QTL Alleles Research Articles

Genomic Advances in Biofortification of Iron and Zinc in Wheat (Triticum aestivum L.)

Majority of population that depend on wheat are found to be deficient in iron and zinc. About 20% of calories worldwide are derived from wheat. Milling of wheat reduces the bioavaibility of Fe and Zn in wheat grains. Micronutrient deficiency is the main cause of malnutrition worldwide and hidden hunger in underdeveloped countries. To overcome this problem it becomes necessary to develop varieties that are rich in iron and zinc content. Biofortification gets around these issues by enhancing the micronutrient content of wheat. The genetic approaches of biofortification particularly the non-conventional methods have proved to be the most efficient ones. These method includes QTL mapping approach, GWAS and transgenics. Although conventional methods for a long time has been used for developing varieties of wheat rich in Fe and Zn but conventional breeding for certain traits may be inconvenient and time-consuming and are prone to errors due to their reliance on traditional phenotyping or visual assessments. Several research have been undertaken to map QTLs of Fe and Zn concentration in wheat grains and have been used in elite genetic backgrounds to improve micronutrient content. Genomic studies revealed through GWAS exhibit high QTL resolution and allele coverage, which can be used for improvement of Fe and Zn content in wheat. Genetic engineering techniques or transgenics approaches allows genetic alteration of crops to improve the nutritional quality of wheat. Genomic approach of biofortification of wheat has proved to be the most efficient methods for increasing iron and zinc content in the crop.

Genetic mapping reveals new loci and alleles for flowering time and plant height using the double round-robin population of barley.

Flowering time and plant height are two critical determinants of yield potential in barley (Hordeum vulgare). Despite their role in plant physiological regulation, a complete overview of the genetic complexity of flowering time and plant height regulation in barley is still lacking. Using a double round-robin population originated from the crossings of 23 diverse parental inbred lines, we aimed to determine the variance components in the regulation of flowering time and plant height in barley as well as to identify new genetic variants by single and multi-population QTL analyses and allele mining. Despite similar genotypic variance, we observed higher environmental variance components for plant height than flowering time. Furthermore, we detected new QTLs for flowering time and plant height. Finally, we identified a new functional allelic variant of the main regulatory gene Ppd-H1. Our results show that the genetic architecture of flowering time and plant height might be more complex than reported earlier and that a number of undetected, small effect, or low-frequency genetic variants underlie the control of these two traits.

Contrasting allelic effects for pistachio salinity tolerance in juvenile and mature trees

Breeding perennial tree crops often requires prediction of mature performance from juvenile data. To assess the utility of juvenile screens to predict salinity tolerance of mature pistachio trees, we compared performance of 3-month ungrafted seedlings and 4-year-old grafted rootstocks under salinity stress. The QTL allele associated with higher salt exclusion from seedling leaves conferred lower growth in saline field conditions, suggesting that mapping QTL in seedlings may be easier than discerning the optimal allele for field performance.

Genetic Dissection of Morphological Variation Between Cauliflower and a Rapid Cycling Brassica oleracea line.

To improve resolution to small genomic regions and sensitivity to small-effect loci in the identification of genetic factors conferring the enlarged inflorescence and other traits of cauliflower while also expediting further genetic dissection, 104 near-isogenic introgression lines (NIILs) covering 78.56% of the cauliflower genome, were selected from an advanced backcross population using cauliflower [B. oleracea var. botrytis L., mutant for Orange gene (ORG)] as the donor parent and a rapid cycling line (TO1434) as recurrent parent. Subsets of the advanced backcross population and NIILs were planted in the field for eight seasons, finding 141 marker-trait associations for 15 leaf-, stem- and flower-traits. Exemplifying the usefulness of these lines, we delineated the previously-known flower color gene to a 4.5 MB interval on C3; a gene for small plant size to a 3.4 MB region on C8; and a gene for large plant size and flowering time to a 6.1 MB region on C9. This approach unmasked closely linked QTL alleles with opposing effects (on chr. 8), and revealed both alleles with expected phenotypic effects and effects opposite the parental phenotypes. Selected B. oleracea NIILs with short generation time add new value to widely used research and teaching materials.

Pedigree-based QTL analysis of flower size traits in two multi-parental diploid rose populations.

Rose (Rosa spp.) is one of the most economically important ornamental species worldwide. Flower diameter, flower weight, and the number of petals and petaloids are key flower-size parameters and attractive targets for DNA-informed breeding. Pedigree-based analysis (PBA) using FlexQTL software was conducted using two sets of multi-parental diploid rose populations. Phenotypic data for flower diameter (Diam), flower weight (fresh (FWT)/dry (DWT)), number of petals (NP), and number of petaloids (PD) were collected over six environments (seasons) at two locations in Texas. The objectives of this study were to 1) identify new and/or validate previously reported QTL(s); 2) identify SNP haplotypes associated with QTL alleles (Q-/q-) of a trait and their sources; and 3) determine QTL genotypes for important rose breeding parents. Several new and previously reported QTLs for NP and Diam traits were identified. In addition, QTLs associated with flower weight and PD were identified for the first time. Two major QTLs with large effects were mapped for all traits. The first QTL was at the distal end of LG1 (60.44-60.95 Mbp) and was associated with Diam and DWT in the TX2WOB populations. The second QTL was consistently mapped in the middle region on LG3 (30.15-39.34 Mbp) and associated with NP, PD, and flower weight across two multi-parent populations (TX2WOB and TX2WSE). Haplotype results revealed a series of QTL alleles with differing effects at important loci for most traits. This work is distinct from previous studies by conducting co-factor analysis to account for the DOUBLE FLOWER locus while mapping QTL for NP. Sources of high-value (Q) alleles were identified, namely, 'Old Blush' and Rosa wichuraiana from J14-3 for Diam, while 'Violette' and PP-J14-3 were sources for other traits. In addition, the source of the low-value (q) alleles for Diam was 'Little Chief', and Rosa wichuraiana through J14-3 was the source for the remaining traits. Hence, our results can potentially inform parental/seedling selections as means to improve ornamental quality in roses and a step towards implementing DNA-informed techniques for use in rose breeding programs.

Unique Salt-Tolerance-Related QTLs, Evolved in Vigna riukiuensis (Na+ Includer) and V. nakashimae (Na+ Excluder), Shed Light on the Development of Super-Salt-Tolerant Azuki Bean (V. angularis) Cultivars.

Wild relatives of crops have the potential to improve food crops, especially in terms of improving abiotic stress tolerance. Two closely related wild species of the traditional East Asian legume crops, Azuki bean (Vigna angularis), V. riukiuensis "Tojinbaka" and V. nakashimae "Ukushima" were shown to have much higher levels of salt tolerance than azuki beans. To identify the genomic regions responsible for salt tolerance in "Tojinbaka" and "Ukushima", three interspecific hybrids were developed: (A) azuki bean cultivar "Kyoto Dainagon" × "Tojinbaka", (B) "Kyoto Dainagon" × "Ukushima" and (C) "Ukushima" × "Tojinbaka". Linkage maps were developed using SSR or restriction-site-associated DNA markers. There were three QTLs for "percentage of wilt leaves" in populations A, B and C, while populations A and B had three QTLs and population C had two QTLs for "days to wilt". In population C, four QTLs were detected for Na+ concentration in the primary leaf. Among the F2 individuals in population C, 24% showed higher salt tolerance than both wild parents, suggesting that the salt tolerance of azuki beans can be further improved by combining the QTL alleles of the two wild relatives. The marker information would facilitate the transfer of salt tolerance alleles from "Tojinbaka" and "Ukushima" to azuki beans.

Identification of Fusarium wilt resistance loci in two major genetic backgrounds for oil palm breeding

Fusarium wilt (FW) caused by Fusarium oxysporum f. sp. elaeidis is the main disease of oil palm in Africa and is a latent threat to other producing regions. A long-term work based on a genetic survey of FW resistance using field observations and pre-nursery screening tests with inoculation resulted in FW resistant planting material whose resistance has not been overcome in 40 years. The genetic determinism of FW resistance has never been studied. Such information would eventually enable marker assisted selection (MAS) to ensure continuous improvement of planting material, through multi-trait selection (yield and disease or multiple diseases) and diversification of the genetic base. In this study, we used a pedigree-based QTL mapping approach that took advantage of the extensive pre-nursery FW resistance data recorded in the framework of a reciprocal recurrent selection program in Benin Republic. Eight QTL regions were mapped in two major genetic backgrounds and favorable QTL alleles were identified in the current breeding populations. The QTL pattern was specific to the population studied in terms of number, location and genetic variance explained, highlighting the different genetic architecture of FW resistance depending on the genetic background. To investigate a putative trade-off between FW resistance and yield, FW resistance QTL genotypes were predicted in a population that was formerly evaluated for yield in the field. The effects on yield of a FW QTL were offset in the commercial planting material thanks to different effects on different yield components in both heterotic groups. These results shed light on FW resistance in oil palm and provide valuable information for the implementation of MAS in the breeding program. Considering that pre-nursery screening tests are widely used, the approach presented here could be implemented in other breeding programs to provide further insights into FW resistance, especially in the context of wider genetic diversity.

Genome-Wide Association Study Reveals the Genetic Basis of Five Quality Traits in Chinese Wheat.

Bread wheat is a highly adaptable food crop grown extensively around the world and its quality genetic improvement has received wide attention. In this study, the genetic loci associated with five quality traits including protein content (PC), gluten content (GC), baking value (BV), grain hardness (HA), and sedimentation value (SV) in a population of 253 Chinese wheat grown in Inner Mongolia were investigated through genome wide association mapping. A total of 103 QTL containing 556 SNPs were significantly related to the five quality traits based on the phenotypic data collected from three environments and BLUP data. Of these QTL, 32 QTL were continuously detected under at least two experiments. Some QTL such as qBV3D.2/qHA3D.2 on 3D, qPC5A.3/qGC5A on 5A, qBV5D/qHA5D on 5D, qBV6B.2/qHA6B.3 on 6B, and qBV6D/qHA6D.1 on 6D were associated with multiple traits. In addition, distribution of favorable alleles of the stable QTL in the association panel and their effects on five quality traits were validated. Analysis of existing transcriptome data revealed that 34 genes were specifically highly expressed in grains during reproductive growth stages. The functions of these genes will be characterized in future experiments. This study provides novel insights into the genetic basis of quality traits in wheat.

Resequencing worldwide spinach germplasm for identification of field resistance QTLs to downy mildew and assessment of genomic selection methods.

Downy mildew, commercially the most important disease of spinach, is caused by the obligate oomycete Peronospora effusa. In the past two decades, new pathogen races have repeatedly overcome the resistance used in newly released cultivars, urging the need for more durable resistance. Commercial spinach cultivars are bred with major R genes to impart resistance to downy mildew pathogens and are effective against some pathogen races/isolates. This work aimed to evaluate the worldwide USDA spinach germplasm collections and commercial cultivars for resistance to downy mildew pathogen in the field condition under natural inoculum pressure and conduct genome wide association analysis (GWAS) to identify resistance-associated genomic regions (alleles). Another objective was to evaluate the prediction accuracy (PA) using several genomic prediction (GP) methods to assess the potential implementation of genomic selection (GS) to improve spinach breeding for resistance to downy mildew pathogen. More than four hundred diverse spinach genotypes comprising USDA germplasm accessions and commercial cultivars were evaluated for resistance to downy mildew pathogen between 2017-2019 in Salinas Valley, California and Yuma, Arizona. GWAS was performed using single nucleotide polymorphism (SNP) markers identified via whole genome resequencing (WGR) in GAPIT and TASSEL programs; detected 14, 12, 5, and 10 significantly associated SNP markers with the resistance from four tested environments, respectively; and the QTL alleles were detected at the previously reported region of chromosome 3 in three of the four experiments. In parallel, PA was assessed using six GP models and seven unique marker datasets for field resistance to downy mildew pathogen across four tested environments. The results suggest the suitability of GS to improve field resistance to downy mildew pathogen. The QTL, SNP markers, and PA estimates provide new information in spinach breeding to select resistant plants and breeding lines through marker-assisted selection (MAS) and GS, eventually helping to accumulate beneficial alleles for durable disease resistance.

EFFECTIVENESS OF PREDICTING THE PRODUCTIVE QUALITIES OF BEEF CATTLE BY QTL ASSOCIATED SNP

The article presents the results of assessing the possibilities of predicting the meat productivity of Kazakh white-headed and Auliekol cattle by increasing alleles of QTL associated SNP. 4 polymorphic sites were selected for each of the breeds. Priority in the selection of targets were given to those with a higher frequency of occurrence of an alternative allele (at least 15%), location in different functional regions of the genome and genes, and distribution by chromosomes, as well as belonging to known QTL. Analysis of the genotypes of the sample showed that homozygosity for all 4 minor alleles (increasing) were not detected simultaneously in any animal in the sample. It was also not possible to identify animals carrying 7 alleles at the same time. The presence of 3 or more "increasing" alleles in animals of the Kazakh white-headed breed, regardless of the specific polymorphic variant, indicated that its live weight index in 12 months would exceed the average for the sample by 10 kg, and in comparison, with animals that do not carry any such allele – by 15 kg. The identification of 5 or more increasing alleles may probably indicate an even more significant increase in the live weight of the animal at 12 months (20 kg). The Auliekol breed, as in the case of the Kazakh white-headed breed, approximates the trait value to the upper limit of the trait norm as the number of increasing alleles increase. In this case, it can be stated that for the development and application of small diagnostic panels to predict increased productivity of animals, it is enough to detect from 3 to 6 increasing alleles. However, due to the insufficient amount of data, it is worth treating this data with caution at this stage of work. Increasing the sample will allow more specific data to be obtained in the future.

Detection and Verification of QTL for Salinity Tolerance at Germination and Seedling Stages Using Wild Barley Introgression Lines.

Salinity is one of the major environmental factors that negatively affect crop development, particularly at the early growth stage of a plant and consequently the final yield. Therefore, a set of 50 wild barley (Hordeum vulgare ssp. spontaneum, Hsp) introgression lines (ILs) was used to detect QTL alleles improving germination and seedling growth under control, 75 mM, and 150 mM NaCl conditions. Large variation was observed for germination and seedling growth related traits that were highly heritable under salinity stress. In addition, highly significant differences were obtained for five salinity tolerance indices and between treatments as well. A total of 90 and 35 significant QTL were identified for ten investigated traits and for tolerance indices, respectively. The Hsp introgression alleles are involved in improving salinity tolerance at forty (43.9%) out of 90 QTL including introgression lines S42IL-109 (2H), S42IL-116 (4H), S42IL-132 (6H), S42IL-133 (7H), S42IL-148 (6H), and S42IL-176 (5H). Interestingly, seven exotic QTL alleles were successfully validated in the wild barley ILs including S42IL-127 (5H), 139 (7H), 125 (5H), 117 (4H), 118 (4H), 121 (4H), and 137 (7H). We conclude that the barley introgression lines contain numerous germination and seedling growth-improving novel QTL alleles, which are effective under salinity conditions.

Insights into the genetic basis of the pre-breeding potato clones developed at the Julius Kühn Institute for high and durable late blight resistance

AbstractDue to the high yield losses caused by late blight in potato cultivation, the development of resistant pre-breeding material is of great importance for cultivar breeding. The gene pool of the Julius Kühn Institute (JKI) includes a large collection of resistant clones whose resistance has not yet been analysed in detail with markers for relevant resistance genes. A panel of 52 pre-breeding potato clones developed at the JKI via interspecific crosses and highly resistant to late blight were tested for the presence of seven resistance genes (Rpi-blb1/Rpi-sto1, Rpi-blb2, Rpi-blb3/R2/Rpi-abpt, R1, R3a, R3b, Rpi-phu1) and one QTL allele (QTL_phu-stn) from Solanum species S. bulbocastanum, S. demissum, S. phureja and S. stoloniferum, respectively. Molecular marker assays based on sequence-specific primers revealed that 36 of the 52 pre-breeding clones carried either 1, 2, 3 or 4 resistance genes introgressed from these wild Solanum species. Results indicate that these resistance genes were retained over generations of breeding. Although highly resistant to late blight, 16 pre-breeding clones did not carry any of these resistance genes. Resistance in the gene pool may, thus, be based not only on individual resistance genes but also on QTL effects. Results help to better understand both inheritance and expression of late blight resistance of this unique gene pool and may be used for breeding programmes.

Genetic Mapping Reveals Novel Exotic and Elite QTL Alleles for Salinity Tolerance in Barley

Soil salinity is one of the constraints of crop production in Egypt. The aims of this study were to identify genomic regions associated with grain weight and its related traits along with their salinity tolerance indices and to identify the most salinity tolerant and high-yielding genotypes. Therefore, we evaluated an advanced backcross mapping population of barley in newly reclaimed soil under two salinity levels of groundwater aquifers in South of Sinai, Egypt. We detected significant QTL associated with grain weight related attributes and the salinity tolerance index (STI) distributed throughout the whole genome of barley, which can be used to enhance salinity tolerance. Moreover, the markers bPb-3739 (4H, 96.3 cM), AF043094A (5H, 156 cM), bPb-8161 (7H, 2.22 cM), and bPb-5260 (7H, 115.6 cM), were the most important identified genomic regions corresponding to vernalization, dwarfing and dehydrin genes, which are correlated with salinity tolerance. Additionally, the doubled haploid lines SI001, SI043, SI044, SI028, SI242, SI035, and SI005 had the highest STI values based on yield average. The present study demonstrated that wild and elite barley do harbor novel valuable alleles, which can enrich the genetic basis of cultivated barley and improve quantitative agronomic traits under salinity conditions.

Mapping and characterization QTLs for phenological traits in seven pedigree-connected peach families

BackgroundEnvironmental adaptation and expanding harvest seasons are primary goals of most peach [Prunus persica (L.) Batsch] breeding programs. Breeding perennial crops is a challenging task due to their long breeding cycles and large tree size. Pedigree-based analysis using pedigreed families followed by haplotype construction creates a platform for QTL and marker identification, validation, and the use of marker-assisted selection in breeding programs.ResultsPhenotypic data of seven F1 low to medium chill full-sib families were collected over 2 years at two locations and genotyped using the 9 K SNP Illumina array. Three QTLs were discovered for bloom date (BD) and mapped on linkage group 1 (LG1) (172–182 cM), LG4 (48–54 cM), and LG7 (62–70 cM), explaining 17–54%, 11–55%, and 11–18% of the phenotypic variance, respectively. The QTL for ripening date (RD) and fruit development period (FDP) on LG4 was co-localized at the central part of LG4 (40–46 cM) and explained between 40 and 75% of the phenotypic variance. Haplotype analyses revealed SNP haplotypes and predictive SNP marker(s) associated with desired QTL alleles and the presence of multiple functional alleles with different effects for a single locus for RD and FDP.ConclusionsA multiple pedigree-linked families approach validated major QTLs for the three key phenological traits which were reported in previous studies across diverse materials, geographical distributions, and QTL mapping methods. Haplotype characterization of these genomic regions differentiates this study from the previous QTL studies. Our results will provide the peach breeder with the haplotypes for three BD QTLs and one RD/FDP QTL to create predictive DNA-based molecular marker tests to select parents and/or seedlings that have desired QTL alleles and cull unwanted genotypes in early seedling stages.

QTL mapping of biomass and forage quality traits measured using near-infrared reflectance spectroscopy (NIRS) in switchgrass

Switchgrass (Panicum virgatum L.) is a perennial warm-season grass that can serve dual purposes, forage and biofuel feedstock. Because the cell wall accounts for more than half the dry matter weight, breeding for both objectives will largely depend on cell wall components which include cellulose, hemicellulose, and lignin. We used NIRS to measure crude protein, neutral detergent fiber, acid detergent fiber, hemicellulose, cellulose, and Klason lignin to conduct QTL mapping in an F1 population derived from a cross between tetraploid lowlands AP13 and B6 with 285 progenies. Of the three major cell wall components of the dry matter, cellulose was the highest (34.51–41.40%), followed by hemicellulose (25.48–33.55%), and Klason lignin (9.70–13.23%). Mapping of biomass and forage quality traits was done using two linkage maps with 2772 SNP markers. We identified 37 significant QTL for all six traits with the highest percentage variance explained by individual QTL in all traits ranging from 4.89 to 8.57%. There are 9 chromosome regions with colocalized QTL of different traits, indicating either pleiotropic gene action or tight linkage between the genes. Improvement of switchgrass for forage and biofuel feedstock quality would benefit from the selection of QTL that contribute directly to the target phenotypes. The frequency of favorable QTL alleles can be enhanced through Genomic Selection.

Strategies and considerations for implementing genomic selection to improve traits with additive and non-additive genetic architectures in sugarcane breeding.

Simulations highlight the potential of genomic selection to substantially increase genetic gain for complex traits in sugarcane. The success rate depends on the trait genetic architecture and the implementation strategy. Genomic selection (GS) has the potential to increase the rate of genetic gain in sugarcane beyond the levels achieved by conventional phenotypic selection (PS). To assess different implementation strategies, we simulated two different GS-based breeding strategies and compared genetic gain and genetic variance over five breeding cycles to standard PS. GS scheme 1 followed similar routines like conventional PS but included three rapid recurrent genomic selection (RRGS) steps. GS scheme 2 also included three RRGS steps but did not include a progeny assessment stage and therefore differed more fundamentally from PS. Under an additive trait model, both simulated GS schemes achieved annual genetic gains of 2.6-2.7% which were 1.9 times higher compared to standard phenotypic selection (1.4%). For a complex non-additive trait model, the expected annual rates of genetic gain were lower for all breeding schemes; however, the rates for the GS schemes (1.5-1.6%) were still greater than PS (1.1%). Investigating cost-benefit ratios with regard to numbers of genotyped clones showed that substantial benefits could be achieved when only 1500 clones were genotyped per 10-year breeding cycle for the additive genetic model. Our results show that under a complex non-additive genetic model, the success rate of GS depends on the implementation strategy, the number of genotyped clones and the stage of the breeding program, likely reflecting how changes in QTL allele frequencies change additive genetic variance and therefore the efficiency of selection. These results are encouraging and motivate further work to facilitate the adoption of GS in sugarcane breeding.

QTL detection in a pedigreed breeding population of diploid potato

Diploid hybrid potato breeding is emerging as an alternative to breeding tetraploid potato clones. The development of diploid breeding varieties involves recent, shallow pedigrees with a limited number of founders. Within this context, alternative QTL detection methodologies should be considered to enable identification of relevant QTLs and characterize the founders of the pedigree. To that end, we are using a dataset of multiple diploid potato hbox {F}_3 families under selection derived by a cross between an inbred Solanum chacoense and an outbred diploid Solanum tuberosum, and identify QTLs for tuber fresh weight. We used three methods for QTL detection: (1) a Genome Wide Association Study model, (2) a linkage approach tailored to the population under study and (3) a more general approach for modelling multiallelic QTLs in complex pedigrees using identity-by-descent (IBD) probabilities. We show that all three approaches enable detection of QTLs in the population under study, but the method that makes better use of IBD information has a more direct and detailed interpretation by linking QTL alleles to the founders.

SNP-based QTL mapping for panicle traits in the japonica super rice cultivar Liaoxing 1

Panicle traits directly associated with yield are a target of selection in rice breeding. Although abundant QTL for panicle traits have been identified, there is little information about the genetic basis of panicle traits in japonica super rice (JSR) cultivars. In this study, we identified QTL for panicle traits in three environments using a population of recombinant inbred lines (RILs) derived from the JSR cultivar Liaoxing 1. A total of 197 RILs were genotyped with 285 polymorphic SNP markers. Phenotypic data and best linear unbiased prediction (BLUP) value of primary branch number (BNP), secondary branch number (BNS), grain number on primary branch (GNP), grain number on secondary branch (GNS), grain number per panicle (GN), panicle length (PL) and grain density (GD) were used for QTL mapping. A total of 105 QTL for seven panicle traits were detected in single environments using their BLUP values. Individual QTL explained 0.51%–52.22% of the phenotypic variation. Of the 105, 49 were also detected by joint multi-environment analyses. Five stable QTL: qGD9, qPL9, qGNP9, qGN6, and qBNS6.2 were identified in multiple environments. qGD9, qGNP9, and qPL9, co-localizing on chromosome 9, likely correspond to the known gene DEP1. Importantly, qGN6 and qBNS6.2 in a co-localization region were identified as novel QTL, and their Liaoxing 1 alleles had a positive effect. Several RILs with the QTL allele combinations qGD9/qPL9/qGNP9 and qGN6/qBNS6.2 showed greater GN. Further investigation of the putative gene underlying qGN6/qBNS6.2 would shed light on the molecular mechanism of JSR.

Identification and characterization of QTLs for fruit quality traits in peach through a multi-family approach

BackgroundFruit quality traits have a significant effect on consumer acceptance and subsequently on peach (Prunus persica (L.) Batsch) consumption. Determining the genetic bases of key fruit quality traits is essential for the industry to improve fruit quality and increase consumption. Pedigree-based analysis across multiple peach pedigrees can identify the genomic basis of complex traits for direct implementation in marker-assisted selection. This strategy provides breeders with better-informed decisions and improves selection efficiency and, subsequently, saves resources and time.ResultsPhenotypic data of seven F1 low to medium chill full-sib families were collected over 2 years at two locations and genotyped using the 9 K SNP Illumina array. One major QTL for fruit blush was found on linkage group 4 (LG4) at 40–46 cM that explained from 20 to 32% of the total phenotypic variance and showed three QTL alleles of different effects. For soluble solids concentration (SSC), one QTL was mapped on LG5 at 60-72 cM and explained from 17 to 39% of the phenotypic variance. A major QTL for titratable acidity (TA) co-localized with the major locus for low-acid fruit (D-locus). It was mapped at the proximal end of LG5 and explained 35 to 80% of the phenotypic variance. The new QTL for TA on the distal end of LG5 explained 14 to 22% of the phenotypic variance. This QTL co-localized with the QTL for SSC and affected TA only when the first QTL is homozygous for high acidity (epistasis). Haplotype analyses revealed SNP haplotypes and predictive SNP marker(s) associated with desired QTL alleles.ConclusionsA multi-family-based QTL discovery approach enhanced the ability to discover a new TA QTL at the distal end of LG5 and validated other QTLs which were reported in previous studies. Haplotype characterization of the mapped QTLs distinguishes this work from the previous QTL studies. Identified predictive SNPs and their original sources will facilitate the selection of parents and/or seedlings that have desired QTL alleles. Our findings will help peach breeders develop new predictive, DNA-based molecular marker tests for routine use in marker-assisted breeding.

Phenotyping and QTL mapping for cold tolerance at the germination and seedling stages in Argentine temperate rice

In Argentina, the yield potential of rice (Oryza sativa L.) under suboptimal temperatures of temperate regions and during early sowing in tropical regions depends on its low-temperature germinability (LTG) and subsequent cold tolerance at the seedling stage (CTS). This study focused on the phenotyping and identification of contrasting henotypes for LTG and CTS of 18 rice genotypes genotyped with 49 markers previously linked to cold tolerance. The selected markers revealed phenotypic variability among the genotypes evaluated. The results also demonstrated that both traits are regulated by different genes and that CTS is associated with differential alleles of candidate gene (CG)-based markers. Biplot clustering analysis allowed the selection of two cultivars, H298a/90 and Puita INTA CL, contrasting for LTG, CTS and CG alleles. An F2 population (n = 128) derived from these two cultivars was genotyped with 43 SSR- and CG-based markers and 89 F2:3 families (~ 1800 seedlings) phenotyped for CTS. Single-marker analysis detected two major QTL that had been previously reported for CTS: qCTS11, which explained 18.35% of the phenotypic variance at 7 days of treatment, and qCTS12, which explained 26.62% and 47.94% of the phenotypic variance at 7 and 14 days of treatment, respectively. Marker-assisted introgression of QTL alleles favorable for CTS into Puita INTA CL, which has high LTG, could contribute to obtaining breeding lines with early seedling vigor adapted to the sowing season in Argentina.