Chinese Spring Genome Research Articles

Characterization of a Powdery Mildew Resistance Gene in Wheat Breeding Line Jingzi 102 Using Bulk Segregant RNA Sequencing.

Wheat (Triticum aestivum L.) is one of the most important crops worldwide. Powdery mildew caused by Blumeria graminis f. sp. tritici is a destructive disease threatening wheat yield and quality. The utilization of resistant genes and cultivars is considered the most economical, environmentally friendly, and effective method to control powdery mildew. Wheat breeding line Jingzi 102 was highly resistant to powdery mildew at both seedling and adult plant stages. Genetic analysis of F1, F2, and F2:3 populations of "Jingzi 102 × Shixin 828" showed that the resistance of Jingzi 102 against powdery mildew isolate E09 at the seedling stage was controlled by a single dominant gene, temporarily designated PmJZ. Using bulked segregant RNA sequencing combined with molecular markers analysis, PmJZ was located on the long arm of chromosome 2B and flanked by markers BJK695-1 and CIT02g-20 with the genetic distances of 1.2 and 0.5 centimorgan, respectively, corresponding to the bread wheat genome of Chinese Spring (International Wheat Genome Sequencing Consortium RefSeq v2.1) 703.8 to 707.6 Mb. PmJZ is most likely different from the documented Pm genes on chromosome 2BL based on their physical positions, molecular markers analysis, and resistance spectrum. Based on the gene annotation information, five genes related to disease resistance could be considered as the candidate genes of PmJZ. To accelerate the application of PmJZ, the flanking markers BJK695-1 and CIT02g-20 can serve for marker-assisted selection of PmJZ in wheat disease-resistance breeding.

Characterization and Mapping of a Rolling Leaf Mutant Allele rlT73 on Chromosome 1BL of Wheat.

Leaf rolling is regarded as an important morphological trait in wheat breeding. Moderate leaf rolling is helpful to keep leaves upright and improve the photosynthesis of plants, leading to increased yield. However, studies on the identification of genomic regions/genes associated with rolling leaf have been reported less frequently in wheat. In this study, a rolling leaf mutant, T73, which has paired spikelets, dwarfism, and delayed heading traits, was obtained from a common wheat landrace through ethyl methanesulfonate mutagenesis. The rlT73 mutation caused an increase in the number of epidermal cells on the abaxial side and the shrinkage of bulliform cells on the adaxial side, leading to an adaxially rolling leaf phenotype. Genetic analysis showed that the rolling leaf phenotype was controlled by a single recessive gene. Further Wheat55K single nucleotide polymorphism array-based bulked segregant analysis and molecular marker mapping delimited rlT73 to a physical interval of 300.29-318.33 Mb on the chromosome arm 1BL in the Chinese Spring genome. We show that a point mutation at the miRNA165/166 binding site of the HD zipper class III transcription factor on 1BL altered its transcriptional level, which may be responsible for the rolling leaf phenotype. Our results suggest the important role of rlT73 in regulating wheat leaf development and the potential of miRNA-based gene regulation for crop trait improvement.

Wheat stripe rust resistance locus YR63 is a hot spot for evolution of defence genes – a pangenome discovery

BackgroundStripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), poses a threat to global wheat production. Deployment of widely effective resistance genes underpins management of this ongoing threat. This study focused on the mapping of stripe rust resistance gene YR63 from a Portuguese hexaploid wheat landrace AUS27955 of the Watkins Collection.ResultsYR63 exhibits resistance to a broad spectrum of Pst races from Australia, Africa, Asia, Europe, Middle East and South America. It was mapped to the short arm of chromosome 7B, between two single nucleotide polymorphic (SNP) markers sunCS_YR63 and sunCS_67, positioned at 0.8 and 3.7 Mb, respectively, in the Chinese Spring genome assembly v2.1. We characterised YR63 locus using an integrated approach engaging targeted genotyping-by-sequencing (tGBS), mutagenesis, resistance gene enrichment and sequencing (MutRenSeq), RNA sequencing (RNASeq) and comparative genomic analysis with tetraploid (Zavitan and Svevo) and hexaploid (Chinese Spring) wheat genome references and 10+ hexaploid wheat genomes. YR63 is positioned at a hot spot enriched with multiple nucleotide-binding and leucine rich repeat (NLR) and kinase domain encoding genes, known widely for defence against pests and diseases in plants and animals. Detection of YR63 within these gene clusters is not possible through short-read sequencing due to high homology between members. However, using the sequence of a NLR member we were successful in detecting a closely linked SNP marker for YR63 and validated on a panel of Australian bread wheat, durum and triticale cultivars.ConclusionsThis study highlights YR63 as a valuable source for resistance against Pst in Australia and elsewhere. The closely linked SNP marker will facilitate rapid introgression of YR63 into elite cultivars through marker-assisted selection. The bottleneck of this study reinforces the necessity for a long-read sequencing such as PacBio or Oxford Nanopore based techniques for accurate detection of the underlying resistance gene when it is part of a large gene cluster.

Lifting of the 1,000 wheat exome project SNPs from Triticum aestivum cv. Chinese Spring assembly RefSeq v1.0 to RefSeq v2.1

ObjectiveThe 1,000 wheat exome project captured the single nucleotide variants in the coding regions of a diverse set of 890 wheat accessions to analyse the contribution of introgression to adaptation of wheat. However, this highly useful single nucleotide polymorphism (SNP) dataset is based on RefSeq v1.0 of the International Wheat Genome Sequencing Consortium (IWGSC) assembly of the bread wheat genome of Chinese Spring. This reference sequence has recently been updated using optical maps and long-read sequencing to produce the improved RefSeq v2.1. Our objective was to develop a reliable high-density SNP dataset positioned onto RefSeq v2.1 because it is the current standard reference sequence used by wheat researchers.ResultsThe 3,039,822 SNPs originally positioned on RefSeq v1.0 were projected to v2.1 using Liftoff with four different flanking regions, and 2,946,536 SNPs were consistently lifted to the same location irrespective of the flanking region lengths. Of these, 2,799,166 were located on the ‘+’ ve strand. The distribution of the SNPs across the 21 chromosomes on RefSeq v2.1 was similar to that of RefSeq v1.0. Among the SNPs that were based on unanchored scaffolds in RefSeq v1.0, 11,938 were projected to one of the 21 pseudomolecules in the upgraded assembly. This SNP dataset constitutes a much-needed standardized resource for the wheat research community.

Precisely mapping a major QTL for grain weight on chromosome 5B of the founder parent Chuanmai42 in the wheat-growing region of southwestern China.

QTgw.saas-5B was validated as a major thousand-grain weight-related QTL in a founder parent used for wheat breeding and then precisely mapped to a 0.6 cM interval. Increasing the thousand-grain weight (TGW) is considered to be one of the most important ways to improve yield, which is a core objective among wheat breeders. Chuanmai42, which is a wheat cultivar with high TGW and a high and stable yield, is a parent of more than 30 new varieties grown in southwestern China. In this study, a Chuanmai42-derived recombinant inbred line (RIL) population was used to dissect the genetic basis of TGW. A major QTL (QTgw.saas-5B) mapped to the Xgwm213-Xgwm540 interval on chromosome 5B of Chuanmai42 explained up to 20% of the phenotypic variation. Using 71 recombinants with a recombination in the QTgw.saas-5B interval identified from a secondary RIL population comprising 1818 lines constructed by crossing the QTgw.saas-5B near-isogenic line with the recurrent parent Chuannong16, QTgw.saas-5B was delimited to a 0.6cM interval, corresponding to a 21.83Mb physical interval in the Chinese Spring genome. These findings provide the foundation for QTgw.saas-5B cloning and its use in molecular marker-assisted breeding.

Fine mapping of the Hairy glume (Hg) gene in a chromosome variation region at the distal terminus of 1AS.

Trichomes are differentiated epidermal cells and exist on above-ground organs of nearly all land plants with important roles in resistance to a wide range of biotic and abiotic stresses. We attempted to obtain candidate gene (s) for Hairy glume (Hg), responsible for the trichome on wheat glume, by using bulked segregant exome capture sequencing (BSE-Seq), while Hg was only mapped in 0.52–3.26 Mb of 1AS. To further fine map this gene and identify candidate genes in this region, a near isogenic line-derived population consisting of 2,050 F2 lines was generated in the present study. By analyzing this population, Hg was fine mapped into a 0.90 cM region covering a physical distance of ~825.03 Kb encompassing 6 high- and 23 low-confidence genes in the reference genome of Chinese Spring. A presence-absence variation was identified in the fine mapping region through analyses of sequence-tagged sites markers and genome sequences of the hairy glume parent of the near isogenic lines. The results presented here will be useful for further cloning Hg in wheat.

Chromosome painting reveals inter-chromosomal rearrangements and evolution of subgenome D of wheat.

Aegilops species represent the most important gene pool for breeding bread wheat (Triticum aestivum). Thus, understanding the genome evolution, including chromosomal structural rearrangements and syntenic relationships among Aegilops species or between Aegilops and wheat, is important for both basic genome research and practical breeding applications. In the present study, we attempted to develop subgenome D-specific fluorescence in situ hybridization (FISH) probes by selecting D-specific oligonucleotides based on the reference genome of Chinese Spring. The oligo-based chromosome painting probes consisted of approximately 26 000 oligos per chromosome and their specificity was confirmed in both diploid and polyploid species containing the D subgenome. Two previously reported translocations involving two D chromosomes have been confirmed in wheat varieties and their derived lines. We demonstrate that the oligo painting probes can be used not only to identify the translocations involving D subgenome chromosomes, but also to determine the precise positions of chromosomal breakpoints. Chromosome painting of 56 accessions of Ae. tauschii from different origins led us to identify two novel translocations: a reciprocal 3D-7D translocation in two accessions and a complex 4D-5D-7D translocation in one accession. Painting probes were also used to analyze chromosomes from more diverse Aegilops species. These probes produced FISH signals in four different genomes. Chromosome rearrangements were identified in Aegilops umbellulata, Aegilops markgrafii, and Aegilops uniaristata, thus providing syntenic information that will be valuable for the application of these wild species in wheat breeding.

The fine mapping of dwarf gene Rht5 in bread wheat and its effects on plant height and main agronomic traits.

Rht5 was narrowed to an approximately 1Mb interval and had pleiotropic effects on plant height, spike length and grain size. TraesCS3B02G025600 was predicted as the possible candidate gene. Plant height is an important component related to plant architecture, lodging resistance, and yield performance. The utilization of dwarf genes has made great contributions to wheat breeding and production. In this study, two F2 populations derived from the crosses of Jinmai47 and Ningchun45 with Marfed M were employed to identify the genetic region of reduce plant height 5 (Rht5), and their derived lines were used to evaluate its effects on plant height and main agronomic traits. Rht5 was fine-mapped between markers Kasp-25 and Kasp-23, in approximately 1Mb region on chromosome 3BS, which harbored 17 high-confidence annotated genes based on the reference genome of Chinese Spring (IWGSC RefSeq v1.1). TraesCS3B02G025600 were predicted as the possible candidate gene based on its differential expression and sequence variation between dwarf and tall lines and parents. The results of phenotypic evaluation showed that Rht5 had pleiotropic effects on plant height, spike length, culm diameter, grain size and grain yield. The plant height of Rht5 dwarf lines was reduced by an average of 32.67% (32.53cm) and 27.84% (33.62cm) in the Jinmai47 and Ningchun45 population, respectively. While Rht5 showed significant and negative pleiotropic effects on culm diameter, aboveground biomass, grain yield, spike length, spikelet number, grain number per spike, grain size, grain weight and filling degree of basal second internode. The culm lodging resistance index (CLRI) of dwarf lines was significantly higher than that of tall lines in the two population. In conclusion, these results lay a foundation for understanding the dwarfing mechanism of Rht5.

Identification of a recessive gene YrZ15-1370 conferring adult plant resistance to stripe rust in wheat-Triticum boeoticum introgression line.

A novel recessive gene YrZ15-1370 derived from Triticum boeoticum confers adult-plant resistance to wheat stripe rust. Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most damaging diseases of wheat globally and resistance is the effectively control strategy. Triticum boeoticum Boiss (T. monococcum L. ssp. aegilopoides, 2n = 2x = 14, AbAb) accession G52 confers a high level of adult-plant resistance against a mixture of the Chinese prevalent Pst races. To transfer the resistance to common wheat, a cross was made between G52 and susceptible common wheat genotype Crocus. A highly resistant wheat-T. boeoticum introgression line Z15-1370 (F5 generation) with 42 chromosomes was selected cytologically and by testing with Pst races. F1, F2, and F2:3 generations of the cross between Z15-1370 and stripe rust susceptible common wheat Mingxian169 were developed. Genetic analysis revealed that the resistance in Z15-1370 was controlled by a single recessive gene, tentatively designated YrZ15-1370. Using the bulked segregant RNA-Seq (BSR-Seq) analysis, YrZ15-1370 was mapped to chromosome 6AL and flanked by markers KASP1370-3 and KASP-1370-5 within a 4.3cM genetic interval corresponding to 1.8Mb physical region in the Chinese Spring genome, in which a number of disease resistance-related genes were annotated. YrZ15-1370 differed from previously Yr genes identified on chromosome 6A based on its position and/or origin. The YrZ15-1370 would be a valuable resource for wheat resistance improvement and the flanking markers developed here could be useful tools for marker-assisted selection (MAS) in breeding and further cloning the gene.

A loss-of-function of the dirigent gene TaDIR-B1 improves resistance to Fusarium crown rot in wheat.

A loss-of-function of the dirigent gene TaDIR-B1 improves resistance to Fusarium crown rot in wheat.

Molecular mapping of a novel lesion mimic gene (lm4) associated with enhanced resistance to stripe rust in bread wheat

BackgroundLesion mimics (LMs) are disease-like symptoms that occur randomly on plant green leaves in the absence of pathogens. A previous study showed that LMs are related to enhanced resistance to a broad spectrum of diverse pathogen races and programmed cell death (PCD). Stripe rust is a globally epidemic fungal disease that can substantially reduce the quality and yield of crops. The development of resistant cultivars is an economical and environmentally friendly way to enhance the adaptability and yield stability of crops instead of the use of fungicide applications.ResultsIn this study, a novel LM gene affording Pst resistance was identified and mapped with molecular markers developed for marker-assisted selection (MAS)-based wheat breeding. In this study, a novel LM gene named lm4, which is closely linked (8.06 cM) to SSR markers Xgwm210 and Xgwm455, was identified by using a Yanzhan 1/Neixiang 188 RIL population. The genetic distance of lm4 was then narrowed such that it was flanked by SSR markers with 0.51 cM and 0.77 cM intervals. Two SSR markers, lm4_01_cib and lm4_02_cib, were developed based on the content in the Chinese Spring genome database and wheat 660 K SNP results; these markers can be used to conduct MAS of LMs in wheat. The results also showed that lm4 significantly improved the resistance of stripe rust in wheat.ConclusionsTherefore, lm4 is associated with stripe rust resistance, which may provide theoretical support for future crop disease-resistance breeding and for understanding the plant apoptosis mechanism.

Transcription characteristics of wheat glutamine synthetase isoforms and the sequence analysis of their promoters

<p indent=0mm>As a key enzyme for nitrogen assimilation in wheat, glutamine synthetase is grouped into two classes: cytosolic GS and chloroplastic GS (TaGS2), and cytosolic GS includes TaGS1, TaGSr, and TaGSe. In order to study the expression characteristics and regulatory mechanisms of GS isozymes in chromosome A, B, and D of heterohexaploid wheat, transcripts of TaGS isoforms were analyzed based on the third-generation sequencing technology transcriptome analysis, and 12 promoters of TaGS isozymes of Yumai 49 were cloned based on Chinese Spring genome, and the sequence of the promoters were analyzed. The results showed that TaGS1 was mainly transcribed on chromosome 6B, TaGSe and TaGSr on chromosome 4D, and TaGS2 on chromosome 2D. Furthermore, the distance from initiation codon ATG to initiation site of transcript for each promoter of TaGS was distinct. Promoter element analysis showed that the promoter of TaGS1 in 6B had more W-box, AC-I, ABRE, as-1, and methyl jasmonic response elements, the promoter of TaGSe in 4D had more stress response elements (MYB, MBS, LTR, etc.) and auxin response element, the promoter of TaGSr in 4D had more WRE3 and transcript factor response elements, the promoter of TaGS2 in 2D had more A-box, WRE3, ARE, and an AT enrichment region. In summary, the number, type and order of cis-elements of different promoters of TaGS isozymes were distinct, which provided the foundation for further study on the regulation mechanism of TaGS isozymes.

QTL mapping for adult-plant resistance to powdery mildew in Chinese elite common wheat Chuanmai104

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major fungal disease of wheat worldwide. The economic and environmentally friendly strategy is developing the wheat varieties with resistance to powdery mildew in wheat-breeding program. Chuanmai104 (CM104, Triticum aestivum L.), derived from synthetic hexaploid wheat, was an elite wheat variety with high adult-plant resistance to powdery mildew. The phenotype of powdery mildew resistance was conducted on a set of 234 recombinant inbred lines (RIL, F8) derived from the cross of CM104 and high susceptible wheat landrace Baimaomai (BMM) in five environments in this study. Three QTLs were identified on chromosomes 7D and 4A by the high-density wheat 50 K single-nucleotide polymorphism array, designed as QPm.saas-7DS, QPm.saas-4AL and QPm.saas-4AS, respectively. Of the three QTLs, QPm.saas-7DS derived from BMM and QPm.saas-4AL derived from CM104 were minor locus, QPm.saas-4AS derived from CM104 was detected as a new major locus for adult-plant resistance to powdery mildew in all environments and localized in a 1.06 Mb interval of the genomic region on chromosome arm 4AS referenced to Chinese Spring genome explained up to 26.5% of the phenotypic variances. The newly major locus QPm.saas-4AS would be supplied as a resistant source in wheat-breeding program.

A durum wheat adult plant stripe rust resistance QTL and its relationship with the bread wheat Yr80 locus.

A stripe rust resistance QTL in durum wheat maps near the bread wheat Yr80 locus with the latter reduced to 15 candidate genes. Some wheat adult plant resistance (APR) genes provide partial resistance in the later stages of plant development to rust diseases and are an important component in protecting wheat crops from these fungal pathogens. These genes provide protection in both bread wheat and durum wheat. Here, we have mapped APR to wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici, in a cross between durum cultivars Stewart and Bansi. Two resistance QTLs derived from the Stewart parent were identified in multi-generational field trials. One QTL is located on chromosome 1BL and maps to the previously identified Yr29/Lr46/Sr58/Pm39 multi-pathogen APR locus. The second locus, located on chromosome 3BL, maps near the recently described bread wheat APR gene, Yr80. Fine mapping in durum and bread wheat families shows that the durum 3BL locus and Yr80 are closely located, with the later APR gene reduced to 15 candidate genes present in the Chinese Spring genome sequence. Distorted segregation of the durum 3BL region was observed with the Stewart locus preferentially transmitted through pollen when compared with the equivalent Bansi region.

Identification of herbicide resistance loci using a genome-wide association study and linkage mapping in Chinese common wheat

Carfentrazone-ethyl and tribenuron-methyl, the two widely used herbicides for weed control in field crops, frequently cause phytotoxicity to wheat seedlings in the field. In this study, a total of 697 wheat accessions containing three panels were scanned using wheat 90 K and 660 K SNP arrays to identify important herbicide resistance loci. Genome-wide association study (GWAS) revealed 329 significant single-nucleotide polymorphisms (SNPs) with phenotypic variance explained (PVE) of 11.3% to 27.6%. Among these SNPs, 15 were detected in multiple environments and they were mainly distributed on chromosomes 1B, 2D, 5B, 5D, 6D, and 7D. Further analysis indicated that gHR-5B (467–587 Mb), gHR-7D (46–52 Mb), and gHR-1B (517–580 Mb) were important herbicide resistance loci in wheat. Linkage mapping in a bi-parental population detected one QTL (qHR-1B) with PVE of 7.44% to 8.28%. This is reliable locus because its physical position (554–566 Mb) overlapped with gHR-1B by GWAS in the genome of Chinese Spring. This study provided some herbicide-resistant germplasm and important genetic loci for identifying genes of common wheat.

Fine-Mapping of the Powdery Mildew Resistance Gene mlxbd in the Common Wheat Landrace Xiaobaidong.

Powdery mildew, which is caused by Blumeria graminis f. sp. tritici (Bgt), is a disease of wheat worldwide. Xiaobaidong is a Chinese wheat landrace, which still maintains good resistance against powdery mildew. To obtain more genetic markers closely linked to the powdery mildew resistance gene mlxbd and narrow the candidate region for its isolation, new simple sequence repeats and cross intron-spanning markers were designed based on the genome sequence of Triticum aestivum cultivar Chinese Spring chromosome 7BL. The flanking markers 7BLSSR49 and WGGC5746 were found to be tightly linked to mlxbd at genetic distances of 0.4 cM and 0.3 cM, respectively. The resistance locus was mapped to a 63.40 kb and 0.29 Mb region of the Chinese Spring genome and Zavitan genome, respectively. The linked markers of mlxbd could be used as diagnostic markers for mlxbd. The linked molecular markers and delineated genomic region in the sequenced Chinese Spring genome will assist the future map-based cloning of mlxbd.

The semidominant mutation w5 impairs epicuticular wax deposition in common wheat (Triticum aestivum L.).

The semidominant EMS-induced mutant w5 affects epicuticular wax deposition and mapped to an approximately 194-kb region on chromosome 7DL. Epicuticular wax is responsible for the glaucous appearance of plants and protects against many biotic and abiotic stresses. In wheat (Triticum aestivum L.), β-diketone is a major component of epicuticular wax in adult plants and contributes to the glaucousness of the aerial organs. In the present study, we identified an ethyl methanesulfonate-induced epicuticular wax-deficient mutant from the elite wheat cultivar Jimai22. Compared to wild-type Jimai22, the mutant lacked β-diketone and failed to form the glaucous coating on all aerial organs. The mutant also had significantly increased in cuticle permeability, based on water loss and chlorophyll efflux. Genetic analysis indicated that the mutant phenotype is controlled by a single, semidominant gene on the long arm of chromosome 7D, which was not allelic to the known wax gene loci W1-W4, and was therefore designated W5. W5 was finely mapped to an ~ 194-kb region (flanked by the molecular markers SSR2 and STARP11) that harbored four annotated genes according to the reference genome of Chinese Spring (RefSeq v1.0). Collectively, these data will broaden the knowledge of the genetic basis underlying epicuticular wax deposition in wheat.

Analysis of Wheat Bread-Making Gene (wbm) Evolution and Occurrence in Triticale Collection Reveal Origin via Interspecific Introgression into Chromosome 7AL

Bread-making quality is a crucial trait for wheat and triticale breeding. Several genes significantly influence these characteristics, including glutenin genes and the wheat bread-making (wbm) gene. World wheat collection screening showed that only a few percent of cultivars carry the valuable wbm variant, providing a useful source for wheat breeding. In contrast, no such analysis has been performed for triticale (wheat (AABB genome) × rye (RR) amphidiploid) collections. Despite the importance of the wbm gene, information about its origin and genomic organization is lacking. Here, using modern genomic resources available for wheat and its relatives, as well as PCR screening, we aimed to examine the evolution of the wbm gene and its appearance in the triticale genotype collection. Bioinformatics analysis revealed that the wheat Chinese Spring genome does not have the wbm gene but instead possesses the orthologous gene, called wbm-like located on chromosome 7A. The analysis of upstream and downstream regions revealed the insertion of LINE1 (Long Interspersed Nuclear Elements) retrotransposons and Mutator DNA transposon in close vicinity to wbm-like. Comparative analysis of the wbm-like region in wheat genotypes and closely related species showed low similarity between the wbm locus and other sequences, suggesting that wbm originated via introgression from unknown species. PCR markers were developed to distinguish wbm and wbm-like sequences, and triticale collection was screened resulting in the detection of three genotypes carrying wbm-specific introgression, providing a useful source for triticale breeding programs.

Identification of the quantitative trait loci controlling spike-related traits in hexaploid wheat (Triticum aestivum L.).

Totally, 48 loci responsible for six spike-related traits were identified in wheat, and a major locus QGl-4A for grain length was mapped and validated for marker-assisted selection in breeding. Wheat yield is determined by the number of spikes, number of grains per spike (GN), and one-thousand kernel weight (TKW), among which GN and TKW are greatly related to the spike development and thus the spike-related traits, including spike length (SL), number of spikelet per spike (SN), grain length (GL) and grain width (GW). To identify the key loci governing the spike-related traits (SL, SN, GN, TKW, GL and GW), we conducted the quantitative trait loci (QTL) analysis combined with wheat 660K SNP chip and Kompetitive allele-specific PCR (KASP) assay, using the F2 and F2:3 populations derived from Luohan6 (LH6) with big spike and grain and Zhengmai366 with small spike and grain, and identified a total of 48 QTLs on 18 chromosomes. Moreover, a major stable QTL for GL on chromosome 4A, designated as QGl-4A, was mapped into a 0.37cM interval between KASP markers Xib4A-10 and Xib4A-12, corresponding to 20Mb physical region in the Chinese Spring genome. This QTL explained 17.30% and 5.12% of the phenotypic variation for GL in the F2 and F2:3 populations. Further association analysis of flanking markers Xib4A-10 and Xib4A-12 in 192 wheat varieties showed that these two markers could be used for marker-assisted selection in breeding. These results provide valuable information for map-based cloning of the target genes involved in the regulation of spike-related traits in common wheat.

QTL mapping for nitrogen use efficiency and agronomic traits at the seedling and maturity stages in wheat

Wheat is one of the most important staple food crops in many parts of the world. Nitrogen (N) is often considered to be the most important mineral nutrient element for crop growth and development. Nitrogen use efficiency (NUE) comprises nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). We constructed a high-density genetic map using a set of 184 recombinant inbred lines (RILs) derived from the cross ‘Tainong 18 × Linmai 6’ (TL-RILs). In this study, 14 seedling traits and 17 maturity traits related to NUE and agronomic traits of wheat were investigated using the TL-RILs under hydroponic culture trials with high N (HN), moderate N (MN) and low N (LN) levels in two time frames, and under field trials with HN and LN levels in two growing seasons. A total of 121 and 130 quantitative trait loci (QTLs) we detected at seedling and maturity stages, respectively. Of these, 47 relatively high-frequency QTLs (RHF-QTLs) and 16 QTL clusters were found. The most important cluster, C9, included morphological, biomass, yield, NUpE and NUtE traits at the same time. The contributions for most QTLs were high, with the highest contribution of 30.00%. Seventeen RHF-QTLs were detected in this cluster, and it showed a favorable relationship between the RHF-QTLs for breeding programs. The markers in the region of cluster C9 should be valuable in marker-assisted selection (MAS). The sequence of DArT marker D-3940950 in the C9 region was identified to the RhtB1 gene with the similarity of 100% by BLAST against the Chinese Spring genome (IWGSCv1.0). The correlation analysis suggested that the morphological/biomass traits and eight yield traits can be considered as the primary morphological indexes for the evaluation of NUE instead of using element determinations, and the outcomes make it easy to identify NUE on a large scale.