Main Quantitative Trait Loci Research Articles

Genetic and QTL analysis of sugars and acids content in sweet cherry (Prunus avium L.)

Abstract Sweet cherry is very appreciated by consumers because of its attractive appearance and taste, which is determined by the balanced sweet-sour flavor. In this work, the genetics of soluble solid content (SSC), titratable acidity (TA), sugars and organic acids was investigated in sweet cherry to facilitate breeding improvement for fruit quality. The fruits of five sweet cherry populations (N = 372), three F1 and two F2, were sampled over two years to evaluate SSC, TA, and the content of individual sugars (glucose, fructose, sorbitol, and sucrose) and organic acids (malic, quinic, oxalic, citric and shikimic) by ultra-performance liquid chromatography (UPLC). Glucose, followed by fructose, was the most abundant sugar, while malic acid was the predominant acid. Sorbitol and malic acid were the most stable compounds between years, and had the highest heritability, being also the best correlated to SSC and TA respectively, revealing their relevance for breeding. Significantly positive correlations were observed among sugars and SSC, and acids and TA, but high interannual variability between years was observed for all traits. QTL mapping for SSC, sugars, TA, and organic acids was performed using a multi-family approach with FlexQTL™. Twenty QTLs were detected consistently during the two phenotyped years, and several relevant regions with overlapping QTLs for sugars and acids were also identified. The results confirmed major stable SSC and TA QTLs on the linkage groups 4 and 6, respectively. Within the main LG4 SSC QTL region, where maturity and fruit development time QTLs have been previously detected, three stable sugar (glucose, sorbitol, and sucrose) and two acid (quinic, shikimic) QTLs were also identified, suggesting a pleiotropic effect of ripening date on the content of these compounds. The major malic acid QTL overlapped with TA QTL on LG6, thus TA QTL mapping in LG6 may correspond to malic acid QTLs. Haplotype analyses of major SSC and sugars QTL in LG4, and TA and malic acid in LG6 revealed haplotypes of breeding interest. Several candidate genes previously identified in other Prunus fruit species, like peach, were found to collocate with the QTLs detected herein. This work reports QTLs regions and haplotypes of sugar and acid content in a Prunus non-climacteric stone fruit for the first time.

CaGAUT1, a main QTL gene, positively regulates fruit cracking in pepper

CaGAUT1, a main QTL gene, positively regulates fruit cracking in pepper

Multiple Localization Analysis of the Major QTL-sfw 2.2 for Controlling Single Fruit Weight Traits in Melon Based on SLAF Sequencing.

Cucumis melo is an annual dicotyledonous trailing herb. It is fruity, cool, and refreshing to eat and is widely loved by consumers worldwide. The single fruit weight is an important factor affecting the yield, and thus the income and economic benefits, of melon crops. In this study, to identify the main QTLs (quantitative trait locus) controlling the single fruit weight of melon and thereby identify candidate genes controlling this trait, specific-locus amplified fragment sequencing (SLAF) analysis was performed on the offspring of female 1244 plants crossed with male MS-5 plants. A total of 115 individual plants in the melon F2 population were analyzed to construct a genetic linkage map with a total map distance of 1383.88 cM by the group in the early stages of the project, which was divided into 12 linkage groups with a total of 10,596 SLAF markers spaced at an average genetic distance of 0.13 cM. A total of six QTLs controlling single fruit weight (sfw loci) were detected. Seven pairs of markers with polymorphisms were obtained by screening candidate intervals from the SLAF data. The primary QTL sfw2.2 was further studied in 300 F2:3 family lines grown in 2020 and 2021, respectively, a positioning sfw2.2 between the markers CY Indel 11 and CY Indel 16, between 18,568,142 and 18,704,724 on chromosome 2. This interval contained 136.58 kb and included three genes with functional annotations, MELO3C029673, MELO3C029669, and MELO3C029674. Gene expression information for different fruit development stages was obtained from 1244 and MS-5 fruits on the 15d, 25d, and 35d after pollination, and qRT-PCR (quantitative reverse transcription-PCR) indicated that the expression of the MELO3C029669 gene significantly differed between the parents during the three periods. The gene sequences between the parents of MELO3C029669 were analyzed and compared, a base mutation was found to occur in the intronic interval between the parents of the gene, from A-G. Phylogenetic evolutionary tree analysis revealed that the candidate gene MELO3C029669 is most closely related to Pisum sativum Fimbrin-5 variant 2 and most distantly related to Cucumis melo var. makuwa. Therefore, it was hypothesized that MELO3C029669 is the primary major locus controlling single fruit weight in melon. These results not only provide a theoretical basis for further studies to find genes with functions in melon single fruit weight but also lay the foundation for accelerating breakthroughs and innovations in melon breeding.

Improving complex agronomic and domestication traits in the perennial grain crop intermediate wheatgrass with genetic mapping and genomic prediction.

The perennial grass Thinopyrum intermedium (intermediate wheatgrass [IWG]) is being domesticated as a food crop. With a deep root system and high biomass, IWG can help reduce soil and water erosion and limit nutrient runoff. As a novel grain crop undergoing domestication, IWG lags in yield, seed size, and other agronomic traits compared to annual grains. Better characterization of trait variation and identification of genetic markers associated with loci controlling the traits could help in further improving this crop. The University of Minnesota's Cycle 5 IWG breeding population of 595 spaced plants was evaluated at two locations in 2021 and 2022 for agronomic traits plant height, grain yield, and spike weight, and domestication traits shatter resistance, free grain threshing, and seed size. Pairwise trait correlations were weak to moderate with the highest correlation observed between seed size and height (0.41). Broad-sense trait heritabilities were high (0.68-0.77) except for spike weight (0.49) and yield (0.44). Association mapping using 24,284 genome-wide single nucleotide polymorphism markers identified 30 main quantitative trait loci (QTLs) across all environments and 32 QTL-by-environment interactions (QTE) at each environment. The genomic prediction model significantly improved predictions when parents were used in the training set and significant QTLs and QTEs used as covariates. Seed size was the best predicted trait with model predictive ability (r) of 0.72; yield was predicted moderately well (r=0.45). We expect this discovery of significant genomic loci and mostly high trait predictions from genomic prediction models to help improve future IWG breeding populations.

Screening and analysis of candidate genes conferring alkalinity tolerance in rice (Oryza sativa L.) at the bud burst stage based on QTL-seq and RNA-seq

BackgroundSoil salinization is one of the key factors restricting the production of cropland. Once rice is subjected to alkali stress at the bud burst stage, the yield will suffer irreparable serious loss. Compared with salt tolerance, studies on QTL mapping and candidate gene analysis of rice alkali tolerance are limited. ResultsIn this study, we used the F2:3 population derived from the alkali-tolerant cultivar LD21 and the alkali-sensitive cultivar WL138 to construct an alkali-tolerant DNA mixing pool, and the BSA (Bulked Segregation Analysis) method was used for re-sequencing. The main QTL qRSLB9 controlling the relative shoot length of rice under alkali stress was mapped by QTL-seq. The candidate interval was narrowed to 346.5 kb by regional linkage mapping, which containing 6 DEGs screened through transcriptome sequencing. The qRT-PCR and candidate gene sequencing showed that LOC_Os09g24260 was most likely to control relative shoot length (RSL) in rice as a major gene who encodes the WD domain, G-beta repeat domain-containing protein. ConclusionsBased on these results, LOC_Os09g24260 was the candidate gene of qRSLB9 conferring alkalinity tolerance to rice at the bud burst stage. Our study provides valuable genetic information and materials for breeding new rice varieties with alkalinity tolerance.How to cite: Wang J, Bian J, Liu L, et al. Screening and analysis of candidate genes conferring alkalinity tolerance in rice (Oryza sativa L.) at the bud burst stage based on QTL-seq and RNA-seq. Electron J Biotechnol 2024;71. https://doi.org/10.1016/j.ejbt.2024.07.002.

Mapping of main and hidden epistatic QTL effects in spring wheat population using medium parental FHB resistance

Fusarium head blight (FHB) is a devastating disease lowering the yield and quality of wheat. Intensive use of limited allelic pools critically affects wheat resistance, while advancing pathogenic alleles. This study presents new alleles raised from moderate rather than elite crosses. ‘Parshall’ has indigenous moderate resistance that was crossed with the moderate susceptible ‘Reeder’ and developed the 110 RIL population (noted as PR) that was tested across three states and years in the USA, under open-field and greenhouse conditions. Heading- and FHB-related traits of incidence, severity, and index were assessed. A genetic map (1417 cM) of SNP/DArT markers was generated. Composite interval mapping produced 45 QTL. Permutated LOD assessment identified two consistent QTL (4AL and 4BL) of type I and II resistance. Significant markers at the 4A QTL showed correlation with previous FHB resistance, while at the 4B QTL with pathogen responsive regions. The 1- and 2-D genome scans identified 16 QTL and six pairs of interacting markers for resistance, with additive effects between 0.17% and 2.19%; respectively. Additionally, additive × environment interaction was between 0.04% and 3.18% confirming the high environmental effect. Three pairs of QTL with additive × additive effects between 0.15% and 0.30% were revealed by FHB epistasis. However, the additive × additive environmental interaction at these three loci varied between 0.03% and 1%, confirming the G × E effect on FHB resistance. Hidden heritable epistasis was discovered in PR-population for FHB resistance. PR-alleles will help breeders develop lines mitigating epidemic environments and changeable climates, to boost yield facing hanger, food scarce, and secure worldwide penurious economies.

Identification of Resistance QTLs to Black Leaf Streak Disease (Due to Pseudocercospora fijiensis) in Diploid Bananas (Musa acuminata)

Black Leaf Streak Disease (BLSD), caused by the fungus Pseudocercospora fijiensis, is a recent pandemic and the most economically and environmentally important leaf disease of banana. To assist breeding of varieties with durable resistance to the rapidly evolving P. fijiensis, we used a diploid genitor ‘IDN 110’ with partial resistance to BLSD to search for QTLs. We assessed diploid progeny of 73 hybrids between ‘IDN 110’ and the diploid cultivar ‘Khai Nai On’, which is susceptible to BLSD. Hybrids were phenotyped with artificial inoculation under controlled conditions. This method allowed us to focus on resistance in the early stages of the interaction already identified as strongly influencing BLSD epidemiology. Progeny were genotyped by sequencing. As both parents are heterozygous for large reciprocal translocations, the distribution of recombination was assessed and revealed regions with low recombination rates. Fourteen non-overlapping QTLs of resistance to BLSD were identified of which four main QTLs from the ‘IDN110‘ parent, located on chromosomes 06, 07, 08, and 09, were shown to be of interest for marker-assisted selection. Genes that underline those four QTLs are discussed in the light of previous literature.

Dissection of the E8 locus in two early maturing Canadian soybean populations.

Soybean [Glycine max (L.) Merr.] is a short-day crop for which breeders want to expand the cultivation range to more northern agro-environments by introgressing alleles involved in early reproductive traits. To do so, we investigated quantitative trait loci (QTL) and expression quantitative trait loci (eQTL) regions comprised within the E8 locus, a large undeciphered region (~7.0 Mbp to 44.5 Mbp) associated with early maturity located on chromosome GM04. We used a combination of two mapping algorithms, (i) inclusive composite interval mapping (ICIM) and (ii) genome-wide composite interval mapping (GCIM), to identify major and minor regions in two soybean populations (QS15524F2:F3 and QS15544RIL) having fixed E1, E2, E3, and E4 alleles. Using this approach, we identified three main QTL regions with high logarithm of the odds (LODs), phenotypic variation explained (PVE), and additive effects for maturity and pod-filling within the E8 region: GM04:16,974,874-17,152,230 (E8-r1); GM04:35,168,111-37,664,017 (E8-r2); and GM04:41,808,599-42,376,237 (E8-r3). Using a five-step variant analysis pipeline, we identified Protein far-red elongated hypocotyl 3 (Glyma.04G124300; E8-r1), E1-like-a (Glyma.04G156400; E8-r2), Light-harvesting chlorophyll-protein complex I subunit A4 (Glyma.04G167900; E8-r3), and Cycling dof factor 3 (Glyma.04G168300; E8-r3) as the most promising candidate genes for these regions. A combinatorial eQTL mapping approach identified significant regulatory interactions for 13 expression traits (e-traits), including Glyma.04G050200 (Early flowering 3/E6 locus), with the E8-r3 region. Four other important QTL regions close to or encompassing major flowering genes were also detected on chromosomes GM07, GM08, and GM16. In GM07:5,256,305-5,404,971, a missense polymorphism was detected in the candidate gene Glyma.07G058200 (Protein suppressor of PHYA-105). These findings demonstrate that the locus known as E8 is regulated by at least three distinct genomic regions, all of which comprise major flowering genes.

The genetic architecture of the adaptive potential of Arabidopsis thaliana in response to Pseudomonas syringae strains isolated from south‐west France

AbstractPhytopathogens are a threat for global food production and security. Emergence or re‐emergence of plant pathogens is highly dependent on the environmental conditions affecting pathogen spread and survival. Under climate change, a geographic expansion of pathogen distribution poleward has been observed, potentially resulting in disease outbreaks on crops and wild plants. Therefore, estimating the adaptive potential of plants to novel epidemics and describing the underlying genetic architecture is a primary need to propose agricultural management strategies reducing pathogen outbreaks and to breed novel plant cultivars adapted to pathogens that might spread under climate change. To address this challenge, we inoculated Pseudomonas syringae strains isolated from Arabidopsis thaliana populations from south‐west of France on the highly genetically polymorphic TOU‐A A. thaliana population from north‐east France. While no adaptive potential was identified in response to most P. syringae strains, the TOU‐A population displayed a variable disease response to the JACO‐CL strain belonging to the P. syringae phylogroup 7 (PG7). This strain carried a reduced type III secretion system (T3SS) characteristic of the PG7 as well as flexible genomic traits and potential novel effectors. Genome‐wide association mapping on 192 TOU‐A accessions revealed a polygenic architecture of disease response to JACO‐CL. The main quantitative trait locus (QTL) region encompasses two R genes and the AT5G18310 gene encoding ubiquitin hydrolase, a target of the AvrRpt2 P. syringae effector. Altogether, our results pave the way for a better understanding of the genetic and molecular basis of the adaptive potential in an ecologically relevant A. thaliana–P. syringae pathosystem.

BSA-Seq for the Identification of Major Genes for EPN in Rice.

Improving rice yield is one of the most important food issues internationally. It is an undeniable goal of rice breeding, and the effective panicle number (EPN) is a key factor determining rice yield. Increasing the EPN in rice is a major way to increase rice yield. Currently, the main quantitative trait locus (QTL) for EPN in rice is limited, and there is also limited research on the gene for EPN in rice. Therefore, the excavation and analysis of major genes related to EPN in rice is of great significance for molecular breeding and yield improvement. This study used japonica rice varieties Dongfu 114 and Longyang 11 to construct an F5 population consisting of 309 individual plants. Two extreme phenotypic pools were constructed by identifying the EPN of the population, and QTL-seq analysis was performed to obtain three main effective QTL intervals for EPN. This analysis also helped to screen out 34 candidate genes. Then, EPN time expression pattern analysis was performed on these 34 genes to screen out six candidate genes with higher expression levels. Using a 3K database to perform haplotype analysis on these six genes, we selected haplotypes with significant differences in EPN. Finally, five candidate genes related to EPN were obtained.

Almond population genomics and non-additive GWAS reveal new insights into almond dissemination history and candidate genes for nut traits and blooming time.

Domestication drastically changed crop genomes, fixing alleles of interest and creating different genetic populations. Genome-wide association studies (GWASs) are a powerful tool to detect these alleles of interest (and so QTLs). In this study, we explored the genetic structure as well as additive and non-additive genotype-phenotype associations in a collection of 243 almond accessions. Our genetic structure analysis strongly supported the subdivision of the accessions into five ancestral groups, all formed by accessions with a common origin. One of these groups was formed exclusively by Spanish accessions, while the rest were mainly formed by accessions from China, Italy, France, and the USA. These results agree with archaeological and historical evidence that separate modern almond dissemination into four phases: Asiatic, Mediterranean, Californian, and southern hemisphere. In total, we found 13 independent QTLs for nut weight, crack-out percentage, double kernels percentage, and blooming time. Of the 13 QTLs found, only one had an additive effect. Through candidate gene analysis, we proposed Prudul26A013473 as a candidate gene responsible for the main QTL found in crack-out percentage, Prudul26A012082 and Prudul26A017782 as candidate genes for the QTLs found in double kernels percentage, and Prudul26A000954 as a candidate gene for the QTL found in blooming time. Our study enhances our knowledge of almond dissemination history and will have a great impact on almond breeding.

Novel quantitative trait loci from an interspecific Brassica rapa derivative improve pod shatter resistance in Brassica napus.

Pod shatter is a trait of agricultural relevance that ensures plants dehisce seeds in their native environment and has been subjected to domestication and selection for non-shattering types in several broadacre crops. However, pod shattering causes a significant yield reduction in canola (Brassica napus L.) crops. An interspecific breeding line BC95042 derived from a B. rapa/B. napus cross showed improved pod shatter resistance (up to 12-fold than a shatter-prone B. napus variety). To uncover the genetic basis and improve pod shatter resistance in new varieties, we analysed F2 and F2:3 derived populations from the cross between BC95042 and an advanced breeding line, BC95041, and genotyped with 15,498 DArTseq markers. Through genome scan, interval and inclusive composite interval mapping analyses, we identified seven quantitative trait loci (QTLs) associated with pod rupture energy, a measure for pod shatter resistance or pod strength, and they locate on A02, A03, A05, A09 and C01 chromosomes. Both parental lines contributed alleles for pod shatter resistance. We identified five pairs of significant epistatic QTLs for additive x additive, additive dominance and dominance x dominance interactions between A01/C01, A03/A07, A07/C03, A03/C03, and C01/C02 chromosomes for rupture energy. QTL effects on A03/A07 and A01/C01 were in the repulsion phase. Comparative mapping identified several candidate genes (AG, ABI3, ARF3, BP1, CEL6, FIL, FUL, GA2OX2, IND, LATE, LEUNIG, MAGL15, RPL, QRT2, RGA, SPT and TCP10) underlying main QTL and epistatic QTL interactions for pod shatter resistance. Three QTLs detected on A02, A03, and A09 were near the FUL (FRUITFULL) homologues BnaA03g39820D and BnaA09g05500D. Focusing on the FUL, we investigated putative motifs, sequence variants and the evolutionary rate of its homologues in 373 resequenced B. napus accessions of interest. BnaA09g05500D is subjected to purifying selection as it had a low Ka/Ks ratio compared to other FUL homologues in B. napus. This study provides a valuable resource for genetic improvement for yield through an understanding of the genetic mechanism controlling pod shatter resistance in Brassica species.

Novel QTL for Lateral Root Density and Length Improve Phosphorus Uptake in Rice (Oryza sativa L.)

The rice root system consists of two types of lateral roots, indeterminate larger L-types capable of further branching, and determinate, short, unbranched S-types. L-type laterals correspond to the typical lateral roots of cereals whereas S-type laterals are unique to rice. Both types contribute to nutrient and water uptake and genotypic variation for density and length of these laterals could be exploited in rice improvement to enhance adaptations to nutrient and water-limited environments. Our objectives were to determine how best to screen for lateral root density and length and to identify markers linked to genotypic variation for these traits. Using different growing media showed that screening in nutrient solution exposed genotypic variation for S-type and L-type density, but only the lateral roots of soil-grown plants varied for their lengths. A QTL mapping population developed from parents contrasting for lateral root traits was grown in a low-P field, roots were sampled, scanned and density and length of lateral roots measured. One QTL each was detected for L-type density (LDC), S-type density on crown root (SDC), S-type density on L-type (SDL), S-type length on L-type (SLL), and crown root number (RNO). The QTL for LDC on chromosome 5 had a major effect, accounting for 46% of the phenotypic variation. This strong positive effect was confirmed in additional field experiments, showing that lines with the donor parent allele at qLDC5 had 50% higher LDC. Investigating the contribution of lateral root traits to P uptake using stepwise regressions indicated LDC and RNO were most influential, followed by SDL. Simulating effects of root trait differences conferred by the main QTL in a P uptake model confirmed that qLDC5 was most effective in improving P uptake followed by qRNO9 for RNO and qSDL9 for S-type lateral density on L-type laterals. Pyramiding qLDC5 with qRNO9 and qSDL9 would be possible given that trade-offs between traits were not detected. Phenotypic selection for the RNO trait during variety development would be feasible, however, the costs of doing so reliably for lateral root density traits is prohibitive and markers identified here therefore provide the first opportunity to incorporate such traits into a breeding program.

High-density GBS-based genetic linkage map construction and QTL identification associated with leaf cuticular wax, adaxial stomatal density and leaf water retention capacity in banana

The drought tolerance quantitative trait locus (QTL) in Banana has not been studied to date. In this study, the susceptible parent Musa acuminata ssp. burmannicoides Colla –'Calcutta-4' and the resistant parent Musa balbisiana collection 'Bee hee kela' were crossed to produce an F1 mapping population of 96 individuals for the purpose of mapping drought tolerance traits in banana. Consequently, an entirely novel mapping population was developed using progenitor lines with distinct genomic compositions (A genome and B genome). We employed, the GBS (Genotype By Sequencing) technique to develop a genetic linkage map. The map contained a total of 1015 SNP markers, 11 linkage groups, and a total distance of 4828.88cM. The average distance between markers was 4.9cm. The two primary methods that a plant loses water are through stomata and cuticle transpiration, both of which is not beneficial for the plant. Thus, in the present investigation, the AB mapping population's adaxial stomatal count is measured using a microscopic technique, and leaf cuticular wax was estimated using a spectroscopic method. In addition, the leaf's water retention capacity was estimated. Genetic analysis showed that the drought tolerance traits exhibited moderate to moderately high PCV, GCV, and GAM values, as well as high heritability. Using the GBS-based genetic linkage map and phenotyping information, the QTL analysis identified five main QTLs for drought tolerance on chromosomes 2, 5, and 8. They were designated as wax13_1, wax15_1, wax15_2, lwrc_1, and asd_1. The PVE (per cent) of the identified QTLs varied between 15.9 and 19.8 percent. To our knowledge, this is the first report on the employing of SNP markers to identify QTLs associated with drought tolerance traits in banana. This study's findings will be helpful in fine-mapping and marker-assisted selection in banana for drought related traits.

QTL mapping and improvement of pre-harvest sprouting resistance using japonica weedy rice.

The stability of cultivation and production in terms of crop yield has been threatened by climate change due to global warming. Pre-harvest sprouting (PHS) is a threat to crops, especially staple foods, including rice, because of reductions in yield and quality. To address the problem of precocious germination before harvest, we performed quantitative trait loci (QTL) analysis for PHS using F8 RILs populations derived from japonica weedy rice in Korea. QTL analysis revealed that two stable QTLs, qPH7 and qPH2, associated with PHS resistance were identified on chromosomes 7 and 2, respectively, explaining approximately 38% of the phenotypic variation. The QTL effect in the tested lines significantly decreased the degree of PHS, based on the number of QTLs included. Through fine mapping for main QTL qPH7, the region for the PHS was found to be anchored within 23.575-23.785 Mbp on chromosome 7 using 13 cleaved amplified sequence (CAPS) markers. Among 15 open reading frames (ORFs) within the detected region, one ORF, Os07g0584366, exhibited upregulated expression in the resistant donor, which was approximately nine times higher than that of susceptible japonica cultivars under PHS-inducing conditions. Japonica lines with QTLs related to PHS resistance were developed to improve the characteristics of PHS and design practical PCR-based DNA markers for marker-assisted backcrosses of many other PHS-susceptible japonica cultivars.

QTL localisation of seed-related traits in Tibetan hulless barley based on a high-density single-nucleotide polymorphism genetic map

The effective use of high-quality and high-yielding germplasm resources is of great importance for the development of hulless barley varieties. Therefore, the search for such resources has long been a goal of the breeding community. In this study, a genotyping-by-sequencing (GBS) analysis was performed on an F2 (Nierumuzha × Kunlun 10) population. A high-density genetic map of hulless barley was constructed, which contained 1 475 efficient single-nucleotide polymorphism markers with 7 052 bin markers. The total length of the seven chromosomes was 1 139.4 cM, with an average marker distance of 0.59 cM. Based on this high-density linkage map, a total of 54 quantitative trait loci (QTLs) related to the seed traits were detected, including seed colour (SC), thousand kernel weight (TKW), seed average area (SAA), seed perimeter (SP), seed length (SL), seed width (SW), seed length/width (SLW), seed diameter (SD), and seed circular degree (SCD). These QTLs explained 3.32–35.73% (mean = 11.45%) of the phenotypic interpretation, including 24 main QTLs and 30 epistatic QTLs. A total of 24 candidate genes were identified within the QTL region, including one SC-associated transcription factor (ANT1), two TSW-related genes, a transcription factor (NAC021), a gene associated with the non-homologous end joining (NHEJ) pathway (ku70), three SAA-associated genes (LOL2, NAC021, TSK), two SL-associated genes (MADS21, MADS4), six SW-associated genes (FIP1, NAC021, DREB 1A, HVA22A, CYP78A6, SAUR71), five LW-related genes (NAM-B2, CRY1, LHY, CYP710A1, WRKY72), two SP-related genes (SKIP11, TCP18), two SD-related genes (NAC021, SKIP8), and three SCD-related genes (MYB1R1, RAX3, NAC100). These genes are involved in the regulation of the cell development, material transport, signal transduction, and plant morphogenesis and play an important role in the regulation of agronomic traits in hulless barley. The high-density genetic mapping and QTL identification of the seed traits in hulless barley provide a valuable genetic resource and the basis for further molecular marker-assisted selection and genomic studies.

QUANTITATIVE GENETIC ANALYSIS OF PHENOLIC ACIDS IN OILSEED RAPE MEAL

Rapeseed meal, a by-product of oilseed extraction related to the agri-food and biofuel industries due to its favourable composition of essential amino acids, is currently utilised for animal feed. In this study, 166 doubled haploid (DH) rapeseed lines from the segregating Brassica napus doubled haploid population YE2-DH were genetically and chemically analysed for phenolic acids. The relationship between seed colour and phenolic acid fractions in B. napus was investigated using these analyses to improve the quality of rapeseed meal. High-performance liquid chromatography assays were used to estimate phenolic acid content, and the outcomes were used to identify quantitative trait loci (QTL). Nine quantitative feature loci for three distinct phenolic acid compounds were mapped to seven linkage groups. A minor QTL for sinapine was located on linkage group C05 in the same interval as the QTL for seed colour. On chromosome A09, two loci for phenolic acids colocalised with the main QTL for seed colour. Closely linked molecular markers for the target traits (seed colour, phenolic acids) identified during this study could be useful tools for breeding new oilseed rape cultivars with lower levels of antinutritive compounds.

Genome-wide association study and genomic prediction of tolerance to acute hypoxia in rainbow trout

Hypoxia is one of the major threats to the aquaculture sector resulting in substantial economic losses to the fish farmers. Thus, tolerance to hypoxia is of high economic interest to be genetically improved by breeding programs. Rainbow trout (Oncorhynchus mykiss) is one of the most cultured salmonid species worldwide, with well-developed breeding programs. Still, studies of genetic potential to improve hypoxia tolerance in this species are rare. In the present study, 1320 individuals of rainbow trout were used for a genome-wide association study of acute hypoxia tolerance based on imputed high-density genotypes to explore the genetic architecture and related candidate genes affecting hypoxia response. Three significant (Omy31_1, Omy31_2, Omy20) and two putative (Omy15, Omy28) quantitative trait loci (QTLs) were detected, but each of them only explained between 0.2% and 0.8% of the genetic variance of acute hypoxia tolerance. However, heritability was estimated at a moderate value of 0.24–0.28, that suggests a solid potential to improve hypoxia tolerance in the studied rainbow trout population by genetic selection. Moreover, it was shown that genomic prediction for hypoxia tolerance would lead to a relative increase of ∼11% for genomic selection (GS) accuracy compared to the pedigree-based selection, considering a reference population of 1000 individuals. Finally, fifteen genes (ids, fmr1, arx, lonrf3, commd5, map4k4, smu1, b4galt1, re1, abca1, noa1, igfbp7, noxo1, bcl2a, mylk3) were proposed as potential functional candidates involved in hypoxia tolerance. Taking all proposed candidate genes (6 out of 15 genes) and high linkage disequilibrium (r2) values within the main QTL (Omy31_1), we may hypothesize that the complex response to acute hypoxia in rainbow trout, i.e., the interplay between behavioural, morphological, and physiological responses, is primarily encoded by a supergene. However, further functional validation of their effects may help to specify the biological mechanisms triggering a response to acute hypoxia in rainbow trout.

Genetic Dissection of Phosphorus Use Efficiency and Genotype-by-Environment Interaction in Maize.

Genotype-by-environment interaction (G-by-E) is a common but potentially problematic phenomenon in plant breeding. In this study, we investigated the genotypic performance and two measures of plasticity on a phenotypic and genetic level by assessing 234 maize doubled haploid lines from six populations for 15 traits in seven macro-environments with a focus on varying soil phosphorus levels. It was found intergenic regions contributed the most to the variation of phenotypic linear plasticity. For 15 traits, 124 and 31 quantitative trait loci (QTL) were identified for genotypic performance and phenotypic plasticity, respectively. Further, some genes associated with phosphorus use efficiency, such as Zm00001eb117170, Zm00001eb258520, and Zm00001eb265410, encode small ubiquitin-like modifier E3 ligase were identified. By significantly testing the main effect and G-by-E effect, 38 main QTL and 17 interaction QTL were identified, respectively, in which MQTL38 contained the gene Zm00001eb374120, and its effect was related to phosphorus concentration in the soil, the lower the concentration, the greater the effect. Differences in the size and sign of the QTL effect in multiple environments could account for G-by-E. At last, the superiority of G-by-E in genomic selection was observed. In summary, our findings will provide theoretical guidance for breeding P-efficient and broadly adaptable varieties.

Identification of QTL and candidate genes associated with biomass yield and Feed Quality in response to water deficit in alfalfa (Medicago sativa L.) using linkage mapping and RNA-Seq

Biomass yield and Feed Quality are the most important traits in alfalfa (Medicago sativa L.), which directly affect its economic value. Drought stress is one of the main limiting factors affecting alfalfa production worldwide. However, the genetic and especially the molecular mechanisms for drought tolerance in alfalfa are poorly understood. In this study, linkage mapping was performed in an F1 population by combining 12 phenotypic data (biomass yield, plant height, and 10 Feed Quality-related traits). A total of 48 significant QTLs were identified on the high-density genetic linkage maps that were constructed in our previous study. Among them, nine main QTLs, which explained more than 10% phenotypic variance, were detected for biomass yield (one), plant height (one), CP (two), ASH (one), P (two), K(one), and Mg (one). A total of 31 candidate genes were identified in the nine main QTL intervals based on the RNA-seq analysis under the drought condition. Blast-P was further performed to screen candidate genes controlling drought tolerance, and 22 functional protein candidates were finally identified. The results of the present study will be useful for improving drought tolerance of alfalfa varieties by marker-assisted selection (MAS), and provide promising candidates for further gene cloning and mechanism study.