Genetic mapping of a novel recessive allele for non-glaucousness in wild diploid wheat <Emphasis Type="Italic">Aegilops tauschii</Emphasis>: implications for the evolution of common wheat

Cuticular wax on the aerial surface of plants has a protective function against many environmental stresses. The bluish–whitish appearance of wheat leaves and stems is called glaucousness. Most modern cultivars of polyploid wheat species exhibit the glaucous phenotype, while in a wild wheat progenitor, Ae. tauschii, both glaucous and non-glaucous accessions exist. Iw2, a wax inhibitor locus on the short arm of chromosome 2D, is the main contributor to this phenotypic variation in Ae. tauschii, and the glaucous/non-glaucous phenotype of Ae. tauschii is usually inherited by synthetic hexaploid wheat. However, a few synthetic lines show the glaucous phenotype although the parental Ae. tauschii accessions are non-glaucous. Molecular marker genotypes indicate that the exceptional non-glaucous Ae. tauschii accessions share the same genotype in the Iw2 chromosomal region as glaucous accessions, suggesting that these accessions have a different causal locus for their phenotype. This locus was assigned to the long arm of chromosome 3D using an F₂ mapping population and designated W4, a novel glaucous locus in Ae. tauschii. The dominant W4 allele confers glaucousness, consistent with phenotypic observation of Ae. tauschii accessions and the derived synthetic lines. These results implied that glaucous accessions of Ae. tauschii with the W2W2iw2iw2W4W4 genotype could have been the D-genome donor of common wheat.     

Low molecular weight glutenin subunit gene composition at <Emphasis Type="Italic">Glu</Emphasis>-<Emphasis Type="Italic">D3</Emphasis> loci of <Emphasis Type="Italic">Aegilops tauschii</Emphasis> and common wheat and a further view of wheat evolution

Key message

A comprehensive comparison of LMW-GS genes between Ae. tauschii and its progeny common wheat.

Abstract

Low molecular weight glutenin subunits (LMW-GSs) are determinant of wheat flour processing quality. However, the LMW-GS gene composition in Aegilops tauschii, the wheat D genome progenitor, has not been comprehensively elucidated and the impact of allohexaploidization on the Glu-D3 locus remains elusive. In this work, using the LMW-GS gene molecular marker system and the full-length gene-cloning method, LMW-GS genes at the Glu-D3 loci of 218 Ae. tauschii and 173 common wheat (Triticum aestivum L.) were characterized. Each Ae. tauschii contained 11 LMW-GS genes, and the whole collection was divided into 25 haplotypes (AeH01–AeH25). The Glu-D3 locus in common wheat lacked the LMW-GS genes D3-417, D3-507 and D3-552, but shared eight genes of identical open reading frame (ORF) sequences when compared to that of Ae. tauschii. Therefore, the allohexaploidization induces deletions, but exerts no influence on LMW-GS gene coding sequences at the Glu-D3 locus. 92.17% Ae. tauschii had 7-9 LMW-GSs, more than the six subunits in common wheat. The haplotypes AeH16, AeH20 and AeH23 of Ae. tauschii ssp. strangulate distributed in southeastern Caspian Iran were the main putative D genome donor of common wheat. These results facilitate the utilization of the Ae. tauschii glutenin gene resources and the understanding of wheat evolution.

     

Identification of <Emphasis Type="Italic">Pm58</Emphasis> from <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Key message

A novel powdery mildew-resistance gene, designated Pm58, was introgressed directly from Aegilops tauschii to hexaploid wheat, mapped to chromosome 2DS, and confirmed to be effective under field conditions. Selectable KASP? markers were developed for MAS.

Abstract

Powdery mildew caused by Blumeria graminis (DC.) f. sp. tritici (Bgt) remains a significant threat to wheat (Triticum aestivum L.) production. The rapid breakdown of race-specific resistance to Bgt reinforces the need to identify novel sources of resistance. The d-genome species, Aegilops tauschii, is an excellent source of disease resistance that is transferrable to T. aestivum. The powdery mildew-resistant Ae. tauschii accession TA1662 (2n?=?2x?=?DD) was crossed directly with the susceptible hard white wheat line KS05HW14 (2n?=?6x?=?AABBDD) followed by backcrossing to develop a population of 96 BC₂F₄ introgression lines (ILs). Genotyping-by-sequencing was used to develop a genome-wide genetic map that was anchored to the Ae. tauschii reference genome. A detached-leaf Bgt assay was used to screen BC₂F_4:6 ILs, and resistance was found to segregate as a single locus (χ?=?2.0, P value?=?0.157). The resistance gene, referred to as Pm58, mapped to chromosome 2DS. Pm58 was evaluated under field conditions in replicated trials in 2015 and 2016. In both years, a single QTL spanning the Pm58 locus was identified that reduced powdery mildew severity and explained 21% of field variation (P value?<?0.01). KASP? assays were developed from closely linked GBS-SNP markers, a refined genetic map was developed, and four markers that cosegregate with Pm58 were identified. This novel source of powdery mildew-resistance and closely linked genetic markers will support efforts to develop wheat varieties with powdery mildew resistance.

     

Genetic analysis of the traits introgressed from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. to bread wheat and determined by chromosome 5A genes

A winter bread wheat accession from the Arsenal collection was genetically examined to study the results of introgression, which substantially changed the physiological and morphological traits of the original spring cultivar Rodina. Apart from its winter habit, the accession was characterized by awned speltoid spikes, suggesting introgression into chromosome 5A, which carries marker genes in the order Vrn-A1-Q-B1. Genetic analysis showed that the chromosome fragment introgressed from Aegilops speltoides recombined well with the homeologous region of bread wheat chromosome 5A in the region between the Vrn-A1 and Q genes. Recombination between the Vrn-A1 and B1 genes was not detected, and it was assumed that the order of the marker genes of chromosome 5A was inverted to produce Q-Vrn-A1-B1. When the winter introgression line was crossed with Triticum spelta L., an interaction of two dominant genes determining the spike character was for the first time detected in F₁, increasing the spike length and the number of spikelets, and followed with transgression in F₂. It was assumed that Ae. speltoides had a homeoallelic speltoid gene, which was designated as Q ^S .     

Characterization of morphology and resistance to <Emphasis Type="Italic">Blumeria graminis</Emphasis> of winter triticale monosomic addition lines with chromosome 2D of <Emphasis Type="Italic">Aegilops</Emphasis><Emphasis Type="Italic">tauschii</Emphasis>

Key message

Allocation of the chromosome 2D of Ae. tauschii in triticale background resulted in changes of its organization, what is related to varied expression of genes determining agronomically important traits.

Abstract

Monosomic alien addition lines (MAALs) are crucial for transfer of genes from wild relatives into cultivated varieties. This kind of genetic stocks is used for physical mapping of specific chromosomes and analyzing alien genes expression. The main aim of our study is to improve hexaploid triticale by transferring D-genome chromatin from Aegilops tauschii × Secale cereale (2n = 4x = 28, DDRR). In this paper, we demonstrate the molecular cytogenetics analysis and SSR markers screening combined with phenotype analysis and evaluation of powdery mildew infection of triticale monosomic addition lines carrying chromosome 2D of Ae. tauschii. We confirmed the inheritance of chromosome 2D from the BC₂F₄ to the BC₂F₆ generation of triticale hybrids. Moreover, we unveiled a high variable region on the short arm of chromosome 2D, where chromosome rearrangements were mapped. These events had direct influence on plant height of hybrids what might be connected with changes at Rht8 loci. We obtained 20 semi-dwarf plants of BC₂F₆ generation carrying 2D chromosome with the powdery mildew resistance, without changes in spike morphology, which can be used in the triticale breeding programs.

     

Mapping stripe rust resistance gene <Emphasis Type="Italic">YrZH22</Emphasis> in Chinese wheat cultivar Zhoumai 22 by bulked segregant RNA-Seq (BSR-Seq) and comparative genomics analyses

Key message

A stripe rust resistance gene YrZH22 was mapped by combined BSR-Seq and comparative genomics analyses to a 5.92 centimorgan (cM) genetic interval spanning a 4 Mb physical genomic region on wheat chromosome 4BL1.

Abstract

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most destructive diseases of wheat and severely threatens wheat production worldwide. The widely grown Chinese wheat cultivar Zhoumai 22 is highly resistant to the current prevailing PST race CYR34 (V26). Genetic analysis of F_5:6 and F_6:7 recombinant inbred line (RIL) populations indicated that adult-plant stripe rust resistance in Zhoumai 22 is controlled by a single gene, temporarily designated YrZH22. By applying bulked segregant RNA-Seq (BSR-Seq), 7 SNP markers were developed and SNP mapping showed that YrZH22 is located between markers WGGB105 and WGGB112 on chromosome arm 4BL. The corresponding genomic regions of the Chinese Spring 4BL genome assembly and physical map of Aegilops tauschii 4DL were selected for comparative genomics analyses to develop nine new polymorphic markers that were used to construct a high-resolution genetic linkage map of YrZH22. YrZH22 was delimited in a 5.92 cM genetic interval between markers WGGB133 and WGGB146, corresponding to 4.1 Mb genomic interval in Chinese Spring 4BL and a 2.2 Mb orthologous genomic region in Ae. tauschii 4DL. The genetic linkage map of YrZH22 will be valuable for fine mapping and positional cloning of YrZH22, and can be used for marker-assisted selection in wheat breeding.

     

Use of foreign genetic variability to improve the quality of wheat grain

Foreign genetic variability, which is represented by different wild-growing relatives of wheat such as Ae. umbellulata (UU, 2n = 14), Ae. cylindrica (CCDD, 2n = 28), Ae. tauschii (DD, 2n = 14), Ae. ventricosa (DDUnUn, 2n = 28), Ae. variabilis (UUSS, 2n = 28), and T. palmovae (AADD, 2n = 28) is used in interspecies crossings with the wheat cultivar T. aestivum for the purpose of transferring exotic Gli/Glu alleles into the genome of the crop. As a result, a series of new exotic Gli/Glu alleles is introgressed into the genome of wheat cultivar. An essential negative as well as positive influence of the wild exotic alleles on the baking quality indicators of the flour and the consistency of the wheat endosperm is discovered in the course of the study. The new genetic material with the improved grain quality indicators is recommended for use in wheat selection.     

<Emphasis Type="Italic">Pm61</Emphasis>: a recessive gene for resistance to powdery mildew in wheat landrace Xuxusanyuehuang identified by comparative genomics analysis

Key message

A single recessive powdery mildew resistance gene Pm61 from wheat landrace Xuxusanyuehuang was mapped within a 0.46-cM genetic interval spanning a 1.3-Mb interval of the genomic region of chromosome arm 4AL.

Abstract

Epidemics of powdery mildew incited by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) have caused significant yield reductions in many wheat (Triticum aestivum)-producing regions. Identification of powdery mildew resistance genes is required for sustainable improvement of wheat for disease resistance. Chinese wheat landrace Xuxusanyuehuang was resistant to several Bgt isolates at the seedling stage. Genetic analysis based on the inoculation of Bgt isolate E09 on the F₁, F₂, and F_2:3 populations produced by crossing Xuxusanyuehuang to susceptible cultivar Mingxian 169 revealed that the resistance of Xuxusanyuehuang was controlled by a single recessive gene. Bulked segregant analysis and simple sequence repeat (SSR) mapping placed the gene on chromosome bin 4AL-4-0.80-1.00. Comparative genomics analysis was performed to detect the collinear genomic regions of Brachypodium distachyon, rice, sorghum, Aegilops tauschii, T. urartu, and T. turgidum ssp. dicoccoides. Based on the use of 454 contig sequences and the International Wheat Genome Sequence Consortium survey sequence of Chinese Spring wheat, four EST-SSR and seven SSR markers were linked to the gene. An F₅ recombinant inbred line population derived from Xuxusanyuehuang?×?Mingxian 169 cross was used to develop the genetic linkage map. The gene was localized in a 0.46-cM genetic interval between Xgwm160 and Xicsx79 corresponding to 1.3-Mb interval of the genomic region in wheat genome. This is a new locus for powdery mildew resistance on chromosome arm 4AL and is designated Pm61.

     

Analysis of 5S rDNA changes in synthetic allopolyploids <Emphasis Type="Italic">Triticum</Emphasis> × <Emphasis Type="Italic">Aegilops</Emphasis>

Changes of 5S rDNA at the early stage of allopolyploidization were investigated in three synthetic allopolyploids: Aegilops sharonensis × Ae. umbellulata (2n = 28), Triticum urartu × Ae. tauschii (2n = 28), and T. dicoccoides × Ae. tauschii (2n = 42). Fluorescent in situ hybridization (FISH) revealed quantitative changes affecting separate loci of one of the parental genomes in S₃ plants of each hybrid combination. Southern hybridization with genomic DNA of the allopolyploid T. urartu × Ae. tauschii (TMU38 × TQ27) revealed a lower intensity of signals from Ae. tauschii fragments compared with those derived from T. urartu. This confirmed the signal reduction revealed for chromosome 1D of this hybrid by FISH. Neither Southern hybridization nor PCR testing of 5–15 plants of the S₂-S₃ generations revealed an appearance of new 5S rDNA fragments or a complete disappearance of parental fragments from the allopolyploids under study. No changes were found by aligning nine 5S rDNA sequences of the allopolyploid TMU38 × TQ27 with corresponding sequences of the parental species. The similarity between one of the synthetic allopolyploids examined and a natural allopolyploid with the same genome composition points to an early formation of the 5S rDNA organization unique for each allopolyploid.     

Chromosomal structural changes and microsatellite variations in newly synthesized hexaploid wheat mediated by unreduced gametes

Allohexaploid wheat was derived from interspecific hybridization, followed by spontaneous chromosome doubling. Newly synthesized hexaploid wheat by crossing Triticum turgidum and Aegilops tauschii provides a classical model to understand the mechanisms of allohexaploidization in wheat. However, immediate chromosome level variation and microsatellite level variation of newly synthesized hexaploid wheat have been rarely reported. Here, unreduced gametes were applied to develop synthesized hexaploid wheat, NA0928, population by crossing T. turgidum ssp. dicoccum MY3478 and Ae. tauschii SY41, and further S0–S3 generations of NA0928 were assayed by sequential cytological and microsatellite techniques. We demonstrated that plentiful chromosomal structural changes and microsatellite variations emerged in the early generations of newly synthesized hexaploid wheat population NA0928, including aneuploidy with whole-chromosome loss or gain, aneuploidy with telosome formation, chromosome-specific repeated sequence elimination (indicated by fluorescence in situ hybridization) and microsatellite sequence elimination (indicated by sequencing), and many kinds of variations have not been previously reported. Additionally, we reported a new germplasm, T. turgidum accession MY3478 with excellent unreduced gametes trait, and then succeeded to transfer powdery mildew resistance from Ae. tauschii SY41 to synthesized allohexaploid wheat population NA0928, which would be valuable resistance resources for wheat improvement.     

Discovery and characterization of two new stem rust resistance genes in <Emphasis Type="Italic">Aegilops sharonensis</Emphasis>

Key message

We identified two novel wheat stem rust resistance genes, Sr-1644-1Sh and Sr-1644-5Sh in Aegilops sharonensis that are effective against widely virulent African races of the wheat stem rust pathogen.

Abstract

Stem rust is one of the most important diseases of wheat in the world. When single stem rust resistance (Sr) genes are deployed in wheat, they are often rapidly overcome by the pathogen. To this end, we initiated a search for novel sources of resistance in diverse wheat relatives and identified the wild goatgrass species Aegilops sharonesis (Sharon goatgrass) as a rich reservoir of resistance to wheat stem rust. The objectives of this study were to discover and map novel Sr genes in Ae. sharonensis and to explore the possibility of identifying new Sr genes by genome-wide association study (GWAS). We developed two biparental populations between resistant and susceptible accessions of Ae. sharonensis and performed QTL and linkage analysis. In an F₆ recombinant inbred line and an F₂ population, two genes were identified that mapped to the short arm of chromosome 1S^sh, designated as Sr-1644-1Sh, and the long arm of chromosome 5S^sh, designated as Sr-1644-5Sh. The gene Sr-1644-1Sh confers a high level of resistance to race TTKSK (a member of the Ug99 race group), while the gene Sr-1644-5Sh conditions strong resistance to TRTTF, another widely virulent race found in Yemen. Additionally, GWAS was conducted on 125 diverse Ae. sharonensis accessions for stem rust resistance. The gene Sr-1644-1Sh was detected by GWAS, while Sr-1644-5Sh was not detected, indicating that the effectiveness of GWAS might be affected by marker density, population structure, low allele frequency and other factors.

     

Tight repulsion linkage between <Emphasis Type="Italic">Sr36</Emphasis> and <Emphasis Type="Italic">Sr39</Emphasis> was revealed by genetic,cytogenetic and molecular analyses

Key message

The shortening of Aegilops speltoides segment did not facilitate recombination between stem rust resistance genes Sr36 and Sr39 . Robustness of marker rwgs28 for marker-assisted selection of Sr39 was demonstrated.

Abstract

Stem rust resistance genes Sr39 and Sr36 were transferred from Aegilops speltoides and Triticum timopheevii, respectively, to chromosome 2B of wheat. Genetic stocks RL6082 and RWG1 carrying Sr39 on a large and a shortened Ae. speltoides segments, respectively, and the Sr36-carrying Australian wheat cultivar Cook were used in this study. This investigation was planned to determine the genetic relationship between these genes. Stem rust tests on F₃ populations derived from RL6082/Cook and RWG1/Cook crosses showed tight repulsion linkage between Sr39 and Sr36. The genomic in situ hybridization analysis of heterozygous F₃ family from the RWG1/Cook population showed that the translocated segments do not overlap. Meiotic analysis on the F₁ plant from RWG1/Cook showed two univalents at the metaphase and anaphase stages in a majority of the cells indicating absence of pairing. Since meiotic pairing has been reported to initiate at the telomere, pairing and recombination may be inhibited due to very little wheat chromatin in the distal end of the chromosome arm 2BS in RWG1. The Sr39-carrying large Ae. speltoides segment transmitted preferentially in the RL6082/Cook F₃ population, whereas the Sr36-carrying T. timopheevii segment over-transmitted in the RWG1/Cook cross. Genotyping with the co-dominant Sr39- and Sr36-linked markers rwgs28 and stm773-2, respectively, matched the phenotypic classification of F₃ families. The RWG1 allele amplified by rwgs28 was diagnostic for the shortened Ae. speltoides segment and alternate alleles were amplified in 29 Australian cultivars. Marker rwgs28 will be useful in marker-assisted pyramiding of Sr39 with other genes.

     

Genetic diversity of <Emphasis Type="Italic">avenin-like b</Emphasis> genes in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss

Avenin-like storage proteins influence the rheological properties and processing quality in common wheat, and the discovery of new alleles will benefit wheat quality improvement. In this study, 13 avenin-like b alleles (TaALPb7D-A–M) were discovered in 108 Aegilops tauschii Coss. accessions. Ten alleles were reported for the first time, while the remaining three alleles were the same as alleles in other species. A total of 15 nucleotide changes were detected in the 13 alleles, resulting in only 11 amino acid changes because of synonymous mutations. Alleles TaALPb7D-E, TaALPb7D-G, and TaALPb7D-J encoded the same protein. These polymorphic sites existed in the N-terminus, Repetitive region (Left), Repetitive region (Right) and C-terminus domains, with no polymorphisms in the signal peptide sequence nor in those encoding the 18 conserved cysteine residues. Phylogenetic analysis divided the TaALPb7Ds into four clades. The Ae. tauschii alleles were distributed in all four clades, while the alleles derived from common wheat, TaALPb7D-G and TaALPb7D-C, belonged to clade III and IV, respectively. Alleles TaALPb7D-G and TaALPb7D-C were the most widely distributed, being present in nine and six countries, respectively. Iran and Turkey exhibited the highest genetic diversity with respect to TaALPb7D alleles, accessions from these countries carrying seven and six alleles, respectively, which implied that these countries were the centers of origin of the avenin-like b gene. The new alleles discovered and the phylogenetic analysis of avenin-like b genes will provide breeding materials and a theoretical basis for wheat quality improvement.     

A population of wheat multiple synthetic derivatives: an effective platform to explore,harness and utilize genetic diversity of <Emphasis Type="Italic">Aegilops tauschii</Emphasis> for wheat improvement

Key message

The multiple synthetic derivatives platform described in this study will provide an opportunity for effective utilization of Aegilops tauschii traits and genes for wheat breeding.

Abstract

Introducing genes from wild relatives is the best option to increase genetic diversity and discover new alleles necessary for wheat improvement. A population harboring genomic fragments from the diploid wheat progenitor Aegilops tauschii Coss. in the background of bread wheat (Triticum aestivum L.) was developed by crossing and backcrossing 43 synthetic wheat lines with the common wheat cultivar Norin 61. We named this population multiple synthetic derivatives (MSD). To validate the suitability of this population for wheat breeding and genetic studies, we randomly selected 400 MSD lines and genotyped them by using Diversity Array Technology sequencing markers. We scored black glume as a qualitative trait and heading time in two environments in Sudan as a quantitative trait. Our results showed high genetic diversity and less recombination which is expected from the nature of the population. Genome-wide association (GWA) analysis showed one QTL at the short arm of chromosome 1D different from those alleles reported previously indicating that black glume in the MSD population is controlled by new allele at the same locus. For heading time, from the two environments, GWA analysis revealed three QTLs on the short arms of chromosomes 2A, 2B and 2D and two on the long arms of chromosomes 5A and 5D. Using the MSD population, which represents the diversity of 43 Ae. tauschii accessions representing most of its natural habitat, QTLs or genes and desired phenotypes (such as drought, heat and salinity tolerance) could be identified and selected for utilization in wheat breeding.

     

Molecular analysis of the phylogenetic relationships among the diploid <Emphasis Type="Italic">Aegilops</Emphasis> species of the section <Emphasis Type="Italic">Sitopsis</Emphasis>

RAPD analysis was used to study the intraspecific variation and phylogenetic relationships of Sgenome diploid Aegilops species regarded as potential donors of the B genome of cultivated wheat. In total, 21 DNA specimens from six S-genome diploid species were examined. On a dendrogram, Ae. speltoides and Ae. aucheri formed the most isolated cluster. Among the other species, Ae. searsii was the most distant while Ae. longissima and Ae. sharonensis were the closest species. The maximum difference between individual accessions within one species was approximately the same (0.18–0.22) in Ae. bicornis, Ae. longissima, Ae. sharonensis, and Ae. searsii. The difference between the clusters of questionable species Ae. speltoides and Ae. aucheri corresponded to the intraspecific level; the difference between closely related Ae. longissima and Ae. sharonensis corresponded to the interspecific level.     

Inheritance of the Translocation in Chromosome 2D of Common Wheat from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch with Leaf Rust Resistance Gene

The variety of common spring wheat Chelyaba 75 carries a translocation from Aegilops speltoides Tausch in the chromosome 2D, which contains the leaf rust resistance gene and gametocidal genes. The length of this translocation was determined by molecular-genetic analysis. It is shown that the long arm of chromosome 2D is completely replaced by the long arm of chromosome 2S; it is possible that translocation involves the near-centromere region of the short arm. According to molecular analysis data, the translocation from Ae. speltoides in the Chelyaba 75 variety differs from the 2S chromosome region carrying the Lr35/Sr39 genes. This makes it possible to designate the leaf rust resistance gene of the Chelyaba 75 as LrSp2. The inheritance of LrSp2 in four populations from crossing Chelyaba 75 with different varieties of common wheat was studied. Estimation of leaf rust resistance of F₂ and F₃ hybrids in field conditions (2015–2016) revealed the absence of susceptible plants. The presence of 2DS.2SL translocation in hybrid plants was confirmed by molecular analysis. The results indicate the action of the gametocidal gene localized in the 2DS.2SL translocation and the fact that its tight linkage to the LrSp2 gene is inherited in a series of generations.     

Identification and mapping of <Emphasis Type="Italic">MLIW30</Emphasis>, 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.     

Induced Homoeologous Pairing for Transfer of Useful Variability for High Grain Fe and Zn from <Emphasis Type="Italic">Aegilops kotschyi</Emphasis> into Wheat

Biofortification of bread wheat by the transfer of useful variability of high grain Fe and Zn from Aegilops kotschyi through induced homoeologous pairing is the most feasible approach to alleviate micronutrient malnutrition worldwide. Deficiency of chromosome 5B in interspecific hybrids allows homoeologous pairing and recombination of chromosomes of wheat with those of the related species. The interspecific hybrid plants without 5B chromosome showed much higher chromosome pairing than did the plants with 5B. The F₁ plants without 5B chromosome were selected and repeatedly backcrossed with wheat cultivar PBW343. The chromosome number of BC₂F₁ plants ranged from 43 to 60 with several univalents and multivalents. Molecular markers and GISH analysis confirmed the introgression of U/S chromosomes of Ae. kotschyi and their fragments in wheat. The BC₂F₂ plants showed up to 125 % increase in Fe and 158 % increase in Zn compared to PBW343 with Lr24 and Yr36. Induced homoeologous pairing in the absence of 5B was found to be an effective approach for transfer of useful variability for enhanced grain Fe and Zn content for biofortification of wheat for high grain micronutrient content.