Accessions Of Wild Emmer Wheat Research Articles

Characterizing Agronomic and Shoot Morphological Diversity across 263 Wild Emmer Wheat Accessions

Wild emmer, the direct progenitor of modern durum and bread wheat, has mostly been studied for grain quality, biotic, and abiotic stress-related traits. Accordingly, it should also have a certain amount of diversity for morphological and agronomic traits. Despite having a high chance of huge diversity, it has not been deeply explored. In the current study, 263 wild emmer accessions collected from different regions of Israel, Turkey, Lebanon, and Syria were characterized for a total of 19 agronomic and shoot morphological traits. Three trials were carried out in Western Australia, which demonstrated a large variation in these traits. The average phenotypic diversity (H’) was 0.91 as quantified by Shannon’s diversity index. A high heritability was recorded for most of the traits, where biomass/plant and yield/plant were identified as the most potential traits. Correlation analysis revealed several significant associations between traits, including significant positive correlation between yield and tiller number, first leaf area, spike length, and biomass/plant. The principal component analysis (PCA) demonstrated that most of the traits contributed to the overall observed variability. The cluster analysis categorized 263 accessions into five clusters on average. On the other hand, accessions were categorized into eight populations based on the collection region and a comparative analysis demonstrated considerable variations between populations for plant height, spike length, and flag leaf area. Despite the low yield, several wild emmer accessions demonstrated superior performance compared to modern bread wheat cultivars, when selection was based on combining yield with multiple traits. These observations indicate that wild emmer contains a broad gene pool for several agronomic and shoot morphological traits, which can be utilized for bread and durum wheat improvement.

Harnessing the diversity of wild emmer wheat for genetic improvement of durum wheat

Key messageThe multiple derivative lines (MDLs) characterized in this study offer a promising strategy for harnessing the diversity of wild emmer wheat for durum and bread wheat improvement.Crop domestication has diminished genetic diversity and reduced phenotypic plasticity and adaptation. Exploring the adaptive capacity of wild progenitors offer promising opportunities to improve crops. We developed a population of 178 BC1F6 durum wheat (Triticum turgidum ssp. durum) lines by crossing and backcrossing nine wild emmer wheat (T. turgidum ssp. dicoccoides) accessions with the common durum wheat cultivar ‘Miki 3’. Here, we describe the development of this population, which we named as multiple derivative lines (MDLs), and demonstrated its suitability for durum wheat breeding. We genotyped the MDL population, the parents, and 43 Sudanese durum wheat cultivars on a Diversity Array Technology sequencing platform. We evaluated days to heading and plant height in Dongola (Sudan) and in Tottori (Japan). The physical map length of the MDL population was 9 939 Mb with an average of 1.4 SNP/Mb. The MDL population had greater diversity than the Sudanese cultivars. We found high gene exchange between the nine wild emmer accessions and the MDL population, indicating that the MDL captured most of the diversity in the wild emmer accessions. Genome-wide association analysis identified three loci for days to heading on chromosomes 1A and 5A in Dongola and one on chromosome 3B in Tottori. For plant height, common genomic loci were found on chromosomes 4A and 4B in both locations, and one genomic locus on chromosome 7B was found only in Dongola. The results revealed that the MDLs are an effective strategy towards harnessing wild emmer wheat diversity for wheat genetic improvement.

Comparison of the Agronomic, Cytological, Grain Protein Characteristics, as Well as Transcriptomic Profile of Two Wheat Lines Derived From Wild Emmer

Two advanced wheat lines BAd7-209 and BAd23-1 without the functional gene GPC-B1 were obtained from a cross between common wheat cultivar Chuannong 16 (CN16) and wild emmer wheat accession D97 (D97). BAd7-209 showed superior quality parameters than those of BAd23-1 and CN16. We found that the components of glutenins and gliadins in BAd7-209 and BAd23-1 were similar, whereas BAd7-209 had higher amount of glutenins and gliadins than those of BAd23-1. RNA sequencing analysis on developing grains of BAd7-209 and BAd23-1 as well as their parents revealed 382 differentially expressed genes (DEGs) between the high–grain protein content (GPC) (D97 + BAd7-209) and the low-GPC (CN16 + BAd23-1) groups. DEGs were mainly associated with transcriptional regulation of the storage protein genes, protein processing in endoplasmic reticulum, and protein export pathways. The upregulated gluten genes and transcription factors (e.g., NAC, MYB, and bZIP) may contribute to the high GPC in BAd7-209. Our results provide insights into the potential regulation pathways underlying wheat grain protein accumulation and contribute to make use of wild emmer for wheat quality improvement.

Fine mapping of powdery mildew resistance gene MlWE74 derived from wild emmer wheat (Triticum turgidum ssp. dicoccoides) in an NBS-LRR gene cluster.

Powdery mildew resistance gene MlWE74, originated from wild emmer wheat accession G-748-M, was mapped in an NBS-LRR gene cluster of chromosome 2BS. Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a globally devastating disease. Wild emmer wheat (Triticum turgidum var. dicoccoides) is a valuable genetic resource for improving disease resistance in common wheat. A powdery mildew resistance gene was transferred to hexaploid wheat line WE74 from wild emmer accession G-748-M. Genetic analysis revealed that the powdery mildew resistance in WE74 is controlled by a single dominant gene, herein temporarily designated MlWE74. Bulked segregant analysis (BSA) and molecular mapping delimited MlWE74 to the terminal region of chromosome 2BS flanking by markers WGGBD412 and WGGBH346 within a genetic interval of 0.25cM and corresponding to 799.9kb genomic region in the Zavitan reference sequence. Sequence annotation revealed two phosphoglycerate mutase-like genes, an alpha/beta-hydrolases gene, and five NBS-LRR disease resistance genes that could serve as candidates for map-based cloning of MlWE74. The geographical location analysis indicated that MlWE74 is mainly distributed in Rosh Pinna and Amirim regions, in the northern part of Israel, where environmental conditions are favorable to the occurrence of powdery mildew. Moreover, the co-segregated marker WGGBD425 is helpful in marker-assisted transfer of MlWE74 into elite cultivars.

Fine mapping of a powdery mildew resistance gene MlIW39 derived from wild emmer wheat (Triticum turgidum ssp. dicoccoides).

Powdery mildew resistance gene MlIW39, originated from wild emmer wheat accession IW39, was mapped to a 460.3 kb genomic interval on wheat chromosome arm 2BS. Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is destructive disease and a significant threat to wheat production globally. The most effective way to control this disease is genetic resistance. However, when resistance genes become widely deployed in agriculture, their effectiveness is compromised by virulent variants that were previously minor components of the pathogen population or that arise from mutation. This necessitates continual search for new sources of resistance in both wheat and its near relatives. In this study, we produced a common wheat line 8D49 (87-1/IW39//2*87-1), which has all-stage immunity to Bgt isolate E09 and many other Chinese Bgt isolates, by transferring powdery mildew resistance from Israeli wild emmer wheat (WEW) accession IW39 to the susceptible common wheat line 87-1. Genetic analysis indicated that the powdery mildew resistance in 8D49 was controlled by a single dominant gene, temporarily designated MlIW39. Genetic linkage analyses with molecular markers showed that MlIW39 was located in a 0.7 cm genetic region between markers QB-3-16 and 7Seq546 on the short arm of chromosome 2B. Fine mapping using three large F2 populations delimited MlIW39 to a physical interval of approximately 460.3 kb region in the WEW reference genome (Zavitan v1.0) that contained six annotated protein-coding genes, four of which had gene structures similar to known disease resistance genes. This provides a foundation for map-based cloning of MlIW39. Markers 7Seq622 and 7Seq727 co-segregating with MlIW39 can be utilized for marker-assisted selection in further genetic studies and wheat breeding.

A novel miniature transposon-like element discovered in the coding sequence of a gene that encodes for 5-formyltetrahydrofolate in wheat

BackgroundTransposable elements (TEs) comprise over 80% of the wheat genome and usually possess unique features for specific super-families and families. However, the role of TEs in wheat evolution and reshaping the wheat genome remains largely unclear.ResultsIn this study, we discovered a miniature (307 bp in length) TE-like sequence in exon 6 of a gene that encodes for 5-formyltetrahydrofolate, in two accessions of wild emmer wheat (T. turgidum ssp. dicoccoides) and has interfered with the gene translation by creating a shorter reading frame as a result of a stop codon. The sequence that was termed Mariam, does not show any structural similarity to known TEs. It does not possess terminal inverted repeats (TIRs) that would allow us to assign this element to one of the TIR DNA super-families, and it does not possess characteristic features of SINE, such as a Pol-III promotor or a poly-A tail. In-silico analysis of five publicly available genome drafts of Triticum and Aegilops species revealed that Mariam element appears in a very low copy number (1–3 insertions) in diploid wheat species and ~ 12 insertions in tetraploid and hexaploidy wheat species. In addition, Mariam element was found to be unique to wheat, as it was not found in other plant genomes. The dynamic nature of Mariam in the wheat genome was assessed by site-specific PCR analysis and revealed that it retained activity in wild emmer populations in a population-specific manner.ConclusionsThis study provides additional insight into the evolutionary impact of TEs in wheat.

The novel function of the Ph1 gene to differentiate homologs from homoeologs evolved in Triticum turgidum ssp. dicoccoides via a dramatic meiosis-specific increase in the expression of the 5B copy of the C-Ph1 gene.

The Ph1 gene is the principal regulator of homoeologous chromosome pairing control (HECP) that ensures the diploid-like meiotic chromosome pairing behavior of polyploid wheat. The HECP control was speculated to have evolved after the first event of polyploidization. With the objective to accurately understand the evolution of the HECP control, wild emmer wheat accessions previously known to differ for HECP control were characterized for the structure and expression of the candidatePh1 gene, C-Ph1. The C-TdPh1-5A and 5B gene copies of emmer wheat showed 98 and 99% DNA sequence similarity respectively with the corresponding hexaploid wheat copies. Further, the C-TdPh1-5B carried the C-Ph1-5B specific structural changes and transcribed three splice variants as observed in the hexaploid wheat. Further, single nucleotide changes differentiating accessions varying for HECP control were identified. Analyzed by quantitative expression analysis, the wild emmer accessions with HECP control showed ~ 10,000-fold higher transcript abundance of the C-TdPh1-5B copy during prophase-I compared to accessions lacking the control. Differential transcriptional regulation of C-TdPh1-5B splice variants further revealed that C-Ph1-5Balt1 variant is mainly responsible for differential accumulation of C-Ph1-5B copy in accessions with HECP control. Taken together, these results showed that the HECP control evolved via transcriptional regulation of splice variants during meiosis.

Genome Based Meta-QTL Analysis of Grain Weight in Tetraploid Wheat Identifies Rare Alleles of GRF4 Associated with Larger Grains.

The domestication and subsequent genetic improvement of wheat led to the development of large-seeded cultivated wheat species relative to their smaller-seeded wild progenitors. While increased grain weight (GW) continues to be an important goal of many wheat breeding programs, few genes underlying this trait have been identified despite an abundance of studies reporting quantitative trait loci (QTL) for GW. Here we perform a QTL analysis for GW using a population of recombinant inbred lines (RILs) derived from the cross between wild emmer wheat accession ‘Zavitan’ and durum wheat variety ‘Svevo’. Identified QTLs in this population were anchored to the recent Zavitan reference genome, along with previously published QTLs for GW in tetraploid wheat. This genome-based, meta-QTL analysis enabled the identification of a locus on chromosome 6A whose introgression from wild wheat positively affects GW. The locus was validated using an introgression line carrying the 6A GW QTL region from Zavitan in a Svevo background, resulting in >8% increase in GW compared to Svevo. Using the reference sequence for the 6A QTL region, we identified a wheat ortholog to OsGRF4, a rice gene previously associated with GW. The coding sequence of this gene (TtGRF4-A) contains four single nucleotide polymorphisms (SNPs) between Zavitan and Svevo, one of which reveals the Zavitan allele to be rare in a core collection of wild emmer and completely absent from the domesticated emmer genepool. Similarly, another wild emmer accession (G18-16) was found to carry a rare allele of TtGRF4-A that also positively affects GW and is characterized by a unique SNP absent from the entire core collection. These results exemplify the rich genetic diversity of wild wheat, posit TtGRF4-A as a candidate gene underlying the 6A GW QTL, and suggest that the natural Zavitan and G18-16 alleles of TtGRF4-A have potential to increase wheat yields in breeding programs.

Genetic Mapping of Loci for Resistance to Stem Rust in a Tetraploid Wheat Collection.

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a major biotic constraint to wheat production worldwide. Disease resistant cultivars are a sustainable means for the efficient control of this disease. To identify quantitative trait loci (QTLs) conferring resistance to stem rust at the seedling stage, an association mapping panel consisting of 230 tetraploid wheat accessions were evaluated for reaction to five Pgt races under greenhouse conditions. A high level of phenotypic variation was observed in the panel in response to all of the races, allowing for genome-wide association mapping of resistance QTLs in wild, landrace, and cultivated tetraploid wheats. Twenty-two resistance QTLs were identified, which were characterized by at least two marker-trait associations. Most of the identified resistance loci were coincident with previously identified rust resistance genes/QTLs; however, six regions detected on chromosomes 1B, 5A, 5B, 6B, and 7B may be novel. Availability of the reference genome sequence of wild emmer wheat accession Zavitan facilitated the search for candidate resistance genes in the regions where QTLs were identified, and many of them were annotated as NOD (nucleotide binding oligomerization domain)-like receptor (NLR) genes or genes related to broad spectrum resistance.

Characterization of an Integrated Active Glu-1Ay Allele in Common Wheat from Wild Emmer and Its Potential Role in Flour Improvement.

Glu-1Ay, one of six genes encoding a high molecular weight glutenin subunit (HMW-GS), is frequently silenced in hexaploid common wheat. Here, an active allele of Glu-1Ay was integrated from wild emmer wheat (Triticum turgidum ssp. dicoccoides) accession D97 into the common wheat (Triticum aestivum) cultivar Chuannong 16 via the repeated self-fertilization of the pentaploid interspecific hybrid, culminating in the selection of a line TaAy7-40 shown to express the wild emmer Glu-1Ay allele. The open reading frame of this allele was a 1830 bp long sequence, demonstrated by its heterologous expression in Escherichia coli to encode a 608-residue polypeptide. Its nucleotide sequence was 99.2% identical to that of the sequence within the wild emmer parent. The TaAy7-40 introgression line containing the active Glu-1Ay allele showed higher protein content, higher sodium dodecyl sulfate (SDS) sedimentation value, higher content of wet gluten in the flour, higher grain weight, and bigger grain size than Chuannong 16. The end-use quality parameters of the TaAy7-40 were superior to those of the medium gluten common wheat cultivars Mianmai 37 and Neimai 9. Thus, the active Glu-1Ay allele might be of potential value in breeding programs designed to improve wheat flour quality.

Transposable elements generate population-specific insertional patterns and allelic variation in genes of wild emmer wheat (Triticum turgidum ssp. dicoccoides)

BackgroundNatural populations of the tetraploid wild emmer wheat (genome AABB) were previously shown to demonstrate eco-geographically structured genetic and epigenetic diversity. Transposable elements (TEs) might make up a significant part of the genetic and epigenetic variation between individuals and populations because they comprise over 80% of the wild emmer wheat genome. In this study, we performed detailed analyses to assess the dynamics of transposable elements in 50 accessions of wild emmer wheat collected from 5 geographically isolated sites. The analyses included: the copy number variation of TEs among accessions in the five populations, population-unique insertional patterns, and the impact of population-unique/specific TE insertions on structure and expression of genes.ResultsWe assessed the copy numbers of 12 TE families using real-time quantitative PCR, and found significant copy number variation (CNV) in the 50 wild emmer wheat accessions, in a population-specific manner. In some cases, the CNV difference reached up to 6-fold. However, the CNV was TE-specific, namely some TE families showed higher copy numbers in one or more populations, and other TE families showed lower copy numbers in the same population(s).Furthermore, we assessed the insertional patterns of 6 TE families using transposon display (TD), and observed significant population-specific insertional patterns. The polymorphism levels of TE-insertional patterns reached 92% among all wild emmer wheat accessions, in some cases. In addition, we observed population-specific/unique TE insertions, some of which were located within or close to protein-coding genes, creating allelic variations in a population-specific manner. We also showed that those genes are differentially expressed in wild emmer wheat.ConclusionsFor the first time, this study shows that TEs proliferate in wild emmer wheat in a population-specific manner, creating new alleles of genes, which contribute to the divergent evolution of homeologous genes from the A and B subgenomes.

Identification and mapping of MLIW30, a novel powdery mildew resistance gene derived from wild emmer wheat

Powdery mildew, caused by Blumeria graminis f.sp. tritici (Bgt), is a destructive foliar disease of common wheat in areas with cool or maritime climates. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the progenitor of both domesticated tetraploid durum wheat and hexaploid bread wheat, harbors abundant genetic diversity related to resistance to powdery mildew that can be utilized for wheat improvement. An F2 segregating population was obtained from a cross between resistant bread wheat line 2L6 and susceptible cultivar Liaochun 10, after which genetic analysis of F2 and F2-derived F3 families was performed by inoculating plants with isolate Bgt E09. The results of this experiment demonstrated that powdery mildew resistance in 2L6, which was derived from wild emmer wheat accession IW30, was controlled by a single dominant gene, temporarily designated MLIW30. Nineteen SSR markers and two STS markers linked with MLIW30 were acquired by applying bulked segregant analysis. Finally, MLIW30 was located to the long arm of chromosome 4A and found to be flanked by simple sequence repeat markers XB1g2000.2 and XB1g2020.2 at 0.1 cM. Because no powdery mildew resistance gene in or derived from wild emmer wheat has been reported in wheat chromosome 4A, MLIW30 might be a novel Pm gene.

Flour Quality and Related Molecular Characterization of High Molecular Weight Glutenin Subunit Genes from Wild Emmer Wheat Accession TD-256.

To clarify the effect of high molecular weight glutenin subunit (HMW-GS) from wild emmer wheat on flour quality, which has the same mobility as that from common wheat, the composition and molecular characterization of HMW-GS from wild emmer wheat accession TD-256, as well as its flour quality, were intensively analyzed. It is found that the mobilities of Glu-A1 and Glu-B1 subunits from TD-256 are consistent with those of bread wheat cv. 'XiaoYan 6'. Nevertheless, dough rheological properties of TD-256 reveal its poor flour quality. In the aspect of molecular structure from HMW-GS, only two conserved cysteine residues can be observed in the deduced protein sequence of 1Bx14* from TD-256, while most Glu-1Bx contain four conserved cysteine residues. In addition, as can be predicted from secondary structure, the quantity both of α-helixes and their amino acid residues of the subunits from TD-256 is fewer than those of common wheat. Though low molecular weight glutenin subunit (LMW-GS) and gliadin can also greatly influence flour quality, the protein structure of the HMW-GS revealed in this work can partly explain the poor flour quality of wild emmer accession TD-256.

Special HMW-GSs and their genes of Triticum turgidum subsp. dicoccoides accession D141 and the potential utilization in common wheat

High molecular weight glutenin subunits (HMW-GSs) are the critical components of wheat seed storage proteins. They play a crucial role in determining dough viscoelastic properties and end-use quality of wheat flour. To investigate the potential utilization of the special HMW-GSs from wild emmer wheat (2n = 4x = 28, AABB) accession D141 in common wheat (2n = 6x = 42, AABBDD), continued to our previous report of the 1Ay and its coding sequence, the other three HMW-GSs, 1Ax, 1Bx13.1 and 1By16.1, and their coding genes were isolated, characterized and transferred from D141. The 1Ax gene was silent because of containing a premature stop codon TGA at position 835–837. The ORFs of 1Bx13.1 and 1By16.1 were 2373 and 2157 bp in length, and encoded 789 and 717 amino acid residues, respectively. Compared with the other 20 Glu-1Bx alleles in GenBank, seven SNPs and one 18-bp deletion were detected in 1Bx13.1. Compared with the other 10 Glu-1By alleles in GenBank, nine SNPs were observed in 1By16.1. The mobility of 1Bx13.1 and 1By16.1 on the SDS-PAGE gel was most similar to that of 1Bx13 and 1By16 from common wheat (T. aestivum, 2n = 6x = 42, AABBDD) cv. ‘Jimai 20′, respectively. Protein secondary structure prediction showed that the combination of 1Bx13.1 + 1By16.1 possessed more α-helixes with more amino acid residues than that of 1Bx13 + 1By16. It suggested that 1Bx13.1 + 1By16.1 from wild emmer accession D141 might have more positive effects on bread-making quality than the superior subunit combination 1Bx13 + 1By16. The HMW-GS composition analysis of F1 and F2 between common wheat for female and wild emmer accession D141 for male, indicated that the special HMW-GSs from wild emmer accession D141 could be easily introduced into common wheat (2n = 42) by general inter-species hybridization.

Analysis of dough rheological property and gluten quality characteristics in wild emmer wheat (Triticum dicoccoides (Körn. ex Asch. et Graebn.) Schweinf.)

Improvement of flour quality is one of the main objectives in the process of wheat breeding. It is supposed that wild emmer wheat can provide a lot of genetic variants of the endosperm storage proteins in enhancing bread-making quality. However, the flour quality of wild emmer wheat itself, which is generally believed to be poor, is lack of awareness yet. In this work, dough rheological properties of 27 accessions of wild emmer wheat were intensively analyzed through the micro-doughlab. The results showed that the mean values of water absorption (WA), development time, stability time (ST), and degree of softening (four dough rheological parameters) for all the samples were 77.2 %, 1.73, 1.68 min and 116.6 BU, respectively. Surprisingly, the coefficient of variation of ST was apparently higher than those of the other three listed parameters, indicating that there may be a large difference among the flour quality of wild emmer wheat. Based on the four dough rheological parameters mentioned above, the cluster analysis of the 27 accessions of wild emmer wheat revealed good flour quality in some test materials, while majority of them showed poor property. Typically, two accessions of TD-129 and TD-51, with significantly different flour quality, are selected and systematically analyzed to deeply understand the flour quality of wild emmer wheat. It is exciting to find that the main quality parameters of TD-129 reach the normal level or even the strong gluten quality in absence of wheat D genome, with the values of WA, ST, Mid-line peak time, angle of descent and gluten index reaching 74.55 %, 9.55, 2.63 min, 12° and 46.5 %, respectively. These results imply that the endosperm storage proteins of TD-129 might contain valuable high-quality genes, which could be transferred to bread wheat in an attempt to improve baking quality.

Mapping the glaucousness suppressor Iw1 from wild emmer wheat “PI 481521”

Many species of Triticeae display a glaucous phenotype. In wheat, glaucousness/waxiness on spikes, leaves and shoots is controlled by wax production genes (W loci) and epistatic inhibitors (Iw loci). In this study, a suppressor of glaucousness from wild emmer wheat (Triticum turgidum ssp. dicoccoides) accession “PI 481521” was investigated in a pair of durum (T. turgidum ssp. durum cv. “Langdon”, LDN)—wild emmer wheat chromosome substitution lines, LDN and “LDNDIC521-2B”. Genetic analysis revealed that the non-glaucous phenotype of LDNDIC521-2B was controlled by the dominant glaucous suppressor Iw1 on the short arm of chromosome 2B. In total, 371 2B-specific marker differences were identified between LDN and LDNDIC521-2B. The location of the Iw1 gene was mapped using an F2 population that stemmed from LDN and LDNDIC521-2B, generating a partial linkage map that included 19 simple sequence repeats (SSR) and ten gene-based markers. On the current map, the Iw1 gene was located within the Xgwm614–BE498111 interval, and cosegregated with BQ788707, CD893659, CD927782, CD938589, and Xbarc35. Mapping of Iw1 in LDNDIC521-2B, a publically accessible and widely distributed line, will provide valuable information for marker-assisted selection of the agronomically important trait of glaucousness.

Characterization of wild emmer wheat Triticum dicoccoides germplasm for vernalization alleles

The flowering in winter and wild wheats is induced by extended exposure to cold temperatures, a process called vernalization while spring wheats do not have any such requirement. In the present study, we analyzed 45 accessions of wild emmer wheat T. dicoccoides for the allelic composition of the vernalization genes at VRN-A1 and VRN-B1 loci. Three gene based markers for VRN-A1 and two for VRN-B1 locus were used. Thirty five T. dicoccoides accessions had only winter type allele vrn-A1 at VRN-A1 locus. One accession each had VRN-A1a and Vrn-A1d allele, and two accessions each showed the presence of VRN-A1b and Vrn-A1c, potent spring type alleles. Three accessions, however, had multiple alleles at VRN-A1 locus. At the VRN-B1 locus 35 accessions had winter type allele vrn-B1 and 10 accession had dominant Vrn-B1 allele. These T. dicoccoides accessions constitute a very useful resource for incorporation of alternative vernalization alleles in the cultivated wheat gene pool for developing better adaptive wheat varieties.

Wheat in the Mediterranean revisited--tetraploid wheat landraces assessed with elite bread wheat Single Nucleotide Polymorphism markers.

BackgroundSingle Nucleotide Polymorphism (SNP) panels recently developed for the assessment of genetic diversity in wheat are primarily based on elite varieties, mostly those of bread wheat. The usefulness of such SNP panels for studying wheat evolution and domestication has not yet been fully explored and ascertainment bias issues can potentially affect their applicability when studying landraces and tetraploid ancestors of bread wheat. We here evaluate whether population structure and evolutionary history can be assessed in tetraploid landrace wheats using SNP markers previously developed for the analysis of elite cultivars of hexaploid wheat.ResultsWe genotyped more than 100 tetraploid wheat landraces and wild emmer wheat accessions, some of which had previously been screened with SSR markers, for an existing SNP panel and obtained publically available genotypes for the same SNPs for hexaploid wheat varieties and landraces. Results showed that quantification of genetic diversity can be affected by ascertainment bias but that the effects of ascertainment bias can at least partly be alleviated by merging SNPs to haplotypes. Analyses of population structure and genetic differentiation show strong subdivision between the tetraploid wheat subspecies, except for durum and rivet that are not separable. A more detailed population structure of durum landraces could be obtained than with SSR markers. The results also suggest an emmer, rather than durum, ancestry of bread wheat and with gene flow from wild emmer.ConclusionsSNP markers developed for elite cultivars show great potential for inferring population structure and can address evolutionary questions in landrace wheat. Issues of marker genome specificity and mapping need, however, to be addressed. Ascertainment bias does not seem to interfere with the ability of a SNP marker system developed for elite bread wheat accessions to detect population structure in other types of wheat.

Transfer and mapping of a gene conferring later-growth-stage powdery mildew resistance in a tetraploid wheat accession

Wheat powdery mildew is a severe foliar disease and causes significant yield losses in epidemic years. Breeding and using resistant cultivars is the most widely employed strategy to curb this disease. To identify and transfer powdery mildew resistance genes in wild emmer wheat accession TA1410 into common wheat, a resistant F3 line derived from the cross of TA1410 × durum wheat line Zhongyin1320 was crossed with common wheat cultivar Yangmai158. The homozygous resistant BC5F2 lines derived from the backcross with Yangmai158 exhibited susceptibility at seedling stage and conferred increasing resistance when the plants were closer to heading stage. In two segregating BC5F3 families investigated at heading stage, the segregation of the resistance fit a 3:1 ratio, suggesting that a single dominant gene controls the resistance. This resistance gene, designated HSM1, was mapped to the 0.6-cM Xmag5825.1–Xgwm344 interval on chromosome 7AL and co-segregated with Xrga-C3 and Xrga-C6. A mapping position comparison with other powdery mildew resistance genes on this chromosome suggested that HSM1 belongs to the Pm1 resistance gene cluster. HSM1 is a useful candidate gene for resistance breeding, particularly in winter-wheat growing areas.

A possible breakage of linkage disequilibrium between mitochondrial and chloroplast genomes during Emmer and Dinkel wheat evolution

In wheat (Triticum) and Aegilops, chloroplast and mitochondrial genomes have been studied for over three decades to clarify the phylogenetic relationships among species, and most of the maternal lineages of polyploid species have been clarified. Mitochondrial genomes of Emmer (tetraploid with nuclear genome AABB) and Dinkel (hexaploid with AABBDD) wheat are classified into two different types, VIIa and VIIb, by the presence-absence of the third largest HindIII fragment (named H3) in the mitochondrial DNA. Although the mitochondrial genome in the genera often provides useful information to clarify the phylogenetic relationship among closely related species, the phylogenetic significance of this dimorphism has yet not been clarified. In this study, to facilitate analysis using a large number of accessions, a sequence characterized amplified region (SCAR) marker that distinguishes the type VIIb mitochondrial genome from type VIIa was first developed. Mitochondrial genome type was determined for each of 30 accessions of wild and cultivated Emmer wheat and 25 accessions of Dinkel wheat. The mitochondrial genome type for each accession was compared with the plastogroup that had been determined using chloroplast microsatellite markers. Unexpectedly, the distribution of mitochondrial genome type was not in accordance with that of the plastogroups, suggesting occasional paternal leakage of either the mitochondrial or chloroplast genome during speciation and differentiation of Emmer and Dinkel wheat. An alternative possibility that substoichiometric shifting is involved in the observed dimorphism of the mitochondrial genome is also discussed.