Heterogeneous Inbred Families Research Articles

The construction of a maize-teosinte introgression population and quantitative trait loci analysis of their 21 agronomic traits

Teosinte is a progenitor species of maize (Zea mays ssp. mays) that retains a significant reservoir of genetic resources unaltered via the domestication process. To harness and explore the genetic reservoirs inherent in teosinte, we used the cultivated publicly inbred line H95 and wild species PI566673 (Zea mays ssp. mexicana) to develop a set of introgression lines (ILs), including 366 BC2F5 lines. Using these lines, 12481 high-quality polymorphic homozygous single nucleotide polymorphisms were converted into 2358 bin markers based on Genotyping by Target Sequencing technology. The homozygous introgression ratio in the ILs was approximately 12.1 % and the heterozygous introgression ratio was approximately 5.7 %. Based on the population phenotypic data across 21 important agronomic traits collected in Sanya and Beijing, 185 and 156 quantitative trait loci (QTLs) were detected in Sanya and Beijing, respectively, with 64 stable QTLs detected in both locations. We detected 12 QTL clusters spanning 10 chromosomes consisting of diverse QTLs related to yield traits such as grain size and weight. In addition, we identified useful materials in the ILs for further gene cloning of related variations. For example, some heterogeneous inbred families with superior genetic purity, shorter target heterozygotes, and some ILs exhibit clear morphological variation associated with plant growth, development, and domestication, manifesting traits such as white stalks, sharp seeds, and cob shattering. In conclusion, our results provide a robust foundation for delving into the genetic reservoirs of teosinte, presenting a wealth of genetic resources and offering insight into the genetic architecture underlying maize agronomic traits.

Genetic Dissection of Major Rice QTLs for Strong Culms and Fine Mapping of qWS5 for Breeding Application in Transplanted System

BackgroundRice is one of the major staples that feeds about one half of the global populations, and it is important to identify the genetic loci for the traits related to yield improvement. Lodging will cause severe yield loss when it happens, and stem diameter has been characterized as an important trait for lodging resistance. However, most QTLs for stem diameter have not been finely dissected due to their sensitivity to environmental fluctuation.ResultIn this study, we performed QTL analysis for stem diameter using populations derived from Nipponbare (NIP) and strong culm variety YYP1, and confirmed the single and combined effect of three major QTLs by recombinant inbred lines (RILs). Based on the QTL location, we found that qWS5 is a novel QTL not well characterized before. To finely dissect the novel locus, several recombinant heterogeneous inbred families (HIFs) were selected from the RILs for linkage analysis and their derived nearly isogenic lines (NILs) were subjected to detailed trait investigation throughout different years. The HIF-NILs strategy confined the QTL to about 380 kb region supported by repeated genotype and phenotype data, and it lays the foundation for QTL cloning in the future. In addition, introgression of the QTL to an elite japonica variety SD785 was performed by successive backcrossing, and it confirmed the value of qWS5 in increasing stem diameter and other agronomic traits during rice breeding.ConclusionsWe prove that qWS5 is a novel QTL with relatively stable effect for stem diameter and the QTL can be finely mapped to small region by the HIF-NILs strategy. The result will facilitate the improvement of rice lodging resistance by molecular marker assisted selection breeding.

Pangenome-Wide Association Study and Transcriptome Analysis Reveal a Novel QTL and Candidate Genes Controlling both Panicle and Leaf Blast Resistance in Rice

Cultivating rice varieties with robust blast resistance is the most effective and economical way to manage the rice blast disease. However, rice blast disease comprises leaf and panicle blast, which are different in terms of resistance mechanisms. While many blast resistant rice cultivars were bred using genes conferring resistance to only leaf or panicle blast, mining durable and effective quantitative trait loci (QTLs) for both panicle and leaf blast resistance is of paramount importance. In this study, we conducted a pangenome-wide association study (panGWAS) on 9 blast resistance related phenotypes using 414 international diverse rice accessions from an international rice panel. This approach led to the identification of 74 QTLs associated with rice blast resistance. One notable locus, qPBR1, validated in a F4:5 population and fine-mapped in a Heterogeneous Inbred Family (HIF), exhibited broad-spectrum, major and durable blast resistance throughout the growth period. Furthermore, we performed transcriptomic analysis of 3 resistant and 3 sensitive accessions at different time points after infection, revealing 3,311 differentially expressed genes (DEGs) potentially involved in blast resistance. Integration of the above results identified 6 candidate genes within the qPBR1 locus, with no significant negative effect on yield. The results of this study provide valuable germplasm resources, QTLs, blast response genes and candidate functional genes for developing rice varieties with enduring and broad-spectrum blast resistance. The qPBR1, in particular, holds significant potential for breeding new rice varieties with comprehensive and durable resistance throughout their growth period.

Inheritance of the Resistance to Acanthoscelides obtectus (Say.) in a Heterogeneous Inbred Families Population of Common Bean (Phaseolus vulgaris L.)

The bean weevil Acanthoscelides obtectus is one of the world’s main pests of stored beans. The heterogeneous inbred family (HIF) population of near-isogenic lines (NILs) could be an exceptional strategy to study the inheritance of the resistance against A. obtectus. We developed a HIF population of 148 NILs of R-bufa-80-12. The objectives of this research were as follows: (1) to study and understand the genetics of the attack resistance to A. obtectus in a HIF population and (2) to identify the best lines to provide weevil resistance. The pure lines of the HIF population showed a great variability for all the analyzed traits. The traits studied in this research have a normal distribution showing continuous variation, so they are considered to be quantitatively inherited. The heritabilities for resistance traits were low and very low, ranging from 0.09 to 0.17. The heritability for 100 seed weight was the highest, with a significant value of 0.90. The best lines of the HIF population for resistance to A. obtectus comprised Line-45, Line-129, Line-124, Line-142 and Line-47. In general, these lines presented lower preference of adults, and lower consumption in grams and in percentages. However, lines 45 and 129 are the most interesting from a commercial point of view because they combine resistance and seed weight.

Novel exotic alleles of EARLY FLOWERING 3 determine plant development in barley.

EARLY FLOWERING 3 (ELF3) is an important regulator of various physiological and developmental processes and hence may serve to improve plant adaptation which will be substantial for future plant breeding. To expand the limited knowledge on barley ELF3 in determining agronomic traits, we conducted field studies with heterogeneous inbred families (HIFs) derived from selected lines of the wild barley nested association mapping population HEB-25. During two growing seasons, phenotypes of nearly isogenic HIF sister lines, segregating for exotic and cultivated alleles at the ELF3 locus, were compared for ten developmental and yield-related traits. We determine novel exotic ELF3 alleles and show that HIF lines, carrying the exotic ELF3 allele, accelerated plant development compared to the cultivated ELF3 allele, depending on the genetic background. Remarkably, the most extreme effects on phenology could be attributed to one exotic ELF3 allele differing from the cultivated Barke ELF3 allele in only one SNP. This SNP causes an amino acid substitution (W669G), which predictively has an impact on the protein structure of ELF3, thereby possibly affecting phase separation behaviour and nano-compartment formation of ELF3 and, potentially, also affecting its local cellular interactions causing significant trait differences between HIF sister lines.

Quantitative trait loci for rolled leaf in a wheat EMS mutant from Jagger.

Two QTLs with major effects on rolled leaf trait were consistently detected on chromosomes 1A (QRl.hwwg-1AS) and 5A (QRl.hwwg-5AL) in the field experiments. Rolled leaf (RL) is a morphological strategy to protect plants from dehydration under stressed field conditions. Identification of quantitative trait loci (QTLs) underlining RL is essential to breed drought-tolerant wheat cultivars. A mapping population of 154 recombinant inbred lines was developed from the cross between JagMut1095, a mutant of Jagger, and Jagger to identify quantitative trait loci (QTLs) for the RL trait. A linkage map of 3106cM was constructed with 1003 unique SNPs from 21 wheat chromosomes. Two consistent QTLs were identified for RL on chromosomes 1A (QRl.hwwg-1AS) and 5A (QRl.hwwg-5AL) in all field experiments. QRl.hwwg-1AS explained 24-56% of the phenotypic variation and QRl.hwwg-5AL explained up to 20% of the phenotypic variation. The combined percent phenotypic variation associated with the two QTLs was up to 61%. Analyses of phenotypic and genotypic data of recombinants generated from heterogeneous inbred families of JagMut1095 × Jagger delimited QRl.hwwg-1AS to a 6.04Mb physical interval. This work lays solid foundation for further fine mapping and map-based cloning of QRl.hwwg-1AS.

An exotic allele of barley EARLY FLOWERING 3 contributes to developmental plasticity at elevated temperatures.

Increase in ambient temperatures caused by climate change affects various morphological and developmental traits of plants, threatening crop yield stability. In the model plant Arabidopsis thaliana, EARLY FLOWERING 3 (ELF3) plays prominent roles in temperature sensing and thermomorphogenesis signal transduction. However, how crop species respond to elevated temperatures is poorly understood. Here, we show that the barley ortholog of AtELF3 interacts with high temperature to control growth and development. We used heterogeneous inbred family (HIF) pairs generated from a segregating mapping population and systematically studied the role of exotic ELF3 variants in barley temperature responses. An exotic ELF3 allele of Syrian origin promoted elongation growth in barley at elevated temperatures, whereas plant area and estimated biomass were drastically reduced, resulting in an open canopy architecture. The same allele accelerated inflorescence development at high temperature, which correlated with early transcriptional induction of MADS-box floral identity genes BM3 and BM8. Consequently, barley plants carrying the exotic ELF3 allele displayed stable total grain number at elevated temperatures. Our findings therefore demonstrate that exotic ELF3 variants can contribute to phenotypic and developmental acclimation to elevated temperatures, providing a stimulus for breeding of climate-resilient crops.

Identification and validation of a QTL for spikelet number on chromosome arm 6BL of common wheat (Triticum aestivum L.)

To provide food security for a growing world population, it will be necessary to increase yields of staple crops such as wheat (Triticum aestivum L.). Yield is a complex, polygenic trait influenced by grain weight and number, which are negatively correlated with one another. Spikelet number is an important determinant of grain number, but allelic variants impacting its expression are often associated with heading date, constraining their use in wheat germplasm that must be adapted for specific environments. Identification and characterization of genetic variants affecting spikelet number will increase selection efficiency through their deployment in breeding programs. In this study, a quantitative trait locus (QTL) on chromosome arm 6BL for spikelet number was identified and validated using an association mapping panel, a recombinant inbred line population, and seven derived heterogeneous inbred families. The superior allele, QSn.csu-6Bb, was associated with an increase of 0.248 to 0.808 spikelets per spike across multiple environments that varied for mean spikelet number. Despite epistatic interactions between QSn.csu-6B and three other loci (WAPO-A1, VRN-D3, and PPD-B1), genotypes with a greater number of superior alleles at these loci consistently exhibit higher spikelet number. The frequency of superior alleles at these loci varies among winter wheat varieties adapted to different latitudes of the US Great Plains, revealing opportunities for breeders to select for increased spikelet number using simple molecular markers. This work lays the foundation for the positional cloning of the genetic variant underlying the QSn.csu-6B QTL to strengthen our understanding of spikelet number determination in wheat.

Fine Mapping of a Vigor QTL in Chickpea (Cicer arietinum L.) Reveals a Potential Role for Ca4_TIFY4B in Regulating Leaf and Seed Size

Plant vigor is a complex trait for which the underlying molecular control mechanisms remain unclear. Vigorous plants tend to derive from larger seeds and have greater early canopy cover, often with bigger leaves. In this study, we delimited the size of a major vigor quantitative trait locus (QTL) on chickpea chromosome 4–104.4 kb, using recombinant association analysis in 15 different heterogeneous inbred families, derived from a Rupali/Genesis836 recombinant inbred line population. The phenotypic and molecular genetic analysis provided evidence for a role of the gene Ca4_TIFY4B, in determining leaf and seed size in chickpea. A non-synonymous single-nucleotide polymorphism (SNP) in the high-vigor parent was located inside the core motif TIFYCG, resulting in a residue change T[I/S]FYCG. Complexes formed by orthologs of Ca4_TIFY4B (PEAPOD in Arabidopsis), Novel Interactor of JAZ (CaNINJA), and other protein partners are reported to act as repressors regulating the transcription of downstream genes that control plant organ size. When tested in a yeast 2-hybrid (Y2H) assay, this residue change suppressed the interaction between Ca4_TIFY4B and CaNINJA. This is the first report of a naturally occurring variant of the TIFY family in plants. A robust gene-derived molecular marker is available for selection in chickpea for seed and plant organ size, i.e., key component traits of vigor.

Validation and genetic characterisation of a seed weight quantitative trait locus, qSW17.1, in progenies of cultivated and wild soybean

Context Seed weight is an important agronomic trait for determining yield and appearance quality of soybean (Glycine max (L.) Merr.). Understanding the genetic basis of seed weight might lead to improvement of these traits in soybean by optimising different genes or alleles controlling seed weight. Aims A major quantitative trait locus (QTL) for seed weight, qSW17.1, was identified previously. In this study, we used progenies of cultivated soybean and wild soybean (Glycine soja Sieb. and Zucc.) for further validation and characterisation of qSW17.1. Methods A BC4F2 population, a heterogeneous inbred family (HIF) population, and a pair of qSW17.1 near-isogenic lines (NILs) developed from progenies of a cross between cultivated soybean variety Jackson and wild soybean accession JWS156-1 were cultivated under field conditions. QTL analysis and candidate gene mining were conducted. Key results A QTL corresponding to qSW17.1, which explained 19.84% and 31.71% of the total phenotypic variance in BC4F2 and HIF populations, respectively, was detected. The NIL with the cultivated soybean allele showed higher shoot biomass than the NIL with the wild soybean allele under hydroponic growth conditions, suggesting that the large-seed-size allele of qSW17.1 might be beneficial in soybean seedling establishment. qSW17.1 was delimited to a physical interval of 2515 kb on chromosome 17. Glyma.17G108500 showed a large (~3.27-fold) difference in expression between the two NILs, and was considered a candidate gene underlying qSW17.1. Implications Our results provide valuable information regarding the genetic basis of seed weight control in soybean and its utilisation in soybean molecular breeding.

Molecular Mapping and Analysis of an Excellent Quantitative Trait Loci Conferring Adult-Plant Resistance to Stripe Rust in Chinese Wheat Landrace Gaoxianguangtoumai.

The Chinese wheat landrace “Gaoxianguangtoumai” (GX) has exhibited a high level of adult-plant resistance (APR) to stripe rust in the field for more than a decade. To reveal the genetic background for APR to stripe rust in GX, a set of 249 F6:8 (F6, F7, and F8) recombinant inbred lines (RILs) was developed from a cross between GX and the susceptible cultivar “Taichung 29.” The parents and RILs were evaluated for disease severity at the adult-plant stage in the field by artificial inoculation with the currently predominant Chinese Puccinia striiformis f. sp. tritici races during three cropping seasons and genotyped using the Wheat 55K single-nucleotide polymorphism (SNP) array to construct a genetic map with 1,871 SNP markers finally. Two stable APR quantitative trait loci (QTL), QYr.GX-2AS and QYr.GX-7DS in GX, were detected on chromosomes 2AS and 7DS, which explained 15.5–27.0% and 11.5–13.5% of the total phenotypic variation, respectively. Compared with published Yr genes and QTL, QYr.GX-7DS and Yr18 may be the same, whereas QYr.GX-2AS is likely to be novel. Haplotype analysis revealed that QYr.GX-2AS is likely to be rare which presents in 5.3% of the 325 surveyed Chinese wheat landraces. By analyzing a heterogeneous inbred family (HIF) population from a residual heterozygous plant in an F8 generation of RIL, QYr.GX-2AS was further flanked by KP2A_36.85 and KP2A_38.22 with a physical distance of about 1.37Mb and co-segregated with the KP2A_37.09. Furthermore, three tightly linked Kompetitive allele-specific PCR (KASP) markers were highly polymorphic among 109 Chinese wheat cultivars. The results of this study can be used in wheat breeding for improving resistance to stripe rust.

Characterisation of a 4A QTL for Metribuzin Resistance in Wheat by Developing Near-Isogenic Lines.

Wheat (Triticum aestivum L.) production is constantly affected by weeds in the farming system. Chemical-based weed management is widely practiced; broad-spectrum herbicides such as metribuzin have been successfully used to control weeds in Australia and elsewhere of the world. Breeding metribuzin-resistant wheat through genetic improvement is needed for effective control of weeds. Quantitative trait loci (QTLs) mapping efforts identified a major QTL on wheat chromosome 4A, explaining up to 20% of the phenotypic variance for metribuzin resistance. The quantitative nature of inheritance of this QTL signifies the importance of near-isogenic lines (NILs), which can convert a quantitative trait into a Mendelian factor for better resolution of the QTL. In the current study, NILs were developed using a heterogeneous inbred family method combined with a fast generation-cycling system in a population of Chuan Mai 25 (resistant) and Ritchie (susceptible). Seven pairs of NILs targeting the 4A QTL for metribuzin resistance were confirmed with a molecular marker and phenotyping. The resistant allele from the resistant parent increased metribuzin resistance by 63–85% (average 69%) compared with the susceptible allele from the susceptible parent. Segregation analysis in the NIL pairs for thousand grain weight (TGW) (g), biomass per plant (kg), tillers per plant, plant height (cm), yield per plant, and powdery mildew visual score (0–9) indicated that these traits were linked with metribuzin resistance. Similarly, TGW was observed to co-segregate with metribuzin resistance in most confirmed NILs, signifying that the two traits are controlled by closely linked genes. The most contrasting NILs can be further characterised by transcriptomic and proteomic analyses to identify the candidate genes responsible for metribuzin resistance.

Ultra-High-Density QTL Marker Mapping for Seedling Photomorphogenesis Mediating Arabidopsis Establishment in Southern Patagonia.

Arabidopsis thaliana shows a wide range of genetic and trait variation among wild accessions. Because of its unparalleled biological and genomic resources, Arabidopsis has a high potential for the identification of genes underlying ecologically important complex traits, thus providing new insights on genome evolution. Previous research suggested that distinct light responses were crucial for Arabidopsis establishment in a peculiar ecological niche of southern Patagonia. The aim of this study was to explore the genetic basis of contrasting light-associated physiological traits that may have mediated the rapid adaptation to this new environment. From a biparental cross between the photomorphogenic contrasting accessions Patagonia (Pat) and Columbia (Col-0), we generated a novel recombinant inbred line (RIL) population, which was entirely next-generation sequenced to achieve ultra-high-density saturating molecular markers resulting in supreme mapping sensitivity. We validated the quality of the RIL population by quantitative trait loci (QTL) mapping for seedling de-etiolation, finding seven QTLs for hypocotyl length in the dark and continuous blue light (Bc), continuous red light (Rc), and continuous far-red light (FRc). The most relevant QTLs, Rc1 and Bc1, were mapped close together to chromosome V; the former for Rc and Rc/dark, and the latter for Bc, FRc, and dark treatments. The additive effects of both QTLs were confirmed by independent heterogeneous inbred families (HIFs), and we explored TZP and ABA1 as potential candidate genes for Rc1 and Bc1QTLs, respectively. We conclude that the Pat × Col-0 RIL population is a valuable novel genetic resource to explore other adaptive traits in Arabidopsis.

Validation of functional polymorphisms affecting maize plant height by unoccupied aerial systems discovers novel temporal phenotypes.

Plant height (PHT) in maize (Zea mays L.) has been scrutinized genetically and phenotypically due to relationship with other agronomically valuable traits (e.g., yield). Heritable variation of PHT is determined by many discovered quantitative trait loci; however, phenotypic effects of such loci often lack validation across environments and genetic backgrounds, especially in the hybrid state grown by farmers rather than the inbred state more often used by geneticists. A previous genome-wide association study using a topcrossed hybrid diversity panel identified two novel quantitative trait variants controlling both PHT and grain yield. Here, heterogeneous inbred families demonstrated that these two loci, characterized by two single nucleotide polymorphisms (SNPs), cause phenotypic variation in inbred lines, but that size of these effects were variable across four different genetic backgrounds, ranging from 1 to 10 cm. Weekly unoccupied aerial system flights demonstrated the two SNPs had larger effects, varying from 10 to 25 cm, in early growth while effects decreased toward the end of the season. These results show that allelic effect sizes of economically valuable loci are both dynamic in temporal growth and dynamic across genetic backgrounds, resulting in informative phenotypic variability overlooked following traditional phenotyping methods. Public genotyping data show recent favorable allele selection in elite temperate germplasm with little change across tropical backgrounds. As these loci remain rarer in tropical germplasm, with effects most visible early in growth, they are useful for breeding and selection to expand the genetic basis of maize.

Fine mapping identifies NAD-ME1 as a candidate underlying a major locus controlling temporal variation in primary and specialized metabolism in Arabidopsis.

Plant metabolism is modulated by a complex interplay between internal signals and external cues. A major goal of all quantitative metabolomic studies is to clone the underlying genes to understand the mechanistic basis of this variation. Using fine-scale genetic mapping, in this work we report the identification and initial characterization of NAD-DEPENDENT MALIC ENZYME 1 (NAD-ME1) as the candidate gene underlying the pleiotropic network Met.II.15 quantitative trait locus controlling variation in plant metabolism and circadian clock outputs in the Bay×Sha Arabidopsis population. Transcript abundance and promoter analysis in NAD-ME1Bay-0 and NAD-ME1Sha alleles confirmed allele-specific expression that appears to be due a polymorphism disrupting a putative circadian cis-element binding site. Analysis of transfer DNA insertion lines and heterogeneous inbred families showed that transcript variation of the NAD-ME1 gene led to temporal shifts of tricarboxylic acid cycle intermediates, glucosinolate (GSL) accumulation, and altered regulation of several GSL biosynthesis pathway genes. Untargeted metabolomic analyses revealed complex regulatory networks of NAD-ME1 dependent upon the daytime. The mutant led to shifts in plant primary metabolites, cell wall components, isoprenoids, fatty acids, and plant immunity phytochemicals, among others. Our findings suggest that NAD-ME1 may act as a key gene to coordinate plant primary and secondary metabolism in a time-dependent manner.

Mapping quantitative trait loci and predicting candidate genes for leaf angle in maize

Leaf angle of maize is a fundamental determinant of plant architecture and an important trait influencing photosynthetic efficiency and crop yields. To broaden our understanding of the genetic mechanisms of leaf angle formation, we constructed a F3:4 recombinant inbred lines (RIL) population to map QTL for leaf angle. The RIL was derived from a cross between a model inbred line (B73) with expanded leaf architecture and an elite inbred line (Zheng58) with compact leaf architecture. A sum of eight QTL were detected on chromosome 1, 2, 3, 4 and 8. Single QTL explained 4.3 to 14.2% of the leaf angle variance. Additionally, some important QTL were confirmed through a heterogeneous inbred family (HIF) approach. Furthermore, twenty-four candidate genes for leaf angle were predicted through whole-genome re-sequencing and expression analysis in qLA02-01and qLA08-01 regions. These results will be helpful to elucidate the genetic mechanism of leaf angle formation in maize and benefit to clone the favorable allele for leaf angle. Besides, this will be helpful to develop the novel maize varieties with ideal plant architecture through marker-assisted selection.

Functional Validation of Glutamine synthetase and Glutamate synthase Genes in Durum Wheat near Isogenic Lines with QTL for High GPC

Durum wheat (Triticum turgidum L. ssp. durum) is a minor crop grown on about 17 million hectares of land worldwide. Several grain characteristics determine semolina’s high end-use quality, such as grain protein content (GPC) which is directly related to the final products’ nutritional and technological values. GPC improvement could be pursued by considering a candidate gene approach. The glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle represents a bottleneck in the first step of nitrogen assimilation. QTL for GPC have been located on all chromosomes, and several major ones have been reported on 2A and 2B chromosomes, where GS2 and Fd-GOGAT genes have been mapped. A useful and efficient method to validate a putative QTL is the constitution of near-isogenic lines (NILs) by using the marker found to be associated to that QTL. Here, we present the development of two distinct sets of heterogeneous inbred family (HIF)- based NILs segregating for GS2 and Fd-GOGAT genes obtained from heterozygous lines at those loci, as well as their genotypic and phenotypic characterizations. The results allow the validation of the previously identified GPC QTL on 2A and 2B chromosomes, along with the role of these key genes in GPC control.

Dissection and validation of a QTL cluster linked to Rht-B1 locus controlling grain weight in common wheat (Triticum aestivum L.) using near-isogenic lines.

This study dissected and validated a QTL cluster associated with thousand grain weight on chromosome 4B using multiple near-isogenic lines in common wheat. Grain size and weight are crucial components of wheat yield. Previously, we identified a QTL cluster for thousand grain weight (TGW) on chromosome 4B using the Nongda3338 (ND3338)/Jingdong6 (JD6) doubled haploid population. Here, near-isogenic lines (NILs) in the ND3338 background were developed to dissect and validate the QTL cluster. Based on six independent BC3F3:4 heterogeneous inbred families, the 4B QTL cluster was divided into two linked QTL intervals (designated 4B.1 and 4B.2 QTL). For the 4B.1 QTL, the Rht-B1 gene, of which Rht-B1b allele reduces plant height (PH) by 21.18-29.34cm (34.34-53.71%), was demonstrated to be the most likely candidate gene with pleiotropic effects on grain size and TGW. For the 4B.2 QTL, the NILJD6 consistently showed an increase in TGW of 3.51-7.68g (8.84-22.77%) compared with NILND3338 across different field trials, along with a significant increase in PH of 2.26-6.71cm (3.92-12.01%). Moreover, both QTL intervals had a larger effect on grain width than on grain length. Additionally, the first significant difference in 100-grain fresh weight and 100-grain dry weight between the NIL pairs of the 4B.1 QTL interval (Rht-B1) was observed at 6days after pollination (DAP), while the differences were first visible at 30 DAP for the 4B.2 QTL interval. Collectively, our work provides a new example of QTL dissection for grain weight in wheat and lays a foundation for further map-based cloning of the major QTL that have potential applications in wheat molecular breeding for high yield.

Phenotypic and genotypic characterization of near-isogenic lines targeting a major 4BL QTL responsible for pre-harvest sprouting in wheat

BackgroundResistance to pre-harvest sprouting (PHS) is one of the major objectives in wheat breeding programs. However, the complex quantitative nature of this trait presents challenges when breeding for PHS resistance. Characterization of PHS using near-isogenic lines (NILs) targeting major quantitative trait locus/loci (QTL/QTLs) can be an effective strategy for the identification of responsible genes and underlying mechanisms.ResultsIn this study, multiple pairs of NILs were developed and confirmed for a major QTL located on the 4BL chromosome arm that contributes to PHS resistance in wheat, using a combined heterogeneous inbred family method and a fast generation cycling system. Phenotypic characterization of these confirmed NILs revealed significant differences in PHS resistance between the isolines, where the presence of the resistant allele increased the resistance to sprouting on spikes by 54.0–81.9% (average 70.8%) and reduced seed germination by 59.4–70.5% (average 66.2%). The 90 K SNP genotyping assay on the confirmed NIL pairs identified eight SNPs on 4BL, associated with five candidate genes; two of the candidate genes were related to seed dormancy. Agronomic traits in the NIL pairs were investigated; both plant height and grain number per spike were positively correlated with PHS susceptibility.ConclusionsThis study confirmed multiple pairs of NILs and identified SNPs between PHS isolines, which are valuable resources for further fine-mapping of this locus to clone the major genes for PHS resistance and investigate the possible functional regulation of these genes on important agronomic traits, such as plant height and grain number per spike.

Identification of a candidate gene for a QTL for spikelet number per spike on wheat chromosome arm 7AL by high-resolution genetic mapping

Key messageA high-resolution genetic map combined with haplotype analyses identified a wheat ortholog of rice gene APO1 as the best candidate gene for a 7AL locus affecting spikelet number per spike.A better understanding of the genes controlling differences in wheat grain yield components can accelerate the improvements required to satisfy future food demands. In this study, we identified a promising candidate gene underlying a quantitative trait locus (QTL) on wheat chromosome arm 7AL regulating spikelet number per spike (SNS). We used large heterogeneous inbred families ( > 10,000 plants) from two crosses to map the 7AL QTL to an 87-kb region (674,019,191–674,106,327 bp, RefSeq v1.0) containing two complete and two partial genes. In this region, we found three major haplotypes that were designated as H1, H2 and H3. The H2 haplotype contributed the high-SNS allele in both H1 × H2 and H2 × H3 segregating populations. The ancestral H3 haplotype is frequent in wild emmer (48%) but rare (~ 1%) in cultivated wheats. By contrast, the H1 and H2 haplotypes became predominant in modern cultivated durum and common wheat, respectively. Among the four candidate genes, only TraesCS7A02G481600 showed a non-synonymous polymorphism that differentiated H2 from the other two haplotypes. This gene, designated here as WHEAT ORTHOLOG OF APO1 (WAPO1), is an ortholog of the rice gene ABERRANT PANICLE ORGANIZATION 1 (APO1), which affects spikelet number. Taken together, the high-resolution genetic map, the association between polymorphisms in the different mapping populations with differences in SNS, and the known role of orthologous genes in other grass species suggest that WAPO-A1 is the most likely candidate gene for the 7AL SNS QTL among the four genes identified in the candidate gene region.