QTL analysis of cadmium and zinc accumulation in the heavy metal hyperaccumulator Thlaspi caerulescens

Thlaspi caerulescens (Tc; 2n = 14) is a natural Zn, Cd and Ni hyperaccumulator species belonging to the Brassicaceae family. It shares 88% DNA identity in the coding regions with Arabidopsis thaliana (At) (Rigola et al. 2006). Although the physiology of heavy metal (hyper)accumulation has been intensively studied, the molecular genetics are still largely unexplored. We address this topic by constructing a genetic map based on AFLP markers and expressed sequence tags (ESTs). To establish a genetic map, an F(2) population of 129 individuals was generated from a cross between a plant from a Pb/Cd/Zn-contaminated site near La Calamine, Belgium, and a plant from a comparable site near Ganges (GA), France. These two accessions show different degrees of Zn and, particularly, Cd accumulation. We analyzed 181 AFLP markers (of which 4 co-dominant) and 13 co-dominant EST sequences-based markers and mapped them to seven linkage groups (LGs), presumably corresponding to the seven chromosomes of T. caerulescens. The total length of the genetic map is 496 cM with an average density of one marker every 2.5 cM. This map was used for Quantitative Trait Locus (QTL) mapping in the F(2). For Zn as well as Cd concentration in root we mapped two QTLs. Three QTLs and one QTL were mapped for Zn and Cd concentration in shoot, respectively. These QTLs explain 23.8-60.4% of the total variance of the traits measured. We found only one common locus (LG6) for Zn and Cd (concentration in root) and one common locus for shoot and root concentrations of Zn (LG1) and of Cd (LG3). For all QTLs, the GA allele increased the trait value except for two QTLs for Zn accumulation in shoot (LG1 and LG4) and one for Zn concentration in root (LG1).     

A Consensus Microsatellite-Based Linkage Map for the Hermaphroditic Bay Scallop (Argopecten irradians) and Its Application in Size-Related QTL Analysis

Bay scallop (Argopecten irradians) is one of the most economically important aquaculture species in China. In this study, we constructed a consensus microsatellite-based genetic linkage map with a mapping panel containing two hybrid backcross-like families involving two subspecies of bay scallop, A. i. irradians and A. i. concentricus. One hundred sixty-one microsatellite and one phenotypic (shell color) markers were mapped to 16 linkage groups (LGs), which corresponds to the haploid chromosome number of bay scallop. The sex-specific map was 779.2 cM and 781.6 cM long in female and male, respectively, whereas the sex-averaged map spanned 849.3 cM. The average resolution of integrated map was 5.9 cM/locus and the estimated coverage was 81.3%. The proportion of distorted markers occurred more in the hybrid parents, suggesting that the segregation distortion was possibly resulted from heterospecific interaction between genomes of two subspecies of bay scallop. The overall female-to-male recombination rate was 1.13∶1 across all linked markers in common to both parents, and considerable differences in recombination also existed among different parents in both families. Four size-related traits, including shell length (SL), shell height (SH), shell width (SW) and total weight (TW) were measured for quantitative trait loci (QTL) analysis. Three significant and six suggestive QTL were detected on five LGs. Among the three significant QTL, two (qSW-10 and qTW-10, controlling SW and TW, respectively) were mapped on the same region near marker AiAD121 on LG10 and explained 20.5% and 27.7% of the phenotypic variance, while the third (qSH-7, controlling SH) was located on LG7 and accounted for 15.8% of the phenotypic variance. Six suggestive QTL were detected on four different LGs. The linkage map and size-related QTL obtained in this study may facilitate marker-assisted selection (MAS) in bay scallop.     

Construction of an RAPD linkage map and localization of QTLs for oleic acid level using recombinant inbreds in mustard (Brassica juncea).

RAPD markers were employed for construction of a linkage map and localization of QTLs for oleic acid level using a set of 94 recombinant inbred lines (RILs) of mustard (Brassica juncea L.) as a mapping population. Only 30% of the 235 random primers used were useful in terms of polymorphism detected and the reproducibility of those patterns. Normal Mendelian segregation was observed for the majority of the 130 markers obtained with 71 informative primers; only 13.1% deviated (P < 0.01) from the expected 1:1 ratio. One-hundred and fourteen markers were assigned to 21 linkage groups (LGs) covering a total length of 790.4 cM with an average distance of 6.93 cM between markers. Two quantitative trait loci (QTL) for oleic acid level were mapped to 14- and 10.6-cM marker intervals on two different LGs. Both loci together explained 32.2% of phenotypic variance. One major QTL explained 28.5% of the trait variance observed in this species.     

Comparative mapping of Raphanus sativus genome using Brassica markers and quantitative trait loci analysis for the Fusarium wilt resistance trait

Fusarium wilt (FW), caused by the soil-borne fungal pathogen Fusarium oxysporum is a serious disease in cruciferous plants, including the radish (Raphanus sativus). To identify quantitative trait loci (QTL) or gene(s) conferring resistance to FW, we constructed a genetic map of R. sativus using an F₂ mapping population derived by crossing the inbred lines ‘835’ (susceptible) and ‘B2’ (resistant). A total of 220 markers distributed in 9 linkage groups (LGs) were mapped in the Raphanus genome, covering a distance of 1,041.5 cM with an average distance between adjacent markers of 4.7 cM. Comparative analysis of the R. sativus genome with that of Arabidopsis thaliana and Brassica rapa revealed 21 and 22 conserved syntenic regions, respectively. QTL mapping detected a total of 8 loci conferring FW resistance that were distributed on 4 LGs, namely, 2, 3, 6, and 7 of the Raphanus genome. Of the detected QTL, 3 QTLs (2 on LG 3 and 1 on LG 7) were constitutively detected throughout the 2-year experiment. QTL analysis of LG 3, flanked by ACMP0609 and cnu_mBRPGM0085, showed a comparatively higher logarithm of the odds (LOD) value and percentage of phenotypic variation. Synteny analysis using the linked markers to this QTL showed homology to A. thaliana chromosome 3, which contains disease-resistance gene clusters, suggesting conservation of resistance genes between them.     

Genetic mapping of hop (Humulus lupulus L.) applied to the detection of QTLs for alpha-acid content.

The map locations and effects of quantitative trait loci (QTLs) were estimated for alpha-acid content in hop (Humulus lupulus L.) using amplified fragment length polymorphism (AFLP) and microsatellite marker (simple sequence repeat (SSR)) genetic linkage maps constructed from a double pseudotestcross. The mapping population consisted of 111 progeny from a cross between the German hop cultivar 'Magnum', which exhibits high levels of alpha-acids, and a wild Slovene male hop, 2/1. The progeny segregated quantitatively for alpha-acid content determined in 2002, 2003, and 2004. The maternal map consisted of 96 markers mapped on 14 linkage groups defining 661.90 cM of total map distance. The paternal map included 70 markers assigned to 12 linkage groups covering 445.90 cM of hop genome. QTL analysis indicated 4 putative QTLs (alpha1, alpha2, alpha3, and alpha4) on linkage groups (LGs) 03, 01, 09, and 03 of the female map, respectively. QTLs explained 11.9%-24.8% of the phenotypic variance. The most promising QTL to be used in marker-assisted selection is alpha2, the peak of which colocated exactly with the AFLP marker. Three chalcone synthase-like genes (chs2, chs3, and chs4) involved in hop bitter acid synthesis mapped together on LG04 of the female map. Saturation of the maps, particularly the putative QTL regions, will be carried out using SSR markers, and the stability of the QTLs will be tested in the coming years.     

Mapping of Quantitative Trait Loci for Butter Content and Hardness in Cocoa Beans (Theobroma cacao L.)

Cocoa butter is an important raw material for the chocolate, pharmaceutical, and cosmetic industries. The butter content and quality in cocoa beans are genetically controlled characteristics, and affect its commercial value and industrial applicability. In the present work, an F₂ population derived from the cross between the ICS-1 and Scavina-6 cocoa clones was used for molecular mapping. A linkage map was constructed based on amplified fragment length polymorphism, random amplified polymorphic DNA, and simple sequence repeat markers, resulting in a total of 273 markers, distributed in 14 linkage groups (LGs). Phenotyping of butter content was performed after ether extraction and butter hardness was determined by sweeping differential calorimetry. One quantitative trait locus (QTL) associated to butter content was mapped at linkage group 9 (LG9) and two QTLs for butter hardness were identified at linkage groups 9 and 7 (LG9 and LG7). The two QTLs mapped at the LG9 explained 51.0% and 28.8% of the phenotypic variation for butter content and hardness, respectively. These QTLs were concentrated in the same map region, suggesting a close genetic linkage or pleiotropic effect. The QTLs identified may be useful in further marker-assisted selection breeding programs aimed at cocoa butter quality improvement.     

Mapping Genetic Loci for Quantitative Traits of Golden Shell Color,Mineral Element Contents,and Growth-Related Traits in Pacific Oyster (<Emphasis Type="Italic">Crassostrea gigas</Emphasis>)

Golden shell color and mineral content are important economic traits of Pacific oyster (Crassostrea gigas). In this study, we mapped a series of quantitative trait loci (QTLs) that control zinc (Zn) and magnesium (Mg) content, shell color and growth performance to two sex-averaged linkage maps from the FAM-A and FAM-B families. In total, ten QTLs were identified in seven linkage groups (LGs) in the FAM-B family, and seven QTLs were identified in four linkage groups in the FAM-A family. Two QTLs affecting the trait of golden shell color were identified in LG8 of the FAM-A and LG10 of the FAM-B families, which could explain 20.2 and 10.5% of the phenotypic variations, respectively. Two QTLs for Zn content were identified that could contribute to 17.9 and 34.44% of the phenotypic variations in FAM-A. Six QTLs for Zn and Mg contents were identified in four LGs (LG1, LG2, LG5, and LG9) in FAM-B, which explained 13.5–26.7% of the phenotypic variations. In addition, seven QTLs related to oyster growth were recognized in both FAM-A and FAM-B families accounting for 14.6–36.7% of the phenotypic variations. All of the DNA markers in QTL regions were blasted and 14 genes associated with above traits were identified. The mRNA expression of these genes was determined by quantitative RT-PCR. These QTLs and candidate genes could be used as potential targets for marker-assisted selection in C. gigas breeding.     

Constructing a new integrated genetic linkage map and mapping quantitative trait loci for vegetative mycelium growth rate in Lentinula edodes

The most saturated linkage map for Lentinula edodes to date was constructed based on a monokaryotic population of 146 single spore isolates (SSIs) using sequence-related amplified polymorphism (SRAP), target region amplification polymorphism (TRAP), insertion–deletion (InDel) markers, and the mating-type loci. Five hundred and twenty-four markers were located on 13 linkage groups (LGs). The map spanned a total length of 1006.1 cM, with an average marker spacing of 2.0 cM. Quantitative trait loci (QTLs) mapping was utilized to uncover the loci regulating and controlling the vegetative mycelium growth rate on various synthetic media, and complex medium for commercial cultivation of L. edodes. Two and 13 putative QTLs, identified respectively in the monokaryotic population and two testcross dikaryotic populations, were mapped on seven different LGs. Several vegetative mycelium growth rate-related QTLs uncovered here were clustered on LG4 (Qmgr1, Qdgr1, Qdgr2 and Qdgr9) and LG6 (Qdgr3, Qdgr4 and Qdgr5), implying the presence of main genomic areas responsible for growth rate regulation and control. The QTL hotspot region on LG4 was found to be in close proximity to the region containing the mating-type A (MAT-A) locus. Moreover, Qdgr2 on LG4 was detected on different media, contributing 8.07 %–23.71 % of the phenotypic variation. The present study provides essential information for QTL mapping and marker-assisted selection (MAS) in L. edodes.     

A complete genetic linkage map and QTL analyses for bast fibre quality traits, yield and yield components in jute (Corchorus olitorius L.)

We report the first complete microsatellite genetic map of jute (Corchorus olitorius L.; 2n = 2 × = 14) using an F₆ recombinant inbred population. Of the 403 microsatellite markers screened, 82 were mapped on the seven linkage groups (LGs) that covered a total genetic distance of 799.9 cM, with an average marker interval of 10.7 cM. LG5 had the longest and LG7 the shortest genetic lengths, whereas LG1 had the maximum and LG7 the minimum number of markers. Segregation distortion of microsatellite loci was high (61%), with the majority of them (76%) skewed towards the female parent. Genomewide non-parametric single-marker analysis in combination with multiple quantitative trait loci (QTL)-models (MQM) mapping detected 26 definitive QTLs for bast fibre quality, yield and yield-related traits. These were unevenly distributed on six LGs, as co-localized clusters, at genomic sectors marked by 15 microsatellite loci. LG1 was the QTL-richest map sector, with the densest co-localized clusters of QTLs governing fibre yield, yield-related traits and tensile strength. Expectedly, favorable QTLs were derived from the desirable parents, except for nearly all of those for fibre fineness, which might be due to the creation of new gene combinations. Our results will be a good starting point for further genome analyses in jute.     

Both stable and unstable QTLs for resistance to powdery mildew are detected in apple after four years of field assessments

Powdery mildew, caused by the ascomycete fungus Podosphaera leucotricha, is one of the most damaging diseases of apple worldwide. Polygenically determined resistance might contribute to a significant increase of resistance to this disease in new cultivars. A quantitative trait locus (QTL) analysis was performed in an F₁ progeny derived from a cross between the apple cultivar Discovery and the apple hybrid TN10-8. Powdery mildew incidence was assessed during four years (five seasons) in spring and/or autumn in a French local orchard. Seven additive and/or dominant QTLs were detected over the five seasons, with effects (R ²) ranging from 7.5% to 27.4% of the progeny phenotypic variation. Two QTLs, on linkage groups (LGs) 2 and 13, were consistently identified and accounted together from 29% to 37% of the phenotypic variation according to the year of assessment. The other QTLs were identified during one (LGs 1, 14), two (LG10), or three (LGs 8, 17) seasons. Their instability indicated a changing genetic determinism according to the year of assessment, for which several hypotheses may be put forward. The QTLs on LGs 2 and 8 mapped close to clusters of resistance gene analogs (RGAs) and major genes for resistance to mildew or apple scab previously identified. The stable QTLs identified on LGs 2 and 13, together with the strong effect QTL located on LG 8, are of special interest for breeding purposes, especially if combined with other major resistance genes.     

Linkage analysis and identification of quantitative trait loci associated with freeze tolerance and turf quality traits in St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm-season turfgrass commonly grown in the southern USA. In this study, the first linkage map for all nine haploid chromosomes of the species was constructed for cultivar ‘Raleigh’ and cultivar ‘Seville’ using a pseudo-F₂ mapping strategy. A total of 160 simple sequence repeat markers were mapped to nine linkage groups (LGs) covering a total distance of 1176.24 cM. To demonstrate the usefulness of the map, quantitative trait loci (QTL) were mapped controlling field winter survival, laboratory-based freeze tolerance, and turf quality traits. Multiple genomic regions associated with these traits were identified. Moreover, overlapping QTL were found for winterkill and spring green up on LG 3 (99.21 cM); turf quality, turf density, and leaf texture on LG 3 (68.57–69.50 cM); and surviving green tissue and regrowth on LGs 1 (38.31 cM), 3 (77.70 cM), 6 (49.51 cM), and 9 (34.20 cM). Additional regions, where QTL identified in both field and laboratory-based/controlled environment freeze testing co-located, provided strong support that these regions are good candidates for true gene locations. These results present the first complete linkage map produced for St. Augustinegrass, providing a template for further genetic mapping. Additionally, markers linked to the QTL identified may be useful to breeders for transferring these traits into new breeding lines and cultivars.     

QTLs for muscat flavor and monoterpenic odorant content in grapevine (Vitis vinifera L.)

Little is known about the genetic determinism of muscat flavor in grape, although this trait is of major importance for table grape breeding. We therefore performed a search for QTLs (Quantitative Trait Loci) of both muscat score and berry content in the three main free monoterpene alcohols potentially involved, linalool, nerol and geraniol, based on two years of measures. Parental and consensus framework genetic maps of the cross MTP2687-85 (Olivette × Ribol) × Muscat of Hamburg were built after genotyping the 174 offspring for 139 well-scattered SSR markers. The female, male and consensus framework maps spanned 935, 1365 and 1267 cM, respectively. For QTL detection, simple and composite interval mapping were performed, as well as non parametric Kruskal–Wallis tests. QTLs for muscat score were found on linkage groups (LGs) 1, 5 and 7. For the three ln-transformed monoterpene contents, QTLs with major effects (explaining 17–55 % of total phenotypic variance) were found to be colocated on LG 5, on the male and consensus maps in both years. One additional QTL was found for linalool on LG 2, on female and consensus maps, as well as other colocated ones for nerol and geraniol on LG 13, on male and consensus maps. These additional QTLs had lower effects (9–25%). The contribution of these results to the knowledge of muscat aroma genetic determinism is discussed, as well as their potential usefulness for marker assisted breeding of new aromatic grape varieties.     

Mapping quantitative trait loci (QTL) for body weight, length and condition factor traits in backcross (BC1) family of Common carp (Cyprinus carpio L.)

Body weight and length are economical important traits in aquaculture species influenced by quantitative trait loci (QTL) and environmental factors. In this study, a backcross (BC1) common carp family, with 86 progeny, was utilized to construct genetic map for preliminary QTL mapping. The genetic map was constructed with 366 markers, including 191 SNP from gene, coverage 50 linkage groups with an average marker distance of 18.5 cM. A total of fourteen QTLs associated with body weight (BW), body length (BL) and condition factor (K) were detected on ten linkage groups (LGs). Among these QTLs detected, three (qBW8, qBL8 and qK8) were associated with BW, BL and K respectively, were mapped on LG8. qBW8 and qK8 were identified on similar interval neared locus HLJ2394 explained 14.9 and 20.9 % of the phenotype variance, while qBL8 was identified on separate nearby locus HLJ571 with 30.8 % of phenotype variance. Two QTLs, qBW13 and qK13, related with BW and K separately, were found on LG13 at different locus with phenotype variance of 25.3 and 20.9 %. Other two QTLs, qBW19 and qBL19, associated to BW and BL were mapped on same region near SNP0626 on LG19, and explained 10.3 and 15.6 % of phenotype variance. While other seven QTLs related with BW and BL were located on different LGs. Confidential interval was ranged from 1.1 to 10 cM in the present study. These markers, with lower QTL interval, have great influence on the body weight and length. Therefore, these QTLs will be helpful to find out the genes related with specific trait.     

Identification of quantitative trait loci for resistance to Verticillium wilt and yield parameters in hop (Humulus lupulus L.)

Verticillium wilt (VW) can cause substantial yield loss in hop particularly with the outbreaks of the lethal strain of Verticillium albo-atrum. To elucidate genetic control of VW resistance in hop, an F₁ mapping population derived from a cross of cultivar Wye Target, with the predicted genetic basis of resistance, and susceptible male breeding line BL2/1 was developed to assess wilting symptoms and to perform QTL mapping. The genetic linkage map, constructed with 203 markers of various types using a pseudo-testcross strategy, formed ten major linkage groups (LG) of the maternal and paternal maps, covering 552.98 and 441.1 cM, respectively. A significant QTL for VW resistance was detected at LOD 7 on a single chromosomal region on LG03 of both parental maps, accounting for 24.2–26.0 % of the phenotypic variance. QTL analysis for alpha-acid content and yield parameters was also performed on this map. QTLs for these traits were also detected and confirmed our previously detected QTLs in a different pedigree and environment. The work provides the basis for exploration of QTL flanking markers for possible use in marker-assisted selection.     

Molecular mapping of quantitative trait loci for drought tolerance in maize plants

Drought tolerance is one of the most important but complex traits of crops. We looked for quantitative trait loci (QTLs) that affect drought tolerance in maize. Two maize inbreds and their advanced lines were evaluated for drought-related traits. A genetic linkage map developed using RFLP markers was used to identify QTLs associated with drought-related traits. Twenty-two QTLs were detected, with a minimum of one and a maximum of nine for drought-related traits. A single-QTL was detected for sugar concentration accounting for about 52.2% of the phenotypic variation on chromosome 6. A single-QTL was also identified for each of the traits root density, root dry weight, total biomass, relative water content, and leaf abscisic acid content, on chromosomes 1 and 7, contributing to 24, 0.2, 0.4, 7, and 19% of the phenotypic variance, respectively. Three QTLs were identified for grain yield on chromosomes 1, 5, and 9, explaining 75% of the observed phenotypic variability, whereas four QTLs were detected for osmotic potential on chromosomes 1, 3, and 9, together accounting for 50% of the phenotypic variance. Nine QTLs were detected for leaf surface area on chromosomes 3 and 9, with various degrees of phenotypic variance, ranging from 25.8 to 42.2%. Four major clusters of QTLs were identified on chromosomes 1, 3, 7, and 9. A QTL for yield on chromosome 1 was found co-locating with the QTLs for root traits, total biomass, and osmotic potential in a region of about 15 cM. A cluster of QTLs for leaf surface area were coincident with a QTL for osmotic potential on chromosome 3. The QTLs for leaf area also clustered on chromosome 9, whereas QTLs for leaf abscisic acid content and relative water content coincided on chromosome 7, 10 cM apart. Co-location of QTLs for different traits indicates potential pleiotropism or tight linkage, which may be useful for indirect selection in maize improvement for drought tolerance.     

Quantitative trait loci for aluminum resistance in wheat

Quantitative trait loci (QTL) for wheat resistance to aluminum (Al) toxicity were analyzed using simple sequence repeats (SSRs) in a population of 192 F₆ recombinant inbred lines (RILs) derived from a cross between an Al-resistant cultivar, Atlas 66 and an Al-sensitive cultivar, Chisholm. Wheat reaction to Al was measured by relative root growth and root response to hematoxylin stain in nutrient-solution culture. After screening 1,028 SSR markers for polymorphisms between the parents and bulks, we identified two QTLs for Al resistance in Atlas 66. One major QTL was mapped on chromosome 4D that co-segregated with the Al-activated malate transporter gene (ALMT1). Another minor QTL was located on chromosome 3BL. Together, these two QTLs accounted for about 57% of the phenotypic variation in hematoxylin staining score and 50% of the variation in net root growth (NRG). Expression of the minor QTL on 3BL was suppressed by the major QTL on 4DL. The two QTLs for Al resistance in Atlas 66 were also verified in an additional RIL population derived from Atlas 66/Century. Several SSR markers closely linked to the QTLs were identified and have potential to be used for marker-assisted selection (MAS) to improve Al-resistance of wheat cultivars in breeding programs.     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

Seed and agronomic QTL in low linolenic acid, lipoxygenase-free soybean (Glycine max (L.) Merrill) germplasm.

Linolenic acid and seed lipoxygenases are associated with off flavours in soybean products. F5 recombinant inbred lines (RILs) from a cross between a low linolenic acid line (RG10) and a seed lipoxygenase-free line (OX948) were genotyped for simple sequence repeats (SSR), random amplified polymorphic DNA (RAPD), sequence-tagged sites (STS), and cleaved amplified polymorphic sequence (CAPS) markers and evaluated for seed and agronomic traits at 3 Ontario locations in 2 years. One hundred twenty markers covering 1247.5 cM were mapped to 18 linkage groups (LGs) in the soybean composite genetic map. Seed lipoxygenases L-1 and L-2 mapped as single major genes to the same location on LG G13-F. L-3 mapped to LG G11-E. This is the first report of a map position for L-3. A major quantitative trait locus (QTL) associated with reduced linolenic acid content was identified on LG G3-B2. QTLs for 12 additional seed and agronomic traits were detected. Linolenic acid content, linoleic acid content, yield, seed mass, protein content, and plant height QTL were present in at least 4 of 6 environments. Three to 8 QTLs per trait were detected that accounted for up to 78% of total variation. Linolenic acid and lipoxygenase loci did not overlap yield QTL, suggesting that it should be possible to develop high-yielding lines resistant to oxidative degradation by marker-assisted selection (MAS).     

QTL analysis for ascochyta blight resistance in an intraspecific population of chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.)

In both controlled environment and the field, six QTLs for ascochyta blight resistance were identified in three regions of the genome of an intraspecific population of chickpea using the IDS and AUDPC disease scoring systems. One QTL-region was detected from both environments, whereas the other two regions were detected from each environment. All the QTL-regions were significantly associated with ascochyta blight resistance using either of the disease scoring systems. The QTLs were verified by multiple interval mapping, and a two-QTL genetic model with considerable epistasis was established for both environments. The major QTLs generally showed additive gene action, as well as dominance inter-locus interaction in the multiple genetic model. All the QTLs were mapped near a RGA marker. The major QTLs were located on LG III, which was mapped with five different types of RGA markers. A CLRR-RGA marker and a STMS marker flanked QTL 6 for controlled environment resistance at 0.06 and 0.04 cM, respectively. Other STMS markers flanked QTL 1 for field resistance at a 5.6 cM interval. After validation, these flanking markers may be used in marker-assisted selection to breed for elite chickpea cultivars with durable resistance to ascochyta blight. The tight linkage of RGA markers to the major QTL on LG III will allow map-based cloning of the underlying resistance genes.Communicated by P. Langridge     

Mapping quantitative trait loci for a common bean (Phaseolus vulgaris L.) ideotype.

Breeding a model plant that encompasses individual traits thought to enhance yield potential, known as ideotype breeding, has traditionally focused on phenotypic selection of plants with desirable morphological traits. Broadening this breeding method to the molecular level through the use of molecular markers would avoid the environmental interactions associated with phenotypic selection. A population of 110 F5 recombinant inbred lines (RILs), derived from the cross between WO3391 and 'OAC Speedvale', was used to develop a genetic linkage map consisting of 105 random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and sequence-tagged site (STS) markers. The map has a total length of 641 cM distributed across 8 linkage groups (LGs). Five of them were aligned on the core linkage map of bean. Twenty-one quantitative trait loci (QTLs) were identified over three environments for eight agronomic and architectural traits previously defined for a bean (Phaseolus vulgaris L.) ideotype. The QTLs were mapped to seven LGs with several regions containing QTLs for multiple traits. At least one QTL was located for each trait and a maximum of four were associated with lodging. Total explained phenotypic variance ranged from 10.6% for hypocotyl diameter to 45.4% for maturity. Some of the QTLs identified will be useful for early generation selection of tall, upright, high-yielding lines in a breeding program.