Comparative mapping in F2∶3 and F6∶7 generations of quantitative trait loci for grain yield and yield components in maize

This study was conducted to compare maize quantitative trait loci (QTL) detection for grain yield and yield components in F₂₃ and F₆₇ recombinant inbred (RI) lines from the same population. One hundred and eighty-six F₆₇ RIs from a Mo17×H99 population were grown in a replicated field experiment and analyzed at 101 loci detected by restriction fragment length polymorphisms (RFLPs). Single-factor analysis of variance was conducted for each locus-trait combination to identify QTL. For grain yield, 6 QTL were detected accounting for 22% of the phenotypic variation. A total of 63 QTL were identified for the seven grain yield components with alleles from both parents contributing to increased trait values. Several genetic regions were associated with more than one trait, indicating possible linked and/or pleiotropic effects. In a comparison with 150 F₂₃ lines from the same population, the same genetic regions and parental effects were detected across generations despite being evaluated under diverse environmental conditions. Some of the QTL detected in the F₂₃ seem to be dissected into multiple, linked QTL in the F₆₇ generation, indicating better genetic resolution for QTL detection with RIs. Also, genetic effects at QTL are smaller in the F₆₇ generation for all traits.Abbreviations RFLPs Restriction fragment length polymorphisms - QTL quantitative trait loci - RIs recombinant inbreds Journal Paper no. J-16261 of the Iowa Agric and Home Economics Exp Stn Project no. 3134     

Fine mapping of a malting-quality QTL complex near the chromosome 4H S telomere in barley

Malting quality has long been an active objective in barley (Hordeum vulgare L.) breeding programs. However, it is difficult for breeders to manipulate malting-quality traits because of inheritance complexity and difficulty in evaluation of these quantitative traits. Quantitative trait locus (QTL) mapping provides breeders a promising basis with which to manipulate quantitative trait genes. A malting-quality QTL complex, QTL2, was mapped previously to a 30-cM interval in the short-arm telomere region of barley chromosome 4H in a Steptoe/Morex doubled haploid population by the North American Barley Genome Project, using an interval mapping method with a relatively low-resolution genetic map. The QTL2 complex has moderate effects on several malting-quality traits, including malt extract percentage (ME), -amylase activity (AA), diastatic power (DP), malt -glucan content (BG), and seed dormancy, which makes it a promising candidate gene source in malting barley-cultivar development. Fine mapping QTL2 is desirable for precisely studying barley malting-quality trait inheritance and for efficiently manipulating QTL2 in breeding. A reciprocal-substitution mapping method was employed to fine map QTL2. Molecular marker-assisted backcrossing was used to facilitate the generation of isolines. Fourteen different types of Steptoe isolines, including regenerated Steptoe and 13 different types of Morex isolines, including regenerated Morex, were made within a 41.5-cM interval between MWG634 and BCD265B on chromosome 4H. Duplicates were identified for 12 Steptoe and 12 Morex isoline types. The isolines together with Steptoe and Morex were grown variously at three locations in 2 years for a total of five field environments. Four malting-quality traits were measured: ME, DP, AA, and BG. Few significant differences were found between duplicate isolines for these traits. A total of 15 putative QTLs were mapped; three for ME, four for DP, six for AA, and two for BG. Background genotype seemed to make a difference in expression/detection of QTLs. Of the 15 QTLs identified, ten were from the Morex and only five from the Steptoe background. By combining the results from different years, field environments, and genetic backgrounds and taking into account overlapping QTL segments, six QTLs can be conservatively estimated: two each for ME and AA and one each for DP and BG with chromosome segments ranging from 0.7 cM to 27.9 cM. A segment of 15.8 cM from the telomere (MWG634–CDO669) includes all or a portion of all QTLs identified. Further study and marker-assisted breeding should focus on this 15.8-cM chromosome region.     

Quantitative resistance to barley leaf stripe (Pyrenophora graminea) is dominated by one major locus

A major gene underlying quantitative resistance of barley against Pyrenophora graminea, a seedborne pathogen causing leaf stripe, was mapped with molecular markers in a barley doubled haploid (DH) population derived from the cross Proctor x Nudinka. This quantitative trait locus (QTL) accounts for r ²= 58.5% and was mapped on barley chromosome 1, tightly linked to the naked gene. A second resistance QTL accounting for 29.3% of the variation in the trait was identified on the P arm of barley chromosome 2. Another two minor QTLs were detected by further analysis. None of the QTLs was found in the barley chromosome 2 Vada region studied by Giese et al. (1993).     

Mapping of β-glucan content and β-glucanase activity loci in barley grain and malt

Genetic study of -glucan content and -glucanase activity has been facilitated by recent developments in quantitative trait loci (QTL) analysis. QTL for barley and malt -glucan content and for green and finished malt -glucanase activity were mapped using a 123-point molecular marker linkage map from the cross of Steptoe/Morex. Three QTL for barley -glucan, 6 QTL for malt -glucan, 3 QTL for -glucanase in green malt and 5 QTL for -glucanase in finished malt were detected by interval mapping procedures. The QTL with the largest effects on barley -glucan, malt glucan, green malt -glucanase and finished malt glucanase were identified on chromosomes 2,1,4 and 7, respectively. A genome map-based approach allows for dissection of relationships among barley and malt glucan content, green and finished malt -glucanase activity, and other malting quality parameters.     

Molecular marker-assisted selection for malting quality traits in barley

Selection for malting quality in breeding programs by micromalting and micromashing is time-consuming, and resource-intensive. More efficient and feasible approaches for identifying genotypes with good malting quality would be highly desirable. With the advent of molecular markers, it is possible to map and tag the loci affecting malting quality. The objective of this study was to assess the effectiveness of molecular marker assisted selection for malting quality traits. Two major quantitative trait loci (QTL) regions in six-row barley for malt extract percentage, -amylase activity, diastatic power, and malt -glucan content on chromosomes 1 (QTL1) and 4 (QTL2) have been previously identified. The flanking markers, Brz and Amy2, and WG622 and BCD402B, for these two major QTL regions were used in marker-assisted selection. Four alternative selection strategies; phenotypic selection, genotypic selection, tandem genotypic and phenotypic selection, and combined phenotypic and genotypic selection, were compared for both single and multiple trait selection in a population consisting of 92 doubled haploid lines derived from Steptoe × Morex crosses. Marker assisted selection for QTL1 (tandem genotypic and phenotypic selection, and combined phenotypic and genotypic selection) was more effective than phenotypic selection, but for QTL2 was not as effective as phenotypic selection due to a lack of QTL2 effects in the selection population. The effectiveness of tandem genotypic and phenotypic selection makes marker assisted selection practical for traits which are extremely difficult or expensive to measure such as most malting quality traits. It can substantially eliminate undesirable genotypes by early genotyping and keeping only desirable genotypes for later phenotypic selection.     

What proportion of declared QTL in plants are false?

The false discovery rate (FDR) is the probability that a quantitative trait locus (QTL) is false, given that a QTL has been declared. A misconception in QTL mapping is that the FDR is equal to the comparison-wise significance level, _C. The objective of this simulation study was to determine the FDR in an F₂ mapping population, given different numbers of QTL, population sizes, and trait heritabilities. Markers linked to QTL were detected by multiple regression of phenotype on marker genotype. Phenotypic selection and marker-based recurrent selection were compared. The FDR increased as _C increased. Notably, the FDR was often 10–30 times higher than the _C level used. Regardless of the number of QTL, heritability, or size of the genome, the FDR was 0.01 when _C was 0.0001. The FDR increased to 0.82 when _C was 0.05, heritability was low, and only one QTL controlled the trait. An _C of 0.05 led to a low FDR when many QTL (30 or 100) controlled the trait, but this lower FDR was accompanied by a diminished power to detect QTL. Larger mapping populations led to both lower a FDR and increased power. Relaxed significance levels of _C=0.1 or 0.2 led to the largest responses to marker-based recurrent selection, despite the high FDR. To prevent false QTL from confusing the literature and databases, a detected QTL should, in general, be reported as a QTL only if it was identified at a stringent significance level, e.g., _C0.0001.Communicated by H.C. Becker     

Inheritance of early elongation ability in floating rice revealed by diallel and QTL analyses

In floating rice, stem elongation begins much earlier than in non-floating rice, which is the major survival mechanism for flooding. Inheritance of this early elongation ability was studied using diallel and quantitative trait locus (QTL) analyses. The diallel analysis was undertaken using a set of 6×6 half-diallel crosses involving four floating (Goai, Habiganj Aman VIII, Badal 106, and Oryza rufipogon strain W120) and two non-floating (Latisail and Patnai 23) parents. The additive gene effects were higher than the dominant effects. The dominant alleles were concentrated in the cultivated floating parents (Goai, Habiganj Aman VIII, and Badal 106), whereas the recessive alleles were in the wild floating parent (W120). A QTL analysis using a Patnai 23 × Goai F₂ population detected two putative QTLs. Of these QTLs, the one on chromosome 12 behaved as a partially dominant major gene that explained more than half of the total genetic variation.Communicated by D.J. Mackill     

A partial genome assay for quantitative trait loci in wheat (Triticum aestivum) using different analytical techniques

F₁ plants between two intervarietal chromosome substitution lines of European spring wheat varieties, Sicco (Chinese Spring 5B) and Highbury (Chinese Spring 5B), were used to produce 114 doubled haploid lines, 45 by the Hordeum bulbosum technique and 69 by anther culture. These two sets of lines were characterized for variation at a range of morphological, isozyme and RFLP marker loci, and genetic maps were developed with emphasis on chromosomes 6B, 7A, 7B and 7D. A subset of lines, scored for production traits in field trials in 1986 and 1987, were analysed for quantitative trait loci (QTL). The performance of the lines for the quantitative traits studied showed no overall differences due to the method of production of the lines. QTL were located on the linkage map for ear emergence time, height, tiller weight, yield and 50-grain weight using four analytical methods. Many of these effects showed genotype x year interaction.     

RFLP analysis of genomic regions associated with cooked-kernel elongation in rice

As a result of earlier breeding efforts, portions of the genome of Basmati 370 have been introgressed into a rice breeding line, B8462T3-710. Cooked-kernel elongation was increased in this breeding line to a level equal to that of Basmati 370. The objective of this study was to identify and locate quantitative trait loci (QTLs) associated with cooked-kernel elongation in an F3 population derived from a cross between B8462T3710 and the reduced-elongation recurrent parent variety, Dellmont. DNA from the parental lines and Basmati 370 as a control, were screened for RFLPs using 170 clones chosen to cover the rice genome at intervals of 8 cM on average. Eighteen markers identified RFLPs common to Basmati 370 and B8462T3-710, but different from Dellmont, suggesting possible associations with kernel elongation. The B8462T3-710/Dellmont F3 population was analyzed for segregation of those RFLPs and for kernel elongation. Analysis of variance of the kernel elongation ratio revealed that two markers, 14.6 cM apart on chromosome 8, are significantly associated with this trait (RZ323 P 0.005, RZ562 P 0.05). Interval mapping suggests a single QTL with a close proximity to RZ323. This QTL was tested in F6 lines derived from the same cross and the presence of the B8462T3-710 segment detected by RZ323 caused a highly significant increase of the kernel elongation ratio (P 0.04). In addition, the QTL for kernel elongation and a gene for aroma, which are major components of the grain quality characteristics of Basmati-type rices, showed linkage. The availability of linked markers to the QTL may facilitate early selection for kernel elongation in rice breeding programs.     

Determining the linkage of quantitative trait loci to RFLP markers using extreme phenotypes of recombinant inbreds of soybean (Glycine max L. Merr.)

An experimental test is described for linkages between RFLP markers and quantitative trait loci (QTL). Two hundred and eighty-four F₇-derived recombinant inbred lines (RIL) obtained from crossing the soybean cultivars (Glycine max L. Merr.) Minsoy and Noir 1 were evaluated for maturity, plant height, lodging, and seed yield. RIL exhibiting an extreme phenotype for each trait (earliest and latest plants for maturity, etc.) were selected, and two bulked DNA samples were prepared for each trait. A Southern transfer of the digested bulked DNA was hybridized with restriction fragement length polymorphism (RFLP) probes, and linkages with QTL were established by quantitating the amount of radioactive probe that bound to fragments defining alternative parental RFLP alleles. When an RFLP marker was linked to a QTL, one parental allele predominated in the bulked DNA from a particular phenotype; the other allele was associated with the opposite phenotype. When linkage was absent, radioactivity was associated equally with both alleles for a given phenotype (or with both phenotypes for a given allele). These results confirmed RFLP-QTL associations previously discovered by interval mapping on a smaller segregating population from the same cross. New linkages to QTL were also verified.     

Location of a gene regulating drought-induced abscisic acid production on the long arm of chromosome 5A of wheat

The accumulation of abscisic acid (ABA) by detached and partially dehydrated wheat leaves is known to be inherited in a quantitative manner. The location of genes having a major effect on drought-induced ABA accumulation in wheat was determined using a set of single chromosome substitution lines and populations derived from a cross between a high-ABA- and a low-ABA-producing genotype. Examination of a series of chromosome substitution lines of the high-ABA genotype Ciano 67 into the low-ABA recipient Chinese Spring showed that chromosome 5A carries gene(s) that have a major influence on ABA accumulation in a drought test with detached and partially dehydrated leaves (DLT). A similar DLT was used to examine ABA accumulation in a population of F₂ plants and doubled haploid (DH) lines derived from the cross between Chinese Spring (low-ABA) and SQ1 (high-ABA) in which the F₂ population (139 plants) and DH lines (96 lines) were also mapped partially with molecular markers. Analysis of variance of ABA accumulation between and within marker allele classes in the F₂ confirmed the location of a gene(s) regulating ABA accumulation on the long arm of chromosome 5A. MAPMAKERQTL showed the most likely position for the ABA quantitative trait locus (QTL) to be between the loci Xpsr575 and Xpsr426, about 8 cM from Xpsr426. A similar trend for high ABA accumulation was found in DH lines having the SQ1 allele at marker loci in the same region of chromosome 5AL, but the QTL effect was not significant. The function of the QTL is discussed.     

QTL analysis: further uses of ‘marker regression’

A variety of approaches are available for identifying the location and effect of QTL in segregating populations using molecular markers. However, these have problems in distinguishing two linked QTL, particularly in relation to the size of the test statistic when many independent tests are performed. An empirical method for obtaining the distribution of the test statistic for specific datasets is described, and its power for demonstrating the inadequacy of a single-QTL model is explored through computer simulation. The method is an extension of the previously described technique of marker regression, and it is applied here to demonstrate two situations in which it may be useful. Firstly, we examine the power of the technique to distinguish two, linked QTL from one and compare this ability with that of two contemporary methods, Mapmaker/QTL and regression mapping. Secondly, we show how to combine information from two, or more, populations that may be segregating for different marker loci in a given linkage group. This is illustrated for two populations having in common just two linked marker loci although the sharing of loci is not a pre-requisite. Empirical tests are used to determine whether the same or different QTL are segregating and, if they are the same QTL, whether they are the same alleles. Evidence is discussed which suggests that the upper limit to the number of QTL that can be located for any single quantitative trait in a segregating populations is 12.     

Epistatic expression of quantitative trait loci (QTL) in soybean [Glycine max (L.) Merr.] determined by QTL association with RFLP alleles

Quantitative trait values for seed oil and protein content or for maturity were measured in recombinant inbred lines (RIL) of soybean derived from a cross between two soybean cultivars: Minsoy PI 27890 and Noir 1 PI 290136. Seed oil was found to be inversely correlated to protein content. By analyzing DNA from plants with extreme phenotypes, we were able to identify quantitative trait loci (QTL) for these traits as being linked to several restriction fragment length polymorphism (RFLP) loci, including R183 for oil and protein content and R79 for maturity. Cumulative distributions of trait values were graphed for those RIL with Minsoy alleles and for those with Noir 1 alleles. As already suggested by the alleles found associated with extreme phenotypes, the distributions were consistent with an independent and additive expression of the maturity QTL linked to R79. That is, the cumulative distributions for plants with Minsoy alleles and for plants with Noir 1 alleles were similar in shape, but the entire Noir 1 curve had been shifted to later maturity dates. In contrast, the trait distributions for a locus affecting oil and protein content linked to R183 were not compatible with an additive model. These results suggest that this approach can be used for rapid identification of QTLs with epistatic expression.     

Molecular cloning and expression of multiple cellulase genes of Ruminococcus flavefaciens strain 186 in Escherichia coli

Summary Cellulase genes of the ruminant micro-organism Ruminococcus flavefaciens strain 186 have been cloned and expressed in Escherichia coli using the bacteriophage vector NM1149. Twenty-six clones showed expression of endo--1,4-d-glucanases and were divided into four groups according to their insert sizes of approximately 2, 3, 4 or 9 kilobases (kb). Two of the clones with 4 kb inserts also showed exo--1,4-d glucanase activity while two clones with 9 kb inserts showed -glucosidase activity. One of the clones with 9 kb inserts (M903) showed the activities of all three cellulase activities. In addition, two of the 4 kb-insert clones and one 9 kb-insert clone degraded Avicel (PH101).     

Enhanced power of QTL detection for Fusarium head blight resistance in wheat by means of codominant scoring of hemizygous molecular markers

Based on different marker information content mapping of QTLs for Fusarium head blight resistance in wheat was compared with regard to number and consistency of detected QTLs as well as QTL positions and effects. Therefore, two linkage maps, obtained by dominant and codominant genotyping of hemizygous markers, were constructed with 211 AFLPs, 37 SSRs and the barley RGA marker XaACT/CAA. The codominant marker set comprised 59% codominant markers, whereas the dominant map consisted of only 13%. A segregating wheat population of 94 F₄-RILs was used for QTL analysis. Fusarium head blight resistance was estimated in field trials in six environments. Conventional dominant marker scoring found seven QTLs. The phenotypic variations explained by QTLs detected in single environment analyses ranged from 11.1 to 44.6%. QTL analysis performed with the codominant marker set confirmed not only all QTL positions as revealed by dominant QTL analysis', but also 12 additional QTLs were found. QTLs in single environments explained 36.3 up to 55.7% of the phenotypic variation. In the QTL analysis across all environments, none of the QTLs could be confirmed using dominant marker scoring. However, by codominant QTL analysis' environment-specific QTLs were retrieved. STS marker XaACT/CAA was found to be significantly associated with FHB resistance only by codominant scoring. Support intervals of QTLs commonly found in both marker sets averaged to 10.3 cM in the dominant QTL analysis', whereas the length was shortened to 8.9 cM by codominant genotyping. The advantages of extracting codominant information from dominant markers are discussed.     

Quantitative trait locus analysis of fungal disease resistance factors on a molecular map of grapevine

A full-sibling F1 population comprising 153 individuals from the cross of Regent × Lemberger was employed to construct a genetic map based on 429 molecular markers. The newly-bred red grapevine variety Regent has multiple field-resistance to fungal diseases inherited as polygenic traits, while Lemberger is a traditional fungus-susceptible cultivar. The progeny segregate quantitatively for resistances to Plasmopara viticola and Uncinula necator, fungal pathogens that threaten viticulture in temperate areas. A double pseudo-testcross strategy was employed to construct the two parental maps under high statistical stringency for linkage to obtain a robust marker frame for subsequent quantitative trait locus (QTL) analysis. In total, 185 amplified fragment length polymorphism, 137 random amplified polymorphic DNA, 85 single sequence repeat and 22 sequence characterized amplified region or cleaved amplified polymorphic sequence markers were mapped. The maps were aligned by co-dominant or doubly heterozygous dominant anchor markers. Twelve pairs of homologous linkage groups could be integrated into consensus linkage groups. Resistance phenotypes and segregating characteristics were scored as quantitative traits in three or four growing seasons. Interval mapping reproducibly localized genetic factors that correlated with fungal disease resistances to specific regions on three linkage groups of the maternal Regent map. A QTL for resistance to Uncinula necator was identified on linkage group 16, and QTLs for endurance to Plasmopara viticola on linkage groups 9 and 10 of Regent. Additional QTLs for the onset of berry ripening (veraison), berry size and axillary shoot growth were identified. Berry color segregated as a simple trait in this cross of two red varieties and was mapped as a morphological marker. Six markers derived from functional genes could be localized. This dissection of polygenic fungus disease resistance in grapevine allows the development of marker-assisted selection for breeding, the characterization of genetic resources and the isolation of the corresponding genes.Communicated by H.C. Becker     

Seed quality QTL in a prominent soybean population

Soybean [Glycine max (L.) Merr.] is a versatile crop due to its multitude of uses as a high protein meal and vegetable oil. Soybean seed traits such as seed protein and oil concentration and seed size are important quantitative traits. The objective of this study was to identify representative protein, oil, and seed size quantitative trait loci (QTL) in soybean. A recombinant inbred line (RIL) population consisting of 131 F₆-derived lines was created from two prominent ancestors of North American soybeans (Essex and Williams) and the RILs were grown in six environments. One hundred simple sequence repeat (SSR) markers spaced throughout the genome were mapped in this population. There were a total of four protein, six oil, and seven seed size QTL found in this population. The QTL found in this study may assist breeders in marker-assisted selection (MAS) to retain current positive QTL in modern soybeans while simultaneously pyramiding additional QTL from new germplasm.     

Organization of heterologous DNA inserts on the mouse meiotic chromosome core

With simultaneous immunofluorescence and fluorescent in situ hybridization, we have determined the organization of native and heterologous DNA sequences relative to the cores of meiotic prophase chromosomes. The normal chromatin organization is demonstrated with probes of mouse sequences: a cosmid probe that identities unique sequences and a 720 kb yeast artificial chromosome (YAC) probe that recognizes a specific region of the chromatin domain. The heterologous DNA consists of a 1.8 Mb insertion of 40 tandem head-to-tail phage LIZ vectors and of 11.4 Mb of bacterial/mouse DNA repeats. The lengthy insert is unusual in that it is not contained in the chromatin domain of chromosome 4 and in that it fails to form direct attachments to the chromosome core. The ends are attached indirectly, probably by means of the flanking mouse sequences. At late stages of meiotic prophase, while the terminal attachments remain the same, the DNA becomes highly compacted. Apparently, higher order condensation and core attachment are independent processes. The condensed inserts relax precociously at metaphase I. In the mouse heterozygous for the insert, the two sister inserts are usually merged, as are all four inserts in the homozygous mouse. Evidently chromatin loops with identical sequences can become associated during meiotic prophase. Mouse sequences within a heterologous DNA insert (repeats of bacterial plasmid pBR322 with a mouse -globin insert) were observed to restore some degree of core attachment.     

Single and interacting QTLs for cholesterol gallstones revealed in an intercross between mouse strains NZB and SM

Quantitative trait locus (QTL) mapping was employed to investigate the genetic determinants of cholesterol gallstone formation in a large intercross between mouse strains SM/J (resistant) and NZB/B1NJ (susceptible). Animals consumed a gallstonepromoting diet for 18 weeks. QTL analyses were performed using gallstone weight and gallstone absence/presence as phenotypes; various models were explored for genome scans. We detected seven single QTLs: three new, significant QTLs were named Lith17 [chromosome (Chr) 5, peak=60 cM, LOD=5.4], Lith18 (Chr 5, 76 cM, LOD=4.3), and Lith19 (Chr 8, 0 cM, LOD=5.3); two confirmed QTLs identified previously and were named Lith20 (Chr 9, 44 cM, LOD=2.7) and Lith21 (Chr 10, 24 cM, LOD=2.9); one new, suggestive QTL (Chr 17) remains unnamed. Upon searching for epistatic interactions that contributed to gallstone susceptibility, the final suggestive QTL on Chr 7 was determined to interact significantly with Lith18 and, therefore, was named Lith22 (65 cM). A second interaction was identified between Lith19 and a locus on Chr 11; this QTL was named Lith23 (13 cM). mRNA expression analyses and amino acid haplotype analyses likely eliminated Slc10a2 as a candidate gene for Lith19. The QTLs identified herein largely contributed to gallstone formation rather than gallstone severity. Cloning the genes underlying these murine QTLs should facilitate prediction and cloning of the orthologous human genes.Abbreviations: CI, confidence interval; F₁,first filial generation; F₂, second filial (intercross) generation; LOD, logarithm of the odds ratio; NZB, NZB/B1NJ; QTL, quantitative trait locus; SM, SM/J. The nucleotide sequence data for Slc10a2 were submitted to GenBank and were assigned the accession numbers AY529655 (strain SM) and AY529656 (strain NZB).     

Interval mapping of quantitative trait loci for reproductive,morphological, and seed traits of soybean (Glycine max L.)

Quantitative trait loci (QTL) were mapped in segregating progeny from a cross between two soybean (Glycine max (L.) Merr.) cultivars: Minsoy (PI 27.890) and Noir 1 (PI 290.136). The 15 traits analyzed included reproductive, morphological, and seed traits, seed yield and carbon isotope discrimination ratios (¹³C/¹²C). Genetic variation was detected for all of the traits, and transgressive segregation was a common phenomenon. One hundred and thirty-two linked genetic markers and 24 additional unlinked markers were used to locate QTL by interval mapping and one-way analysis of variance, respectively. Quantitative trait loci controlling 11 of the 15 traits studied were localized to intervals in 6 linkage groups. Quantitative trait loci for developmental and morphological traits (R1, R5, R8, plant height, canopy height, leaf area, etc.) tended to be clustered in three intervals, two of which were also associated with seed yield. Quantitative trait loci for seed oil were separated from all the other QTL. Major QTL for maturity and plant height were linked to RFLP markers R79 (31% variation) and G173 (53% variation). Quantitative trait loci associated with unlinked markers included possible loci for seed protein and weight. Linkage between QTL is discussed in relation to the heritability and genetic correlation of the traits.