Minor Quantitative Trait Loci Research Articles

QTL mapping of a natural genetic polymorphism for long-term parasite persistence in Daphnia populations.

Knowing the determinants of the geographic ranges of parasites is important for understanding their evolutionary ecology, epidemiology and their potential to expand their range. Here we explore the determinants of geographic range in the peculiar case of a parasite species - the microsporidian Hamiltosporidium tvaerminnensis - that has a limited geographic distribution in a wide-spread host - Daphnia magna. We conducted a quantitative trait loci (QTLs) analysis with monoclonal F2 D. magna populations originating from a cross between a susceptible northern European genotype and a resistant central European genotype. Contrary to our expectations, long-term persistence turned out to be a quantitative trait across the F2 offspring. Evidence for two QTLs, one epistatic interaction and for further minor QTL was found. This finding contrasts markedly with the previously described bimodal pattern for long-term parasite persistence in natural host genotypes across Europe and leaves open the question of how a quantitative genetic trait could determine the disjunct geographic distribution of the parasite across Europe.

Mapping Quantitative Trait Loci (QTL) for Resistance to Late Blight in Tomato.

Late blight caused by Phytophthora infestans (Montagne, Bary) is a devastating disease of tomato worldwide. There are three known major genes, Ph-1, Ph-2, and Ph-3, conferring resistance to late blight. In addition to these three genes, it is also believed that there are additional factors or quantitative trait loci (QTL) conferring resistance to late blight. Precise molecular mapping of all those major genes and potential QTL is important in the development of suitable molecular markers and hence, marker-assisted selection (MAS). The objective of the present study was to map the genes and QTL associated with late blight resistance in a tomato population derived from intra-specific crosses. To achieve this objective, a population, derived from the crossings of NC 1CELBR × Fla. 7775, consisting of 250 individuals at F2 and F2-derived families, were evaluated in replicated trials. These were conducted at Mountain Horticultural Crops Reseach & Extension Center (MHCREC) at Mills River, NC, and Mountain Research Staion (MRS) at Waynesville, NC in 2011, 2014, and 2015. There were two major QTL associated with late blight resistance located on chromosomes 9 and 10 with likelihood of odd (LOD) scores of more than 42 and 6, explaining 67% and 14% of the total phenotypic variation, respectively. The major QTLs are probably caused by the Ph-2 and Ph-3 genes. Furthermore, there was a minor QTL on chromosomes 12, which has not been reported before. This minor QTL may be novel and may be worth investigating further. Source of resistance to Ph-2, Ph-3, and this minor QTL traces back to line L3707, or Richter’s Wild Tomato. The combination of major genes and minor QTL may provide a durable resistance to late blight in tomato.

Identification and Validation of New Alleles of FALSIFLORA and COMPOUND INFLORESCENCE Genes Controlling the Number of Branches in Tomato Inflorescence.

The architecture of inflorescences shows extensive diversity in both branching frequency and flower number, which eventually, determines agricultural productivity. In this study, F2 (second filial) populations derived from a cross between Solanum lycopersicum 10AS111A (highly-branched inflorescence) and the S. pimpinellifolium PI124039 (inflorescence having a single branch) were used to decipher the genetic control of branch number (BN) of inflorescence in plants bearing small-sized tomato fruits. The segregation ratio of single- and moderately-branched types to the highly-branched type was significantly different from 3:1 but not different from 15:1 at p < 0.05, suggesting that more than one gene controls the branch number of the inflorescences. Through genome-wide comparison of single-nucleotide polymorphism (SNP) profiles between the highly-branched type bulk and the single-branch type bulk constructed using the F2 plants, we identified a major quantitative trait locus (QTL) on chromosome 3 (58.75–61.4 Mb) and a minor QTL on chromosome 2 (32.95–37.1 Mb), which explained 15.7% and 6.1% of the BN variation, respectively. FALSIFLORA (FA) and COMPOUND INFLORESCENCE (S) genes, located in the QTL peak regions, caught our attention. Sequence comparison of the FA and S genes and their promoter regions from the two parental lines revealed that both contain missense mutations in the coding regions. Segregation analysis of FA and S alleles by high-resolution melting (HRM) method confirmed that alleles for both genes from 10AS111A significantly increased the BN and the size of inflorescence. In conclusion, we propose that SNPs in coding sequences might cause changes in the function of FA and S genes, which might be important determinants of BN.

Genome-Wide Analysis of Tar Spot Complex Resistance in Maize Using Genotyping-by-Sequencing SNPs and Whole-Genome Prediction.

Tar spot complex (TSC) is one of the most destructive foliar diseases of maize ( L.) in tropical and subtropical areas of Central and South America, causing significant grain yield losses when weather conditions are conducive. To dissect the genetic architecture of TSC resistance in maize, association mapping, in conjunction with linkage mapping, was conducted on an association-mapping panel and three biparental doubled-haploid (DH) populations using genotyping-by-sequencing (GBS) single-nucleotide polymorphisms (SNPs). Association mapping revealed four quantitative trait loci (QTL) on chromosome 2, 3, 7, and 8. All the QTL, except for the one on chromosome 3, were further validated by linkage mapping in different genetic backgrounds. Additional QTL were identified by linkage mapping alone. A major QTL located on bin 8.03 was consistently detected with the largest phenotypic explained variation: 13% in association-mapping analysis and 13.18 to 43.31% in linkage-mapping analysis. These results indicated that TSC resistance in maize was controlled by a major QTL located on bin 8.03 and several minor QTL with smaller effects on other chromosomes. Genomic prediction results showed moderate-to-high prediction accuracies in different populations using various training population sizes and marker densities. Prediction accuracy of TSC resistance was >0.50 when half of the population was included into the training set and 500 to 1,000 SNPs were used for prediction. Information obtained from this study can be used for developing functional molecular markers for marker-assisted selection (MAS) and for implementing genomic selection (GS) to improve TSC resistance in tropical maize.

Genetic Analysis and QTL Mapping of Resistance to Gummy Stem Blight in Cucumis sativus Seedling Stage.

Gummy stem blight (GSB), caused by Didymella bryoniae (syn. Stagonosporopsis cucurbitacearum), is an important disease of cucumber (Cucumis sativus L.) worldwide. To better understand the resistance to GSB in cucumber seedlings, a set of 160 F9 recombinant inbred lines (RILs) and a total of 405 pairs of SSR primers were employed to detect quantitative trait loci (QTLs) conferring the resistance. Genetic analysis indicated that the resistance to GSB in PI 183967 seedlings was quantitative and mainly governed by two pairs of major QTLs and multiple minor QTLs. Six QTLs, gsb3.1, gsb3.2, gsb3.3, gsb4.1, gsb5.1, and gsb6.1, for resistance to GSB in cucumber seedlings were detected. The stable locus gsb5.1 on Chr.5 was repeatedly detected in three seasons. Locus gsb5.1 accounted for the highest phenotypic variation, 17.9%, and was flanked by SSR15321 and SSR07711 within the genetic distance of 0.5 cM. There were 102 candidate genes predicted in the region harboring the stable QTL gsb5.1, of which seven genes were related to disease resistance. These results can provide a good base for further study and molecular markers for fine-mapping the major QTL conferring GSB resistance in cucumber.

QTL analysis of the developmental response to L-glutamate in Arabidopsis roots and its genotype-by-environment interactions.

Primary root growth in Arabidopsis and a number of other species has previously been shown to be remarkably sensitive to the presence of external glutamate, with glutamate signalling eliciting major changes in root architecture. Using two recombinant inbred lines from reciprocal crosses between Arabidopsis accessions C24 and Col-0, we have identified one large-effect quantitative trait locus (QTL), GluS1, and two minor QTLs, GluS2 and GluS3, which together accounted for 41% of the phenotypic variance in glutamate sensitivity. The presence of the GluS1 locus on chromosome 3 was confirmed using a set of C24/Col-0 isogenic lines. GluS1 was mapped to an interval between genes At3g44830-At3g46880. When QTL mapping was repeated under a range of environmental conditions, including temperature, shading and nitrate supply, a strong genotype-by-environment interaction in the controls for the glutamate response was identified. Major differences in the loci controlling this trait were found under different environmental conditions. Here we present evidence for the existence of loci on chromosomes 1 and 5 epistatically controlling the response of the GluS1 locus to variations in ambient temperature, between 20°C and 26°C. In addition, a locus on the long arm of chromosome 1 was found to play a major role in controlling the ability of external nitrate signals to antagonize the glutamate effect. We conclude that there are multiple loci controlling natural variation in glutamate sensitivity in Arabidopsis roots and that epistatic interactions play an important role in modulating glutamate sensitivity in response to changes in environmental conditions.

Genome-wide study of an elite rice pedigree reveals a complex history of genetic architecture for breeding improvement

Improving breeding has been widely utilized in crop breeding and contributed to yield and quality improvement, yet few researches have been done to analyze genetic architecture underlying breeding improvement comprehensively. Here, we collected genotype and phenotype data of 99 cultivars from the complete pedigree including Huanghuazhan, an elite, high-quality, conventional indica rice that has been grown over 4.5 million hectares in southern China and from which more than 20 excellent cultivars have been derived. We identified 1,313 selective sweeps (SSWs) revealing four stage-specific selection patterns corresponding to improvement preference during 65 years, and 1113 conserved Huanghuazhan traceable blocks (cHTBs) introduced from different donors and conserved in >3 breeding generations were the core genomic regions for superior performance of Huanghuazhan. Based on 151 quantitative trait loci (QTLs) identified for 13 improved traits in the pedigree, we reproduced their improvement process in silico, highlighting improving breeding works well for traits controlled by major/major + minor effect QTLs, but was inefficient for traits controlled by QTLs with complex interactions or explaining low levels of phenotypic variation. These results indicate long-term breeding improvement is efficient to construct superior genetic architecture for elite performance, yet molecular breeding with designed genotype of QTLs can facilitate complex traits improvement.

Both major and minor QTL associated with plant height can be identified using near-isogenic lines in maize

Plant height (PH) and ear height (EH) are important agronomic traits in maize (Zea mays L.) breeding. To investigate the influence of the genetic background on the detection of quantitative trait locus (QTL) conferring PH and EH, related mapping populations were developed from a near isogenic line (NIL) and its recurrent parent. Through joint-environment analyses, a total of four QTLs for PH were identified within the introgressed regions of the used NIL. Compared with the mapping results of RILs, extra PH QTLs could be detected within the target region of the used NIL on chromosome 4, but a previous PH QTL within this region was lost. The missed detection of a previous PH QTL also occurred on chromosome 6. As such, the genetic background of the recurrent parent exerted its influence on the detection of height QTL in this study. Meanwhile, according to the analyses of recombination events, qPEH6, a major height QTL on chromosome 6, was narrowed down to a region of approximately 1 Mb. Sequence analysis revealed that GRMZM2G014119, which encodes an ubiquitin-like protein related to the auxin response, was roughly assumed to be the candidate gene responsible for qPEH6.

Genetic Analysis and QTL Mapping of Fruit Peduncle Length in Cucumber (Cucumis sativus L.).

Mechanized harvesting of cucumbers offers significant advantages compared to manual labor as both shortages and costs of labor increase. However the efficient use of machines depends on breeding plants with longer peduncles, but the genetic and molecular basis of fruit peduncle development in cucumber is not well understood. In this study, F2 populations were developed from a cross between two inbred lines, 1101 with a long peduncle and 1694 with a short peduncle. These were grown at two field sites, Hainan, with a tropical marine climate, in December 2014, and Beijing, with a warm temperate climate, in May 2015. Electron microscope examination of the pith cells in the peduncles of the two parental lines showed that line 1101 had significantly greater numbers of smaller cells compared to line 1694. The inheritance of cucumber fruit peduncle length (FPL) was investigated by the mixed major gene and polygene inheritance model. Genetic analysis indicated that FPL in cucumber is quantitatively inherited and controlled by one additive major gene and additive-dominant polygenes (D-2 model). A total of 1460 pairs of SSR (simple sequence repeat) primers were analyzed to identify quantitative trait loci (QTLs). Two similar genetic maps with 78 SSR markers which covered 720.6 cM in seven linkage groups were constructed based on two F2 populations. QTL analysis from the data collected at the two field sites showed that there are two minor QTLs on chromosome 1, named qfpl1.1 and qfpl1.2, and one major QTL on chromosome 6, named qfpl6.1. The marker UW021226, which was the closest one to qfpl6.1, had an accuracy rate of 79.0% when tested against plants selected from populations of the two parents. The results from this study provide insights into the inheritance and molecular mechanism of the variation of FPL in cucumber, and further research will be carried out to fine map qfpl6.1 to develop more accurate markers for MAS breeding.

Development of a high-density genetic linkage map and identification of flowering time QTLs in adzuki bean (Vigna angularis).

A high-density linkage map is crucial for the identification of quantitative trait loci (QTLs), positional cloning, and physical map assembly. Here, we report the development of a high-density linkage map based on specific length amplified fragment sequencing (SLAF-seq) for adzuki bean and the identification of flowering time-related QTLs. Through SLAF library construction and Illumina sequencing of a recombinant inbred line (RIL) population, a total of 4425 SLAF markers were developed and assigned to 11 linkage groups (LGs). After binning the SLAF markers that represented the same genotype, the final linkage map of 1628.15 cM contained 2032 markers, with an average marker density of 0.80 cM. Comparative analysis showed high collinearity with two adzuki bean physical maps and a high degree of synteny with the reference genome of common bean (Phaseolus vulgaris). Using this map, one major QTL on LG03 and two minor QTLs on LG05 associated with first flowering time (FLD) were consistently identified in tests over a two-year period. These results provide a foundation that will be useful for future genomic research, such as identifying QTLs for other important traits, positional cloning, and comparative mapping in legumes.

Genetic mapping and confirmation of quantitative trait loci for grain chalkiness in rice

Grain chalkiness is a highly undesirable trait affecting rice grain quality and milled rice yield. In order to clarify the genetic basis of chalkiness, a recombinant inbred line population (RIL) derived from a cross between Beilu130 (a japonica cultivar with high chalkiness) and Jin23B (an indica cultivar with low chalkiness) was developed for quantitative trait locus (QTL) mapping. A total of 10 QTLs for white belly rate (WBR) and white core rate (WCR) were detected on eight different chromosomes over 2 years. Two QTLs for WBR (qWBR2 and qWBR5) showed similar chromosomal locations with GW2 and qSW5/GW5, which have been cloned previously to control the grain width and should be the right candidate genes. Three novel minor QTLs controlling WCR, qWCR1, qWCR3, and qWCR4 were further validated in near isogenic F2 populations (NIL-F2) and explained 26.1, 18.3, and 21.1% of the phenotypic variation, respectively. These QTLs could be targets for map-based cloning of the candidate genes to elucidate the molecular mechanism of chalkiness and for marker-assisted selection (MAS) in rice grain quality improvement.

SNP analysis for anthracnose resistance inCapsicumspp.

Anthracnose, caused by Colletotrichum spp., is a serious problem for chili production in Asia, and other tropical and subtropical regions worldwide. Two key resistance genotypes including Capsicum chinense 'PBC932' and C. baccatum 'PBC80' have been shared among chili breeders in Asia. SNPs (single nucleotide polymorphisms) were mapped to identify quantitative trait loci (QTLs) that were responsible for the anthracnose resistance in two chili populations derived from 'PBC93' and 'PBC80'. Of 1036 SNPs developed from C. annuum, 288 were mapped in the F2 population of C. annuum 'Bangchang' × C. chinense 'PBC932' using Joinmap 3.0 (LOD 6.0-10.0). The map contained 12 linkage groups spanning 824 cM. Two minor QTLs were identified on the same location of LG2 between two SNP loci, which were 14 cM apart, using MapQTL 4.0 and the interval mapping approach. Each QTL accounted for almost 20% of the resistance variance on the mature green and ripe fruit. Out of 1165 SNPs developed from C. baccatum, 403 were mapped with the F2 population of C. baccatum 'PBC80' × 'CA1316'. The map contained 12 LGs covering 1270 cM. Three major QTLs were identified on the same location of LG10 between two SNP loci, which were 17 cM apart. Each of the three QTLs accounted for more than 85% of each trait variance, which were the resistance assessed by microinjection with Colletotrichum pathotypes PCa2 or PCa3 and the resistance assessed by high-pressure spray with PCa3.

A GBS-SNP-based linkage map and quantitative trait loci (QTL) associated with resistance to Fusarium oxysporum f. sp. niveum race 2 identified in Citrullus lanatus var. citroides.

A major QTL for resistance to Fusarium oxysporum f. sp. niveum race 2 was mapped to a narrow 1.2 Mb interval using a high-density GBS-SNP linkage map, the first map of Citrullus lanatus var. citroides. Fusarium wilt, a fungal disease caused by Fusarium oxysporum f. sp. niveum (Fon), devastates watermelon crop production worldwide. Several races, which are differentiated by host range, of the pathogen exist. Resistance to Fon race 2, a particularly virulent strain prevalent in the United States, does not exist in edible cultivars of the sweet cultivated watermelon Citrullus lanatus var. lanatus (Cll) and has been well described in a few plant introductions of the wild subspecies of watermelon, C. lanatus var. citroides (Clc). Clc provides a vital source of genetic diversity, as well as resistance to numerous diseases. Unfortunately, both genetic diversity and disease resistance are lacking in Cll due to the narrow genetic base. Despite the importance of Clc to continued watermelon improvement, intra-variety genetic studies are lacking. Here, we present the first Clc genetic linkage map, generated with 2495 single nucleotide polymorphisms developed through genotyping-by-sequencing, and use it to identify quantitative trait loci associated with Fon race 2 resistance. Multiple QTL mapping in a Clc F2:3 population (N=173) identified one major and four minor QTL. The major QTL explained 43% of the variation in Fon race 2 resistance and was delimited to a 1.2-Mb interval on chromosome 9, a region spanning 44 genes.

A Major QTL, Which Is Co-located with cly1, and Two Minor QTLs Are Associated with Glume Opening Angle in Barley (Hordeum vulgare L.).

Cleistogamous and chasmogamous are two opposing phenomena for flowering in barley. Cleistogamy limits the rate of outcrossing, and increases the cost of producing hybrid barley seeds. Selecting chasmogamous lines with a large glume opening angle (GOA) is essential for the utilization of barley heterosis. In the current study, 247 DH lines derived from a cross between Yangnongpi7 and Yang0187 were used to identify and validate quantitative trait loci (QTLs) associated with the GOA in different environments using SSR markers. Three QTLs associated with barley GOA were mapped on chromosomes 2H and 7H. The major QTL QGOA-2H-2 was mapped on chromosome 2H with the flanking markers of KDH and GBM1498, explaining 63.92% of the phenotypic variation. The marker KDH was developed from the gene Cly1, which was the candidate gene for QGOA-2H-2. This new marker can be used to identify barley chasmogamous lines with a large GOA. The two minor QTLs were validated at all three locations across two seasons after removing DH lines carrying the candidate gene Cly1 of QGOA-2H-2.

Multiple Minor QTLs Are Responsible for Fusarium Head Blight Resistance in Chinese Wheat Landrace Haiyanzhong.

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, is a devastating disease in wheat (Triticum aestivum L.). Use of host resistance is one of the most effective strategies to minimize the disease damage. Haiyanzhong (HYZ) is a Chinese wheat landrace that shows a high level of resistance to FHB spread within a spike (type II resistance). To map the quantitative trait loci (QTLs) in HYZ and identify markers tightly linked to the QTLs for FHB resistance, a population of 172 recombinant inbred lines (RILs) from a cross between HYZ and Wheaton (FHB susceptible) was genotyped using simple sequence repeats (SSRs) and single-nucleotide polymorphisms (SNPs) derived from genotyping-by-sequencing (GBS), and evaluated for percentage of symptomatic spikelets (PSSs) per spike in three greenhouse experiments. Six QTLs for type II resistance were identified in HYZ, indicating that multiple minor QTLs together can provide a high level of FHB resistance in wheat. The QTL with the largest effect on FHB resistance was mapped on the chromosome arm 5AS, and the other five from HYZ were mapped on the chromosomes 6B, 7D, 3B, 4B and 4D. In addition, two QTLs from Wheaton were mapped on 2B. Critical SNPs linked to the QTLs on chromosomes 5A, 6B, and 2B were converted into KBioscience competitive allele-specific PCR (KASP) assays, which can be used for marker-assisted selection (MAS) to pyramid these QTLs in wheat.

Identification of Genes Potentially Associated with the Fertility Instability of S-Type Cytoplasmic Male Sterility in Maize via Bulked Segregant RNA-Seq.

S-type cytoplasmic male sterility (CMS-S) is the largest group among the three major types of CMS in maize. CMS-S exhibits fertility instability as a partial fertility restoration in a specific nuclear genetic background, which impedes its commercial application in hybrid breeding programs. The fertility instability phenomenon of CMS-S is controlled by several minor quantitative trait locus (QTLs), but not the major nuclear fertility restorer (Rf3). However, the gene mapping of these minor QTLs and the molecular mechanism of the genetic modifications are still unclear. Using completely sterile and partially rescued plants of fertility instable line (FIL)-B, we performed bulk segregant RNA-Seq and identified six potential associated genes in minor effect QTLs contributing to fertility instability. Analyses demonstrate that these potential associated genes may be involved in biological processes, such as floral organ differentiation and development regulation, energy metabolism and carbohydrates biosynthesis, which results in a partial anther exsertion and pollen fertility restoration in the partially rescued plants. The single nucleotide polymorphisms (SNPs) identified in two potential associated genes were validated to be related to the fertility restoration phenotype by KASP marker assays. This novel knowledge contributes to the understanding of the molecular mechanism of the partial fertility restoration of CMS-S in maize and thus helps to guide the breeding programs.

Barley Stripe Rust Resistance QTL: Development and Validation of SNP Markers for Resistance to Puccinia striiformis f. sp. hordei.

Quantitative trait loci (QTL) for barley stripe rust resistance were mapped in recombinant inbred lines (RIL) from a 'Lenetah' × 'Grannelose Zweizeilige' (GZ) cross. GZ is known for a major seedling resistance QTL on chromosome 4H but linked markers suitable for marker-assisted selection have not been developed. This study identified the 4H QTL (log of the likelihood [LOD] = 15.94 at 97.19 centimorgans [cM]), and additional QTL on chromosomes 4H and 6H (LOD = 5.39 at 72.7 cM and 4.24 at 34.46 cM, respectively). A QTL on chromosome 7H (LOD = 2.04 at 81.07 cM) was suggested. All resistance alleles were derived from GZ. Evaluations of adult plant response in Corvallis, OR in 2013 and 2015 provided evidence of QTL at the same positions. However, the minor QTL on 4H was not statistically significant in either location/year, while the 7H QTL was significant in both. The single-nucleotide polymorphism markers flanking the resistance QTL were validated in RIL from a '95SR316A' × GZ cross for their ability to predict seedling resistance. In 95SR316A × GZ, 91 to 92% of RIL with GZ alleles at the major 4H QTL and at least one other were resistant to moderate in reaction. In these populations, at least two QTL were required to transfer the barley stripe rust resistance from GZ.

Two Different Transcripts of a LAMMER Kinase Gene Play Opposite Roles in Disease Resistance.

Alternative splicing of genes can increase protein diversity and affect mRNA stability. Genome-wide transcriptome sequencing has demonstrated that alternative splicing occurs in a large number of intron-containing genes of different species. However, despite the phenomenon having been known for decades, it is largely unknown how the alternatively spliced transcripts function differently. Here, we report that two alternatively spliced transcripts of the rice (Oryza sativa) LAMMER kinase gene OsDR11, long OsDR11L and short OsDR11S, play opposite roles in rice resistance against Xanthomonas oryzae pv oryzae (Xoo), which causes the most damaging bacterial disease in rice worldwide. Overexpressing OsDR11S or suppressing OsDR11L in rice enhanced resistance to Xoo, which was accompanied by an accumulation of jasmonic acid (JA) and induced expression of JA signaling genes. In contrast, suppressing OsDR11S was associated with increased susceptibility to Xoo, along with decreased levels of JA and expression of JA signaling genes. The OsDR11S and OsDR11L proteins colocalized in the nucleus. OsDR11L showed autophosphorylation activity in vitro, while OsDR11S did not. In the presence of OsDR11S, autophosphorylation of OsDR11L was inhibited, and overexpression of OsDR11S suppressed OsDR11L expression. OsDR11 appeared to contribute to a minor quantitative trait locus against Xoo These results suggest that OsDR11L is a negative regulator in rice disease resistance, which may be associated with suppression of JA signaling. The results also suggest that OsDR11S may inhibit the function of OsDR11L at both the transcription and protein kinase activity levels, leading to resistance against Xoo.

Genetic dissection of flour whiteness by unconditional and conditional quantitative trait locus mapping in wheat

SUMMARYFlour whiteness (FW) is an important factor in assessing flour quality and determining the end product quality. It is an integrated sensory indicator reflecting flour colour and is negatively correlated with protein content. In order to dissect the genetic relationship between FW and its five related traits at the quantitative trait locus (QTL)/gene level, a recombinant inbred line population was evaluated under three environments. Quantitative trait loci for FW were analysed by unconditional and conditional QTL mapping. Four unconditional additive QTLs and 16 conditional additive QTLs were detected across the three environments. Of these QTLs, only one major additive QTL (Qfw1D1-1) was consistently identified using both unconditional and conditional QTL analysis. This QTL was independent of flour colour a* (a function of red-green with a positive a* for redness and negative for greenness) and b* (a green-blue value with positive value for yellowness and negative for blueness) and was only slightly affected by flour protein content. A minor additive QTL (Qfw4A-4) was also detected using these two QTL mapping methods, being independent of flour colour a* and b*. Five unconditional and ten conditional epistatic minor QTLs were detected, from which only one pair (Qfw3A-10/Qfw6B-6) was identified by both unconditional and conditional QTL mapping, also independent of flour colour a* and b*. The major QTL (Qfw1D1-1) identified in the current study for the first time can be used for improving wheat FW in marker-assisted breeding.

Inheritance and QTL mapping of glandular trichomes type I density in Cucumis melo L.

To determine the genetic basis of the density of glandular trichomes type I in melon, a six-generation family and a recombinant inbred lines (F7) population have been tested for the character; both genetic groups have been obtained from a cross between the Zimbabwean melon line TGR-1551 (high density of glandular trichomes) and the Spanish cultivar ‘Bola de Oro’ (low density of glandular trichomes). Classic quantitative genetic analysis indicated an oligogenic model for the inheritance of the character with an important additive component and strong epistatic relationships between loci. The quantitative trait locus (QTL) analyses revealed that the character is controlled by one major QTL, tric11, which explained between 23.8 and 58.7 % of its phenotypic variance; other minor QTLs of weaker effect and dependent of the assayed growing conditions were also found to be involved in the character expression. A codominant marker, the microsatellite ECM63, was found to be linked to the major QTL tric11. The validation of this marker in advanced backcrosses confirmed that the TGR-1551 alleles for this QTL increased glandular trichome density. The validation of the detected QTL was also done in other genetic backgrounds, which indicated that ECM63 could be effective in the selection of plants with high density of glandular trichomes type I.