Quantitative Trait Loci Alleles Research Articles

Pooled DNA sequencing in hairy vetch (Vicia villosa Roth) reveals QTL for seed dormancy but not pod dehiscence.

Hairy vetch (Vicia villosa Roth) is a promising legume cover crop, but its use is limited by high rates of pod dehiscence and seed dormancy. We used phenotypically contrasting pooled DNA samples (n=24 with 29-74 individuals per sample) from an ongoing cover crop breeding program across four environments (site-year combinations: Maryland 2020, Maryland 2022, Wisconsin 2021, Wisconsin 2022) to find genetic associations and genomic prediction accuracies for pod dehiscence and seed dormancy. We also combined pooled DNA sample genetic association results with the results of a prior genome-wide association study. Genomic prediction resulted in positive predictive abilities for both traits between environments and with an independent dataset (0.34-0.50), but reduced predictive ability for DNA pools with divergent seed dormancy in the Maryland environments (0.07-0.15). The pooled DNA samples found six significant (false discovery rate q-value<0.01) quantitative trait loci (QTL) for seed dormancy and four significant QTL for pod dehiscence. Unfortunately, the minor alleles of the pod dehiscence QTL increased the rate of pod dehiscence and are not useful for marker-assisted selection. When combined with a prior association study, sixteen seed dormancy QTL and zero pod dehiscence QTL were significant. Combining the association studies did not increase the detection of useful QTL.

A QTL allele from wild soybean enhances protein content without reducing the oil content

Abstract Soybean is one of the chief crops producing protein and oil for human consumption. Wild soybean, the ancestor of cultivated soybean, possesses high seed protein content; therefore, it is a valuable genetic resource that could enhance protein content in the cultivated varieties. To identify the genes responsible for increasing protein content in wild soybean, a population comprising 113 BC4F6 chromosome segment substitution lines (CSSL) was developed from a cross between soybean cultivar ‘Jackson’ and wild soybean accession JWS156-1. The CSSL population was cultivated in the field conditions for 3 years (2018, 2019 and 2020), and the seeds harvested from each line were analysed for protein and oil contents by InfraTec Nova instrument. Quantitative trait locus (QTL) analysis with 243 SSR markers identified 12 QTLs associated with seed protein, oil and protein + oil contents. Among these QTLs, qPro8 and qPro19, two major and stable QTLs for protein content, were detected on chromosomes 8 and 19, respectively. No QTL for oil content was detected in the vicinity of qPro19, indicating that qPro19 did not influence the seed oil content. The effect of qPro19 was validated using near-isogenic lines (NILs) of qPro19. By introducing the qPro19 allele from wild soybean into another soybean variety, ‘Tachiyutaka’, a BC4 line, T-678, that showed enhanced seed protein content, without reducing the seed oil content. This study implied that the qPro19 allele from wild soybean could be a potential genetic resource for breeding programmes aimed to improve soybean seed quality.

Identifying developmental QTL alleles with favorable effect on grain yield components under late-terminal drought in spring barley MAGIC population.

Barley is the fourth most cultivated cereal worldwide, and drought is a major cause of its yield loss by negatively affecting its development. Hence, better understanding developmental mechanisms that control complex polygenic yield-related traits under drought is essential to uncover favorable yield regulators. This study evaluated seven above-ground yield-related traits under well-watered (WW) and late-terminal drought(TD) treatment using 534 spring barley multiparent advanced generation intercross double haploid (DH) lines. The analysis of quantitative trait loci (QTL) for WW, TD, marker by treatment interaction, and drought stress tolerance identified 69, 64, 25, and 25 loci, respectively, for seven traits from which 15 loci were common for at least three traits and 17 were shared by TD and drought stress tolerance. Evaluation of allelic effects for a QTL revealed varying effect of parental alleles. Results showed prominent QTL located on major flowering time gene Ppd-H1 with favorable effects for grain weight under TD when flowering time was not significantly affected, suggesting that this gene might be linked with increasing grain weight by ways other than timing of flowering under late-terminal drought stress. Furthermore, a desirable novel QTL allele was identified on chromosome 5H for grain number under TD nearby sucrose transporter gene HvSUT2. The findings indicated that spring barley multiparent advanced generation intercross population can provide insights to improve yield under complex condition of drought.

Evaluation of three sets of advanced backcrosses of eggplant with wild relatives from different gene pools under low N fertilization conditions.

The development of new cultivars with improved nitrogen use efficiency (NUE) is key for implementing sustainable agriculture practices. Crop wild relatives (CWRs) provide valuable genetic resources for breeding programs aimed at achieving this goal. In this study, three eggplant (Solanum melongena) accessions together with their advanced backcrosses (ABs; BC3 to BC5 generations) were evaluated for 22 morpho-agronomic, physiological, and NUE traits under low nitrogen (LN) fertilization conditions. The ABs were developed with introgressions from the wild relatives Solanum insanum, Solanum dasyphyllum, and Solanum elaeagnifolium. The AB population comprised a total of 25, 59, and 59 genotypes, respectively, with overall donor wild relative genome coverage percentages of 58.8%, 46.3%, and 99.2%. The three S. melongena recurrent parents were also evaluated under control (normal) N fertilization. Reduction of N fertilization in the parents resulted in decreased chlorophyll content-related traits, aerial biomass, stem diameter, and yield and increased NUE, nitrogen uptake efficiency (NUpE), and nitrogen utilization efficiency (NUtE). However, the decrease in yield was moderate, ranging between 62.6% and 72.6%. A high phenotypic variation was observed within each of the three sets of ABs under LN conditions, with some individuals displaying improved transgressive characteristics over the recurrent parents. Using the single primer enrichment technology 5k probes platform for high-throughput genotyping, we observed a variable but high degree of recurrent parent genome recovery in the ABs attributable to the lines recombination, allowing the successful identification of 16 quantitative trait loci (QTL). Different allelic effects were observed for the introgressed QTL alleles. Several candidate genes were identified in the QTL regions associated with plant growth, yield, fruit size, and NUE-related parameters. Our results show that eggplant materials with introgressions from CWRs can result in a dramatic impact in eggplant breeding for a more sustainable agriculture.

Maintenance of UK bread baking quality: Trends in wheat quality traits over 50 years of breeding and potential for future application of genomic-assisted selection.

Improved selection of wheat varieties with high end-use quality contributes to sustainable food systems by ensuring productive crops are suitable for human consumption end-uses. Here, we investigated the genetic control and genomic prediction of milling and baking quality traits in a panel of 379 historic and elite, high-quality UK bread wheat (Triticum eastivum L.) varieties and breeding lines. Analysis of the panel showed that genetic diversity has not declined over recent decades of selective breeding while phenotypic analysis found a clear trend of increased loaf baking quality of modern milling wheats despite declining grain protein content. Genome-wide association analysis identified 24 quantitative trait loci (QTL) across all quality traits, many of which had pleiotropic effects. Changes in the frequency of positive alleles of QTL over recent decades reflected trends in trait variation and reveal where progress has historically been made for improved baking quality traits. It also demonstrates opportunities for marker-assisted selection for traits such as Hagberg falling number and specific weight that do not appear to have been improved by recent decades of phenotypic selection. We demonstrate that applying genomic prediction in a commercial wheat breeding program for expensive late-stage loaf baking quality traits outperforms phenotypic selection based on early-stage predictive quality traits. Finally, trait-assisted genomic prediction combining both phenotypic and genomic selection enabled slightly higher prediction accuracy, but genomic prediction alone was the most cost-effective selection strategy considering genotyping and phenotyping costs per sample.

Genome-wide association study identifies a novel BMI1A QTL allele that confers FLC expression diversity in Arabidopsis thaliana.

Identification and understanding of the genetic basis of natural variations in plants are essential for comprehending their phenotypic adaptation. Here, we report a genome-wide association study (GWAS) of FLOWERING LOCUS C (FLC) expression in 727 Arabidopsis accessions. We identified B LYMPHOMA MOLONEY MURINE LEUKEMIA VIRUS INSERTION REGION 1 HOMOLOG 1A (BMI1A) as a causal gene for one of the FLC expression quantitative trait loci (QTLs). Loss of function in BMI1A increases FLC expression and delays flowering time at 16 °C significantly compared with the wild type (Col-0). BMI1A activity is required for histone H3 lysine 27 trimethylation (H3K27me3) accumulation at the FLC, MADS AFFECTING FLOWERING 4 (MAF4), and MAF5 loci at low ambient temperature. We further uncovered two BMI1A haplotypes associated with the natural variation in FLC expression and flowering time at 16 °C, and demonstrated that polymorphisms in the BMI1A promoter region are the main contributor. Different BMI1A haplotypes are strongly associated with geographical distribution, and the low ambient temperature-sensitive BMI1A variants are associated with a lower mean temperature of the driest quarter of their collection sites compared with the temperature-non-responsive variants, indicating that the natural variations in BMI1A have adaptive functions in FLC expression and flowering time regulation. Therefore, our results provide new insights into the natural variations in FLC expression and flowering time diversity in plants.

Selection index theory for populations under directional and stabilizing selection

BackgroundThe purpose of a selection index is that its use to select animals for breeding maximizes the profit of a breed in future generations. The profit of a breed is in general a quantity that predicts the satisfaction of future owners with their breed, and the satisfaction of the consumers with the products that are produced by the breed. Many traits, such as conformation traits and product quality traits have intermediate optima. Traditional selection index theory applies only to directional selection and cannot achieve any further improvement once the trait means have reached their optima. A well-founded theory is needed that extends the established selection index theory to cover directional as well as stabilizing selection as limiting cases, and that can be applied to maximize the profit of a breed in both situations.ResultsThe optimum selection index shifts the trait means towards the optima and, in the case of stabilizing selection, decreases the phenotypic variance, which causes the phenotypes to be closer to the optimum. The optimum index depends not only on the breeding values, but also on the squared breeding values, the allele contents of major quantitative trait loci (QTL), the QTL heterozygosities, the inbreeding coefficient of the animal, and the kinship of the animal with the population.ConclusionThe optimum selection index drives the alleles of major QTL to fixation when the trait mean approaches the optimum because decreasing the phenotypic variance shifts the trait values closer to the optimum, which increases the profit of the breed. The index weight on the kinship coefficient balances the increased genetic gain that can be achieved in future generations by outcrossing, and the increased genetic gain that can be achieved under stabilizing selection by reducing the phenotypic variance. In a model with dominance variance, it can also account for the effect of inbreeding depression. The combining ability between potential mating partners, which predicts the total merit of their offspring, could become an important parameter for mate allocation that could be used to further shift the phenotypes towards their optimum values.

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

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

Identification of QTL and alleles for agronomic and seed quality traits in C genome using a Brassica napus population diversified with B. oleracea

AbstractA genome‐wide association study (GWAS) was carried out by using a Brassica napus population of 175 lines, developed from six B. napus × B. oleracea interspecific crosses, and 5,743 single nucleotide polymorphism (SNP) markers to identify quantitative trait loci (QTL) for agronomic and seed quality traits and to understand the effect of B. oleracea alleles on these traits. Heritability of these traits varied from 52.9 to 84.1%. About 79% of the SNPs were positioned to the nine C genome chromosomes, while only 21% to the 10 A genome chromosomes; this was largely due to little genetic variation in the A genome of this population, as expected. However, the SNPs were distributed throughout the entire length of the chromosomes suggesting their usefulness in GWAS. The C genome SNPs detected nine genomic regions affecting these traits. This included the genomic regions of C2 and C5 affecting days to flowering, C1 affecting the duration of grain‐filling period, C1, C5, and C8 affecting oil content, and C1, C2, and C6 affecting glucosinolate content; among these, some of the loci has not been reported previously. The QTL alleles of B. oleracea which can be beneficial in oilseed B. napus, such as the C5 QTL allele for the earliness of flowering, were also identified. Several putative candidate genes were identified in the QTL regions. Thus, the results provided evidence of the utility of the B. oleracea gene pool for use in unveiling the unidentified QTL in B. napus as well as its use in breeding.

Identification and validation of stable quantitative trait loci for yield component traits in wheat

Grain weight and grain number are important yield component traits in wheat and identification of underlying genetic loci is helpful for improving yield. Here, we identified eight stable quantitative trait loci (QTL) for yield component traits, including five loci for thousand grain weight (TGW) and three for grain number per spike (GNS) in a recombinant inbred line population derived from cross Yangxiaomai/Zhongyou 9507 across four environments. Since grain size is a major determinant of grain weight, we also mapped QTL for grain length (GL) and grain width (GW). QTGW.caas-2D, QTGW.caas-3B, QTGW.caas-5A and QTGW.caas-7A.2 for TGW co-located with those for grain size. QTGW.caas-2D also had a consistent genetic position with QGNS.caas-2D, suggesting that the pleiotropic locus is a modulator of trade-off effect between TGW and GNS. Sequencing and linkage mapping showed that TaGL3-5A and WAPO-A1 were candidate genes of QTGW.caas-5A and QTGW.caas-7A.2, respectively. We developed Kompetitive allele specific PCR (KASP) markers linked with the stable QTL for yield component traits and validated their genetic effects in a diverse panel of wheat cultivars from the Huang-Huai River Valley region. KASP-based genotyping analysis further revealed that the superior alleles of all stable QTL for TGW but not GNS were subject to positive selection, indicating that yield improvement in the region largely depends on increased TGW. Comparative analyses with previous studies showed that most of the QTL could be detected in different genetic backgrounds, and QTGW.caas-7A.1 is likely a new QTL. These findings provide not only valuable genetic information for yield improvement but also useful tools for marker-assisted selection.

Integrating multi-locus genome-wide association studies with transcriptomic data to identify genetic loci underlying adult root trait responses to drought stress in flax (Linum usitatissimum L.)

Water stress is a major constraint on crop production and, root systems are one of the key features of plants determining drought tolerance and yield. In this study, five root morphological traits and their stability indices were evaluated at the reproductive stage on an association panel consisting of 120 diverse Linum usitatissimum accessions grown under well-watered and water-limiting conditions. To identify quantitative trait loci (QTL) and candidate genes positively influencing root traits under drought, combined multi-locus genome-wide association studies (ML-GWAS) and transcriptomic data analysis were carried out. A total of 112 QTL were identified accounting for 0.45–24.28 % of the phenotypic variation for root-related traits. Fifty QTL were detected by at least two ML-GWAS models, and 26 were co-located with previously reported QTL associated with yield-related traits under drought and early root and shoot development. Phenotypic differences between two contrasting subsets of accessions for the traits assessed were attributable to the accumulation of positive QTL alleles (PQTL), where the subset with the largest number of PQTL registered 154 % and 69 % greater total root length and yield under drought stress, respectively, than the subset with the fewest PQTL. Transcriptomic data analysis identified 766 differentially expressed genes (DEGs) responsive to drought stress in 108 QTL. Annotation of the 766 DEGs yielded functional genes involved in root development, stomatal closure, ROS (reactive oxygen species) scavenging, and hormone responses, among others. Taken together, the combined use of GWAS and transcriptomic data analyses provide the foundation for our enhanced understanding of root trait morphological changes in response to drought stress, and to achieve superior yield resilience/stability under water shortages in flax through enhanced molecular breeding. All data supporting the findings of this study are available within the paper and within its Supplementary data • Large genetic variation observed for adult root traits under drought and irrigated conditions. • Root traits explained 25–32 % of yield variation under drought stress. • A total of 112 QTL were identified for root traits and their stability indices in flax. • Twenty-six QTL co-located with previously reported QTL for yield traits under drought and root and shoot development. • Transcriptomic data analysis identified 766 drought responsive differentially expressed genes within the LD blocks of 108 significant QTL.

QTL analysis of the developmental changes in cell wall components and forage digestibility in maize (Zea mays L.)

Cell wall architecture plays a key role in stalk strength and forage digestibility. Lignin, cellulose, and hemicellulose are the three main components of plant cell walls, and they can impact stalk quality by affecting the structure and strength of the cell wall. To explore cell wall development during secondary cell wall lignification in maize stalks, conventional and conditional genetic mapping were used to identify the dynamic quantitative trait loci (QTLs) of the cell wall components and digestibility traits during five growth stages after silking. Acid detergent lignin (ADL), cellulose (CEL), acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVDMD) were evaluated in a maize recombinant inbred line (RIL) population. ADL, CEL, ADF, and NDF gradually increased from 10 to 40 days after silking (DAS), and then they decreased. IVDMD initially decreased until 40 DAS, and then it increased slightly. Seventy-two QTLs were identified for the five traits, and each accounted for 3.48–24.04% of the phenotypic variation. Six QTL hotspots were found, and they were localized in the 1.08, 2.04, 2.07, 7.03, 8.05, and 9.03 bins of the maize genome. Within the interval of the pleiotropic QTL identified in bin 1.08 of the maize genome, six genes associated with cell wall component biosynthesis were identified as potential candidate genes for stalk strength as well as cell wall-related traits. In addition, 26 conditional QTLs were detected in the five stages for all of the investigated traits. Twenty-two of the 26 conditional QTLs were found at 30 DAS conditioned using the values of 20 DAS, and at 50 DAS conditioned using the values of 40 DAS. These results indicated that cell wall-related traits are regulated by many genes, which are specifically expressed at different stages after silking. Simultaneous improvements in both forage digestibility and lodging resistance could be achieved by pyramiding multiple beneficial QTL alleles identified in this study.

Identification of QTL for Stem Traits in Wheat (Triticum aestivum L.).

Lodging in wheat (Triticum aestivum L.) is a complicated phenomenon that is influenced by physiological, genetics, and external factors. It causes a great yield loss and reduces grain quality and mechanical harvesting efficiency. Lodging resistance is contributed by various traits, including increased stem strength. The aim of this study was to map quantitative trait loci (QTL) controlling stem strength-related features (the number of big vascular bundles, stem diameter, stem wall thickness) using a doubled haploid (DH) population derived from a cross between Baiqimai and Neixiang 5. Field experiments were conducted during 2020–2022, and glasshouse experiments were conducted during 2021–2022. Significant genetic variations were observed for all measured traits, and they were all highly heritable. Fifteen QTL for stem strength-related traits were identified on chromosomes 2D, 3A, 3B, 3D, 4B, 5A, 6B, 7A, and 7D, respectively, and 7 QTL for grain yield-related traits were identified on chromosomes 2B, 2D, 3D, 4B, 7A, and 7B, respectively. The superior allele of the major QTL for the number of big vascular bundle (VB) was independent of plant height (PH), making it possible to improve stem strength without a trade-off of PH, thus improving lodging resistance. VB also showed positive correlations with some of the yield components. The result will be useful for molecular marker-assisted selection (MAS) for high stem strength and high yield potential.

QTL Mapping for Age-Related Eye Pigmentation in the Pink-Eyed Dilution Castaneus Mutant Mouse.

Pink-eyed dilution castaneus (Oca2p-cas) is a mutant gene on mouse chromosome 7 that arose spontaneously in wild Mus musculus castaneus. Homozygotes for Oca2p-cas exhibit pink eyes and a light gray coat throughout life. In an ordinary mutant strain carrying Oca2p-cas, we previously discovered a novel spontaneous mutation that gradually increases melanin pigmentation in the eyes and coat with aging, and we developed a novel mutant strain that was fixed for the novel phenotype. The purpose of this study was to map major quantitative trait loci (QTLs) for the novel pigmentation phenotype and for expression levels of four important melanogenesis genes, microphthalmia-associated transcription factor (Mitf), tyrosinase (Tyr), tyrosinase-related protein-1 (Tyrp1) and dopachrome tautomerase (Dct). We developed 69 DNA markers and created 303 F2 mice from two reciprocal crosses between novel and ordinary mutant strains. The QTL analysis using a selective genotyping strategy revealed a significant QTL for eye pigmentation between 34 and 64 Mb on chromosome 13. This QTL explained approximately 20% of the phenotypic variance. The QTL allele derived from the novel strain increased pigmentation. Although eye pigmentation was positively correlated with Dct expression, no expression QTLs were found, suggesting that the pigmentation QTL on chromosome 13 may not be directly in the pathway of any of the four melanogenesis genes. This study is the first step toward identifying a causal gene for the novel spontaneous phenotype in mice and is expected to discover a new regulatory mechanism for complex melanin biosynthesis during aging.

Identification and validation of quantitative trait loci for a parameter associated with nitrogen partitioning to grain using a population derived from japonica- and indica-type cultivars of rice (Oryza sativa L.)

ABSTRACT Nitrogen (N) partitioning to grain affects productivity and grain quality in rice. The objectives of this study were to clarify the difference between the rice cultivars ‘Momiroman’ (japonica) and ‘Takanari’ (indica) in the relation between the amount of total N in aboveground parts per grain dry weight (TNA/GW) and grain N concentration (GNC), to identify quantitative trait loci (QTLs) associated with the coefficient characterizing this relation by using populations derived from a cross between Momiroman and Takanari, and to verify the effects of the detected QTLs by using near-isogenic lines (NILs). We used 156 F2 plants grown under high N in 2015 and 156 F3 lines grown under high or low N in 2016, and determined N concentrations and contents in grain and aboveground vegetative parts. We found a logarithmic relation between GNC and TNA/GW in Momiroman and Takanari. The regression coefficient (A) was higher in Takanari. Under each N condition, A was calculated for each population and QTL analysis was performed. QTLs for A were detected on chromosomes (Chrs.) 6 and 10 in all conditions; the Takanari alleles of both QTLs increased the value. NILs with the Takanari allele in each region had higher A than NILs with the Momiroman alleles. We conclude that the QTLs for A are associated with N partitioning to grain in rice. Abbreviations: GNA, amount of N in grain; GNC, grain N concentration; GW, grain dry weight; TNA, amount of N in aboveground parts

Identification and Validation of Quantitative Trait Loci for Grain Size in Bread Wheat (Triticum aestivum L.)

Grain width (GW) and grain length (GL) are crucial components affecting grain weight. Dissection of their genetic control is essential for improving yield potential in wheat breeding. Yangmai 12 (YM12) and Yanzhan 1 (YZ1) are two elite cultivars released in the Middle and Lower Yangtze Valleys Wheat Zone (MLYVWZ) and the Yellow-Huai River Valleys Wheat Zone (YRVWZ), respectively. One biparental population derived from YM12/YZ1 cross was employed to perform QTL mapping based on the data from four environments over two years to detect quantitative trait loci (QTL) for GW and GL. A total of eight QTL were identified on chromosomes 1B, 2D, 3B, 4B, 5A, and 6B. Notably, QGW.yz.2D was co-located with QGL.yz.2D, and QGW.yz.4B was co-located with QGL.yz.4B, respectively. QGW.yz.2D and QGL.yz.2D, with the increasing GW/GL allele from YZ1, explained 12.36–18.27% and 13.69–26.53% of the phenotypic variations for GW and GL, respectively. QGW.yz.4B and QGL.yz.4B, with the increasing GW/GL allele from YM12, explained 10.34–11.95% and 10.35–16.04% of the phenotypic variation for GW and GL, respectively. QGL.yz.5A, with the increasing GL allele from YM12, explained 10.04–12.48% of the phenotypic variation for GL. Moreover, the positive alleles of these three QTL regions could significantly increase thousand-grain weight, and QGW.yz.4B/QGL.yz.4B and QGL.yz.5A did not show significant negative effects on grain number per spike. QGL.yz.2D, QGW.yz.4B/QGL.yz.4B, and QGL.yz.5A have not been reported. These three QTL regions were then further validated using Kompetitive Allele-Specific PCR (KASP) markers in 159 wheat cultivars/lines from MLYVWZ and YRVWZ. Combining the positive alleles of the major QTL significantly increased GW and GL. Eleven candidate genes associated with encoding ethylene-responsive transcription factor, oleosin, osmotin protein, and thaumatin protein were identified. Three major QTL and KASP markers reported here will be helpful in developing new wheat cultivars with high and stable yields.

Genomic Regions and Floral Traits Contributing to Low Temperature Tolerance at Young Microspore Stage in a Rice (Oryza sativa L.) Recombinant Inbred Line Population of Sherpa/IRAT109.

Aerobic rice production (AP) consumes less water compared to flooded systems. Developing genotypes and identifying genomic regions associated with low temperature (LT) tolerance at the young microspore stage (YMS) is imperative for AP, particularly for temperate regions. Using a recombinant inbred line population derived from the Australian LT tolerant variety Sherpa, experiments were conducted to map and dissect quantitative trait loci (QTL) associated with spikelet sterility (SS) after exposure to LT and to investigate floral traits contributing to the development of lower SS. Significant genotypic variation for SS was observed in the population after exposure to LT at YMS. Three genomic regions associated with SS, qYMCT3, qYMCT4, and qYMCT8.1 were identified in chromosomes 3, 4, and 8 respectively, using multiple QTL models explaining 22.4% of the genotypic variation. Introgression of the favorable allele from qYMCT3 was estimated to reduce SS by up to 15.4%. A co-locating genomic region with qYMCT3, qDTHW3.1 was identified as the major QTL affecting days to heading and explained as much as 44.7% of the genotypic variation. Whole-genome sequence and bioinformatic analyses demonstrated OsMADS50 as the candidate gene for qYMCT3/qDTHW3.1 and to our knowledge, this was the first attempt in connecting the role of OsMADS50 in both LT and flowering in rice. Differential sets selected for extreme SS showed LT tolerant genotype group produced higher total pollen per spikelet resulting in a higher number of dehisced anthers and pollen on stigma and eventually, lower SS than THE sensitive group. The relationship between these key floral traits with SS was induced only after exposure to LT and was not observed in warm ideal temperature conditions. Identification of elite germplasm with favorable QTL allele and combinations, gene cloning, and pyramiding with additional high-value QTL for key traits should empower breeders to develop AP adapted genotypes for temperate growing regions, and ultimately produce climate-resilient rice.

QTL detection for bread wheat processing quality in a nested association mapping population of semi-wild and domesticated wheat varieties

BackgroundWheat processing quality is an important factor in evaluating overall wheat quality, and dough characteristics are important when assessing the processing quality of wheat. As a notable germplasm resource, semi-wild wheat has a key role in the study of wheat processing quality.ResultsIn this study, four dough rheological characteristics were collected in four environments using a nested association mapping (NAM) population consisting of semi-wild and domesticated wheat varieties to identify quantitative trait loci (QTL) for wheat processing quality. A total of 49 QTL for wheat processing quality were detected, explaining 0.36–10.82% of the phenotypic variation. These QTL were located on all wheat chromosomes except for 2D, 3A, 3D, 6B, 6D and 7D. Compared to previous studies, 29 QTL were newly identified. Four novel QTL, QMlPH-1B.4, QMlPH-3B.4, QWdEm-1B.2 and QWdEm-3B.2, were stably identified in three or more environments, among which QMlPH-3B.4 was a major QTL. Moreover, eight important genetic regions for wheat processing quality were identified on chromosomes 1B, 3B and 4D, which showed pleiotropy for dough characteristics. In addition, out of 49 QTL, 15 favorable alleles came from three semi-wild parents, suggesting that the QTL alleles provided by the semi-wild parent were not utilized in domesticated varieties.ConclusionsThe results show that semi-wild wheat varieties can enrich the existing wheat gene pool and provide broader variation resources for wheat genetic research.

Multiallelic models for QTL mapping in diverse polyploid populations

Quantitative trait locus (QTL) analysis allows to identify regions responsible for a trait and to associate alleles with their effect on phenotypes. When using biallelic markers to find these QTL regions, two alleles per QTL are modelled. This assumption might be close to reality in specific biparental crosses but is unrealistic in situations where broader genetic diversity is studied. Diversity panels used in genome-wide association studies or multi-parental populations can easily harbour multiple QTL alleles at each locus, more so in the case of polyploids that carry more than two alleles per individual. In such situations a multiallelic model would be closer to reality, allowing for different genetic effects for each potential allele in the population. To obtain such multiallelic markers we propose the usage of haplotypes, concatenations of nearby SNPs. We developed “mpQTL” an R package that can perform a QTL analysis at any ploidy level under biallelic and multiallelic models, depending on the marker type given. We tested the effect of genetic diversity on the power and accuracy difference between bi-allelic and multiallelic models using a set of simulated multiparental autotetraploid, outbreeding populations. Multiallelic models had higher detection power and were more precise than biallelic, SNP-based models, particularly when genetic diversity was higher. This confirms that moving to multi-allelic QTL models can lead to improved detection and characterization of QTLs.Key messageQTL detection in populations with more than two functional QTL alleles (which is likely in multiparental and/or polyploid populations) is more powerful when using multiallelic models, rather than biallelic models.

Differential growth of Leptosphaeria maculans in the stem of susceptible and partially resistant oilseed rape (Brassica napus L.) genotypes

Quantitative resistance (QR) to Leptosphaeria maculans in Brassica napus has proven to be very useful for breeding resistant varieties with increased potential for durability. To date, however, QR has been assessed primarily in the field after a long plant developmental cycle and its expression is influenced by environmental conditions. An evaluation method in controlled conditions would offer the possibility to evaluate the level of QR in a shorter time and to study the kinetics of fungal growth in the stem in relation to susceptibility/resistance levels conferred by quantitative trait loci (QTL). We used a cut-petiole inoculation method coupled with both visual and PCR-based phenotyping at different time-points after inoculation, which revealed different kinetics of symptom development and pathogen growth among varieties. The results obtained with this method were partly consistent with field resistance phenotyping data, and allowed detection of the effect of at least two resistance QTL alleles introduced in near-isogenic lines. This method would be useful to compare a wider range of host varieties, to study the spectrum effect of resistance QTL or to decipher the mechanisms underlying this quantitative resistance.