Stem Solidness Research Articles

Untargeted metabolomics profiling of oat (Avena sativa L.) and wheat (Triticum aestivum L.) infested with wheat stem sawfly (Cephus cinctus Norton) reveals differences associated with plant defense and insect nutrition.

Wheat stem sawfly (WSS), Cephus cinctus Norton, is a major pest of common bread wheat (Triticum aestivum L.) and other cultivated cereals in North America. Planting of cultivars with solid stems has been the primary management strategy to prevent yield loss due to WSS infestation, however expression of this phenotype can vary depending on environmental conditions and solid stems hinder biological control of WSS via braconid parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck. In the hollow stems of oat (Avena sativa L.), WSS larvae experience 100% mortality before they reach late instars, but the mechanisms for this observed resistance have not been characterized. The objective of this study was to explore additional sources of resistance outside of the historic solid stem phenotype. Here, we use an untargeted metabolomics approach to examine the response of the metabolome of two cultivars of oat and four cultivars of spring wheat to infestation by WSS. Using liquid chromatography-mass spectrometry (LC-MS), differentially expressed metabolites were identified between oat and wheat which were associated with the phenylpropanoid pathway, phospholipid biosynthesis and signaling, the salicylic acid signaling pathway, indole-3-acetic acid (IAA) degradation, and biosynthesis of 1,4-benzoxazin-3-ones (Bxs). Several phospho- and galacto- lipids were found in higher abundance in oat, and with the exception of early stem solidness cultivar Conan, both species experienced a decrease in abundance once infested. In all wheat cultivars except Conan, an increase in abundance was observed for Bxs HMDBOA-glc and DIBOA-β-D-glucoside after infestation, indicating that this pathway is involved in wheat response to infestation in both solid and hollow stemmed cultivars. Differences between species in compounds involved in IAA biosynthesis, degradation and inactivation suggest that wheat may respond to infestation by inactivating IAA or altering the IAA pool in stem tissue. We propose that the species differences found here likely affect the survival of WSS larvae and may also be associated with differences in stem architecture at the molecular level. Our findings suggest pathways to focus on for future studies in elucidating plant response to WSS infestation.

HaploCatcher: An R package for prediction of haplotypes.

Wheat (Triticum aestivum L.) is crucial to global food security but is often threatened by diseases, pests, and environmental stresses. Wheat-stem sawfly (Cephus cinctus Norton) poses a major threat to food security in the United States, and solid-stem varieties, which carry the stem-solidness locus (Sst1), are the main source of genetic resistance against sawfly. Marker-assisted selection uses molecular markers to identify lines possessing beneficial haplotypes, like that of the Sst1 locus. In this study, an R package titled "HaploCatcher" was developed to predict specific haplotypes of interest in genome-wide genotyped lines. A training population of 1056 lines genotyped for the Sst1 locus, known to confer stem solidness, and genome-wide markers was curated to make predictions of the Sst1 haplotypes for 292 lines from the Colorado State University wheat breeding program. Predicted Sst1 haplotypes were compared to marker-derived haplotypes. Our results indicated that the training set was substantially predictive, with kappa scores of 0.83 for k-nearest neighbors and 0.88 for random forest models. Forward validation on newly developed breeding lines demonstrated that a random forest model, trained on the total available training data, had comparable accuracy between forward and cross-validation. Estimated group means of lines classified by haplotypes from PCR-derived markers and predictive modeling did not significantly differ. The HaploCatcher package is freely available and may be utilized by breeding programs, using their own training populations, to predict haplotypes for whole-genome sequenced early generation material.

Wheat Long Noncoding RNAs from Organelle and Nuclear Genomes Carry Conserved microRNA Precursors Which May Together Comprise Intricate Networks in Insect Responses.

Long noncoding RNAs (lncRNAs) are a diverse class of noncoding RNAs that are typically longer than 200 nucleotides but lack coding potentials. Advances in deep sequencing technologies enabled a better exploration of this type of noncoding transcripts. The poor sequence conservation, however, complicates the identification and annotation of lncRNAs at a large scale. Wheat is among the leading food staples worldwide whose production is threatened by both biotic and abiotic stressors. Here, we identified putative lncRNAs from durum wheat varieties that differ in stem solidness, a major source of defense against wheat stem sawfly, a devastating insect pest. We also analyzed and annotated lncRNAs from two bread wheat varieties, resistant and susceptible to another destructive pest, orange wheat blossom midge, with and without infestation. Several putative lncRNAs contained potential precursor sequences and/or target regions for microRNAs, another type of regulatory noncoding RNAs, which may indicate functional networks. Interestingly, in contrast to lncRNAs themselves, microRNAs with potential precursors within the lncRNA sequences appeared to be highly conserved at the sequence and family levels. We also observed a few putative lncRNAs that have perfect to near-perfect matches to organellar genomes, supporting the recent observations that organellar genomes may contribute to the noncoding transcript pool of the cell.

Evaluation of wheat stem sawfly‐resistant solid stem Qss.msub‐3BL alleles in hard red winter wheat

AbstractHost plant resistance provided by solid stems has been the most effective means for mitigating wheat stem sawfly (WSS) (Cephus cinctus Norton) damage in spring and winter wheat (Triticum aestivum L.). The solid stem trait originates from the spring wheat cultivar “Rescue” and is associated with a quantitative trait locus allele Qss.msub‐3BL.b that explains the majority of the variation for stem solidness. Recently, a new Qss.msub‐3BL solid stem allele, designated Qss.msub‐3BL.c, was identified in the spring wheat cultivar “Conan”. It produces a solid stem phenotype early in plant development but dissipates during plant growth. The Qss.msub‐3BL.c allele provides effective WSS resistance in spring wheat but has not been tested in winter wheat. To examine if the Qss.msub‐3BL.c allele provides adequate WSS resistance in winter wheat, near‐isogenic lines (NILs) were developed using marker‐assisted backcrossing. This enabled comparisons between the hollow stem Qss.msub‐3BL.a, solid stem Qss.msub‐3BL.b and solid stem Qss.msub‐3BL.c alleles for stem solidness, WSS resistance, and agronomic traits in Montana growing environments. Compared to the hollow stem allele, the NILs with the Qss.msub‐3BL.c allele increased stem solidness and reduced WSS stem cutting. However, the Qss.msub‐3BL.c allele resulted in lower solid stem scores and greater WSS stem cutting compared to the Qss.msub‐3BL.b allele. Overall, these findings indicate that the Qss.msub‐3BL.c allele failed to provide sufficient WSS resistance in the winter wheat backgrounds tested in this study.

QTL analysis identified two major all-internodes solidness loci from a completely solid-stemmed spring wheat line.

The culms of solid-stemmed wheat cultivars are filled with "pith" - a parenchymatous tissue largely composed of soft, spongy, and compact parenchyma cells. Breeding solid-stemmed cultivars is the most effective way to decrease the detrimental impact of wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae) on wheat production. Althougha major solid stem gene has been previously identified from durum wheat, it produces an intermediate level of stem solidness in common wheat which is insufficient to provide the required level of WSS resistance. The maximum resistance is achieved when stems are totally filled with pith. Thus, to identify a secondary source of solidness in common wheat, we developed three mapping populations from wheat cvs. Sadash, 'AAC Innova' and 'AAC Cameron', each crossed separatelywith P2711, a completely solid-stemmed hexaploid wheat breeding line. All populations were genotyped using either wheat 15K or 90K Infinium iSelect SNP Assay and high-density linkage maps were generated from individual populations along with consensus maps for chromosomes 3B and 3D from all populations. 'Sadash/P2711' and 'AAC Innova/P2711' populations were subjected to extensive phenotyping in ≥3 environments followed by quantitative trait loci (QTL) analyses using population-specific and consensus linkage maps. We identified two major solid stem QTLs in the distal regions of chromosome arms 3BL and 3DL in both populations in addition to several population-specific or common minor QTLs. Internode-specific QTL analyses detected both major QTLs of chromosomes 3B and 3D across internodes, from top to bottom of the stalk, but minor QTLs were largely detected in upper or middle internodes. Our results suggest that both major QTLs are sufficient to develop highly solid-stemmed cvs; however, the minor loci, which additively enhance the pith expression, can be coupled with major genes to achieve a complete solid stem phenotype in common wheat. Comparative and haplotype analyses showed that the 3B locus is homoeologous to 3D, the former being mapped to a 1.1 Mb genomic region. Major QTLs identified in this study can be incorporated in modern wheat cultivars to achieve maximum WSS resistance from high pith expression.

Unlocking the molecular basis of wheat straw composition and morphological traits through multi-locus GWAS

BackgroundRapid reductions in emissions from fossil fuel burning are needed to curb global climate change. Biofuel production from crop residues can contribute to reducing the energy crisis and environmental deterioration. Wheat is a renewable source for biofuels owing to the low cost and high availability of its residues. Thus, identifying candidate genes controlling these traits is pivotal for efficient biofuel production. Here, six multi-locus genome-wide association (ML-GWAS) models were applied using 185 tetraploid wheat accessions to detect quantitative trait nucleotides (QTNs) for fifteen traits associated with biomass composition.ResultsAmong the 470 QTNs, only 72 identified by at least two models were considered as reliable. Among these latter, 16 also showed a significant effect on the corresponding trait (p.value < 0.05). Candidate genes survey carried out within 4 Mb flanking the QTNs, revealed putative biological functions associated with lipid transfer and metabolism, cell wall modifications, cell cycle, and photosynthesis. Four genes encoded as Cellulose Synthase (CeSa), Anaphase promoting complex (APC/C), Glucoronoxylan 4-O Methyltransferase (GXM) and HYPONASTIC LEAVES1 (HYL1) might be responsible for an increase in cellulose, and natural and acid detergent fiber (NDF and ADF) content in tetraploid wheat. In addition, the SNP marker RFL_Contig3228_2154 associated with the variation in stem solidness (Q.Scsb-3B) was validated through two molecular methods (High resolution melting; HRM and RNase H2-dependent PCR; rhAMP).ConclusionsThe study provides new insights into the genetic basis of biomass composition traits on tetraploid wheat. The application of six ML-GWAS models on a panel of diverse wheat genotypes represents an efficient approach to dissect complex traits with low heritability such as wheat straw composition. The discovery of genes/genomic regions associated with biomass production and straw quality parameters is expected to accelerate the development of high-yielding wheat varieties useful for biofuel production.

Stem solidness as an important factor for wheat protection from European wheat stem sawfly (Cephus pygmaeus L.) in Altai

Background. European wheat stem sawfly (Cephus pygmaeus L.) is the main pest of wheat in Altai Territory, Russia. Resistance of host plants to this insect is based on a solid stem. The effect of a solid stem on the infestation of wheat stem sawfly larvae and on agronomic traits of spring bread wheat under the conditions of Altai Territory has not been studied.Materials and methods. The study was conducted on the experimental field of the Federal Altai Scientific Centre of Agro-BioTechnologies, Barnaul, Russia, in 2019–2021. The index of stem solidness was assessed according to a 20 point scale. The interplay between stem solidness and wheat stem sawfly larvae infestation of wheat plants was studied on 12 genotypes. The effect of stem solidness on agronomic traits was studied on 6 pairs of sister lines. One hundred cultivars were studied for the stem solidness index and 184 cultivars were tested for their resistance to wheat stem sawfly.Results. Stem solidness negatively correlated with wheat stem sawfly infestation (Spearman’s rank correlation coefficient was rs = –0.77 in 2019 and rs = –0.80 in 2020). Sister lines with a solid stem had significantly shorter plant height (–5 cm), less kernels per spikelet (–0.11 kernels), 1000 grain weight (–1.7 g) and grain weight per spike (–0.08 g), but higher grain weight per tiller spike (+0.11 g), compared to sister lines with a hollow stem averaged over two years. Stem solidness had no negative effect on yield or grain quality. Eleven cultivars with a solid stem index higher than 15 points were identified (‘Ershovskaya 33’, ‘Izera’, ‘Kvintus’, ‘KWS Akvilon’, ‘Tybalt’, ‘Cunningham’, ‘KW 240-3-13’, ‘KWS 3.13’, ‘Lillian’, ‘Sparrow’, ‘WW-4’).Conclusion. Stem solidness significantly decreases the damage from wheat stem sawfly and has no negative effect on yield or gluten and protein content in grain. The abovementioned cultivars with a solid stem are recommended for use in breeding for resistance to wheat stem sawfly.

Development and identification of four new synthetic hexaploid wheat lines with solid stems

Stem solidness is an important agronomic trait for increasing the ability of wheat to resist lodging. In this study, four new synthetic hexaploid wheat with solid stems were developed from natural chromosome doubling of F1 hybrids between a solid-stemmed durum wheat (Triticum turgidum ssp. durum, 2n = 4x = 28, AABB) and four Aegilops tauschii (2n = 2x = 14, DD) accessions. The solid expression of the second internode at the base of the stem was stable for two synthetic hexalpoid wheat Syn-SAU-117 and Syn-SAU-119 grown in both the greenhouse and field. The lodging resistance of four synthetic solid-stem wheats is stronger than that of CS, and Syn-SAU-116 has the strongest lodging resistance, followed by Syn-SAU-119. The paraffin sections of the second internode showed that four synthetic wheat lines had large outer diameters, well-developed mechanical tissues, large number of vascular bundles, and similar anatomical characteristics with solid-stemmed durum wheat. The chromosomal composition of four synthetic hexaploid wheat was identified by FISH (fluorescence in situ hybridization) using Oligo-pSc119.2-1 and Oligo-pTa535-1. At adult stage, all four synthetic hexaploid wheat showed high resistance to mixed physiological races of stripe rust pathogen (CYR31, CYR32, CYR33, CYR34). These synthetic hexaploid wheat lines provide new materials for the improvement of common wheat.

Variability of stem solidness among miscanthus genotypes and its role on mechanical properties of polypropylene composites

AbstractMiscanthus (Miscanthus Andersson) is a perennial grass that is attracting growing interest from the biomaterial industry. Our aim was to compare miscanthus genotypes varying in stem solidness, a measure of degree to which pith fills cavity between the outer walls of the stem, and analyze whether this trait influences the mechanical properties of polypropylene composites reinforced with miscanthus particles. Six contrasting genotypes were chosen from a Miscanthus sinensis population to determine morphological variables, stem solidness, and mechanical properties of polypropylene composites including 30% of milled miscanthus particles of two sizes of 100 &lt; × &lt; 200 μm and 200 &lt; × &lt; 300 μm. Although aboveground biomass of miscanthus was closely related to the aboveground volume of the plant, namely stand volume, a few genotypes showed contrasting aboveground biomass production for similar stand volumes. This generated contrasting ratio between aboveground biomass and stand volume, namely plant‐specific weights, for similar plant volumes. A principal component analysis showed that fully pith‐filled stems, namely solid stems, were explained by a large stand volume and plant‐specific weights as well as small stem cross‐sections. Genotypes showing partially filled stems were taller with larger stem cross‐sections but smaller plant‐specific weights. They revealed high lignin and p‐coumaric acid contents. Compared to neat‐polypropylene, Young's modulus increased significantly by 139% and 134% and tensile strength by 39% and 36% for genotypes with partially filled stems compared to genotypes with fully pith‐filled stems, respectively. This difference in reinforcing capacity was similar to that of two particle sizes (139% and 134% for Young's modulus, 41% and 34% for tensile strength, respectively). A good tensile strength was obtained with large cross‐stem section, plant height and lignin and p‐coumaric acid contents. It decreased with plant‐specific weight, hemicellulose and ferulic acid contents. Wider morphological variations in other progenies or Miscanthus species should be explored further using the techniques reported here.

Stability analysis of stem solidness, grain yield, and grain protein concentration in spring wheat

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of wheat (Triticum aestivum L.) in the northern Great Plains, where it is a constant threat in Montana and is resurging in Alberta, Saskatchewan, and North Dakota. Adoption of solid-stemmed cultivars is an important management tool for wheat growers; however, the inconsistent pith expression first noted with the release of ‘Rescue’ has been repeatedly observed in modern cultivars such as ‘Lillian’ in Canada. Given the extensive hectares planted to solid-stemmed wheat cultivars during an outbreak, the identification of cultivars that display stable stem solidness, grain yield, and grain protein concentration across a wide range of environments where stem sawfly infestations occur is desirable. We assessed spring wheat plant responses in eight solid-stemmed and two hollow-stemmed genotypes grown across diverse environments using multiple statistical models. Study sites included southern Alberta and Saskatchewan, Montana, and North Dakota. Most models agreed that the genotypes ‘Choteau’, ‘BW925’, and ‘Mott’ consistently displayed high and stable stem solidness concomitant with high grain yield. ‘Choteau’ and ‘BW925’ also consistently met or exceeded the desired threshold of a 3.75/5 pith rating (averaged from the lower four stem internodes) for optimum resistance, whereas ‘Mott’ developed optimal pith at a specific (early) phenological stage when resistance to wheat stem sawfly infestation is critical. Exploring the stability of stem solidness identified ideal genotypes that would enhance germplasm development efforts, which exemplifies how this approach can facilitate the selection, production, and adoption of solid-stemmed wheat cultivars in regions prone to wheat stem sawfly attack.

Genetic variation of stem characters in wheat and their relation to physiological characters and yield under drought

Stem characters such as stem solidness and stem carbohydrates (water soluble carbohydrates and non-structural carbohydrates estimated as fructan) play an important role in stabilizing grain yield in stressful environments. Ten wheat genotypes were screened for carbohydrate content (Water soluble sugars and fructan) in peduncle along with other stem parameters namely, stem solidness, grain growth rate and stem osmotic potential under irrigated and drought conditions. Data was analyzed for correlation among these parameters along with biomass and yield. The results of present study indicated that stress-tolerant genotype RIL-S1-38 and WH 1235 accumulated higher fructan content in stem and contributed in grain growth rate, reduced osmotic potential and further imparted drought tolerance. Clear differences in stem solidness and fructan content exhibited lesser grain yield reduction under drought condition.

Copy number variation of TdDof controls solid-stemmed architecture in wheat

Stem solidness is an important agronomic trait of durum (Triticum turgidum L. var. durum) and bread (Triticum aestivum L.) wheat that provides resistance to the wheat stem sawfly. This dominant trait is conferred by the SSt1 locus on chromosome 3B. However, the molecular identity and mechanisms underpinning stem solidness have not been identified. Here, we demonstrate that copy number variation of TdDof, a gene encoding a putative DNA binding with one finger protein, controls the stem solidness trait in wheat. Using map-based cloning, we localized TdDof to within a physical interval of 2.1 Mb inside the SSt1 locus. Molecular analysis revealed that hollow-stemmed wheat cultivars such as Kronos carry a single copy of TdDof, whereas solid-stemmed cultivars such as CDC Fortitude carry multiple identical copies of the gene. Deletion of all TdDof copies from CDC Fortitude resulted in the loss of stem solidness, whereas the transgenic overexpression of TdDof restored stem solidness in the TdDof deletion mutant pithless1 and conferred stem solidness in Kronos. In solid-stemmed cultivars, increased TdDof expression was correlated with the down-regulation of genes whose orthologs have been implicated in programmed cell death (PCD) in other species. Anatomical and histochemical analyses revealed that hollow-stemmed lines had stronger PCD-associated signals in the pith cells compared to solid-stemmed lines, which suggests copy number-dependent expression of TdDof could be directly or indirectly involved in the negative regulation of PCD. These findings provide opportunities to manipulate stem development in wheat and other monocots for agricultural or industrial purposes.

Registration of ‘Bobcat’ hard red winter wheat

Abstract‘Bobcat’ (Reg. no. CV‐1161, PI 693235) hard red winter (HRW) wheat (Triticum aestivum L.) was developed and released by the Montana Agricultural Experiment Station in September 2019. Bobcat is of unknown pedigree, derived from a composite of two related single crosses made in 2007: MT0598/98X366‐E29‐1 and 01X258‐C1/MT0598. MT0598 is an unreleased, hollow‐stem experimental line, and 98X366‐E29‐1 and 01X258‐C1 are unreleased, Montana solid‐stem experimental lines. Bobcat was developed using a modified bulk breeding method and selected as an F5:6 head row. Bobcat was tested under the experimental number MTS1588 from 2015 to 2019 in Montana. Quality was evaluated in multilocation Montana trials since 2015. Bobcat is a solid‐stem, high‐yielding HRW wheat cultivar with medium to high test weight, medium maturity, reduced height (Rht‐B1b), medium to high grain protein, and acceptable milling and baking quality. Bobcat was released for its improved host plant resistance to wheat stem sawfly (Cephus cinctus Nort.) conditioned by stem solidness, along with short stature, and improved yield potential relative to ‘Warhorse’, the current predominant solid‐stem cultivar in Montana.

Registration of ‘StandClear CLP’ hard red winter wheat

Abstract‘StandClear CLP’ (Reg. no. CV‐1162, PI 693236) hard red winter (HRW) wheat (Triticum aestivum L.) was developed and released by the Montana Agricultural Experiment Station and exclusively licensed to Loveland Products, Inc., in 2020. StandClear CLP is a two‐gene Clearfield, semisolid‐stem wheat intended for use with the selective imidazolinone (IMI) herbicide imazamox. StandClear CLP resulted from a cross of MTS0531 to an IMI herbicide tolerant F1 plant from a population segregating for two acetohydroxyacid synthase (AHAS) genes [TaAHAS1D and TaAHAS1B]. Original herbicide tolerance donors were IMI ‘Fidel’ (TX12588*4/FS2, BASF) for allele TaAHAS1D via descended experimental lines MTCL0309 and MTCL0510, and proprietary hard red spring wheat line CDC Teal 11A (BASF Corporation) for allele TaAHAS1B. StandClear CLP was selected as a F6:7 headrow in 2014 following multiple cycles of phenotypic mass selection for IMI herbicide tolerance and stem solidness. StandClear CLP was tested under the experimental number MTCS1601 from 2016 to 2019 in Montana for field performance, herbicide tolerance, and end‐use quality. StandClear CLP is a high‐yielding, Clearfield HRW wheat cultivar with intermediate stem solidness, moderate host plant resistance to wheat stem sawfly, and acceptable milling and baking quality.

Additive Genetic Behavior of Stem Solidness in Wheat (Triticum aestivum L.)

Stem solidness in wheat is an important architectural trait to support the erect behavior of the plant. The varieties with high yield potential due to increased sink strength tend to lodge either because of poor anchorage or weak stem. The solid stem can partially counter the tradeoff between biomass driven yield gain irrespective of the plant height. Stem solidness being a complex trait with highly variable expressivity, understanding its genetic behavior in different genetic backgrounds is highly essential to integrate this trait in the breeding program. In this study, the expressivity of a solid stem in different internodes was investigated in nine F2 populations selected from 34 F1s (solid stem × hollow stem and hollow stem × hollow stem). The progeny of solid stem type F1 plants from hollow stem parents indicated the complementation of favorable alleles dispersed among the parents. Non-confirmation to digenic complementary (9:7) model of inheritance and polynomial distribution of the trait in all F2 populations indicates multiple factors complementation in the additive fashion for stem solidness.

Comparison of Three Alleles at a Major Solid Stem QTL for Wheat Stem Sawfly Resistance and Agronomic Performance in Hexaploid Wheat

ABSTRACTSolid stems provide resistance to the wheat stem sawfly (WSS, Cephus cinctus Nort.) in wheat (Triticum aestivum L.). A major quantitative trait locus, designated Qss.msub‐3BL, controls most of the variation for stem solidness. Two alleles that differ for temporal expression of stem solidness have been identified. An allele derived from the cultivar ‘Rescue’, designated Qss.msub‐3BL.b, results in solid stems throughout stem development. An allele derived from the cultivar ‘Conan’, designated Qss.msub‐3BL.c, causes high stem solidness early in plant development, but solidness declines as the plant matures. The objective of this study was to develop near‐isogenic lines (NILs) derived from marker‐assisted backcrossing to compare the impact of Qss.msub‐3BL alleles in different genetic backgrounds on stem solidness, WSS resistance, and agronomic traits. The Conan‐derived allele Qss.msub‐3BL.c resulted in lower WSS infestation than the Rescue‐derived allele Qss.msub‐3BL.b in two genetic backgrounds. Both alleles showed a high level of early stem solidness, though this declined as the stem matured for NIL with the Conan‐derived allele. The Conan‐derived allele Qss.msub‐3BL.c resulted in lower WSS infestation and stem cutting than the allele for hollow stems in two genetic backgrounds. Based on yield trials grown over 2 yr, there were no significant differences in grain yield between the NIL pairs. Our results indicate the Conan‐derived allele at Qss.msub‐3BL results in lower infestation of WSS and does not significantly affect agronomic performance, thus providing a novel source of resistance for the development of WSS‐resistant cultivars.

A Novel QTL in Durum Wheat for Resistance to the Wheat Stem Sawfly Associated with Early Expression of Stem Solidness.

The wheat stem sawfly (WSS) (Cephus cinctus Norton) is a major yield-reducing pest of wheat (Triticum aestivum L.). Varieties with pith-filled, or solid, stems provide a measure of resistance by inhibiting larval survival inside the stem. Durum wheat (Triticum turgidum L.) has resistance to the wheat stem sawfly even in the absence of known genes for stem solidness. To determine the genetic basis of resistance in durum wheat, a susceptible durum wheat, PI 41353, was identified from among 1,211 landrace accessions from around the world screened in WSS-infested sites. A recombinant inbred line (RIL) population of 105 individuals was developed from a cross of PI 41353 with a typically resistant variety, Pierce. The RIL were screened in a total of three WSS-infested locations in Montana over a two year period. A genetic map was constructed with 2,867 SNP-based markers. A quantitative trait locus (QTL) analysis identified six QTL associated with resistance. An allele from resistant cultivar Pierce at a QTL on chromosome 3A, Qss.msub-3AL, caused a 25% reduction in stem cutting. Assessment of near-isogenic lines that varied for alleles at Qss.msub-3AL showed that the Pierce allele was also associated with higher stem solidness as measured early in stem development, which is a critical stage for WSS oviposition and larval development. Stem solidness of Pierce and other resistant durum wheat lines largely disappeared later in plant development. Results suggest a genetic mechanism for WSS resistance observed in durum wheat, and provide an additional source of WSS resistance for hexaploid bread wheat.

Analysis of recombinant inbred line populations derived from wheat landraces to identify new genes for wheat stem sawfly resistance.

Wheat landrace accessions were chosen from areas of the world with historical European wheat stem sawfly (Cephus pygmaeus L.) selection pressure to develop six recombinant inbred line (RIL) populations. Molecular maps were constructed, and resistance due to antibiosis and antixenosis was assessed at sites in Montana naturally infested by Cephus cinctus Norton, the wheat stem sawfly (WSS). Novel QTLs were identified along with QTL previously identified in elite germplasm. A newly identified QTL on chromosome 1B provided a new source for pith-filled solid stems. An allele for resistance on chromosome 4A unrelated to solid stems was identified in four of the six RIL populations. A landrace from Turkey, PI 166471, contained alleles at three QTLs causing high levels of larval mortality. None of the QTLs were related to stem solidness, but their combined effect provided resistance similar to that observed in a solid-stemmed check cultivar. These results show the utility of genetic populations derived from geographically targeted landrace accessions to identify new alleles for insect resistance. New PCR-based molecular markers were developed for introgression of novel alleles for WSS resistance into elite lines. Comparison of results with previous analysis of elite cultivars addresses changes in allele frequencies during the wheat breeding process.

Correction to: A large-scale multiomics analysis of wheat stem solidness and the wheat stem sawfly feeding response, and syntenic associations in barley, Brachypodium, and rice.

The original version of this article contained a mistake. The word "RefSeq v.1" was incorrectly inserted on page 7. The correct sentence should be: To identify the differentially regulated transcripts, clean RNA-Seq reads were mapped onto the T. aestivum Chinese Spring chromosome 3B pseudomolecule.

Registration of ‘Spur’ Hard Red Winter Wheat

‘Spur’ (Reg. No. CV‐1139, PI 683537) hard red winter wheat (Triticum aestivum L.) was developed and released by the Montana Agricultural Experiment Station (MAES) and licensed to the Crop Research Foundation of Wyoming in 2016. Spur was derived from the cross, MT02113*4/MTS0359. MT02113 (‘Karl 92’/UT190) and MTS0359 (‘Rampart’/‘Mironovskaya 61’) are unreleased breeding lines developed by the MAES. Spur resulted from a marker‐assisted backcross program for stem solidness and was selected as a solid‐stem F4 headrow. Spur was tested under the experimental number MTS1024 in Montana yield trials from 2010 to 2014 and in Wyoming from 2014 to 2016. Spur is a high‐yielding, semidwarf hard red winter wheat cultivar with intermediate stem solidness, medium to late maturity, and acceptable milling and baking quality characteristics. Spur's semisolid stem provides some host‐plant resistance to wheat stem sawfly.