India, with 34% and 7% of reported wheat area, respectively. These varieties demonstrate resistance to pests and pathogens, high yield potential, good quality attributes, and suitability for biofortified wheat.

Identification of a hard kernel texture line of synthetic allohexaploid wheat reducing the puroindoline accumulation on the D genome from Aegilops tauschii

Grain hardness is an important factor for wheat breeding. Generally, the grain hardness of hexaploid wheat is determined by two puroindoline (PIN) genes, Pina-D1 and Pinb-D1, at the Hardness locus on chromosome 5D. Here, the grain hardness of 55 synthetic wheat lines from crosses between a durum wheat cultivar and 55 Ae. tauschii accessions were examined, and nucleotide sequence variation in Pina-Dtau1 and Pinb-Dtau1 was analyzed using the Ae. tauschii accessions. Most synthetic wheat lines showed a soft texture with smoothly rounded starch granules, whereas one exceptional line exhibited a hard texture with starch granules that tightly adhered to the matrix proteins and reduced PINA and PINB protein accumulation. The parental Ae. tauschii accession of the hard-textured synthetic line has smoothly rounded starch granules and abundant PIN accumulation in the endosperm. Any genetic change that occurred at the Pin loci was transmitted from the parental Ae. tauschii accession, but the Pina and Pinb transcription was decreased in the hard-textured synthetic line. Therefore, any genetic and/or epigenetic modification in the process of allopolyploidization might have affected the PIN accumulation in synthetic hexaploid wheat lines.

Karyotype mosaicism in early generation synthetic hexaploid wheats.

It is known that both the number and the structure of somatic chromosomes can vary in early generation hexaploid wheats. The phenomenon is generally assumed to arise as a result of the meiotic instability characteristic of freshly created allopolyploids. Here, an analysis of the somatic karyotype of a set of 33 early generation synthetic hexaploid wheats has revealed that variation, taking the form of sub-chromosomal fragments and inter-chromosomal translocations, can also arise in somatic tissue. A possible explanation for the observations was that karyotypic instability in early generation hexaploid wheat probably occurs not just during sporogenesis, but also in somatic tissue. However, other factors such as the use of nitrous oxide during the experiments could also cause the chromosome variations, and additional experimentation would be required to determine the most likely.

A transcriptomic view of the ability of nascent hexaploid wheat to tolerate aneuploidy

BackgroundIn contrast to most animal species, polyploid plant species are quite tolerant of aneuploidy. Here, the global transcriptome of four aneuploid derivatives of a synthetic hexaploid wheat line was acquired, with the goal of characterizing the relationship between gene copy number and transcript abundance.ResultsFor most of the genes mapped to the chromosome involved in aneuploidy, the abundance of transcripts reflected the gene copy number. Aneuploidy had a greater effect on the strength of transcription of genes mapped to the chromosome present in a noneuploid dose than on that of genes mapped elsewhere in the genome. Overall, changing the copy number of one member of a homeologous set had little effect on the abundance of transcripts generated from the set of homeologs as a whole, consistent with the tolerance of aneuploidy exhibited by allopolyploids, whether in the form of a chromosomal deficit (monosomy) or chromosomal excess (trisomy).ConclusionsOur findings shed new light on the genetic regulation of homeoallele transcription and contribute to a deeper understanding of allopolyploid genome evolution, with implications for the breeding of polyploid crops.

Introgression of chromosomal segments conferring early heading date from wheat diploid progenitor, Aegilops tauschii Coss., into Japanese elite wheat cultivars.

The breeding of agriculturally useful genes from wild crop relatives must take into account recent and future climate change. In Japan, the development of early heading wheat cultivars without the use of any major gene controlling the heading date is desired to avoid overlap of the harvesting time before the rainy season. Here, we backcrossed two early heading lines of a synthetic hexaploid wheat, derived from a crossing between durum wheat and the wild wheat progenitor Aegilops tauschii, with four Japanese elite cultivars to develop early heading lines of bread wheat. In total, nine early heading lines that showed a heading date two to eight days earlier than their parental cultivars in field conditions were selected and established from the selfed progenies of the two- or three-times backcrossed populations. The whole appearance and spike shape of the selected early heading lines looked like their parental wheat cultivars. The mature grains of the selected lines had the parental cultivars' characteristics, although the grains exhibited longer and narrower shapes. RNA sequencing-based genotyping was performed to detect single nucleotide polymorphisms between the selected lines and their parental wheat cultivars, which revealed the chromosomal regions transmitted from the parental synthetic wheat to the selected lines. The introgression regions could shorten wheat heading date, and their chromosomal positions were dependent on the backcrossed wheat cultivars. Therefore, early heading synthetic hexaploid wheat is useful for fine-tuning of the heading date through introgression of Ae. tauschii chromosomal regions.

Genetic analysis of Aegilops tauschii-derived seedling resistance to leaf rust in synthetic hexaploid wheat

Seedling resistance to leaf rust available in the synthetic hexaploid wheat line Syn137 was characterised by means of cytogenetic and linkage mapping. Monosomic analysis located a single dominant gene for leaf rust resistance on chromosome 5D. Molecular mapping not only confirmed this location but also positioned the gene to the distal part of the long arm of chromosome 5D. A test of allelism showed that the gene, tentatively named LrSyn137, is independent but closely linked to Lr1. It appears that Syn137 is occasionally heterogeneous for Lr1 since the analysis of the Lr1-specific marker RGA567-5 in the genetic mapping population indicated the presence of Lr1. Syn137 represents another source of genetic variation that can be useful for the diversification of leaf rust resistance in wheat cultivars.

Higher Post-Anthesis Nitrogen Uptake Identified in a Synthetic Hexaploid Wheat Derivative

Two winter wheat cultivars were field tested at the National Agricultural Research and Development Institute Fundulea - Romania, and total plant Nitrogen was determined at anthesis and maturity. The winter wheat line Profund, bred at NARDI Fundulea and previously described as having high and stable positive grain protein deviation from the regression on grain yield, showed higher post-anthesis N uptake than cultivar Pitar, itself described as having a relatively high grain protein concentration. We suggest that the higher N post-anthesis uptake might have been inherited from the synthetic wheat derivative present in its genealogy.