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.     

Genome-wide association mapping reveals a rich genetic architecture of stripe rust resistance loci in emmer wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> ssp. <Emphasis Type="Italic">dicoccum</Emphasis>)

Key message

SNP-based genome scanning in worldwide domesticated emmer germplasm showed high genetic diversity, rapid linkage disequilibrium decay and 51 loci for stripe rust resistance, a large proportion of which were novel.

Abstract

Cultivated emmer wheat (Triticum turgidum ssp. dicoccum), one of the oldest domesticated crops in the world, is a potentially rich reservoir of variation for improvement of resistance/tolerance to biotic and abiotic stresses in wheat. Resistance to stripe rust (Puccinia striiformis f. sp. tritici) in emmer wheat has been under-investigated. Here, we employed genome-wide association (GWAS) mapping with a mixed linear model to dissect effective stripe rust resistance loci in a worldwide collection of 176 cultivated emmer wheat accessions. Adult plants were tested in six environments and seedlings were evaluated with five races from the United States and one from Italy under greenhouse conditions. Five accessions were resistant across all experiments. The panel was genotyped with the wheat 90,000 Illumina iSelect single nucleotide polymorphism (SNP) array and 5106 polymorphic SNP markers with mapped positions were obtained. A high level of genetic diversity and fast linkage disequilibrium decay were observed. In total, we identified 14 loci associated with field resistance in multiple environments. Thirty-seven loci were significantly associated with all-stage (seedling) resistance and six of them were effective against multiple races. Of the 51 total loci, 29 were mapped distantly from previously reported stripe rust resistance genes or quantitative trait loci and represent newly discovered resistance loci. Our results suggest that GWAS is an effective method for characterizing genes in cultivated emmer wheat and confirm that emmer wheat is a rich source of stripe rust resistance loci that can be used for wheat improvement.

     

Mechanisms,origin and heredity of Glu-1Ay silencing in wheat evolution and domestication

Key message

Allotetraploidization drives Glu-1Ay silencing in polyploid wheat.

Abstract

The high-molecular-weight glutenin subunit gene, Glu-1Ay, is always silenced in common wheat via elusive mechanisms. To investigate its silencing and heredity during wheat polyploidization and domestication, the Glu-1Ay gene was characterized in 1246 accessions containing diploid and polyploid wheat worldwide. Eight expressed Glu-1Ay alleles (in 71.81% accessions) and five silenced alleles with a premature termination codon (PTC) were identified in Triticum urartu; 4 expressed alleles (in 41.21% accessions), 13 alleles with PTCs and 1 allele with a WIS 2-1A retrotransposon were present in wild tetraploid wheat; and only silenced alleles with PTC or WIS 2-1A were in cultivated tetra- and hexaploid wheat. Both the PTC number and position in T. urartu Glu-1Ay alleles (one in the N-terminal region) differed from its progeny wild tetraploid wheat (1–5 PTCs mainly in the repetitive domain). The WIS 2-1A insertion occurred?~?0.13 million years ago in wild tetraploid wheat, much later than the allotetraploidization event. The Glu-1Ay alleles with PTCs or WIS 2-1A that arose in wild tetraploid wheat were fully succeeded to cultivated tetraploid and hexaploid wheat. In addition, the Glu-1Ay gene in wild einkorn inherited to cultivated einkorn. Our data demonstrated that the silencing of Glu-1Ay in tetraploid and hexaploid wheat was attributed to the new PTCs and WIS 2-1A insertion in wild tetraploid wheat, and most silenced alleles were delivered to the cultivated tetraploid and hexaploid wheat, providing a clear evolutionary history of the Glu-1Ay gene in the wheat polyploidization and domestication processes.

     

Development of an integrated linkage map of einkorn wheat and its application for QTL mapping and genome sequence anchoring

Key message

An integrated genetic map was constructed for einkorn wheat A genome and provided valuable information for QTL mapping and genome sequence anchoring.

Abstract

Wheat is one of the most widely grown food grain crops in the world. The construction of a genetic map is a key step to organize biologically or agronomically important traits along the chromosomes. In the present study, an integrated linkage map of einkorn wheat was developed using 109 recombinant inbred lines (RILs) derived from an inter sub-specific cross, KT1-1 (T. monococcum ssp. boeoticum) × KT3-5 (T. monococcum ssp. monococcum). The map contains 926 molecular markers assigned to seven linkage groups, and covers 1,377 cM with an average marker interval of 1.5 cM. A quantitative trait locus (QTL) analysis of five agronomic traits identified 16 stable QTL on all seven chromosomes, except 6A. The total phenotypic variance explained by these stable QTL using multiple regressions varied across environments from 8.8 to 87.1 % for days to heading, 24.4–63.0 % for spike length, 48.2–79.6 % for spikelet number per spike, 13.1–48.1 % for plant architecture, and 12.2–26.5 % for plant height, revealing that much of the RIL phenotypic variation had been genetically dissected. Co-localizations of closely linked QTL for different traits were frequently observed, especially on 3A and 7A. The QTL on 3A, 5A and 7A were closely associated with Eps-A ^m 3, Vrn1 and Vrn3 loci, respectively. Furthermore, this genetic map facilitated the anchoring of 237 T. urartu scaffolds onto seven chromosomes with a physical length of 26.15 Mb. This map and the QTL data provide valuable genetic information to dissect important agronomic and developmental traits in diploid wheat and contribute to the genetic ordering of the genome assembly.

     

Sequence divergence between spelt and common wheat

Key message

Sequence comparison between spelt and common wheat reveals that the former has huge potential in enriching the genetic variation of the latter.

Abstract

Genetic variation is the foundation of crop improvement. By comparing genome sequences of a Triticum spelta accession and one of its derived hexaploid lines with the sequences of the international reference genotype Chinese Spring, we detected variants more than tenfold higher than those present among common wheat (T. aestivum L) genotypes. Furthermore, different from the typical ‘V-shaped’ pattern of variant distribution often observed along wheat chromosomes, the sequence variation detected in this study was more evenly distributed along the 3B chromosome. This was also the case between T. spelta and the wild emmer genome. Genetic analysis showed that T. spelta and common wheat formed discrete groups. These results showed that, although it is believed that the spelt and common wheat are evolutionarily closely related and belong to the same species, a significant sequence divergence exists between them. Thus, the values of T. spelta in enriching the genetic variation of common wheat can be huge.

     

Cytogenetic and crossability studies in hulled wheat collected from Central Zagros in Iran

Underutilized hulled wheat species may be valuable sources of genes for wheat improvement. Hulled wheats of mountainous Central Zagros area of Iran are poorly studied with unclear classification status. In this study, the region was extensively searched and hulled wheats were sampled from local farmers’ fields. Cytogenetic studies of several samples revealed that these wheats are tetraploid with a chromosome number of 2n = 28. Considerable level of karyotypic resemblance was detected between these hulled wheats and durum wheat genotypes, suggesting their genomic similarity. To compare the degree of cross compatibility, F1 progenies were produced using three durum accessions and a bread wheat cultivar as female parent in crosses with two of the collected hulled wheat samples, namely Zarneh and Jonghan. The highest crossability rate was observed when Aria, a durum wheat cultivar, was used as female parent. In general, Jonghan showed higher crossability rate with both bread and durum cultivars as compared to Zarneh. The meiotic behavior of F1 genotypes was analyzed to determine genomic characteristics of hulled wheat samples. Microscopic examination of pollen mother cells at meiotic metaphase strongly suggested the AABB type genome for the hulled wheat samples. Meiotic behaviors of hybrids derived from cross with Zarneh as male parent showed more abnormalities than the other male parent. Meiotic restitution, chromosomes laggards and chromosomal bridges were noticed and the extent varied for each cross. It may be concluded that the hulled wheats of Central Zagros that are currently cultivated are mainly tetraploids emmer containing AABB genome and are crossable with durum wheat, producing hybrids mostly with normal meiotic behaviors.     

SNP-based pool genotyping and haplotype analysis accelerate fine-mapping of the wheat genomic region containing stripe rust resistance gene <Emphasis Type="Italic">Yr26</Emphasis>

Key message

NGS-assisted super pooling emerging as powerful tool to accelerate gene mapping and haplotype association analysis within target region uncovering specific linkage SNPs or alleles for marker-assisted gene pyramiding.

Abstract

Conventional gene mapping methods to identify genes associated with important agronomic traits require significant amounts of financial support and time. Here, a single nucleotide polymorphism (SNP)-based mapping approach, RNA-Seq and SNP array assisted super pooling analysis, was used for rapid mining of a candidate genomic region for stripe rust resistance gene Yr26 that has been widely used in wheat breeding programs in China. Large DNA and RNA super-pools were genotyped by Wheat SNP Array and sequenced by Illumina HiSeq, respectively. Hundreds of thousands of SNPs were identified and then filtered by multiple filtering criteria. Among selected SNPs, over 900 were found within an overlapping interval of less than 30 Mb as the Yr26 candidate genomic region in the centromeric region of chromosome arm 1BL. The 235 chromosome-specific SNPs were converted into KASP assays to validate the Yr26 interval in different genetic populations. Using a high-resolution mapping population (>?30,000 gametes), we confined Yr26 to a 0.003-cM interval. The Yr26 target region was anchored to the common wheat IWGSC RefSeq v1.0 and wild emmer WEWSeq v.1.0 sequences, from which 488 and 454 kb fragments were obtained. Several candidate genes were identified in the target genomic region, but there was no typical resistance gene in either genome region. Haplotype analysis identified specific SNPs linked to Yr26 and developed robust and breeder-friendly KASP markers. This integration strategy can be applied to accelerate generating many markers closely linked to target genes/QTL for a trait of interest in wheat and other polyploid species.

     

<Emphasis Type="Italic">VRN1</Emphasis> genes variability in tetraploid wheat species with a spring growth habit

Background

Vernalization genes VRN1 play a major role in the transition from vegetative to reproductive growth in wheat. In di-, tetra- and hexaploid wheats the presence of a dominant allele of at least one VRN1 gene homologue (Vrn-A1,?Vrn-B1, Vrn-G1 or Vrn-D1) determines the spring growth habit. Allelic variation between the Vrn-1 and vrn-1 alleles relies on mutations in the promoter region or the first intron. The origin and variability of the dominant VRN1 alleles, determining the spring growth habit in tetraploid wheat species have been poorly studied.

Results

Here we analyzed the growth habit of 228 tetraploid wheat species accessions and 25 % of them were spring type. We analyzed the promoter and first intron regions of VRN1 genes in 57 spring accessions of tetraploid wheats. The spring growth habit of most studied spring accessions was determined by previously identified dominant alleles of VRN1 genes. Genetic experiments proof the dominant inheritance of Vrn-A1d allele which was widely distributed across the accessions of Triticum dicoccoides. Two novel alleles were discovered and designated as Vrn-A1b.7 and Vrn-B1dic. Vrn-A1b.7 had deletions of 20 bp located 137 bp upstream of the start codon and mutations within the VRN-box when compared to the recessive allele of vrn-A1. So far the Vrn-A1d allele was identified only in spring accessions of the T. dicoccoides and T. turgidum species. Vrn-B1dic was identified in T. dicoccoides IG46225 and had 11 % sequence dissimilarity in comparison to the promoter of vrn-B1. The presence of Vrn-A1b.7 and Vrn-B1dic alleles is a predicted cause of the spring growth habit of studied accessions of tetraploid species. Three spring accessions T. aethiopicum K-19059, T. turanicum K-31693 and T. turgidum cv. Blancal possess recessive alleles of both VRN-A1 and VRN-B1 genes. Further investigations are required to determine the source of spring growth habit of these accessions.

Conclusions

New allelic variants of the VRN-A1 and VRN-B1 genes were identified in spring accessions of tetraploid wheats. The origin and evolution of VRN-A1 alleles in di- and tetraploid wheat species was discussed.

     

Genetic mapping of <Emphasis Type="Italic">Stb19</Emphasis>, a new resistance gene to <Emphasis Type="Italic">Zymoseptoria tritici</Emphasis> in wheat

Key message

A new and dominant R gene Stb19 is identified from a soft wheat cultivar ‘Lorikeet’ and was mapped on the distal region of chromosome 1DS. Two tightly linked KASP markers were also discovered and validated for molecular-assisted breeding programs.

Abstract

A new R gene, designated as Stb19, provides resistance to Zymoseptoria tritici in wheat. This new dominant gene resides on the short arm of chromosome 1D, exhibiting complete resistance to three Z. tritici isolates, WAI332, WAI251, and WAI161, at the seedling stage. A genetic linkage map, based on an F_2:3 population of ‘Lorikeet’ and ‘Summit,’ found the Stb19 gene at a 9.3 cM region on 1DS, closely linked with two Kompetitive Allele-Specific PCR markers, snp_4909967 and snp_1218021. Further, the two markers were tested and validated in another F_2:3 population and 266 different wheat accessions, which gave over 95% accuracy of resistance/susceptibility prediction. Combined with the physical location of the identified SNPs and the previous evidence of gene order on chromosome 1DS (centromere–Sr45–Sr33–Lr21–telomere), Stb19 is proposed to be located between Sr33 and Lr21. Thus, the newly discovered Stb19 along with the KASP markers represents an increase in genetic resources available for wheat breeding resistance to Z. tritici.

     

Crop introduction and accelerated island evolution: archaeobotanical evidence from ‘<Emphasis Type="Italic">Ais Yiorkis</Emphasis> and Pre-Pottery Neolithic Cyprus

Charred plant remains from the Cypriot Pre-Pottery Neolithic site of Krittou Marottou ‘Ais Yiorkis, situated in the foothills of the Troödos Mountains and dated to ca. 7500 cal. b.c., demonstrate the early introduction of two-grained einkorn (Triticum monococcum sensu lato). Grain measurements of two-grained einkorn from ‘Ais Yiorkis are compared to those from Aceramic and early Neolithic sites elsewhere in Cyprus, in northern Syria and central Europe. The grains appear to be larger than domestic grains of a later date from the Levantine mainland. Recent work by Purugganan and Fuller (Evolution 65:171–183, 2011) demonstrates a slow evolutionary rate in increasing grain size relative to the rates of evolution in wild species subject to natural selection. When the measurements of two-grained einkorn wheat from ‘Ais Yiorkis are compared with these same allochronic data the results indicate an accelerated rate in attaining larger grain size on Cyprus than on the mainland. The possibility of a domestication ‘event’ or rapid fixation of larger grain size characteristic of domesticated cereal crops in the context of an initially small island population is suggested by the colonisation by farmers of Cyprus in the Cypro-Pre-Pottery Neolithic.     

High-throughput SNP genotyping of modern and wild emmer wheat for yield and root morphology using a combined association and linkage analysis

Durum wheat (Triticum turgidum var. durum Desf.) is a major world crop that is grown primarily in areas of the world that experience periodic drought, and therefore, breeding climate-resilient durum wheat is a priority. High-throughput single nucleotide polymorphism (SNP) genotyping techniques have greatly increased the power of linkage and association mapping analyses for bread wheat, but as yet there is no durum wheat-specific platform available. In this study, we evaluate the new 384HT Wheat Breeders Array for its usefulness in tetraploid wheat breeding by genotyping a breeding population of F₆ hybrids, derived from multiple crosses between T. durum cultivars and wild and cultivated emmer wheat accessions. Using a combined linkage and association mapping approach, we generated a genetic map including 1345 SNP markers, and identified markers linked to 6 QTLs for coleoptile length (2), heading date (1), anthocyanin accumulation (1) and osmotic stress tolerance (2). We also developed a straightforward approach for combining genetic data from multiple families of limited size that will be useful for evaluating and mapping pre-existing breeding material.     

Localization of Genes Controlling Spherical Grain and Compact Ear in <Emphasis Type="Italic">Triticum antiquorum</Emphasis> Heer ex Udacz.

The inheritance of two taxonomically important characters was studied in hexaploid wheat species (2n = 6x = 42). The monogenic control of spherical grain was demonstrated for Triticum antiquorum Heer ex Udacz. The recessive gene controlling spherical grain in this species was localized to chromosome 3D by monosomic genetic analysis and was shown to be allelic to the s gene determining the same character in the endemic Indian species T. sphaerococcum Perciv. The T. antiquorum and T. sphaerococcum dominant genes controlling compact ears proved to be nonallelic to the corresponding T. compactum Host gene and were designated as C2. Problems of phylogeny and classification of hexaploid wheats are discussed.     

Specific features in using SNP markers developed for allopolyploid wheat

In this work, we analyzed 54 domestic cultivars of hexaploid (common) wheat Triticum aestivum L. (AABBDD genome) and accessions of tetraploid wheats of the Timopheevi group (AAGG) and rye Secale cereale (RR) using 21 SNP markers for common wheat. It was demonstrated that application of the SNP markers developed and verified for particular common wheat cultivars in allele-specific PCR analysis of other cultivars with different geographic origins could lead to an incorrect estimation of the similarity between the genotypes tested. The studied SNP markers of common wheat are inappropriate for analyzing genomes of other cereal species, in particular, T. timopheevii wheats and rye S. cereale.     

QTL mapping of Fusarium head blight resistance in three related durum wheat populations

Key message

The QTL Fhb1 was successfully introgressed and validated in three durum wheat populations. The novel germplasm and the QTL detected will support improvement of Fusarium resistance in durum wheat.

Abstract

Durum wheat (Triticum durum Desf.) is particularly susceptible to Fusarium head blight (FHB) and breeding for resistance is hampered by limited genetic variation within this species. To date, resistant sources are mainly available in a few wild relative tetraploid wheat accessions. In this study, the effect of the well-known hexaploid wheat (Triticum aestivum L.) quantitative trait locus (QTL) Fhb1 was assessed for the first time in durum wheat. Three F7-RIL mapping populations of about 100 lines were developed from crosses between the durum wheat experimental line DBC-480, which carries an Fhb1 introgression from Sumai-3, and the European T. durum cultivars Karur, Durobonus and SZD1029K. The RILs were evaluated in field experiments for FHB resistance in three seasons using spray inoculation and genotyped with SSR as well as genotyping-by-sequencing markers. QTL associated with FHB resistance were identified on chromosome arms 2BL, 3BS, 4AL, 4BS, 5AL and 6AS at which the resistant parent DBC-480 contributed the positive alleles. The QTL on 3BS was detected in all three populations centered at the Fhb1 interval. The Rht-B1 locus governing plant height was found to have a strong effect in modulating FHB severity in all populations. The negative effect of the semi-dwarf allele Rht-B1b on FHB resistance was compensated by combining with Fhb1 and additional resistance QTL. The successful deployment of Fhb1 in T. durum was further substantiated by assessing type 2 resistance in one population. The efficient introgression of Fhb1 represents a significant step forward for enhancing FHB resistance in durum wheat.

     

Development and validation of KASP markers for the greenbug resistance gene <Emphasis Type="Italic">Gb7</Emphasis> and the Hessian fly resistance gene <Emphasis Type="Italic">H32</Emphasis> in wheat

Key message

Greenbug and Hessian fly are important pests that decrease wheat production worldwide. We developed and validated breeder-friendly KASP markers for marker-assisted breeding to increase selection efficiency.

Abstract

Greenbug (Schizaphis graminum Rondani) and Hessian fly [Mayetiola destructor (Say)] are two major destructive insect pests of wheat (Triticum aestivum L.) throughout wheat production regions in the USA and worldwide. Greenbug and Hessian fly infestation can significantly reduce grain yield and quality. Breeding for resistance to these two pests using marker-assisted selection (MAS) is the most economical strategy to minimize losses. In this study, doubled haploid lines from the Synthetic W7984 × Opata M85 wheat reference population were used to construct linkage maps for the greenbug resistance gene Gb7 and the Hessian fly resistance gene H32 with genotyping-by-sequencing (GBS) and 90K array-based single nucleotide polymorphism (SNP) marker data. Flanking markers were closely linked to Gb7 and H32 and were located on chromosome 7DL and 3DL, respectively. Gb7-linked markers (synopGBS773 and synopGBS1141) and H32-linked markers (synopGBS901 and IWB65911) were converted into Kompetitive Allele Specific PCR (KASP) assays for MAS in wheat breeding. In addition, comparative mapping identified syntenic regions in Brachypodium distachyon, rice (Oryza sativa), and sorghum (Sorghum bicolor) for Gb7 and H32 that can be used for fine mapping and map-based cloning of the genes. The KASP markers developed in this study are the first set of SNPs tightly linked to Gb7 and H32 and will be very useful for MAS in wheat breeding programs and future genetic studies of greenbug and Hessian fly resistance.

     

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.

     

Genetic transformation of einkorn (<Emphasis Type="Italic">Triticum monococcum L.</Emphasis> ssp. monococcum L.), a diploid cultivated wheat species

Background

Domesticated einkorn (Triticum monococcum L.) is one of the oldest cultivated cereal crops in the world. Its small genome size (~?5.7 GB), low ploidy (2n?=?2x?=?14, A^mA^m) and high genetic polymorphism make this species very attractive for use as a diploid model for understanding the genomics and proteomics of Triticeae. Einkorn, however, is still a recalcitrant monocotyledonous species for the application of modern biotechnologies, including transgenesis. This paper reports the factors that may influence transgene delivery, integration, expression and inheritance in einkorn.

Results

In this study, we report the successful genetic transformation of einkorn using biolistic-mediated DNA delivery. Immature embryo-derived tissues of spring einkorn were bombarded with a plasmid containing the reporter gene GFP (green fluorescent protein) driven by the rice actin promoter (act1) and the selectable bar gene (bialaphos resistance gene) driven by the maize ubiquitin promoter (ubi1). Adjustments to various parameters such as gas pressure, microcarrier size and developmental stage of target tissue were essential for successful transient and stable transformation. Bombarded einkorn tissues are recalcitrant to regenerating plants, but certain modifications of the culture medium have been shown to increase the production of transgenic events. In various experiments, independent transgenic plants were produced at frequencies ranging from 0.0 to 0.6%. Molecular analysis, marker gene expression and herbicide treatment demonstrated that gfp/bar genes were stably integrated into the einkorn genome and successfully inherited over several generations. The transgenes, as dominant loci, segregated in both Mendelian and non-Mendelian fashion due to multiple insertions. Fertile homozygous T₁-T₂ populations of transgenic einkorn that are resistant to herbicides were selected.

Conclusion

To the best of our knowledge, this is the first report of the production of genetically modified einkorn plants. We believe that the results of our research could be a starting point for the application of the current biotechnological-based technologies, such as transgenesis and genome editing, to accelerate comparative functional genomics in einkorn and other cereals.

     

Genes <Emphasis Type="Italic">WHEAT FRIZZY PANICLE</Emphasis> and <Emphasis Type="Italic">SHAM RAMIFICATION 2</Emphasis> independently regulate differentiation of floral meristems in wheat

Background

Inflorescences of wheat species, spikes, are characteristically unbranched and bear one sessile spikelet at a spike rachis node. Development of supernumerary spikelets (SSs) at rachis nodes or on the extended rachillas is abnormal. Various wheat morphotypes with altered spike morphology, associated with the development of SSs, present an important genetic resource for studies on genetic regulation of wheat inflorescence development.

Results

Here we characterized diploid and tetraploid wheat lines of various non-standard spike morphotypes, which allowed for identification of a new mutant allele of the WHEAT FRIZZY PANICLE (WFZP) gene that determines spike branching in diploid wheat Ttiticum monococcum L. Moreover, we found that the development of SSs and spike branching in wheat T. durum Desf. was a result of a wfzp-A/TtBH-A1 mutation that originated from spontaneous hybridization with T. turgidum convar. сompositum (L.f.) Filat. Detailed characterization of the false-true ramification phenotype controlled by the recessive sham ramification 2 (shr2) gene in tetraploid wheat T. turgidum L. allowed us to suggest putative functions of the SHR2 gene that may be involved in the regulation of spikelet meristem fate and in specification of floret meristems. The results of a gene interaction test suggested that genes WFZP and SHR2 function independently in different processes during spikelet development, whereas another spike ramification gene(s) interact(s) with SHR2 and share(s) common functions.

Conclusions

SS mutants represent an important genetic tool for research on the development of the wheat spikelet and for identification of genes that control meristem activities. Further studies on different non-standard SS morphotypes and wheat lines with altered spike morphology will allow researchers to identify new genes that control meristem identity and determinacy, to elucidate the interaction between the genes, and to understand how these genes, acting in concert, regulate the development of the wheat spike.

     

Mapping of common bunt resistance gene <Emphasis Type="Italic">Bt9</Emphasis> in wheat

Key message

The Bt9 resistance locus was mapped and shown to be distinct from the Bt10 locus. New markers linked to Bt9 have been identified and may be used to breed for resistance towards the seed-borne disease.

Abstract

Increasing organic wheat production in Denmark, and in other wheat-producing areas, in conjunction with legal requirements for organic seed production, may potentially lead to a rise in common bunt occurrence. As systemic pesticides are not used in organic farming, organic wheat production systems may benefit from genetic resistances. However, little is known about the underlying genetic mechanisms and locations of the resistance factors for common bunt resistance in wheat. A double haploid (DH) population segregating for common bunt resistance was used to identify the chromosomal location of common bunt resistance gene Bt9. DH lines were phenotyped in three environments and genotyped with DArTseq and SSR markers. The total length of the resulting linkage map was 2882 cM distributed across all 21 wheat chromosomes. Bt9 was mapped to the distal end of chromosome 6DL. Since wheat common bunt resistance gene Bt10 is also located on chromosome 6D, the possibility of their co-location was investigated. A comparison of marker sequences linked to Bt9 and Bt10 on physical maps of chromosome 6D confirmed that Bt9 and Bt10 are two distinct resistance factors located at the distal (6DL) and proximal (6DS) end, respectively, of chromosome 6D. Five new SSR markers Xgpw4005-1, Xgpw7433, Xwmc773, Xgpw7303 and Xgpw362 and many SNP and PAV markers flanking the Bt9 resistance locus were identified and they may be used in the future for marker-assisted selection.

     

New data on the distribution of hybrid necrosis genes in winter bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivars

Hybrid necrosis genotypes have been identified in 125 Russian cultivars of winter bread wheat. More than half of them (56%) carry the Ne2 gene (genotype ne1ne1Ne2Ne2); others are free of necrosis genes (genotype ne1ne1ne2ne2). The possible causes of the increase in the Ne2 allele frequency and the loss of the Ne1Ne1ne2ne2 genotype in modern Russian cultivars of winter wheat are discussed. The principal component method has been used to compare the structures of the genetic diversity of cultivars differing in the hybrid necrosis genotype. It has been found that the Ne2 allele in winter wheat cultivars from northern Russia has originated from the cultivar Mironovskaya 808, whereas the cultivar Bezostaya 1 is not a source of this gene. In cultivars from southern Russia, the presence of the Ne2 allele is also mainly accounted for by the use of Mironovskaya 808 wheat in their breeding. The recessive genotype is explained by the presence of descendants of the cultivar Odesskaya 16 in the pedigrees of southern Russian winter wheats. The genetic relationship of cultivars with identical and different necrosis genotypes has been analyzed in nine regions of the Russian Federation.