Pollen-mediated intraspecific gene flow from herbicide resistant oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

The cultivation of genetically modified (GM) herbicide resistant oilseed rape (Brassica napus) has increased over the past few years. The transfer of herbicide resistance genes via pollen (gene flow) from GM crops to non-GM crops is of relevance for the realisation of co-existence of different agricultural cultivation forms as well as for weed management. Therefore the likelihood of pollen-mediated gene flow has been investigated in numerous studies. Despite the difficulty to compare different experiments with varying levels of outcrossing, we performed a literature search for world-wide studies on cross-fertilisation in fully fertile oilseed rape. The occurrence and frequency of pollen-mediated intraspecific gene flow (outcrossing rate) can vary according to cultivar, experimental design, local topography and environmental conditions. The outcrossing rate from one field to another depends also on the size and arrangement of donor and recipient populations and on the ratio between donor and recipient plot size. The outcrossing levels specified in the presented studies are derived mostly from experiments where the recipient field is either surrounding the donor field (continuous design) or is located as a patch at different distances from the donor field (discontinuous design). Reports of gene flow in Brassica napus generally show that the amount of cross-fertilisation decreases as the distance from the pollen source increases. The evidence given in various studies reveals that the bulk of GM cross-fertilisation occurs within the first 10 m of the recipient field. The removal of the first 10 m of a non-transgenic field facing a GM crop might therefore be more efficient for reducing the total level of cross-fertilisation in a recipient sink population than to recommend separation distances. Future experiments should investigate cross-fertilisation with multiple adjacent donor fields at the landscape level under different spatial distributions of rapeseed cultivars and different cropping systems. The level of cross-fertilisation occurring over the whole field is mainly important for co-existence and has not been investigated in agricultural scale experiments until now. Potential problems with herbicide resistant oilseed rape volunteers arising from intraspecific gene flow can be largely solved by the choice of suitable cultivars and herbicides as well as by soil management.     

Development of INDELs markers in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) using re-sequencing data

Insertions/deletions (INDELs), a type of abundant length polymorphisms in the plant genomes, combine the characteristics of both simple sequence repeats (SSRs) and single-nucleotide polymorphisms (SNP), and thus can be developed as desired molecular markers for genetic studies and crop breeding. There has been no large-scale characterization of INDELs variations in Brassica napus yet. In this study, we identified a total of 538,691 INDELs in size range of 1–10 bp by aligning whole-genome re-sequencing data of 23 B. napus inbred lines (ILs) to the B. napus genome sequence of ‘Darmor-bzh.’ Of these, 104,190 INDELs were uniquely mapped on the pseudochromosomes of the reference genome. A set of 595 unique INDELs of 2–5 bp in length was selected for experimental validation in the 23 ILs. Of these INDELs, 530 (89.01 %) produced a single PCR product and were single locus. A total of 523 (87.9 %) INDELs were found polymorphic among the 23 ILs. A genetic linkage map containing 108 single-locus INDELs and 89 anchor SSR markers was constructed using 188 recombinant ILs. The majority of INDELs markers on the linkage map showed consistency with the pseudochromosomes of the B. napus cultivar ‘Darmor-bzh.’ The INDELs variations and markers reported here will be valuable resources in future for genetic studies and molecular breeding in oilseed rape.     

Association mapping of quantitative resistance for <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Stem canker caused by the fungus Leptosphaeria maculans is a major disease of Brassica napus. Quantitative resistance factors appear to be important components for effective and durable control of this pathogen. Quantitative trait loci (QTL) for stem canker resistance have previously been identified in the Darmor variety. However, before these QTL can be used in marker-assisted selection (MAS) to breed resistant varieties, they must be validated in a wide range of genetic backgrounds. We used an association mapping approach to confirm the markers located within the QTL previously identified in Darmor and establish their usefulness in MAS. For this, we characterized the molecular diversity of an oilseed rape collection of 128 lines showing a large spectrum of responses to infection by L. maculans, using 72 pairs of primers for simple sequence repeat and other markers. We used different association mapping models which either do or do not take into account the population structure and/or family relatedness. In all, 61 marker alleles were found to be associated with resistance to stem canker. Some of these markers were associated with previously identified QTL, which confirms their usefulness in MAS. Markers located in regions not harbouring previously identified QTL were also associated with resistance, suggesting that new QTL or allelic variants are present in the collection. All of these markers associated with stem canker resistance will help identify accessions carrying desirable alleles and facilitate QTL introgression.     

QTL analysis and the development of closely linked markers for days to flowering in spring oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Days to flowering (DTF) is an important trait impacting cultivar performance in oilseed rape (Brassica napus L.), but the interaction of all loci controlling this trait in spring-type oilseed rape is not fully understood. We identified quantitative trait loci (QTL) for variation in DTF in a doubled haploid (DH) population from the Qinghai–Tibet Plateau that includes 217 lines derived from a cross between spring-type oilseed rape (B. napus L.) line No. 5246 and line No. 4512, the latter of which is responsive to the effective accumulated temperature (EAT). A linkage map was constructed for the DH population, using 202 SSR and 293 AFLP markers. At least 22 DTF QTL were found in multiple environments. Four major QTL were located on linkage groups A7, C2, C8 and C8. Among these QTL, cqDTFA7a and cqDTFC2a were identified in five environments and individually explained 10.4 and 23.0 % of the trait variation, respectively. cqDTFC8, a major QTL observed in spring environments, and a unique winter environment QTL, qDTFC8-3, were identified; these QTL explained 10.0 and 46.5 % of the phenotypic variation, respectively. Minor QTL (for example, cqDTFC2c) and epistatic interactions seemed evident in this population. Two closely linked SSR markers for cqDTFA7a and cqDTFC8 were developed (G1803 and S034). BnAP1, a B. napus gene with homology to Arabidopsis thaliana that was identified as a cqDTFA7a candidate gene, played a major role in this study. The allelic effects of the major and minor QTL on DTF were further validated in the DH population and in 93 breeding genotypes.     

Amino acid contents and transport in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) under different nitrogen conditions

Oilseed rape (Brassica napus L.) needs very high nitrogen fertilizer inputs. Significant amounts of this nitrogen are lost during early leaf shedding and are a source of environmental and economic concern. The objective of this study was to investigate whether the remobilization of leaf amino acids could be limiting for nitrogen use efficiency. Therefore, amino acid concentrations were analyzed in subcellular compartments of leaf mesophyll cells of plants grown under low (0.5 mM NO₃^–) and high (4 mM NO₃^–) nitrogen supply. With high nitrogen supply, young leaves showed an elevated amino acid content, mainly in vacuoles. In old leaves, however, subcellular concentrations were similar under high and low nitrogen conditions, showing that the excess nitrogen had been exported during leaf development. The phloem sap contained up to 650 mM amino acids, more than four times as much than the cytosol of mesophyll cells, indicating a very efficient phloem-loading process. Three amino acid permeases, BnAAP1, BnAAP2, and BnAAP6, were identified and characterized. BnAAP1 and BnAAP6 mediated uptake of neutral and acidic amino acids into Xenopus laevis oocytes at the actual apoplastic substrate concentrations. All three transporters were expressed in leaves and the expression was still detectable during leaf senescence, with BnAAP1 and BnAAP2 mRNA levels increasing from mature to old leaves. We conclude that phloem loading of amino acids is not limiting for nitrogen remobilization from senescing leaves in oilseed rape.     

Defence reactions in the apoplastic proteome of oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> var. <Emphasis Type="Italic">napus</Emphasis>) attenuate <Emphasis Type="Italic">Verticillium longisporum</Emphasis>growth but not disease symptoms

Background

Verticillium longisporum is one of the most important pathogens of Brassicaceae that remains strictly in the xylem during most stages of its development. It has been suggested that disease symptoms are associated with clogging of xylem vessels. The aim of our study was to investigate extracellular defence reactions induced by V. longisporum in the xylem sap and leaf apoplast of Brassica napus var. napus in relation to the development of disease symptoms, photosynthesis and nutrient status.

Results

V. longisporum (strain VL43) did not overcome the hypocotyl barrier until 3 weeks after infection although the plants showed massive stunting of the stem and mild leaf chlorosis. During this initial infection phase photosynthetic carbon assimilation, transpiration rate and nutrient elements in leaves were not affected in VL43-infected compared to non-infected plants. Proteome analysis of the leaf apoplast revealed 170 spots after 2-D-protein separation, of which 12 were significantly enhanced in response to VL43-infection. LS-MS/MS analysis and data base searches revealed matches of VL43-responsive proteins to an endochitinase, a peroxidase, a PR-4 protein and a β-1,3-glucanase. In xylem sap three up-regulated proteins were found of which two were identified as PR-4 and β-1,3-glucanase. Xylem sap of infected plants inhibited the growth of V. longisporum.

Conclusion

V. longisporum infection did not result in drought stress or nutrient limitations. Stunting and mild chlorosis were, therefore, not consequences of insufficient water and nutrient supply due to VL43-caused xylem obstruction. A distinct array of extracellular PR-proteins was activated that might have limited Verticillium spreading above the hypocotyl. In silico analysis suggested that ethylene was involved in up-regulating VL43-responsive proteins.

     

The effect of <Emphasis Type="Italic">INDEHISCENT</Emphasis> point mutations on silique shatter resistance in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>)

Key message

This study elucidates the influence of indehiscent mutations on rapeseed silique shatter resistance. A phenotype with enlarged replum-valve joint area and altered cell dimensions in the dehiscence zone is described.

Abstract

Silique shattering is a major factor reducing the yield stability of oilseed rape (Brassica napus). Attempts to improve shatter resistance often include the use of mutations in target genes identified from Arabidopsis (Arabidopsis thaliana). A variety of phenotyping methods assessing the level of shatter resistance were previously described. However, a comparative and comprehensive evaluation of the methods has not yet been undertaken. We verified the increase of shatter resistance in indehiscent double knock-down mutants obtained by TILLING with a systematic approach comparing three independent phenotyping methods. A positive correlation of silique length and shatter resistance was observed and accounted for in the analyses. Microscopic studies ruled out the influence of different lignification patterns. Instead, we propose a model to explain increased shattering resistance of indehiscent rapeseed mutants by altered cell shapes and sizes within the contact surfaces of replum and valves.

     

Mapping of days to flower and seed yield in spring oilseed <Emphasis Type="Italic">Brassica napus</Emphasis> carrying genome content introgressed from <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Earliness of flowering and maturity and high seed yield are important objectives of breeding spring Brassica napus canola. Previously, we have introgressed earliness of flowering from Brassica oleracea into spring B. napus canola through interspecific crossing between these two species. In this paper, we report quantitative trait locus (QTL) mapping of days to flower and seed yield by use of publicly available markers and markers designed based on flowering time genes and a doubled haploid population, derived from crossing of the spring canola parent and an early flowering line developed from a B. napus × B. oleracea cross, tested in nine field trials for over 5 years. Five genomic regions associated with days to flower were identified on C1, C2, C3, and C6 of which the single QTL of C1 was detected in all trials; in all cases, the allele introgressed from B. oleracea reduced the number of days to flower. BLASTn search in the Brassica genomes located the physical position of the QTL markers and identified putative flowering time genes in these regions. In the case of seed yield, ten QTL from eight linkage groups were detected; however, none could be consistently detected in all trials. The QTL region of C1 associated with days to flower did not show significant association with seed yield in more than 80% of the field trials; however, in a single trial, the allele introgressed from B. oleracea exerted a negative effect on seed yield. Thus, the genomic regions and molecular markers identified in this research could potentially be used in breeding for the development of early flowering B. napus canola cultivars without affecting seed yield in a majority of the environments.     

Phosphite accelerates programmed cell death in phosphate-starved oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) suspension cell cultures

Phosphite (H₂PO₃^–, Phi) prevents the acclimation of plants and yeast to orthophosphate (Pi, HPO₄^2–) deprivation by specifically obstructing the derepression of genes encoding proteins characteristic of their Pi-starvation response. In this study, we report that prolonged (i.e., 3–4 weeks) culture of Brassica napus L. suspension cells in Pi-deficient (–Pi) media leads to programmed cell death (PCD). However, when the B. napus cells were subcultured into –Pi media containing 2 mM Phi, they initiated PCD within 5 days, with 95% cell death observed by day 9. Dying cells exhibited several morphological and biochemical features characteristic of PCD, including protoplast shrinkage, chromatin condensation, and fragmentation of nuclear DNA. Immunoblotting indicated that B. napus cells undergoing PCD upregulated a 30-kDa cysteine endoprotease that is induced during PCD in the inner integument cells of developing B. napus seeds. It is concluded that PCD in B. napus suspension cells is triggered by extended Pi starvation, and that Phi treatment greatly accelerates this process. Our results also infer that the adaptive value of acclimating at the molecular level to Pi-stress is to extend the viability of –Pi B. napus cell cultures by about 3 weeks.Abbreviations APase acid phosphatase (EC 3.1.3.2) - BnCysP B. napus cysteine proteinase - DAPI 4,6-diamidino-2-phenylindole - FDA fluorescein diacetate - PCD programmed cell death - Phi phosphite - +Pi and –Pi Pi-sufficient and -deficient, respectively - PI propidium iodide - PSI Pi-starvation inducible     

Cadmium distribution and microlocalization in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) after long-term growth on cadmium-contaminated soil

Brassica napus (L.) was grown from seeds on a reconstituted soil contaminated with 100 mg Cd kg(-1). Compared with roots and stems, leaves accumulated high amounts of Cd. Although the Cd concentration in the leaves remained high throughout plant growth and no appreciable change was noticed in the total, extractable or soluble Cd in the soil adhering to the roots, the symptoms of Cd toxicity (leaf chlorosis, growth retardation) decreased with time. Cd induced a noticeable accumulation of phytochelatins in young plants (aged 22 days), which decreased in parallel to the disappearance of the symptoms of Cd intoxication. The subcellular distribution of Cd in leaves of Cd-acclimated plants was determined using biochemical, microscopic and metal-imaging techniques. Leaf fractionation by differential centrifugations showed that Cd was present predominantly in the 'soluble' fraction corresponding to the vacuoles and the cytoplasm. Transmission electron microscopic analyses revealed that those cell compartments contained electron-dense granules associated with needle-like structures. Cd, and also high amounts of sulfur, was detected in those structures by electron-spectroscopic imaging. This technique also showed Cd binding to cell walls by a mechanism that does not involve sulfur atoms. In contrast, very little Cd was found in chloroplasts, and this is consistent with the preservation of photosynthesis in plants grown on Cd-polluted soil. The microanalytical results presented here confirm that long-term growth of B. napus on Cd-contaminated soil is accompanied by preferential storage of Cd in the vacuoles and the cell walls. This phenomenon diverted Cd ions from metabolically active compartments (cytosol, chloroplasts, mitochondria), resulting in a reduction of Cd toxicity in the leaves.     

Increasing seed oil content and altering oil quality of <Emphasis Type="Italic">Brassica napus</Emphasis> L. by over-expression of diacylglycerol acyltransferase 1 (<Emphasis Type="Italic">SsDGAT1</Emphasis>) from <Emphasis Type="Italic">Sapium sebiferum</Emphasis> (L.) Roxb.

Sapium sebiferum (L.) Roxb. [S. sebiferum] is one of the most important woody oil trees and traditional herbal medicines in China. Diacylglycerol acyltransferases (DGATs) esterify sn-1,2-diacylglycerol with a long-chain fatty acyl-CoA acting as a key enzyme at the last and rate-limiting step of triacylglycerol (TAG) biosynthesis in eukaryotic organisms. Although at least 61 DGAT1 sequences from 48 organisms have been identified, until now there have been almost no reports on the DGAT1 gene in S. sebiferum (SsDGAT1). In an attempt to clarify SsDGAT1’s function, we cloned the CDS (coding sequence) of SsDGAT1 by RACE (rapid amplification of cDNA ends) technology. The full-length CDS of SsDGAT1 contains 1524 bp, encoding a protein of 507 amino acids. Even recombinant SsDGAT1 was able to restore TAG biosynthesis in the yeast strain S. cerevisiae H1246 TAG-deficient mutant. Moreover, when SsDGAT1 was placed under the control of 35S promoter in Brassica napus L. W10, the total oil content of transgenic rape plants showed an increase of 12.3–14.7 % compared with the wild type. In addition, the transgenic rapeseed with heterologous expression of SsDGAT1 showed an alteration in seed oil composition overall: a significant decrease in oleic acid levels but a tendency towards an increase in linolenic acid levels. The result confirmed that SsDGAT1 may be involved in flux control of oil biosynthesis and could be used specifically to manipulate and improve oil content and composition in plants. These experimental findings suggest that we might be able to develop a plant high in industrial oils by over-expression of SsDGAT1 in S. sebiferum.     

Multi-trait and multi-environment QTL analysis reveals the impact of seed colour on seed composition traits in <Emphasis Type="Italic">Brassica napus</Emphasis>

Brassica napus seed composition traits (fibre, protein, oil and fatty acid profiles), seed colour and yield-associated traits are regulated by a complex network of genetic factors. Although previous studies have attempted to dissect the underlying genetic basis for these traits, a more complete picture of the available quantitative trait loci (QTL) variation and any interaction between the different traits is required. In this study, QTL mapping for eleven seed composition traits, seed colour and a yield-related trait (TSW) was conducted in a spring-type canola-quality B. napus doubled haploid (DH) population from a cross between black-seeded (DH12075) and yellow-seeded (YN01-429) lines across five environments. A major QTL associated with fibre traits (acid detergent fibre, acid detergent lignin and neutral detergent fibre) and seed colour (whiteness index) was mapped on chromosome N9 across the five environments. Multi-trait analysis identified QTL which had pleiotropic effect for seed colour and other composition traits. Multi-environment analysis revealed genetic (QTL) × environment effects on most QTL. These findings provide a more detailed insight into the complex QTL networks controlling seed composition and yield-associated traits in canola-quality B. napus.     

Identification of a major QTL for silique length and seed weight in oilseed rape (Brassica napus L.)

Silique length (SL) and seed weight (SW) are two important yield-related traits controlled by quantitative trait loci (QTL) in oilseed rape (Brassica napus L.). The genetic bases underlying these two traits are largely unknown at present. In this study, we conducted QTL analyses for SL and SW using 186 recombinant inbred lines (RILs) derived from a cross between S1, an EMS mutant with extremely long siliques and large seeds, and S2, an inbred line with regular silique length and seed size. RILs were grown in Wuhan in the 2008/09 (SS09) and 2009/10 (SS10) growing seasons, and mean SL and SW for each line were investigated. Ten non-redundant QTL were identified for SL. Of these, a major QTL, cqSLA9, consistently explained as much as 53.4% of SL variation across environments. The others are minor QTL and individually explained less than 10% of the SL variation. Nine non-redundant QTL were identified for SW. Of which, one major QTL, cqSWA9, explained as much as 28.2% of the total SW variation in the SS09 and SS10 environments. In addition, three additive by additive interactions with small effects were detected for SL, and no interactions were detected for SW. Interestingly, the two major QTL, cqSLA9 for SL and cqSWA9 for SW colocalized in the same chromosomal region and were integrated into a unique QTL, uqA9. The S1 allele at this locus increases both SL and SW, suggesting that uqA9 has pleiotropic effects on both SL and SW. The existence and effect of uqA9 was confirmed in genetically different RILs derived from the cross between S1 and No2127, a resynthesized DH line having regular silique length and seed size. Individuals in one residual heterozygous line for cqSLA9 showed significant difference in silique length. The results in this study revealed that silique length in the S1 mutant is mainly controlled by the cqSLA9 locus, which will be suitable for fine mapping and marker-assisted selection in rapeseed breeding for high yield.     

Interaction of boron and aluminum on the physiological characteristics of rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) seedlings

It has been reported that aluminum (Al) toxicity is a major limiting factor for plant growth and production on acidic soils. Boron (B) is indispensable micronutrient for normal growth of higher plants, and its addition could alleviate Al toxicity. The rape seedlings were grown under three B (0.25, 25 and 500 μM) and two Al concentrations [0 (?Al) and 100 μM (+Al) as AlCl₃·6H₂O]. The results indicated that Al stress severely hampered root elongation and root activity at 0.25 μM B while the normal (25 μM) and excess (500 μM) B improved the biomass of rape seedlings under Al exposure. Additionally, normal and excess B treatment reduced accumulation of Al in the roots and leaves under Al toxicity, which was also confirmed by hematoxylin with light staining. This indicates that both normal and excess B could alleviate Al toxicity. Furthermore, it also decreased the contents of malondialdehyde and soluble protein under Al toxicity. Likewise, superoxide dismutase activity (SOD) improved by 97.82 and 131.96% in the roots, and 168 and 119.88% in the leaves at 25 and 500 µM B, respectively, while the peroxidase and catalase activities dropped as a result of Al stress. The study results demonstrated that appropriate B application is necessary to avoid the harmful consequences of Al toxicity in rape seedlings.     

Clubroot resistance QTL are modulated by nitrogen input in <Emphasis Type="Italic">Brassica napus</Emphasis>

Key message

Nitrogen levels can modulate the effectiveness of clubroot resistance in an isolate- and host-specific manner. While the same QTL were detected under high and low nitrogen, their effects were altered.

Abstract

Clubroot, caused by Plasmodiophora brassicae, is one of the most damaging diseases of oilseed rape and is known to be affected by nitrogen fertilization. However, the genetic factors involved in clubroot resistance have not been characterized under nitrogen-limiting conditions. This study aimed to assess the variability of clubroot resistance under different nitrogen levels and to characterize the impact of nitrogen supply on genetic resistance factors. Linkage analyses and a genome-wide association study were conducted to detect QTL for clubroot resistance and evaluate their sensitivity to nitrogen. The clubroot response of a set of 92 diverse oilseed rape accessions and 108 lines derived from a cross between ‘Darmor-bzh’ (resistant) and ‘Yudal’ (susceptible) was studied in the greenhouse under high- and low-nitrogen conditions, following inoculation with the P. brassicae isolates eH and K92-16. Resistance to each isolate was controlled by a major QTL and a few small-effects QTL. While the same QTL were detected under both high and low nitrogen, their effects were altered. Clubroot resistance to isolate eH, but not K92-16, was greater under a low-N supply versus a high-N supply. New sources of resistance were found among the oilseed rape accessions under both low and high-N conditions. The results are discussed relative to the literature and from a crop improvement perspective.

     

Metabolically engineered male sterility in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Male sterility is of special interest as a mechanism allowing hybrid breeding, especially in important crops such as rapeseed (Brassica napus). Male sterile plants are also suggested to be used as a biological safety method to prevent the spread of transgenes, a risk that is high in the case of rapeseed due to the mode of pollination, out-crossing by wind or insects, and the presence of related, cross-pollinating species in the surrounding ecosystem in Europe. Different natural occurring male sterilities and alloplasmic forms have been tried to be used in rapeseed with more or less success. Due to the difficulties and limitations with these systems, we present a biotechnological alternative: a metabolically engineered male sterility caused by interference with anther-specific cell wall-bound invertase. This is an essential enzyme for carbohydrate supply of the symplastically isolated pollen. The activity of this enzyme is reduced either by antisense interference or by expressing an invertase inhibitor under control of the anther-specific promoter of the invertase with the consequence of a strong decrease of pollen germination ability.     

Detection of QTL for six yield-related traits in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) using DH and immortalized F<Subscript>2</Subscript> populations

The inheritance of yield-related traits in rapeseed (Brassica napus) is poorly understood, and the investigations on mapping of quantitative trait loci (QTL) for such traits are only few. QTL related to six traits were mapped which include plant height (PH), height of lowest primary effective branch (HPB), length of main inflorescence (LMI), silique length (SL), number of primary branches (FB) and silique density (SD). A set of 258 doubled haploid (DH) lines derivatives of a cross between a canola variety Quantum and a resynthesized B. napus line No.2127-17, and a fixed immortalized F₂ (designated as IF₂) population generated by randomly permutated intermating of these DHs were investigated. A genetic linkage map was constructed using 208 SSR and 189 SRAP markers for the DH population. Phenotypic data were collected from three environments for the two populations. Using composite interval mapping analyses, 30 and 22 significant QTL were repeatedly detected across environments for the six traits in the DH and IF₂ populations, respectively. Twenty-nine QTL were common between the two populations. The directions of parental contribution for all common QTL were the same, showing a great potential for marker-assisted selection in improving these traits. Some chromosomal regions harbor QTL for multiple traits, which were consistent with significant phenotypic correlations observed among traits. The results provided a better understanding of the genetic factors controlling yield-related traits in rapeseed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic control of oil content in oilseed rape (Brassica napus L.)

In oilseed rape (Brassica napus L.) like in most oleaginous crops, seed oil content is the main qualitative determinant that confers its economic value to the harvest. Increasing seed oil content is then still an important objective in oilseed rape breeding. In the objective to get better knowledge on the genetic determinism of seed oil content, a genetic study was undertaken in two genetic backgrounds. Two populations of 445 and a 242 doubled haploids (DH) derived from the crosses “Darmor-bzh” × “Yudal” (DY) and “Rapid” × “NSL96/25” (RNSL), respectively, were genotyped and evaluated for oil content in different trials. QTL mapping in the two populations indicate that additive effects are the main factors contributing to variation in oil content. A total of 14 and 10 genomic regions were involved in seed oil content in DY and RNSL populations, respectively, of which five and two were consistently revealed across the three trials performed for each population. Most of the QTL detected were not colocalised to QTL involved in flowering time. Few epistatic QTL involved regions that carry additive QTL in one or the other population. Only one QTL located on linkage group N3 was potentially common to the two populations. The comparisons of the QTL location in this study and in the literature showed that: (i) some of the QTL were more consistently revealed across different genetic backgrounds. The QTL on N3 was revealed in all the studies and the QTL on N1, N8 and N13 were revealed in three studies out of five, (ii) some of the QTL were specific to one genetic background with potentially some original alleles, (iii) some QTL were located in homeologous regions, and (iv) some of the regions carrying QTL for oil content in oilseed rape and in Arabidopsis could be collinear. These results show the possibility to combine favourable alleles at different QTL to increase seed oil content and to use Arabidopsis genomic data to derive markers for oilseed rape QTL and identify candidate genes, as well as the interest to combine information from different segregating populations in order to build a consolidated map of QTL involved in a specific trait.