Aegilops Tauschii Research Articles

Biological and economic characteristics of the allotetraploid with genomic formula DDAuAu from the cereal family

The synthesis of new allopolyploid cereal genotypes is an important task aimed at involving new genetic resources in breeding programs. Diploid species of the genera Triticum and Aegilops – bread wheat relatives – are an important source of agronomically valuable traits. A tetraploid synthetic with genomic formula DDAuAu was obtained by N.A. Navruzbekov through crossing Aegilops tauschii Coss. and Triticum urartu Thum. ex Gandil. The purpose of this work was to study the chromosomal composition and biological and commercially important traits of the tetraploid. Cytogenetic analysis using fluorescent in situ hybridization showed the presence of all chromosomes of the D genome in the chromosomal complement of the synthetic. By means of stepwise vernalization, the winter habit was established for the tetraploid synthetic with the optimum vernalization requirement of 45 days. Under greenhouse conditions, two groups of genotypes were found whose flowering dates differed by 6.5 days, which may indicate an allelism at the Vrn-3 locus. The coloring of various organs of the tetraploid plant, such as coleoptile, stem, anthers, and glumes of the spike, was revealed. The coloration of the aleurone layer of the grain may indicate that the donor species T. urartu is a carrier of the Ba gene that controls its blue color. A new morphotype of leaf pubescence was found. In terms of productivity, the tetraploid is comparable to bread wheat. Grains are characterized by a supersoft structure and high wet gluten content, from 39–45 to 65 %, in the field and greenhouse conditions, respectively. Thus, the tetraploid can be used to create new wheat genotypes as a source of untapped genetic diversity, as well as a new genetic model for studying the patterns of evolution of polyploid plants.

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.

Cellular and physiological responses to drought stress in Aegilops tauschii genotypes

Drought stress is one of the most important limiting factors in crop yield through impact on the cellular and physiological functions of the plant. Therefore, the study of physiological responses of plants can help to better understanding the drought tolerance mechanisms. In this experiment, 125 wild diploid wheat genotypes of Aegilops tauschii were evaluated for the physiological responses under rainfed and supplemental irrigation conditions. The physiological characteristics such as leaf relative water content (RWC), excised leaf water retention (ELWR), relative water loss (RWL), chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, ion leakage, membrane stability index (MSI) and proline content were measured. The results showed that the higher proline content, lower chlorophyll degradation rate and low amount of the membrane stability index (MSI) may inhibit the grain yield reduction under rainfed conditions. It was also found that the lower ion leakage due to the low cell membrane damage may led to the higher yield under rain-fed conditions. The results of regression analysis in both rainfed and supplemental irrigation conditions showed that proline content and total chlorophyll were introduced into the model, and explained the most variation in the grain yield. So, considering the above traits, the genotypes 16, 22, 43, 66 and 106 seems to be more drought tolerant and could be exploited in wheat breeding programs after further assessments.

Increased nitrogen deposition increased the competitive effects of the invasive plant Aegilops tauschii on wheat

Based on an external nitrogen source NH4NO3, the impacts of different nitrogen deposition treatments (i.e., CK, N5, N10, and N15) on the growth of the A. tauschii and its competition with wheat were investigated. This experiment was conducted in pots using simulated N deposition tests. The results showed that: (1) the plant height, leaf area, and tiller number of both monocultured and mixed planted A. tauschii and wheat increased gradually with increasing nitrogen deposition. In the same nitrogen deposition treatment, the tiller number of A. tauschii was significantly higher than that of wheat. (2) In both monoculture and mixed planting pots, the root biomass and root–crown ratios of A. tauschii to wheat decreased with increasing nitrogen deposition. However, the leaf–biomass ratio of the former showed a gradual increasing trend with increasing nitrogen deposition. (3) Under monoculture and mixed planting modes, the chlorophyll content of A. tauschii increased consistently with increasing nitrogen deposition, but the chlorophyll content of wheat first increased and then decreased. Moreover, the SOD activity, relative conductivity, and MDA content of A. tauschii and wheat constantly increased with increasing nitrogen deposition. (4) In the mixed planting pots, the relative yield of A. tauschii was > 1. The competition balance index of this plant was > 0 and increased with increasing nitrogen deposition. In a nutshell, the ability of A. tauschii to compete with wheat is gradually enhanced with increasing nitrogen deposition; and its adaptability to high nitrogen stress surpasses that of the latter.

Progress on wheat A genome illustration and its evolutional analysis

Wheat is one of the main food crops and widely grown in the world. It feeds more than 35% of the world's population. Obtaining high-quality genome sequences of wheat is important for its basic and breeding researches. However, the large and complex genome of wheat once led to its genome sequencing as an "impossible task". Recently, with the development of high-throughput sequencing and assembly technology, many wheat genome sequences have been released, and their sequencing and assembly quality is being improved continuously. In the last two years, five wheat reference genomes with different ploidy levels have been published, including two diploid ancestors Triticum urartu (AA) and Aegilops tauschii (DD), wild and cultivated tetraploid wheat T. turgidum ssp. dicoccoides (BBAA) and hexaploid wheat T. aestivum (BBAADD). Among them, the sequencing and analysis of the T. urartu genome, a donor of polyploid wheat A subgenome, was led by the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences. In this review, we summarize the research progress on structure and evolution analyses of the T. urartu genome to provide some valuable information for promoting the basic and applied researches of wheat.

The improved assembly of 7DL chromosome provides insight into the structure and evolution of bread wheat.

SummaryWheat is one of the most important staple crops worldwide and also an excellent model species for crop evolution and polyploidization studies. The breakthrough of sequencing the bread wheat genome and progenitor genomes lays the foundation to decipher the complexity of wheat origin and evolutionary process as well as the genetic consequences of polyploidization. In this study, we sequenced 3286 BACs from chromosome 7DL of bread wheat cv. Chinese Spring and integrated the unmapped contigs from IWGSC v1 and available PacBio sequences to close gaps present in the 7DL assembly. In total, 8043 out of 12 825 gaps, representing 3 491 264 bp, were closed. We then used the improved assembly of 7DL to perform comparative genomic analysis of bread wheat (Ta7DL) and its D donor, Aegilops tauschii (At7DL), to identify domestication signatures. Results showed a strong syntenic relationship between Ta7DL and At7DL, although some small rearrangements were detected at the distal regions. A total of 53 genes appear to be lost genes during wheat polyploidization, with 23% (12 genes) as RGA (disease resistance gene analogue). Furthermore, 86 positively selected genes (PSGs) were identified, considered to be domestication‐related candidates. Finally, overlapping of QTLs obtained from GWAS analysis and PSGs indicated that TraesCS7D02G321000 may be one of the domestication genes involved in grain morphology. This study provides comparative information on the sequence, structure and organization between bread wheat and Ae. tauschii from the perspective of the 7DL chromosome, which contribute to better understanding of the evolution of wheat, and supports wheat crop improvement.

An ancestral NB-LRR with duplicated 3\u2032UTRs confers stripe rust resistance in wheat and barley

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a global threat to wheat production. Aegilops tauschii, one of the wheat progenitors, carries the YrAS2388 locus for resistance to Pst on chromosome 4DS. We reveal that YrAS2388 encodes a typical nucleotide oligomerization domain-like receptor (NLR). The Pst-resistant allele YrAS2388R has duplicated 3’ untranslated regions and is characterized by alternative splicing in the nucleotide-binding domain. Mutation of the YrAS2388R allele disrupts its resistance to Pst in synthetic hexaploid wheat; transgenic plants with YrAS2388R show resistance to eleven Pst races in common wheat and one race of P. striiformis f. sp. hordei in barley. The YrAS2388R allele occurs only in Ae. tauschii and the Ae. tauschii-derived synthetic wheat; it is absent in 100% (n = 461) of common wheat lines tested. The cloning of YrAS2388R will facilitate breeding for stripe rust resistance in wheat and other Triticeae species.

Population-dependent reproducible deviation from natural bread wheat genome in synthetic hexaploid wheat.

Sequence elimination is one of the main mechanisms that increases the divergence among homoeologous chromosomes after allopolyploidization to enhance the stability of recently established lineages, but it can cause a loss of some economically important genes. Synthetic hexaploid wheat (SHW) is an important source of genetic variation to the natural hexaploid wheat (NHW) genepool that has low genetic diversity. Here, we investigated the change between SHW and NHW genomes by utilizing a large germplasm set of primary synthetics and synthetic derivatives. Reproducible segment elimination (RSE) was declared if a large chromosomal chunk (>5cM) produced no aligned reads in more than five SHWs. RSE in five genomic regions was the major source of variation between SHW and NHW. One RSE eliminated almost the complete short arm of chromosome 1B, which contains major genes for flour quality, disease resistance and different enzymes. The occurrence of RSE was highly dependent on the choice of diploid and tetraploid parental lines, their ancestral subpopulation and admixture, e.g. SHWs derived from Triticum dicoccon or from one of two Aegilops tauschii subpopulations were almost free of RSE, while highly admixed parents had higher RSE rates. The rate of RSE in synthetic derivatives was almost double that in primary synthetics. Genome-wide association analysis detected four loci with minor effects on the occurrence of RSE, indicating that both parental lines and genetic factors were affecting the occurrence of RSE. Therefore, pre-pre-breeding strategies should be applied before introducing SHW into pre-breeding programs to ensure genomic stability and avoid undesirable gene loss.

Cloning and Characterization of Disease Resistance Protein RPM1 Genes against Powdery Mildew in Wheat Line N9134

Powdery mildew (Blumeria graminis f. sp. tritici) is one of the most devastating wheat diseases. The wheat line N9134 contains PmAS846 that was transferred to N9134 from wild emmer wheat, and is still one of the most effective resistance genes in China. A full-length wheat RPM1 gene was obtained by rapid amplification of cDNA ends (RACE) based on the up-regulated probe sequence from differentially expressed transcripts during the N9134 and powdery mildew interaction. The gene was named TaRPM1, and the open reading frame (ORF) is 2721 nucleotides and encodes a polypeptide of 907 amino acids with a predicted isoelectric point of 4.86. Phylogenetic analysis revealed that TaRPM1 was highly homologous on both Aegilops tauschii and Triticum urartu at both the nucleotide and protein level. Using real-time quantitative PCR, the TaRPM1 gene expression level in wheat leaves was found to be sharply up-regulated, while the transcript level was lowly induced in the root and stem. Under the powdery mildew treatment, the transcription profile of TaRPM1 was very strongly expressed at 48 hour post inoculation (hpi), which increased again to 96 hpi and reaching a high level at 120 hpi. Based on sequence similarities and positions, we inferred that the TaRPM1 gene was on wheat chromosome 3D. These results suggested that TaRPM1 plays an important role in the mechanism of innate immunity to infection by the powdery mildew pathogen.

Identification of qPHS.sicau-1B and qPHS.sicau-3D from synthetic wheat for pre-harvest sprouting resistance wheat improvement

Pre-harvest sprouting (PHS) causes serious damage that leads to deterioration in overall quality and decreased yield and reduction of grain yield in cereal. In this study, two major quantitative trait loci (QTLs), qPHS.sicau-3D and qPHS.sicau-1B, were detected in synthetic wheat (SHW-L1) and were derived from Aegilops tauschii AS60 (deep dormant) and Triticum turgidum AS2255 (medium PHS-resistant). qPHS.sicau-1B is located in the region near the telomere of 1BS, and qPHS.sicau-3D is located on the end of 3DL; these QTLs explain approximately 20.99% and 42.47% of the phenotypic variation. Pyramiding of both QTLs showed superior PHS resistance in recombinant inbred lines (RILs). The array-based SNP markers AX-94924265 for qPHS.sicau-1B and AX-94415259 for qPHS.sicau-3D were successfully converted to Kompetitive Allele Specific Polymerase Chain Reaction (KASP) and STS markers. L10-1580 is a light red breeding materials selected from SHW-L1-derived breeding lines that harbors the PHS-tolerant elite alleles which showed similar germination level with SHW-L1 and better resistance than other common wheat parents. L10-1580 harbors the elite alleles AX-94924265_GG/AX-94415259_B which showed similar PHS resistance as SHW-L1 and better resistance than other common wheat parents. Therefore, these QTLs for PHS resistance obtained from synthetic wheat could combine or coexist with other elite agronomic traits in high-yield wheat cultivars.

Genetic Contribution of Synthetic Hexaploid Wheat to CIMMYT\u2019s Spring Bread Wheat Breeding Germplasm

Synthetic hexaploid (SH) wheat (AABBD’D’) is developed by artificially generating a fertile hybrid between tetraploid durum wheat (Triticum turgidum, AABB) and diploid wild goat grass (Aegilops tauschii, D’D’). Over three decades, the International Maize and Wheat Improvement Center (CIMMYT) has developed and utilized SH wheat to bridge gene transfer from Ae. tauschii and durum wheat to hexaploid bread wheat. This is a unique example of success utilizing wild relatives in mainstream breeding at large scale worldwide. Our study aimed to determine the genetic contribution of SH wheat to CIMMYT’s global spring bread wheat breeding program. We estimated the theoretical and empirical contribution of D’ to synthetic derivative lines using the ancestral pedigree and marker information using over 1,600 advanced lines and their parents. The average marker-estimated D’ contribution was 17.5% with difference in genome segments suggesting application of differential selection pressure. The pedigree-based contribution was correlated with marker-based estimates without providing chromosome segment specific variation. Results from international yield trials showed that 20% of the lines were synthetic derived with an average D’ contribution of 15.6%. Our results underline the importance of SH wheat in maintaining and enhancing genetic diversity and genetic gain over years and is important for development of a more targeted introgression strategy. The study provides retrospective view into development and utilization of SH in the CIMMYT Global Wheat Program.

Genome-wide and evolutionary analysis of the class III peroxidase gene family in wheat and Aegilops tauschii reveals that some members are involved in stress responses

BackgroundThe class III peroxidase (PRX) gene family is a plant-specific member of the PRX superfamily that is closely related to various physiological processes, such as cell wall loosening, lignification, and abiotic and biotic stress responses. However, its classification, evolutionary history and gene expression patterns are unclear in wheat and Aegilops tauschii.ResultsHere, we identified 374, 159 and 169 PRXs in Triticum aestivum, Triticum urartu and Ae. tauschii, respectively. Together with PRXs detected from eight other plants, they were classified into 18 subfamilies. Among subfamilies V to XVIII, a conserved exon-intron structure within the “001” exon phases was detected in the PRX domain. Based on the analysis, we proposed a phylogenetic model to infer the evolutionary history of the exon-intron structures of PRX subfamilies. A comparative genomics analysis showed that subfamily VII could be the ancient subfamily that originated from green algae (Chlamydomonas reinhardtii). Further integrated analysis of chromosome locations and collinearity events of PRX genes suggested that both whole genome duplication (WGD) and tandem duplication (TD) events contributed to the expansion of T. aestivum PRXs (TaePRXs) during wheat evolution. To validate functions of these genes in the regulation of various physiological processes, the expression patterns of PRXs in different tissues and under various stresses were studied using public microarray datasets. The results suggested that there were distinct expression patterns among different tissues and PRXs could be involved in biotic and abiotic responses in wheat. qRT-PCR was performed on samples exposed to drought, phytohormone treatments and Fusarium graminearum infection to validate the microarray predictions. The predicted subcellular localizations of some TaePRXs were consistent with the confocal microscopy results. We predicted that some TaePRXs had hormone-responsive cis-elements in their promoter regions and validated these predicted cis-acting elements by sequencing promoters.ConclusionIn this study, identification, classification, evolution, and expression patterns of PRXs in wheat and relative plants were performed. Our results will provide information for further studies on the evolution and molecular mechanisms of wheat PRXs.

Cloning, prokaryotic expression, and subcellular localisation of the TaMAPK10-like gene in common wheat

Mitogen-activated protein kinase (MAPK/MPK) is a group of serine-threonine protein kinases that are activated by different extracellular stimuli. To explore the function of MAPK in wheat infected with powdery mildew, a new wheat germplasm N9134 was used to obtain the full-length MAPK gene and the MAPK sequence was used to identify its prokaryotic expression and subcellular localisation. Wheat MAPK was obtained by homologous gene cloning and designated as TaMAPK10-like. The open reading frame of TaMAPK10-like was 1638 bp, which coded a deduced protein of 545 amino acids. Phylogenetic analysis revealed that TaMAPK10-like was most closely related to MAPK10-like of Aegilops tauschii at the protein level. It had high nucleotide similarity with the reported MAPK gene in A. tauschii, Sorghum bicolor, and Setaria italica, and had features typical of MAPK family genes. Subcellular localisation showed that TaMAPK10-like was mainly located in the cytoplasm along the microtubules, and a small number were located in the cell membrane and the nucleus. A pMD-MAPK10-like fusion expression vector was constructed and the TaMAPK10-like fusion protein was 70 kDa. The expressions of protein in bacteria were best obtained using 0.5 mmol L−1 isopropyl β-d-1-thiogalactopyranoside at 37 °C for 12 h. These results provide the basic data for further understanding the biological function of the TaMAPK10-like gene.

Interspecific Polymorphism of DEP1 Genes and the Spike Shape in Wheats

In the present study, we performed an analysis of DEP1 gene sequences in ten accessions of Triticum macha Decapr. et Menabde, T. antiquorum Heer ex Udacz., T. sphaerococcum Perciv., mutants of common and durum wheat, and one semicompactoid accession of the D genome donor for common wheat Aegilops tauschii Coss. The comparative analysis showed that all studied accessions, except for the near isogenic line Cp-M808(Vrn1), possess one allelic variant of each of the Dep1-A, Dep1-B, and Dep1-D genes. The sequences of the Dep1-A, Dep1-B, and Dep1-D obtained for the wheat accessions and mutants of common and bread wheat are identical to the previously described alleles. Near isogenic lines Cp-M808(Vrn1) and cp-M808(Vrn1) represent the exceptions. We described four new allelic variants for i: Cp-M808(Vrn1) (Dep1-Aа, Dep1-Bb, Dep1-Da, and Dep1-Db) and two new alleles for i: сp-M808(Vrn1) (Dep1-Ba and Dep1-Dc). Thus, accession-specific mutations were detected in DEP1 genes of studied wheat accessions; however, alleles that correlate with a specific spike morphology in wheat were not detected. A new Dep1-Dd allele was identified for a unique semicompactoid accession of Ae. tauschii KT-120-16. This allele differs from the Dep1-D allele of spelt accessions of Ae. tauschii in the presence of several deletions in 5'-UTR. These deletions could affect the expression of the Dep1-Dd gene and thus determine the formation of a compact spike in Ae. tauschii KT-120-16.

Ozone Tolerance Found in Aegilops tauschii and Primary Synthetic Hexaploid Wheat.

Modern wheat cultivars are increasingly sensitive to ground level ozone, with 7–10% mean yield reductions in the northern hemisphere. In this study, three of the genome donors of bread wheat, Triticum urartu (AA), T. dicoccoides (AABB), and Aegilops tauschii (DD) along with a modern wheat cultivar (T. aestivum ‘Skyfall’), a 1970s cultivar (T. aestivum ‘Maris Dove’), and a line of primary Synthetic Hexaploid Wheat were grown in 6 L pots of sandy loam soil in solardomes (Bangor, North Wales) and exposed to low (30 ppb), medium (55 ppb), and high (110 ppb) levels of ozone over 3 months. Measurements were made at harvest of shoot biomass and grain yield. Ae. tauschii appeared ozone tolerant with no significant effects of ozone on shoot biomass, seed head biomass, or 1000 grain + husk weight even under high ozone levels. In comparison, T. urartu had a significant reduction in 1000 grain + husk weight, especially under high ozone (−26%). The older cultivar, ‘Maris Dove’, had a significant reduction in seed head biomass (−9%) and 1000 grain weight (−11%) but was less sensitive than the more recent cultivar ‘Skyfall’, which had a highly significant reduction in its seed head biomass (−21%) and 1000 grain weight (−27%) under high ozone. Notably, the line of primary Synthetic Hexaploid Wheat was ozone tolerant, with no effect on total seed head biomass (−1%) and only a 5% reduction in 1000 grain weight under high ozone levels. The potential use of synthetic wheat in breeding ozone tolerant wheat is discussed.

Genetic variation for phosphorus-use efficiency in diverse wheat germplasm

ABSTRACTPhosphorus (P) is the second most essential element for the growth and development of plants because of its role in vital biochemical reactions in the plant system. The positive response of wheat (Triticum aestivum L.) to P and dwindling raw materials for P fertilizer necessitate identification of P-efficient cultivars of wheat. Thirty wheat genotypes consisting of bread, synthetic, and wild wheats were assessed for P-use efficiency (PUE) at two P levels for identification of P-use efficient and P-deficiency-tolerant genotypes. PUE was measured by recording agro-morphological traits and P concentration in straw and grains. T. dicoccoides, T. boeoticum acc. pau5147, and synthetic wheats derived from different Aegilops tauschii accessions were observed to be P-acquisition efficient, as indicated by shoot P uptake. Hexaploid wheat introgression lines pau16059, pau16063, pau16065, pau16066, and pau16067 were identified to be P-utilization efficient. Synthetic wheats from Ae. tauschii acc. pau14201, pau9796, pau14128, and pau14170; T. boeoticum acc. pau5147; T. dicoccoides acc. pau5366, pau7127, and pau7142; and hexaploid wheat lines pau16065, pau16066, pau16067, and pau16059 were found to be P-deficiency tolerant. Overall, wild germplasm was more efficient in uptake and accumulation of P in the shoots, and hexaploid wheats were more efficient in utilization of the accumulated P in realizing increased grain yields and PUE. These genotypes will be exploited for developing P-use efficient wheat cultivars and identifying genomic regions conditioning PUE.

Conservation and differentiation of polyphenol oxidase (PPO) gene introns in Triticum and Aegilops tauschii Coss.

Two genes (PPO1 and PPO2), located in the homoeologous chromosome group 2 of common wheat, play an important role in controlling the kernel polyphenol oxidase acitivity, which influence indirectly the time-dependent darkening and discoloration in Asian noodles and other wheat-based products. In the present study, intron sequences of PPO genes (PPO1 and PPO2) in Triticum urartu Tumanian ex Gandilyan, T. monococcum L. and Aegilops tauschii Coss., together with NCBI retrieved wheat PPO sequnces in different ploidy levels, were systematically investigated. The results highlighted that PPO intron sequences are conserved at lower classification levels (species/subspecies level), and the allopolyploidization process of common wheat has little effect on them. Sequence differences in PPO gene introns may occur long before the differentiation of the A and D genome of T. urartu and Ae. tauschii, respectively. It’s interesting that different PPO intron regions vary into two different intron splicing rule within one same gene sequence: intron 1 is all fitted to the “GT-AG” splicing rule while intron 2 is the “GC-AG”. In addition, the phylogenetic analysis showed the obvious differences existed in materials from different geographical distribution in T. monococcum ssp. aegilopoies, which suggest that some of them had close genetic relationship with T. urartu. These findings contribute to the application of PPO gene introns in favorable allele screening, functional molecular marker development, and phylogenetic analysis.

Genetic Analysis and Transfer of Favorable Exotic QTL Alleles for Grain Yield Across D Genome Using Two Advanced Backcross Wheat Populations.

Hexaploid wheat evolved through a spontaneous hybridization of tetraploid wheat (Triticum turgidum, AABB) with diploid wild grass (Aegilops tauschii, DD). Recent genome sequencing found alarmingly low genetic diversity and abundance of repeated sequences across D genome as compared to AB genomes. This characteristic feature of D genome often results in a low recombination rate and abrupt changes in chromosome, which are the major hurdles to utilize the genetic potential of D genome in wheat breeding. In the present study, we evaluated two advanced backcross populations designated as B22 (250 BC2F3:6 lines) and Z86 (150 BC2F3:6 lines) to test their yield potential and to enrich the D genome diversity simultaneously. The populations B22 and Z86 were derived by crossing winter wheat cultivars Batis and Zentos with synthetic hexaploid wheat accessions Syn022L and Syn086L, respectively. These populations were genotyped using SNP markers and phenotyped for yield traits in ten environments in Germany. Marker analysis identified lower recombination rate across D genome as compared to A and B genomes in both populations. Further, we compared the genotype data with the trait grain yield to identify favorable exotic introgressions from synthetic wheat accessions. QTL analysis identified seven and 13 favorable exotic QTL alleles associated with enhancement or at least stable grain yield in populations B22 and Z86, respectively. These favorable introgressions were located on all chromosomes from 1D to 7D. The strongest exotic QTL allele on chromosome 1D at SNP marker RAC875_c51493_471 resulted in a relative increase of 8.6% in grain yield as compared to cultivated allele. The identified exotic introgressions will help to refine useful exotic chromosome segments for their incorporation for improving yield and increasing D genome diversity among cultivated varieties.

Fine Mapping of the Wheat Leaf Rust Resistance Gene Lr42.

Leaf rust caused by Puccinia triticina Eriks is one of the most problematic diseases of wheat throughout the world. The gene Lr42 confers effective resistance against leaf rust at both seedling and adult plant stages. Previous studies had reported Lr42 to be both recessive and dominant in hexaploid wheat; however, in diploid Aegilops tauschii (TA2450), we found Lr42 to be dominant by studying segregation in two independent F2 and their F2:3 populations. We further fine-mapped Lr42 in hexaploid wheat using a KS93U50/Morocco F5 recombinant inbred line (RIL) population to a 3.7 cM genetic interval flanked by markers TC387992 and WMC432. The 3.7 cM Lr42 region physically corresponds to a 3.16 Mb genomic region on chromosome 1DS based on the Chinese Spring reference genome (RefSeq v.1.1) and a 3.5 Mb genomic interval on chromosome 1 in the Ae. tauschii reference genome. This region includes nine nucleotide-binding domain leucine-rich repeat (NLR) genes in wheat and seven in Ae. tauschii, respectively, and these are the likely candidates for Lr42. Furthermore, we developed two kompetitive allele-specific polymorphism (KASP) markers (SNP113325 and TC387992) flanking Lr42 to facilitate marker-assisted selection for rust resistance in wheat breeding programs.

An Update of Recent Use of Aegilops Species in Wheat Breeding.

Aegilops species have significantly contributed to wheat breeding despite the difficulties involved in the handling of wild species, such as crossability and incompatibility. A number of biotic resistance genes have been identified and incorporated into wheat varieties from Aegilops species, and this genus is also contributing toward improvement of complex traits such as yield and abiotic tolerance for drought and heat. The D genome diploid species of Aegilops tauschii has been utilized most often in wheat breeding programs. Other Aegilops species are more difficult to utilize in the breeding because of lower meiotic recombination frequencies; generally they can be utilized only after extensive and time-consuming procedures in the form of translocation/introgression lines. After the emergence of Ug99 stem rust and wheat blast threats, Aegilops species gathered more attention as a form of new resistance sources. This article aims to update recent progress on Aegilops species, as well as to cover new topics around their use in wheat breeding.