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Spike architecture influences grain yield in wheat. We report the map-based cloning of a gene determining the number of spikelet nodes per spike in common wheat. The cloned gene is named TaCOL-B5 and encodes a CONSTANS-like protein that is orthologous to COL5 in plant species. Constitutive overexpression of the dominant TaCol-B5 allele but without the region encoding B-boxes in a common wheat cultivar increases the number of spikelet nodes per spike and produces more tillers and spikes, thereby enhancing grain yield in transgenic plants under field conditions. Allelic variation in TaCOL-B5 results in amino acid substitutions leading to differential protein phosphorylation by the protein kinase Ta K4. The TaCol-B5 allele is present in emmer wheat but is rare in a global collection of modern wheat cultivars.

Soil-borne wheat mosaic virus (SBWMV) causes a serious viral disease that can significantly reduce grain yield in winter wheat worldwide. Using resistant cultivars is the only feasible strategy to reduce the losses caused by SBWMV. To fine map the resistance gene Sbwm1, 205 wheat accessions was genotyped using wheat Infinium iSelect Beadchips with 90 K SNPs. Association analysis identified 35 SNPs in 12 wheat genes and one intergenic SNP in the Sbwm1 region that showed a significant association with SBWMV resistance. Those SNPs were converted into Kompetitive Allele-Specific Polymerase assays (KASP) and analyzed in two F6-derived recombinant inbred line (RIL) populations derived from the crosses between two resistant cultivars ‘Wesley’ and ‘Deliver’ and a susceptible line ‘OK03825-5403-6’. Linkage analysis mapped this gene on chromosome 5D at intervals of 5.1 cM and 3.4 cM in the two populations, respectively. The two flanking markers in both populations delimited the gene to a 620 kb region where 19 genes were annotated. Comparative analysis identified a syntenic region of 660 kb in Ae. tauschii with 18 annotated genes and a syntenic region in chromosome 1 of B. distachyon. The candidate region includes several disease resistance related genes and we identified a PTI1-like tyrosine-protein kinase 1 gene as a putative candidate gene for Sbwm1. The two flanking SNPs for Sbwm1 can effectively separate the resistant and susceptible lines in a new diversity panel of 159 wheat germplasm. The results from this study lay a solid foundation for the cloning, functional characterization and marker-assisted selection of Sbwm1.

Key message Heterogeneous Lr34 genes for leaf rust in winter wheat cultivar ‘Duster’ and KASP markers for allelic variation in exon 11 and exon 22 of Lr34. Abstract Wheat, Triticum aestivum (2n = 6x = 42, AABBDD), is a hexaploid species, and each of three homoeologous genomes A, B, and D should have one copy for a gene in its ancestral form if the gene has no duplication. Previously reported leaf rust resistance gene Lr34 has one copy on the short arm of chromosome 7D in hexaploid wheat, and allelic variation in Lr34 is in intron 4, exon 11, exon 12, or exon 22. In this study, we discovered that Oklahoma hard red winter wheat cultivar ‘Duster’ (PI 644,016) has two copies of the Lr34 gene, the resistance allele Lr34a and the susceptibility allele Lr34b. Both Lr34a and Lr34b were mapped in the same linkage group on chromosome 7D in a doubled-haploid population generated from a cross between Duster and a winter wheat cultivar ‘Billings’ which carries the susceptibility allele Lr34c. A chromosomal fragment including Lr34 and at least two neighboring genes on its proximal side but excluding genes on its distal side was duplicated in Duster. The Duster Lr34ab allele was associated with tip necrosis and increased resistance against leaf rust at adult plants in the Duster × Billings DH population tested in the field, demonstrating the function of the Duster Lr34ab allele in wheat. We have developed KASP markers for allelic variation in exon 11 and exon 22 of Lr34 in wheat. These markers can be utilized to accelerate the selection of Lr34 in wheat.

To improve the efficiency of high-density genotype data storage and imputation in bread wheat (Triticum aestivum L.), we applied the Practical Haplotype Graph (PHG) tool. The Wheat PHG database was built using whole-exome capture sequencing data from a diverse set of 65 wheat accessions. Population haplotypes were inferred for the reference genome intervals defined by the boundaries of the high-quality gene models. Missing genotypes in the inference panels, composed of wheat cultivars or recombinant inbred lines genotyped by exome capture, genotyping-by-sequencing (GBS), or whole-genome skim-seq sequencing approaches, were imputed using the Wheat PHG database. Though imputation accuracy varied depending on the method of sequencing and coverage depth, we found 92% imputation accuracy with 0.01× sequence coverage, which was slightly lower than the accuracy obtained using the 0.5× sequence coverage (96.6%). Compared to Beagle, on average, PHG imputation was ∼3.5% (P-value < 2 × 10−14) more accurate, and showed 27% higher accuracy at imputing a rare haplotype introgressed from a wild relative into wheat. We found reduced accuracy of imputation with independent 2× GBS data (88.6%), which increases to 89.2% with the inclusion of parental haplotypes in the database. The accuracy reduction with GBS is likely associated with the small overlap between GBS markers and the exome capture dataset, which was used for constructing PHG. The highest imputation accuracy was obtained with exome capture for the wheat D genome, which also showed the highest levels of linkage disequilibrium and proportion of identity-by-descent regions among accessions in the PHG database. We demonstrate that genetic mapping based on genotypes imputed using PHG identifies SNPs with a broader range of effect sizes that together explain a higher proportion of genetic variance for heading date and meiotic crossover rate compared to previous studies.

Cynodon transvaalensis Burtt‐Davy is frequently used to cross with C. dactylon Pers. in the creation of F1 hybrid cultivars that are some of the most widely used in the worldwide turf industry. However, molecular resource development in this species is limited. Accordingly, the objectives of this study were to construct a high‐density genetic map, and to identify genomic regions associated with establishment rate. In this study, we constructed the first high‐density linkage map for African bermudagrass using a genotyping by sequencing approach based on 109 S1 progenies. A total of 1,246 single nucleotide polymorphisms and 32 simple sequence repeat markers were integrated in the linkage map. The total length of nine linkage groups was 882.3 cM, with an average distance of 0.69 cM per interval. Four genomic regions were identified to be associated with sod establishment rate. The results provide important genetic resources towards understanding the genome as well as marker‐assisted selection for improving the establishment rate in bermudagrass breeding.

Programmed cell death (PCD) and apoptosis have key functions in development and disease resistance in diverse organisms; however, the induction of necrosis remains poorly understood. Here, we identified a semi-dominant mutant allele that causes the necrotic death of the entire seedling (DES) of wheat (Triticum aestivum L.) in the absence of any pathogen or external stimulus. Positional cloning of the lethal allele mDES1 revealed that this premature death via necrosis was caused by a point mutation from Asp to Asn at amino acid 441 in a nucleotide-binding leucine-rich repeat protein containing nucleotide-binding domain and leucine-rich repeats. The overexpression of mDES1 triggered necrosis and PCD in transgenic plants. However, transgenic wheat harboring truncated wild-type DES1 proteins produced through gene editing that exhibited no significant developmental defects. The point mutation in mDES1 did not cause changes in this protein in the oligomeric state, but mDES1 failed to interact with replication protein A leading to abnormal mitotic cell division. DES1 is an ortholog of Sr35, which recognizes a Puccinia graminis f. sp. tritici stem rust disease effector in wheat, but mDES1 gained function as a direct inducer of plant death. These findings shed light on the intersection of necrosis, apoptosis, and autoimmunity in plants.

Winter bread wheat (Triticum aestivum L., 2n = 6 × =42, AABBDD) cultivars “Duster” and “Billings” have occupied significant acreages in the Southern Great Plains for their outstanding yielding ability. In this study, we discovered a major quantitative trait locus (QTL) QYld.osu-1BS for grain yield in a population of 260 doubled haploid (DH) lines derived from the cross of Duster and Billings. When the population was tested under field conditions for 2 years, QYld.osu-1BS explained 13.9% and 23.5% of the total phenotypic variation. However, no crossover was observed among 40 genotyping-by-sequencing markers covering the region from the telomere to 25.3 Mb in the population of 260 DH lines. Furthermore, no crossover was observed in the region from the telomere to 18.4 Mb, when up to 4146 individual plants within F2:4 lines derived from the cross of Duster and Billings were screened. The 1BL-1RS translocation was not observed in the region with the abnormal recombination rate in Duster or Billings. Duster is a unique haplotype in the whole exome capture dataset, compared with 57 cultivars and breeding lines with various genetic backgrounds. Unique sequences of the QYld.osu-1BS allele for the higher grain yield in Duster were identified, and kompetitive allele specific PCR (KASP) markers for the unique sequences were developed for breeding of novel cultivars with increased grain yield in winter wheat.

Summary Wheat (Triticum aestivum) has low nitrogen use efficiency (NUE). The genetic mechanisms controlling NUE are unknown. Positional cloning of a major quantitative trait locus for N‐related agronomic traits showed that the vernalization gene TaVRN‐A1 was tightly linked with TaNUE1, the gene shown to influence NUE in wheat. Because of an Ala180/Val180 substitution, Ta VRN‐A1a and Ta VRN‐A1b proteins interact differentially with Ta ANR1, a protein encoded by a wheat orthologue of Arabidopsis nitrate regulated 1 (ANR1). The transcripts of both TaVRN‐A1 and TaANR1 were down‐regulated by nitrogen. TaANR1 was functionally characterized in TaANR1::RNAi transgenic wheat, and in a natural mutant with a 23‐bp deletion including 10‐bp at the 5′ end of intron 5 and 13‐bp of exon 6 in gDNA sequence in its gDNA sequence, which produced transcript that lacked the full 84‐bp exon 6. Both Ta ANR1 and Ta HOX1 bound to the Ala180/Val180 position of Ta VRN‐A1. Genetically incorporating favourable alleles from TaVRN‐A1, TaANR1 and TaHOX1 increased grain yield from 9.84% to 11.58% in the field. Molecular markers for allelic variation of the genes that regulate nitrogen can be used in breeding programmes aimed at improving NUE and yield in novel wheat cultivars.

TaVrn1, encoding a MADS-box transcription factor (TF), is the central regulator of wheat vernalization-induced flowering. Considering that the MADS-box TF usually works by forming hetero- or homodimers, we conducted yeast-two-hybrid screening and identified an SVP-like MADS-box protein TaVrt2 interacting with TaVrn1. However, the specific function of TaVrt2 and the biological implication of its interaction with TaVrn1 remained unknown. We validated the function of TaVrt2 and TaVrn1 by wheat transgenic experiments and their interaction through multiple protein-binding assays. Population genetic analysis also was used to display their interplay. Transcriptomic sequencing and chromatin immunoprecipitation assays were performed to identify their common targets. TaVrt2 and TaVrn1 are flowering promoters in the vernalization pathway and interact physically in vitro, in planta and in wheat cells. Additionally, TaVrt2 and TaVrn1 were significantly induced in leaves by vernalization, suggesting their spatio-temporal interaction during vernalization. Genetic analysis indicated that TaVrt2 and TaVrn1 had significant epistatic effects on flowering time. Furthermore, native TaVrn1 was up-regulated significantly in TaVrn1-OE (overexpression) and TaVrt2-OE lines. Moreover, TaVrt2 could bind with TaVrn1 promoter directly. A TaVrt2-mediated positive feedback loop of TaVrn1 during vernalization was proposed, providing additional understanding on the regulatory mechanism underlying vernalization-induced flowering.

The genomic revolution opened up the possibility for predicting un-tested phenotypes in schemes commonly referred as genomic selection (GS). Considering the practicality of applying GS in the line development stage of a hard red winter (HRW) wheat variety development program (VDP), effectiveness of GS was evaluated by prediction accuracy, as well as by the response to selection across field seasons that demonstrated challenges for crop improvement under significant climate variability. Important breeding targets for HRW wheat improvement in the southern Great Plains of USA, including Grain Yield, Kernel Weight, Wheat Protein content, and Sodium Dodecyl Sulfate (SDS) Sedimentation Volume as a rapid test for predicting bread-making quality, were used to estimate GS’s effectiveness across harvest years from 2014 (drought) to 2016 (normal). In general, nonparametric algorithms RKHS and RF produced higher accuracies in both same-year/environment cross validations and cross-year/environment predictions, for the purpose of line selection in this bi-parental doubled haploid (DH) population. Further, the stability of GS performance was greatest for SDS Sedimentation Volume but least for Wheat Protein content. To ensure long-term genetic gain, our study on selection response suggested that across this sample of environmental variability, and though there are cases where phenotypic selection (PS) might be still preferential, training conducted under drought stress or in suboptimal conditions could still provide an encouraging prediction outcome, when selection decisions were made in normal conditions. However, it is not advisable to use training information collected from a normal field season to predict trait performance under drought conditions. Further, the superiority of response to selection was most evident if the training population can be optimized.Core IdeasPrediction performance for winter wheat grain yield and end-use quality traits.Prediction accuracy evaluated by cross validations significantly overestimated.Non-parametric algorithms outperform, when considering cross-year predictions.Strategically designing training population improves response to selection.Response to selection varied across growing seasons/environments.

Wheat streak mosaic (WSM) is a devastating disease in the High Plains region that is advancing eastward toward lower elevations. Its control is best achieved by combining known disease resistance genes with resistance to the insect vector. A hard red winter (HRW) wheat (Triticum aestivum L.) germplasm line, OK05312 (Reg. No. GP-995, PI 670019), was co-developed by Oklahoma State University, Kansas State University, the Wheat Genetics Resource Center, and USDA-ARS and released in 2014. It possesses gene Cmc4 and confers strong resistance to the wheat curl mite (WCM, Aceria tosichella Keifer). OK05312 is an F₄–derived line from the double cross TX93V5919/KS96WGRC40//OK94P549/KS96WGRC34 and is expected to provide an improved source of Cmc4 over KS96WGRC40. OK94P549 was the parent line from which HRW cultivar Endurance was selected. OK05312 was released for its high grain yield potential in a late-maturing background with resistance to the with resistance to the wheat soil-borne mosaic–wheat spindle streak mosaic complex and acceptable milling and baking quality. Hence, OK05312 provides wheat breeders an alternative source of WCM resistance and a critical component to mitigate yield losses to WSM and other WCM-transmitted viruses.

The wheat ortholog of the rice gene OsXA21 against bacterial leaf blight showed resistance to multiple pests in bread wheat but different interacting proteins. A quantitative trait locus QYr.osu-5A on the long arm of chromosome 5A in bread wheat (Triticum aestivum L., 2n = 6x = 42; AABBDD) was previously reported to confer consistent resistance in adult plants to predominant stripe rust races, but the gene causing the quantitative trait locus (QTL) is not known. Single-nucleotide polymorphism (SNP) markers were used to saturate the QTL region. Comparative and syntenic regions between wheat and rice (Oryza sativa) were applied to identify candidate genes for QYr.osu-5A. TaXA21-A1, which is referred to as a wheat ortholog of OsXA21-like gene on chromosome 9 in rice, was mapped under the peak of the QYr.osu-5A. TaXA21-A1 not only explained the phenotypic variation in reaction to different stripe rust races but also showed significant effects on resistance to powdery mildew and Hessian fly biotype BP. The natural allelic variation resulted in the alternations of four amino acids in deduced TaXA21-A1 proteins. The interacting proteins of TaXA21-A1 were different from those identified by OsXA21 on rice chromosome 11 against bacterial leaf blight. TaXA21-A1 confers unique resistance against multiple pests in wheat but might not have common protein interactors or thus overlapping functions with OsXA21 in rice. XA21 function has diverged during evolution of cereal crops. The molecular marker developed for TaXA21-A1 would accelerate its application of the candidate gene at the QYr.osu-5A locus in wheat breeding programs.

The vernalization gene VRN-2 in winter wheat cultivars prevents flowering during the winter season, but repression can be removed by low temperature (vernalization) and winter wheat cultivars thus flower in the following spring. VRN-2 was cloned from diploid wheat but its orthologues have not been characterized or utilized in hexaploid common wheat. In this study, VRN-2 was isolated from winter wheat cultivars Jagger and 2174 that were also used to generate a RIL population for genetic mapping. Neither VRN-A2 in genome A nor VRN-D2 in genome D showed allelic variation. Two duplicated copies of VRN-B2 were isolated from 2174, but no VRN-B2 was isolated from Jagger, indicating that Jagger carried a null VRN-B2 allele. Mapping of the VRN-B2 gene indicated that both VRN-B2 copies in 2174 were tightly linked with SNPs on chromosome 4BL, indicating that the duplicated VRN-B2 genes were arranged in a tandem pattern at the same locus. The Jagger null VRN-B2 allele had no significant effect on flowering time in the segregating population. Surprisingly, identical sequences of VRN-B2 were also found in contig sequences from chromosomes 4BS, 2BS, and 5DL in IWGSC Chinese Spring genome sequences. These findings suggest that multiple events of duplication, deletion, and translocation involving VRN-B2 may have occurred in various hexaploid wheat cultivars.

Switchgrass (Panicum virgatum L.) has potential to be a major cellulosic bioenergy crop. Selection for late flowering plants will extend the vegetative growth, likely resulting in larger biomass yields. However, the genetic structure for reproductive maturity in switchgrass is undefined. Accordingly, the major objective of this study was to identify genomic regions associated with reproductive development. Two lowland populations, one consisting of 176 progeny from NL94 (♀) × SL93 (♂) and a first-generation self-fertilized population of 265 progeny from NL94, were field established in a randomized complete block design with three replications at two Oklahoma locations in 2011. Phenotypic data of reproductive maturity in the populations were collected in 2012 and 2013. Significant genetic variation for reproductive maturity was observed within the two populations. Broad-sense heritabilities were 0.46 to 0.77 and 0.28 to 0.74 for the hybrid and selfed populations, respectively. A linkage map with 178 simple sequence repeat (SSR) markers of the hybrid population constructed in this study and a pre-existing linkage map of 439 SSR markers in the selfed population were used for quantitative trait loci (QTL) characterization. QTL analyses revealed that reproductive maturity was controlled by multiple genomic regions. The QTL regions between nfsg-125 and PVE-781/782 on linkage group (LG) 2b, between PVGA-1727/1728 and PVGA-1201/1202 on LG 3b, and between PVCAG-2503/2504 and PVAAG-3253/3254 on LG 7a were associated with reproductive maturity in both populations. The markers linked to the significant QTL could be used to accelerate the development of switchgrass germplasm with later flowering to increase biomass yield.

Crop improvement is a long-term, expensive institutional endeavor. Genomic selection (GS), which uses single nucleotide polymorphism (SNP) information to estimate genomic breeding values, has proven efficient to increasing genetic gain by accelerating the breeding process in animal breeding programs. As for crop improvement, with few exceptions, GS applicability remains in the evaluation of algorithm performance. In this study, we examined factors related to GS applicability in line development stage for grain yield using a hard red winter wheat (Triticum aestivum L.) doubled-haploid population. The performance of GS was evaluated in two consecutive years to predict grain yield. In general, the semi-parametric reproducing kernel Hilbert space prediction algorithm outperformed parametric genomic best linear unbiased prediction. For both parametric and semi-parametric algorithms, an upward bias in predictability was apparent in within-year cross-validation, suggesting the prerequisite of cross-year validation for a more reliable prediction. Adjusting the training population’s phenotype for genotype by environment effect had a positive impact on GS model’s predictive ability. Possibly due to marker redundancy, a selected subset of SNPs at an absolute pairwise correlation coefficient threshold value of 0.4 produced comparable results and reduced the computational burden of considering the full SNP set. Finally, in the context of an ongoing breeding and selection effort, the present study has provided a measure of confidence based on the deviation of line selection from GS results, supporting the implementation of GS in wheat variety development. Electronic supplementary material The online version of this article (doi:10.1007/s11032-017-0715-8) contains supplementary material, which is available to authorized users.

More than half of spring wheat cultivars have a dominant Vrn-A1a allele that has an insertion of a miniature inverted-repeat transposable element (MITE) in its promoter. In this study, we found that the MITE present in the Vrn-A1a gene (MITE_VRN) is a nearly perfect palindrome and it can form highly stable hairpin loops when expressed as RNA. MITE_VRN also possessed sequences of a microRNA in Triticum aestivum (TamiR1123). The P32 labeled TamiR1123 probe detected two RNA molecules on a small RNA gel blot, one expected for MITE_VRN, and the other expected for TamiR1123. These results demonstrated that MITE_VRN was expressed as RNAs and TamiR1123 was originated from the MITE_VRN family. The isogenic line TDD carrying the dominant Vrn-A1a allele with MITE_VRN showed higher TamiR1123 and Vrn-A1a transcript levels than the isogenic line TDE carrying the recessive vrn-A1a allele without MITE_VRN. TamiR1123 were greatly up-regulated by plant age but slightly down-regulated by low temperature and short days. These findings have pointed to alternative regulatory mechanisms for plant development governed by Vrn-A1a in spring wheat.

Winter wheat requires a period of low temperatures to accelerate flowering (vernalization). This requirement could make winter wheat more vulnerable to elevated global temperature via insufficient vernalization. All known vernalization genes are cloned according to qualitative variation in vernalization requirement between spring and winter wheat, but the genes controlling quantitative variation for more or less vernalization requirement among winter wheat cultivars remain unknown. We report here that the gene for the vernalization requirement duration in winter wheat was cloned using a BC(1)F(2:3) population that segregated in a 3:1 ratio of early-flowering plants and late-flowering plants after vernalization for 3 weeks. The positional cloning of the gene for vernalization requirement duration demonstrated that this trait is controlled by TaVRN-A1 at the protein level. The Ala(180) in vrn-A1a, encoded by the dominant allele for 3-week vernalization, was mutated to Val(180) in vrn-A1b, encoded by the recessive allele for 6-week vernalization. Further studies with in vitro protein pull-down assays and immunoprecipitation analyses indicated that the mutated Val(180) in vrn-A1b protein decreased the ability to bind with TaHOX1 (the first homeobox protein in Triticum aestivum). The direct binding of TaVRN-A1 and TaHOX1 proteins was confirmed in the nucleus of living plant cells by bimolecular fluorescence complementation (BiFC) analyses. The TaHOX1 gene was found to be upregulated by low temperatures, and to have a significant genetic effect on heading date, suggesting that TaHOX1 functions in the flowering pathway in winter wheat.

A precise regulation of flowering time is critical for plant reproductive success, and therefore, a better understanding of the natural variation in genes regulating the initiation of the reproductive phase is required to develop well-adapted varieties. In both monocot and dicot species, the FLOWERING LOCUS T (FT) is a central integrator of seasonal signals perceived by the leaves. The encoded mobile protein (florigen) is transmitted to the apical meristem where it induces flowering. The FT homolog in barley (Hordeum vulgare L.), designated HvFT1, was shown to correspond to the vernalization locus VRN-H3, and natural alleles for spring and winter growth habit were identified. In this study, we demonstrate that the HvFT1 allele present in the barley genetic stock (BGS213) associated with a dominant spring growth habit carries at least four identical copies of HvFT1, whereas most barley varieties have a single copy. Increased copy number is associated with earlier transcriptional up-regulation of HvFT1 and a spring growth habit. This allele is epistatic to winter alleles for VRN-H1 and VRN-H2. Among accessions with one HvFT1 copy, haplotype differences in the HvFT1 promoter and first intron are also associated with differences in flowering time, which are modulated by genetic background. These different HvFT1 alleles can be used to develop barley varieties adapted to different or changing environments. Our results, together with studies of other wheat and barley flowering genes, show that copy number variation plays an important role in the regulation of developmental processes in the temperate cereals. © 2013 The Author(s).

Summary Molecular genetic analyses revealed that the WUSCHEL‐related homeobox (WOX) gene superfamily regulates several programs in plant development. Many different mechanisms are reported to underlie these alterations. The WOX family member STENOFOLIA (STF) is involved in leaf expansion in the eudicot Medicago truncutula. Here, we report that when this gene was ectopically expressed in a locally adapted hard red winter wheat cultivar (Triticum aestivum), the transgenic plants showed not only widened leaves but also accelerated flowering and increased chlorophyll content. These desirable traits were stably inherited in the progeny plants. STF binds to wheat genes that have the (GA)n/(CT)n DNA cis element, regardless of sequences flanking the DNA repeats, suggesting a mechanism for its pleiotropic effects. However, the amino acids between position 91 and 262 in the STF protein that were found to bind with the (GA)n motif have no conserved domain with any other GAGA‐binding proteins in animals or plants. We also found that STF interacted with a variety of proteins in wheat in yeast 2 hybrid assays. We conclude that the eudicot STF gene binds to (GA)n/(CT)n DNA elements and can be used to regulate leaf width, flowering time and chlorophyll content in monocot wheat.

Primers used in PCR reactions for identification of allelic variation at vrn-A1, VRN-B1, vrn-D3, and PPD-D1. (DOCX 18Â kb)

Nitrogen (N) and phosphorus (P) deficiencies are major yield limiting factors in many parts of the world. A greenhouse experiment was conducted to study the effects of both N and P deficiency on morphological and physiological responses of wheat cultivars with and without purple coleoptiles in three types of soils. Before the 3-leaf stage, cultivar ‘Jagger’ with greenish coleoptile showed typical green color in leaves even if grown in soils known to be deficient in N and P. After 3-leaf stage, however, ‘Jagger’ grown in the same soils exhibited purple on leaves, which was considered a typical symptom of P deficiency. Before 3-leaf stage, cultivar ‘2174’ with purplish coleoptile showed purple on the tips of leaves even if grown in a soil not deficient in P, indicating that the leaf purple color is genetically controlled. Pre-plant P but not N fertilizer application could alleviate the purple severity of young seedlings (before 3 leaf stage). Top-dressing N fertilizer could alleviate the purple severity, bu...

Winter wheat (Triticum aestivum L.) cultivars that gain commercial acceptance in the U.S. southern Great Plains must provide a definitive grain-yield advantage, season-long dependability in dual-purpose management systems, effective resistance to foliar diseases, and tolerance to soil acidity. Our objective was to corroborate each of those strengths in the hard red winter (HRW) wheat cultivar 'Duster' (Reg. No. CV-1065, PI 644016), which was released in 2006 by the Oklahoma Agricultural Experiment Station and the USDA-ARS to complement 'Endurance' (Reg. No. CV-994, PI 639233) with added dough strength and resistance to Wheat spindle streak mosaic. Duster was selected from a double cross, W0405/ NE78488//W7469C/TX81V6187, made within the former Pioneer HRW-wheat breeding program. Neither Duster nor its immediate parents are known to have a sib-pair or parent-offspring relationship with cultivars currently grown in the Great Plains. Duster is a descendent of an F 2:3 line identified in Oklahoma in 1991, from which pedigree selection produced two F 13 -derived lines that were composited to constitute breeder seed. The experimental line OK93P656H3299-2C04 was tested in the 2005 and 2006 Southern Regional Performance Nursery, where it ranked first and fifth, respectively, for mean grain yield. Data from the Oklahoma Small Grains Variety Performance Tests were primarily used herein to demonstrate competitiveness for economic traits in a wide array of environmental conditions 5 yr following Duster's release.

Yellow rust, also known as stripe rust, is caused by Puccinia striiformis Westend. f. sp. tritici Eriks (PST) and is one of the most common and persistent wheat (Triticum aestivum L.) diseases worldwide. A mapping population of recombinant inbred lines from the cross of ‘Jagger’ (moderately resistant) × ‘2174’ (moderately susceptible) was tested at three sites in Washington where predominant races PST-114 and PST116 naturally occurred, at Rossville, KS, where PST-100 was inoculated, and in Beijing, China, where a predominant Chinese stripe rust race CYR32 was inoculated on adult plants. A major quantitative trait locus for adult-plant stripe rust resistance was located on the short arm of chromosome 2A (QYr.osu-2A), where Jagger was found to carry markers for resistance gene Yr17 from Aegilops ventricosa Tausch (syn. Triticum ventricosum). Therefore, Yr17 is likely the resistance gene on chromosome 2A in Jagger. Markers for Yr17 were found to occur frequently in cultivars from the southern Great Plains but only occasionally in cultivars from other U.S. wheat regions. A novel resistance gene was mapped on the long arm of chromosome 5A (QYr.osu-5A), for which the Jagger allele showed consistent resistance to multiple races of the stripe rust pathogen. A signifi cant genetic effect of the resistance gene Lr34/Yr18 from 2174 was detected only when the population was tested with CYR32 in China. T. Fang, S. Cao, Y. Chen, B.F. Carver, and L. Yan, Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078; K.G. Campbell, USDA-ARS, Wheat Genetics, Quality, Physiology, and Disease Research Unit, Pullman, WA 99164, and Dep. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164; Z.Y. Liu, S. Li, and Z.J. Liu, Dep. of Plant Genetics & Breeding, China Agricultural Univ., Beijing 100193, China; X. Chen and A. Wan, Dep. of Plant Pathology, Washington State Univ., Pullman, WA 99164; R.L. Bowden, USDA-ARS, Hard Winter Wheat Genetics Research Unit, Manhattan, KS 66506. Received 23 Mar. 2011. *Corresponding author (liuling.yan@okstate.edu). Abbreviations: ARS, Agricultural Research Service; AUDPC, area under the disease progress curve; CAU, China Agricultural University; CIM, composite interval mapping; DS, disease severity; HRW, hard red winter; IT, infection type; LOD, logarithm of the odds; PCR, polymerase chain reaction; PST, Puccinia striiformis Westend. f. sp. tritici Eriks; QTL, quantitative trait loci; rAUDPC, relative area under the disease progress curve; RIL, recombinant inbred line; SSR, simple sequence repeat; WSU, Washington State University. Published in Crop Sci. 51:2455–2465 (2011). doi: 10.2135/cropsci2011.03.0161 Published online 1 Sept 2011. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Dual purpose wheat provides valuable forage resources for cattle in the southern Great Plains during winter. In this study, 96 recombinant inbred lines (RILs) were analyzed for variation in concentrations of 11 mineral elements in leaves. The mean concentration was 133.4 mg kg−1 for manganese (Mn) and 293 mg kg−1 for iron (Fe), being much higher than the 30 mg kg −1 recommended for each of these two minor mineral elements. Mean concentrations of zinc (Zn) (24.1 mg kg−1) and copper (Cu) (4.4 mg kg−1) were much lower than recommended concentrations. A highly significant correlation was detected between major minerals, magnesium (Mg) and calcium (Ca) (r = 0.9272**) and between minor minerals, Fe and nickel (Ni) (r = 0.8905**). Copper had no significant correlation with any minerals except Zn (r = 0.2529*), whereas Zn had significant correlations with all of the tested minerals except Cu, Mn, and Ni. The interrelations between different minerals provided information for effective selection strategy for ideal ...

A dominant allele of the vernalization gene Vrn-2 is the wild type conferring winter growth habit, whereas a recessive vrn-2 allele confers spring growth habit. The recessive vrn-2 allele is mutated due to the deletion of the complete gene (a null form) or alternation of a key amino acid in the VRN-2 protein (a nonfunctional form) in diploid wheat or tetraploid wheat. VRN-2 is also denoted ZCCT due to the presence of a zinc finger and a CCT domain in its protein. There are two paralogous ZCCT genes at the VRN-2 locus in diploid Triticum monococcum and three paralogous ZCCT genes on each of the A and B genomes in tetraploid wheat, but little is known about the allelic variation in VRN-2 in hexaploid wheat. In the study reported here, we performed a one-shot PCR to simultaneously amplify the promoter regions of the three ZCCT-1 genes from hexaploid wheat, including the 302-bp fragment from ZCCT-A1, the 294-bp fragment from ZCCT-B1, and the 320-bp fragment from ZCCT-D1. Each amplicon could be differentiated by electrophoresis in an acrylamide/bisacrylamide gel. This PCR marker for different lengths of the three ZCCT-1 genes was used to search for null alleles in hexaploid wheat. A null allele was found in each of ZCCT-A1, ZCCT-B1, and ZCCT-D1 among 74 cultivars and genetic stocks of U.S. hexaploid wheat. Among 54 Chinese wheat cultivars, breeding lines, and landraces, we identified three accessions carrying a single null allele at ZCCT-A1, three accessions carrying a null allele at ZCCT-B1, and one accession carrying a double null allele at both ZCCT-A1 and ZCCT-D1. The potential application of these natural ZCCT-1 mutant materials in wheat breeding programs and studies on the genetics of wheat is discussed.

Leaf rust, caused by Puccinia triticina Eriks, is one of the most common and persistent wheat diseases in the US Great Plains. We report that the Lr34 gene was mapped in the center of a QTL for leaf rust reaction and explained 18-35% of the total phenotypic variation in disease severity of adult plants in a Jagger x 2174 population of recombinant inbred lines (RILs) field-tested for 3 years. The sequence of the complete Lr34 gene was determined for the susceptible Jagger allele and for the resistant 2174 allele. The two alleles had exactly the same sequence as the resistant allele reported previously in Chinese Spring at three polymorphic sites in intron 4, exon 11, and exon 12. A G/T polymorphism was found in exon 22, where a premature stop codon was found in the susceptible Jagger allele (Lr34E22s), confirming a previous report, due to a point mutation compared with the resistant 2174 allele (Lr34E22r). We have experimentally demonstrated a tight association between the point mutation at exon 22 of Lr34 and leaf rust susceptibility in a segregating biparental population. A PCR marker was developed to distinguish between the Lr34E22r and Lr34E22s alleles. A survey of 33 local hard winter wheat cultivars indicated that 7 cultivars carry the Lr34E22s allele and 26 cultivars carry the Lr34E22r allele. This study significantly improves our genetic understanding of allelic variation in the Lr34 gene and provides a functional molecular tool to improve leaf rust resistance in a major US wheat gene pool.

The orderly development of winter wheat through its life cycle can be marked at three stages: stem elongation, heading date, and physiological maturity. The duration of a developmental phase between two stages is important in yield component generation. In this study the three developmental stages were characterized and 350 markers were mapped in a population of recombinant inbred lines (RILs) generated from a cross between two winter wheat cultivars (‘Jagger’ and ‘2174’). Three major QTLs were found to control variation in developmental process, and each of them was tightly associated with a known flowering gene, VRN-A1 on chromosome 5A, PPD-D1 on chromosome 2D, and VRN-D3 on chromosome 7D. The average contribution of the gene marker for each QTL to the total phenotypic variation (R2) was evaluated over 3 years. The effect of VRN-A1 ranged from 21.5% at stem elongation to 17.4% at physiological maturity. The effect of PPD-D1 was minor (6.7%) at stem elongation but increased to 29.7% at heading and 20.1% at physiological maturity. The effect of VRN-D3 was not detected at stem elongation but increased to 14.6% at heading and to 20.5% at physiological maturity. Hence, the VRN-A1 locus, the PPD-D1 locus, and the VRN-D3 locus had greatest impact on development at stem elongation, heading date, and physiological maturity, respectively. Whereas the Jagger VRN-A1 and VRN-D3 alleles accelerated development, the Jagger PPD-D1 allele delayed the developmental process due to its sensitivity to photoperiod. Our findings suggest that through the appropriate combination of alleles at these three loci one would be able to regulate the various developmental phases to accommodate different agricultural needs.

Powdery mildew significantly affects grain yield and end-use quality of winter wheat in the southern Great Plains. Employing resistance resources in locally adapted cultivars is the most effective means to control powdery mildew. Two types of powdery mildew resistance exist in wheat cultivars, i.e., qualitative and quantitative. Qualitative resistance is controlled by major genes, is race-specific, is not durable, and is effective in seedlings and in adult plants. Quantitative resistance is controlled by minor genes, is non-race-specific, is durable, and is predominantly effective in adult plants. In this study, we found that the segregation of powdery mildew resistance in a population of recombinant inbred lines developed from a cross between the susceptible cultivar Jagger and the resistant cultivar 2174 was controlled by a major QTL on the short arm of chromosome 1A and modified by four minor QTLs on chromosomes 1B, 3B, 4A, and 6D. The major QTL was mapped to the genomic region where the Pm3 gene resides. Using specific PCR markers for seven Pm3 alleles, 2174 was found to carry the Pm3a allele. Pm3a explained 61% of the total phenotypic variation in disease reaction observed among seedlings inoculated in the greenhouse and adult plants grown in the field and subjected to natural disease pressure. The resistant Pm3a allele was present among 4 of 31 cultivars currently being produced in the southern Great Plains. The genetic effects of several minor loci varied with different developmental stages and environments. Molecular markers associated with these genetic loci would facilitate incorporating genetic resistance to powdery mildew into improved winter wheat cultivars.

Responses to photoperiod and low temperature are the two primary adaptive mechanisms which enable wheat plants to synchronize developmental processes with changes in seasonal climate. In this study, the developmental process was characterized at two stages: stem length during the onset of stem elongation and heading date. These two developmental events were monitored and mapped in recombinant inbred lines (RILs) of a population generated from a cross between two complementary and locally adapted hard winter wheat cultivars. 'Intrada' undergoes stem elongation earlier but reaches heading later, whereas 'Cimarron' undergoes stem elongation later but reaches heading earlier. Variation in the developmental process in this population was associated with three major QTLs centered on Xbarc200 on chromosome 2B, PPD-D1 on chromosome 2D, and Xcfd14 on chromosome 7D. The Intrada Xbarc200 and Xcfd14 alleles and the Cimarron PPD-D1 allele accelerated both stem elongation and heading stages, or the Cimarron Xbarc200 and Xcfd14 alleles and the Intrada PPD-D1 allele delayed both stem elongation and heading stages. Integrative effects of the three QTLs accounted for 43% (initial stem length) and 68% (heading date) of the overall phenotypic variation in this population. PPD-D1 is a reasonable candidate gene for the QTL on chromosome 2D, PPD-B1 could be associated with the QTL on chromosome 2B, but VRN-D3 (=FT-D1) was not linked with the QTL on chromosome 7D, suggesting that this is a novel locus involved in winter wheat development. Because the PPD-D1 QTL was observed to interact with other two QTLs, all of these QTLs could play a role in the same pathway as involved in photoperiod response of winter wheat.

Winter wheat (Triticum spp.) varieties require long exposures to low temperatures to flower, a process called vernalization. The VRN2 locus includes two completely linked zinc finger-CCT domain genes (ZCCT1 and ZCCT2) that act as flowering repressors down-regulated during vernalization. Deletions or mutations in these two genes result in the elimination of the vernalization requirement in diploid wheat (Triticum monococcum). However, natural allelic variation in these genes has not been described so far in polyploid wheat (tetraploid Triticum turgidum and hexaploid Triticum aestivum). A tetraploid wheat population segregating for both VRN-A2 and VRN-B2 loci facilitated the characterization of different alleles. Comparisons between functional and nonfunctional alleles revealed that both ZCCT1 and ZCCT2 genes are able to confer vernalization requirement and that different ZCCT genes are functional in different genomes. ZCCT1 and ZCCT2 proteins from nonfunctional vrn2 alleles have mutations at arginine amino acids at position 16, 35, or 39 of the CCT domain. These positions are conserved between CCT and HEME ACTIVATOR PROTEIN2 (HAP2) proteins, supporting a model in which the action of CCT domains is mediated by their interactions with HAP2/HAP3/HAP5 complexes. This study also revealed natural variation in gene copy number, including a duplication of the functional ZCCT-B2 gene and deletions or duplications of the complete VRN-B2 locus. Allelic variation at the VRN-B2 locus was associated with a partially dominant effect, which suggests that variation in the number of functional ZCCT genes can be used to expand allelic diversity for heading time in polyploid wheat and, hopefully, improve its adaptation to different environments.