Chinese Wheat Germplasm Research Articles

Low-Temperature Effects on the Growth and Phytochemical Properties of Wheat Sprouts

Sprouting is associated with nutritional value, as microgreens stimulate the accumulation of health-promoting phytochemicals. The purpose of this study was to examine the growth rates and cell protection activity against oxidative stress in sprouts of seven wheat varieties, and to investigate the influence of low temperatures on their phytochemical characteristics. Among the seven wheat varieties (five Korean varieties, Australian standard white, and Chinese wild-type wheat germplasm), purple wheat (Ariheuk) had the fastest growth pattern for 8 days and provided the most protection to skin cells and hepatocytes against oxidative stress. Following low-temperature treatment (<4 °C) for 1–4 days, cold exposure had a similar effect on the growth of purple wheat sprouts during an 8-day period. However, growth was negatively affected by exposure to low temperatures for more than 5 days. Purple wheat sprouts treated with low temperatures for 4 days had considerably higher total polyphenol and total flavonoid contents, as well as a higher antioxidant capacity than untreated wheat sprouts. These findings suggest that low-temperature treatment promotes the expression of phytochemicals in purple wheat sprouts. Thus, purple wheat sprouts are considered a high-value crop that could be used as a functional food material.

Physio-Morphological and Biochemical Trait-Based Evaluation of Ethiopian and Chinese Wheat Germplasm for Drought Tolerance at the Seedling Stage

For Ethiopia’s wheat production, drought is a major natural disaster. Exploration of drought-resistant varieties from a bulk of wheat germplasm conserved in the gene bank is of paramount importance for breeding climate change-resilient modern cultivars. The present study was aimed at identifying the best performing drought-resistant genotypes under non-stress and polyethylene glycol simulated (PEG) stress conditions in a growth chamber. Forty diverse Ethiopian bread and durum wheat cultivars along with three Chinese bread wheat cultivars possessing strong drought resistance and susceptibility were evaluated. After acclimation with the natural environment, the seedlings were imposed to severe drought stress (20% PEG6000), and 15 seedling traits including photosynthetic and free proline were investigated. Our findings indicated that drought stress caused a profound decline in plant water consumption (83.0%), shoot fresh weight (64.9%), stomatal conductance (61.6%), root dry weight (55.2%), and other investigated traits except root to shoot length ratio and proline content which showed a significant increase under drought stress. A significant and positive correlation was found between photosynthetic pigments in both growth conditions. Proline exhibited a negative correlation with most of the investigated traits except root to shoot length ratio and all photosynthetic pigments which showed a positive and non-significant association. Our result also showed a wide range of genetic variation (CV) ranging from 3.23% to 47.3%; the highest in shoot dry weight (SDW) (47.3%) followed by proline content (44.63%) and root dry weight (36.03%). Based on multivariate principal component biplot analysis and average sum of ranks (ASR), G12, G16 and G25 were identified as the best drought tolerant and G6, G42, G4, G11, and G9 as bottom five sensitive. The potential of these genotypes offers further investigation at a molecular and cellular level to identify the novel gene associated with the stress response.

Genome-Wide Association Mapping of Seedling Biomass and Root Traits Under Different Water Conditions in Wheat

Drought is a major threat to global wheat production. In this study, an association panel containing 200 Chinese wheat germplasms was used for genome-wide association studies (GWASs) of genetic loci associated with eight root and seedling biomass traits under normal water and osmotic stress conditions. The following traits were investigated in wheat seedlings at the four-leaf stage: root length (RL), root number (RN), root fresh weight (RFW), root dry weight (RDW), shoot fresh weight (SFW), shoot dry weight (SDW), total fresh weight (TFW), and total dry weight (TDW). A total of 323 and 286 SNPs were detected under two water environments, respectively. Some of these SNPs were near known loci for root traits. Eleven SNPs on chromosomes 1B, 2B, 4B, and 2D had pleiotropic effects on multiple traits under different water conditions. Further analysis indicated that several genes located inside the 4 Mb LD block on each side of these 11 SNPs were known to be associated with plant growth and development and thus may be candidate genes for these loci. Results from this study increased our understanding of the genetic architecture of root and seedling biomass traits under different water conditions and will facilitate the development of varieties with better drought tolerance.

Dissecting the genetic basis of grain morphology traits in Chinese wheat by genome wide association study

Grain size and shape have significant effects on grain weight and is also an important breeding target due to market and industry requirements. In this study, the genetic loci associated with six grain morphology traits including thousand grain weight, grain length (GL), grain width, grain length to width ratio (GLWR), grain area (GA) and grain perimeter (GP) in a population of 300 Chinese wheat germplasm were investigated through genome wide association mapping. A total of 189 SNPs were significantly related to the six grain traits based on the BLUP data from three environments. Of these SNPs, 24 SNPs for GA, GL, GLWR, and GP were continuously detected under all three experiments. These SNPs were distributed on chromosome 2A, 2B, 2D, 4D, 5A, and 6D, respectively. Some SNPs such as Affx-88368872 on 2A, Affx-109472887 on 6D, and Affx-108968182, Affx-111286671, Affx-110418048, Affx-109838962, Affx-88484232 on 5A were associated with multiple traits. In addition, a chromosome region tagged by 11 SNPs (585,117,524–595,658,182 bp) on chromosome 2D had significant effects on GLWR. Several genes inside the regions on chromosome 5A and 2D may play crucial roles in determining seed size and weight. We will characterize the function of these genes in grain development in our future experiments. This study provides novel insights into the genetic basis of grain morphology traits in wheat.

Genome-Wide Association Study Reveals the Genetic Architecture of Stripe Rust Resistance at the Adult Plant Stage in Chinese Endemic Wheat.

Chinese endemic wheat, comprising Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum), Yunnan hulled wheat (T. aestivum ssp. yunnanense), and Xinjiang rice wheat (T. petropavlovskyi), are genetically and morphologically unique. To examine the adult plant resistance to stripe rust among Chinese endemic wheat germplasms, a panel of 213 accessions was inoculated with mixed virulent races of wheat stripe rust (Puccinia striiformis f. sp. tritici) in four different field environments. Four traits associated with stripe rust resistance, infection type, final disease severity, disease index, and area under the disease progress curve, were used to evaluate the accessions. The phenotypic datasets were used for 55K single-nucleotide polymorphism (SNP) array-based genome-wide association studies to identify effective resistance loci. Eighty-nine accessions with stable resistance were identified in at least three of the four environments by phenotypic evaluation. Eleven markers located on chromosomes 1A, 2B, 5A, 5D, 7B, and 7D by the genome-wide association studies analysis showed significant associations with at least two resistance-associated traits in two of the environments. These loci, corresponding to seven genomic regions based on linkage disequilibrium decay distance, explained 9.3 to 26.0% of the total phenotypic variation. Five quantitative trait loci (QTLs) on chromosomes 1A, 2B, 7B, and 7D overlapped or were in close proximity to previously reported QTLs based on the consensus and physical maps using the reference sequence of bread wheat (IWGSC RefSeq v1.0). The other two QTLs were potential novel QTLs given their physical positions. Haplotype variants of QTL QYr.sicau-2BS showed subspecies-specific inheritance of the stripe rust resistance locus. Resistant loci among Chinese endemic wheat germplasms could be introduced into common wheat cultivars, and the high-confidence SNP markers will aid in marker-assisted selection in breeding for stripe rust disease resistance.

Identification of a novel genomic region associated with resistance to Fusarium crown rot in wheat.

Genome-wide association study (GWAS) on 358 Chinese wheat germplasms and validation in a biparental population identified a novel significant genomic region on 5DL for FCR resistance. Fusarium crown rot (FCR) is a chronic and severe disease in many dryland wheat-producing areas worldwide. In the last few years, the incidence and severity of FCR progressively increased in China, and the disease has currently become a new threat to local wheat crops. Here, we report a genome-wide association study (GWAS) on a set of 358 Chinese germplasms with the wheat 55K SNP array. A total of 104 SNPs on chromosomes 1BS, 1DS, 2AL, 5AL, 5DS, 5DL, 6BS and 7BL were significantly associated with seedling resistance to FCR in the association panel. Of these SNPs, a novel 13.78Mb region targeted by five SNPs on chromosome arm 5DL was continually detected in all three trials. The effects of this region on FCR resistance was confirmed in biparental population. qRT-PCR showed that within this 5DL region, several genes encoding TIR-NBS-LRR proteins and proteins related to mycotoxins deoxynivalenol (DON) detoxification increased rapidly in the disease-resistant variety 04 Zhong 36 than the susceptible variety Xinmai 26 after inoculation. Our study provides new insights into gene discovery and creation of new cultivars with desirable alleles for improving FCR resistance in wheat.

Distribution and Nucleotide Diversity of Yr15 in Wild Emmer Populations and Chinese Wheat Germplasm.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating fungal disease of wheat. The wild emmer gene, Yr15 (Wtk1), which confers a strong broad-spectrum resistance to Pst isolates, is composed of kinase and pseudokinase domains. The analysis of 361 wild emmer accessions from a wide range of natural habitats confirms that functional Wtk1 is distributed mainly along a narrow axis from Mt. Carmel to Mt. Hermon regions, in the northern part of Israel, where environmental conditions are favorable to the onset of stripe rust. An analysis of full-length Wtk1 DNA sequences from 49 wild emmer accessions identified three haplotypes and extremely low nucleotide diversity (π = 0.00002). The sequence diversity of Wtk1 is 9.5 times lower than that of broad-spectrum partial resistance gene Yr36 (π = 0.00019), and both are in sharp contrast to the high level of nucleotide diversity previously reported for race-specific resistance genes (e.g., Lr10 and Pm3). However, the nonfunctional wtk1 sequences possess high level of nucleotide diversity (π = 0.07). These results may reflect the different resistance mechanisms and the different evolutionary processes that shaped these resistance genes. Yr15 was absent in 189 Chinese wheat landraces and was present in only 1.02% of the 583 tested modern Chinese wheat cultivars. These results corroborate our previous results showing that Yr15 was absent in 94% of a worldwide collection of 513 wheat cultivars, therefore indicating the importance of Yr15 in wheat stripe rust resistance breeding programs in China and elsewhere around the globe.

Genome-Wide Association Mapping of Resistance to Fusarium Head Blight Spread and Deoxynivalenol Accumulation in Chinese Elite Wheat Germplasm.

Improving resistance to Fusarium head blight (FHB) in wheat is crucial in the integrated management of the disease and prevention of deoxynivalenol (DON) contamination in grains. To identify novel sources of resistance, a genome-wide association study (GWAS) was performed using a panel of 213 accessions of elite wheat germplasm of China. The panel was evaluated for FHB severity in four environments and DON content in grains in two environments. High correlations across environments and high heritability were observed for FHB severity and DON content in grains. The panel was also genotyped with the 90K Illumina iSelect single nucleotide polymorphism (SNP) array and 11,461 SNP markers were obtained. The GWAS revealed a total of six and three loci significantly associated with resistance to fungal spread and DON accumulation in at least two environments, respectively. QFHB-2BL.1 tagged by IWB52433 and QFHB-3A tagged by IWB50548 were responsible for resistance to both fungal spread and DON accumulation. In summary, this study provided an overview of FHB resistance resources in elite Chinese wheat germplasm and identified novel resistance loci that could be used for wheat improvement.

Preliminary Exploration of the Source, Spread, and Distribution of Rht24 Reducing Height in Bread Wheat

Rht24 is a major dwarfing allele that not only reduces plant height but also increases grain weight. The objective of this study was to trace the source, spread, and distribution of Rht24 and determine its frequency in conjunction with other important dwarfing alleles for Rht1 (Rht‐B1b), Rht2 (Rht‐D1b), and Rht8. Allele‐specific cleaved amplified polymorphic sequence (CAPS) markers were developed for accurate and effective genotyping of Rht1 and Rht2, and closely linked flanking markers were used for genotyping of Rht8 and Rht24. Marker analysis showed that Rht24 occurs at a higher frequency (84.2%) than other important dwarfing alleles in elite wheat (Triticum aestivum L.) varieties and usually couples with Rht2 or Rht8. Genotyping of old varieties and landraces showed that Rht24 was widely used in wheat breeding before the Green Revolution (GR). ‘Akakomugi’ and ‘Norin 10’, the donors of Rht8 and GR genes Rht1 and Rht2, respectively, harbored Rht24, so Rht24 likely followed the transfer routes of GR genes and Rht8 to spread worldwide. Pedigree analysis showed that many Chinese elite lines and backbone parents were derived from Akakomugi, contributing to the high frequency of Rht24 in Chinese varieties. Additionally, Norin 10‐derived semidwarf varieties from the CIMMYT were widely used in Chinese wheat breeding. Finally, Rht24 was also detected in 30 old Chinese varieties and landraces. Overall, these findings show that the presence of Rht24 in modern Chinese elite varieties originated from Akakomugi, Norin 10, or Chinese landraces. Thus, Rht24 was introgressed early, spread widely, and became genetically fixed in a wide range of modern Chinese wheat germplasm.

Allelic effects and variations for key bread-making quality genes in bread wheat using high-throughput molecular markers

We developed and validated high-throughput Kompetitive Allele-Specific PCR (KASP) assays for key genes underpinning bread-making quality, including the wbm gene on chromosome 7AL and over-expressed glutenin Bx7OE (Glu-B1al) gene. Additionally, we used pre-existing KASP assay for Sec1 (1B.1R translocation) gene on chromosome 1B. The newly developed KASP assays were compared with gel-based markers for reliability and phenotypically validated in a diversity panel for Mixograph, Rapid Visco Analyzer (RVA) and Mixolab traits. Genotypes carrying the 1B.1R translocation had significantly lower Mixolab parameters than those without the translocation. Similarly, superior effects of the wbm+ and Bx7OE alleles on Mixograph and RVA properties and their extremely low frequencies in global wheat collections supported the idea of using these genes for bread-making quality improvement. The allele frequencies of wbm+ and Bx7OE were extremely low in historical Chinese and CIMMYT wheat germplasm, but were relatively higher in synthetic hexaploid wheats and their breeding derivatives. In both the Vavilov and Watkins global landrace collections, the frequency of wbm+ was 6.4 and 3.5%, and frequency of Bx7OE was 3.2% and 7.0%, respectively. The high-throughput marker resources and large-scale global germplasm screening provided further opportunities to exploit these genes in wheat breeding to enhance bread-making quality.

Population structure of Chinese southwest wheat germplasms resistant to stripe rust and powdery mildew using the DArT-seq technique

ABSTRACT: Understanding genetic variability in existing wheat accessions is critical for collection, conservation and use of wheat germplasms. In this study, 138 Chinese southwest wheat accessions were investigated by genotyping using two resistance gene makers (Pm21 and Yr26) and DArT-seq technique. Finally, about 50% cultivars (lines) amplified the specific allele for the Yr26 gene (Gwm11) and 40.6% for the Pm21 gene (SCAR1265). By DArT-seq analysis, 30,485 markers (6486 SNPs and 23999 DArTs) were obtained with mean polymorphic information content (PIC) value 0.33 and 0.28 for DArT and SNP marker, respectively. The mean Dice genetic similarity coefficient (GS) was 0.72. Two consistent groups of wheat varieties were identified using principal coordinate analysis (PCoA) at the level of both the chromosome 6AS and the whole-genome, respectively. Group I was composed of non-6VS/6AL translocation lines of different origins, while Group II was composed of 6VS/6AL translocation (T6VS/6AL) lines, most of which carried the Yr26 and Pm21 genes and originated from Guizhou. Besides, a model-based population structure analysis revealed extensive admixture and further divided these wheat accessions into six subgroups (SG1, SG2, SG3, SG4, SG5 and SG6), based on their origin, pedigree or disease resistance. This information is useful for wheat breeding in southwestern China and association mapping for disease resistance using these wheat germplasms in future.

Characterization of Fusarium Head Blight Resistance Gene Fhb1 and Its Putative Ancestor in Chinese Wheat Germplasm

Characterization of <i>Fusarium</i> Head Blight Resistance Gene <i>Fhb1</i> and Its Putative Ancestor in Chinese Wheat Germplasm

Diversity, distribution of Puroindoline genes and their effect on kernel hardness in a diverse panel of Chinese wheat germplasm

BackgroundKernel hardness, which has great influence on the end-use properties of common wheat, is mainly controlled by Puroindoline genes, Pina and Pinb. Using EcoTILLING platform, we herein investigated the allelic variations of Pina and Pinb genes and their association with the Single Kernel Characterization System (SKCS) hardness index in a diverse panel of wheat germplasm.ResultsThe kernel hardness varied from 1.4 to 102.7, displaying a wide range of hardness index. In total, six Pina and nine Pinb alleles resulting in 15 genotypes were detected in 1787 accessions. The most common alleles are the wild type Pina-D1a (90.4%) and Pina-D1b (7.4%) for Pina, and Pinb-D1b (43.6%), Pinb-D1a (41.1%) and Pinb-D1p (12.8%) for Pinb. All the genotypes have hard type kernel hardness of SKCS index (>60.0), except the wild types of Pina and Pinb combination (Pina-D1a/Pinb-D1a). The most frequent genotypes in Chinese and foreign cultivars was Pina-D1a/Pinb-D1b (46.3 and 39.0%, respectively) and in Chinese landraces was Pina-D1a/Pinb-D1a (54.2%). The frequencies of hard type accessions are increasing from 35.5% in the region IV, to 40.6 and 61.4% in the regions III and II, and then to 77.0% in the region I, while those of soft type are accordingly decreasing along with the increase of latitude. Varieties released after 2000 in Beijing, Hebei, Shandong and Henan have higher average kernel hardness index than that released before 2000.ConclusionThe kernel hardness in a diverse panel of Chinese wheat germplasm revealed an increasing of kernel hardness generally along with the latitude across China. The wild type Pina-D1a and Pinb-D1a, and one Pinb mutant (Pinb-D1b) are the most common alleles of six Pina and nine Pinb alleles, and a new double null genotype (Pina-D1x/Pinb-D1ah) possessed relatively high SKCS hardness index. More hard type varieties were released in recent years with different prevalence of Pin-D1 combinations in different regions. This work would benefit the understanding of the selection and molecular processes of kernel hardness across China and different breeding stages, and provide useful information for the improvement of wheat quality in China.

Identification of major loci for seed dormancy at different post-ripening stages after harvest and validation of a novel locus on chromosome 2AL in common wheat

A long-period duration of seed dormancy helps to reduce pre-harvest sprouting (PHS) damage in common wheat when a long period of rainfall or high humidity occurs. Identification of genes or loci underlying seed dormancy duration is of high importance for investigating genetic mechanism of PHS tolerance of wheat. In the present study, the germination index (GI) of different mapping populations at 5 days (GI5), 15 days (GI15), and 30 days (GI30) after harvest (DAH) was recorded during the 2011–2012, 2012–2013, 2013–2014, and 2014–2015 cropping seasons. Field sprouting (FS) values were also determined in 2012–2013 and 2014–2015 cropping seasons. Association analysis was performed in 260 wheat varieties and advanced lines differing in seed dormancy (SD) using 557 SSR and 14 gene-specific markers for PHS/SD-related genes. The result indicated that a total of 47 loci were significantly (P < 0.01) associated with SD using both the general linear model (GLM) and mixed linear model (MLM). Five major loci were consistently detected at different post-ripening stages after harvest, including four for GI5 and GI15 on chromosomes 3AS, 3BL, 5AL, and 5BL responsible for middle-duration SD, and one for GI5, GI15, and GI30 on 2AL associated with longer-duration SD. The major locus on 2AL (designated Qsd.ahau-2AL) is likely to be a novel QTL, which was linked to Xwmc658 by mapping analysis in 165 recombinant inbred lines (RILs) derived from the Jing 411 × Wanxianbaimaizi cross and 728 F2 plants from Jimai 20 × Suiningtuotuomai. Furthermore, a CAPS marker CAPS-2AL was developed for Qsd.ahau-2AL locus and was validated using the 728 F2 plants and 201 accessions of the Chinese mini-core collection. Our results also revealed that the TaMFT-like gene on 3AS had a more significant association with dormancy duration than the other six genes underlying SD/PHS resistance in Chinese wheat germplasm. This study provides useful information for marker-assisted selection in wheat breeding and enhances our understanding of molecular genetics of SD in wheat.

Registration of Near-Isogenic Winter Wheat Germplasm Contrasting in Fhb1 for Fusarium Head Blight Resistance

The Chinese wheat germplasm Ning7840 (Triticum aestivum L.) contains Fhb1, a quantitative trait locus (QTL) for Fusarium head blight (FHB) resistance that explains as much as 53% of the phenotypic variation in segregating populations. Ning7840 has been widely used as a resistant parent in breeding programs worldwide, but because of its poor adaptation in the United States, its progenies usually exhibit reduced grain yield due to the transfer of undesirable genes from Ning7840. The development of five near-isogenic lines (NILs: ‘Clark’*7/Ning7840) (NIL75, Reg. No. GS-174, PI 668559; NIL78, Reg. No. GS-175, PI 668560; NIL80, Reg. No. GS-176, PI 668561; NIL90, Reg. No. GS-177, PI 668562; NIL98, Reg. No. GS-178, PI 668563) contrasting in Fhb1 alleles was intended to overcome this potential limitation. Marker-assisted backcrossing was used to develop the NILs. Approximately 2000 BC7F2 plants from the backcross of Ning7840 by Clark (recurrent parent) were screened with two Fhb1-flanking markers (Xgwm533 and Xgwm493), and selected BC7F3 families were evaluated for FHB resistance in greenhouses. Both genotypic and phenotypic data confirm the presence of Fhb1 in the four resistant NILs and absence in the one susceptible NIL. All resistant NILs had significantly higher FHB resistance and lower deoxynivalenol content than Clark and the susceptible NIL but yield similar to Clark (P = 0.295). Marker-assisted backcross efficiently transferred Fhb1 into U.S. hard winter wheat without transferring undesirable traits from Ning7840, and these Fhb1 NILs should be useful parents for effective use of Fhb1 in U.S. winter wheat.

Characterization of Chinese wheat germplasm for resistance to Fusarium head blight at CIMMYT, Mexico

Fusarium head blight (FHB) poses a challenge for wheat breeders worldwide; there are limited sources of resistance and the genetic basis for resistance is not well understood. In the mid-1980s, a shuttle breeding and germplasm exchange program launched between CIMMYT-Mexico and China, enabled the incorporation of FHB resistance from Chinese bread wheat germplasm into CIMMYT wheat. Most of the Chinese wheat materials conserved in the CIMMYT germplasm bank had not been fully characterized for FHB reaction under Mexican environments, until 2009, when 491 Chinese bread wheat lines were evaluated in a FHB screening nursery in Mexico, and 304 (61.9 %) showed FHB indices below 10 %. Subsequent testing occurred in 2010 for plant height (PH), days to heading (DH), and leaf rust response. In 2012, 140 elite lines with good agronomic types were further evaluated for field FHB reaction and deoxynivalenol (DON) accumulation. Most of the tested lines showed good resistance: 116 (82.9 %) entries displayed FHB indices lower than 10 %, while 89 (63.6 %) had DON contents lower than 1.0 ppm. Significant negative correlations were observed between FHB traits (FHB index, DON content, and Fusarium damaged kernels) and PH, DH, and anther extrusion. A subset of 102 elite entries was selected for haplotyping using markers linked to 10 well known FHB quantitative trait loci (QTL). 57 % of the lines possessed the same 2DL QTL marker alleles as Wuhan 1 or CJ 9306, and 26.5 % had the same 3BS QTL allele as Sumai 3. The remaining known QTL were of low frequency. These materials, especially those with none of the above tested resistance QTL (26.5 %), could be used in breeding programs as new resistance sources possessing novel genes for FHB resistance and DON tolerance.

Characterization of DFR allelic variations and their associations with pre-harvest sprouting resistance in a set of red-grained Chinese wheat germplasm

Pre-harvest sprouting (PHS) of wheat greatly reduces the quality and economic value of grain, and PHS resistance is one of the most important traits in wheat breeding. Red-grained wheat varieties are generally more resistant to PHS than white-grained ones; however, some are still susceptible. The red pigment of red-grained wheat is synthesized through the flavonoid biosynthetic pathway, in which the dihydroflavonol-4-reductase gene (DFR) is one of the genes involved in anthocyanin synthesis. In this study, a set of 120 red-grained Chinese wheat cultivars and lines with distinct PHS resistance were used to characterize TaDFR genotype variations and their association with PHS resistance. Whereas no variation or functional variation of TaDFR genes was detected on chromosomes 3A and 3D, a novel TaDFR allele, designated TaDFR-Bb, was explored on chromosome 3B. Compared with TaDFR-Ba, an 8 bp insertion (CTCTAGGA) was identified in the promoter region of TaDFR-B in most of the PHS resistant red-grained wheat varieties and advanced lines. Based on this, a CAPS marker was designed and validated with a set of Chinese red-grained wheat cultivars and lines with distinct PHS resistance. In most cases, TaDFR-Bb was associated with higher PHS resistance. An association study indicated that wheat varieties with the 8 bp insertion (average seed germination index 23.6 %) were significantly more resistant (P < 0.01) to PHS than those without the insertion (average seed germination index 69.5 %). Further study on gene expression demonstrated that the insertion led to increased TaDFR-B expression in cultivars with PHS resistance. Transient expression of TaDFR-B in coleoptiles of wheat cv. Chinese Spring revealed that increasing TaDFR gene expression did not induce the synthesis of anthocyanins.

Novel insights into the composition, variation, organization, and expression of the low-molecular-weight glutenin subunit gene family in common wheat

Low-molecular-weight glutenin subunits (LMW-GS), encoded by a complex multigene family, play an important role in the processing quality of wheat flour. Although members of this gene family have been identified in several wheat varieties, the allelic variation and composition of LMW-GS genes in common wheat are not well understood. In the present study, using the LMW-GS gene molecular marker system and the full-length gene cloning method, a comprehensive molecular analysis of LMW-GS genes was conducted in a representative population, the micro-core collections (MCC) of Chinese wheat germplasm. Generally, >15 LMW-GS genes were identified from individual MCC accessions, of which 4–6 were located at the Glu-A3 locus, 3–5 at the Glu-B3 locus, and eight at the Glu-D3 locus. LMW-GS genes at the Glu-A3 locus showed the highest allelic diversity, followed by the Glu-B3 genes, while the Glu-D3 genes were extremely conserved among MCC accessions. Expression and sequence analysis showed that 9–13 active LMW-GS genes were present in each accession. Sequence identity analysis showed that all i-type genes present at the Glu-A3 locus formed a single group, the s-type genes located at Glu-B3 and Glu-D3 loci comprised a unique group, while high-diversity m-type genes were classified into four groups and detected in all Glu-3 loci. These results contribute to the functional analysis of LMW-GS genes and facilitate improvement of bread-making quality by wheat molecular breeding programmes.

Molecular characterization of vernalization and response genes in bread wheat from the Yellow and Huai Valley of China

BackgroundFlowering time greatly influences the adaptation of wheat cultivars to diverse environmental conditions and is mainly controlled by vernalization and photoperiod genes. In wheat cultivars from the Yellow and Huai Valleys, which represent 60%-70% of the total wheat production in China, the large-scale genotyping of wheat germplasms has not yet been performed in terms of vernalization and photoperiod response alleles, limiting the use of Chinese wheat germplasms to a certain extent.ResultsIn this study, 173 winter wheat cultivars and 51 spring wheat cultivars from China were used to identify allelic variations of vernalization and photoperiod genes as well as copy number variations of Ppd-B1 and Vrn-A1. Two new co-dominant markers were developed in order to more precisely examine Vrn-A1b, Vrn-B1a, and Vrn-B1b. Two novel alleles at the Vrn-B3 locus were discovered and were designated Vrn-B3b and Vrn-B3c. Vrn-B3b had an 890-bp insertion in the promoter region of the recessive vrn-B3 allele, and Vrn-B3c allele had 2 deletions (a 20-bp deletion and a 4-bp deletion) in the promoter region of the dominant Vrn-B3a allele. Cultivar Hemai 26 lacked the Vrn-A1 gene. RT-PCR indicated that the 890-bp insertion in the Vrn-B3b allele significantly reduced the transcription of the Vrn-B3 gene. Cultivars Chadianhong with the Vrn-B3b allele and Hemai 26 with a Vrn-A1-null allele possessed relatively later heading and flowering times compared to those of Yanzhan 4110, which harbored recessive vrn-B3 and vrn-A1 alleles. Through identification of photoperiod genes, 2 new polymorphism combinations were found in 6 winter wheat cultivars and were designated Hapl-VII and Hapl-VIII, respectively. Distribution of the vernalization and photoperiod genes indicated that all recessive alleles at the 4 vernalization response loci, truncated “Chinese Spring” Ppd-B1 allele at Ppd-B1 locus and Hapl-I at the Ppd-D1 locus were predominant in Chinese winter wheat cultivars.ConclusionThis study illustrated the distribution of vernalization and photoperiod genes and identified 2 new Vrn-B3 alleles, 1 Vrn-A1-null allele, and two new Ppd-D1 polymorphism combinations, using developed functional markers. Results of this study have the potential to provide useful information for screening relatively superior wheat cultivars for better adaptability and maturity.

TaCKX6‐D1, the ortholog of rice OsCKX2, is associated with grain weight in hexaploid wheat

The cytokinin oxidase/dehydrogenase (CKX) gene plays a principal role in controlling cytokinin levels and has been shown to be a major quantitative trait locus (QTL) affecting grain number in rice. However, the function and evaluation of the haplotypes of the wheat CKX gene have yet to be illustrated. In this study, TaCKX6-D1, a wheat ortholog of rice OsCKX2, was cloned and its haplotype variants were determined to be significantly associated with the 1000-grain weight on the basis of linkage mapping, association analysis and gene expression analysis. Five TaCKX6-D1 haplotypes, designated a-e, were identified. An indel marker was developed to identify haplotype a, which was associated with higher grain weight. Haplotype a showed decreased expression relative to haplotype b in seeds at 8 d after pollination. Sequence variations among modern cultivars, landraces and wild species suggest a significant domestication signature at the TaCKX6-D1 locus in Chinese wheat germplasm. TaCKX6-D1 may serve as a useful gene for the breeding of high-yielding wheat. A strategy for allele mining and utilization of TaCKX6-D1 was proposed. Our study also sheds light on the mechanisms of grain development and domestication of wheat, as well as the functional divergence of orthologs in comparative genomics.