Construction of an oilseed rape (Brassica napus L.) genetic map with SSR markers

We constructed a Brassica napus genetic map with 240 simple sequence repeats (SSR) primer pairs from private and public origins. SSR, or microsatellites, are highly polymorphic and efficient markers for the analysis of plant genomes. Our selection of primer pairs corresponded to 305 genetic loci that we were able to map. In addition, we also used 52 sequence-characterized amplified region primer pairs corresponding to 58 loci that were developed in our lab. Genotyping was performed on six F2 populations, corresponding to a total of 574 F2 individual plants, obtained according to an unbalanced diallel cross design involving six parental lines. The resulting consensus map presented 19 linkage groups ranging from 46.2 to 276.5 cM, which we were able to name after the B. napus map available at , thus enabling the identification of the A genome linkage groups originating from the B. rapa ancestor and the C genome linkage groups originating from the B. oleracea ancestor in the amphidiploid genome of B. napus. Some homoeologous regions were identified between the A and the C genomes. This map could be used to identify more markers, which would eventually be linked to genes controlling important agronomic characters in rapeseed. Furthermore, considering the good genome coverage we obtained, together with an observed homogenous distribution of the loci across the genome, this map is a powerful tool to be used in marker-assisted breeding. Electronic Supplementary Material Supplementary material is available for this article at     

Microsatellite markers for genome analysis in Brassica. I. development in Brassica napus and abundance in Brassicaceae species

One hundred and twenty one microsatellites were identified by screening a λ phage library of Brassica napus. The distribution of these microsatellites within Brassicaceae species was estimated using 81 locus-specific primer pairs. Most of them (83%) amplified fragments either from Brassica oleracea or Brassica campestris, or from both species, whereas less than 30% detected loci in Brassica nigra. The same was true (30–35%) for more-distantly related crucifer species such as Diplotaxis ssp., Brassica tournefortii, Sinapis alba, Raphanus sativus and Eruca sativa. Only 16 microsatellite-specific primer pairs (19.8%) amplified fragments from Arabidopsis thaliana. Moreover, 61 of the primer pairs detecting 198 polymorphisms were used to estimate the extent of genetic diversity among 32 Brassica napus varieties and breeding lines. On average, four alleles per locus were observed. The spring and winter types of oilseed rape could be clearly distinguished by using the microsatellite markers in a cluster analysis. The results demonstrated the high efficiency of these markers for monitoring genetic diversity. Received: 14 April 2000 / Accepted: 3 July 2000     

Comparison of the genetic maps of Brassica napus and Brassica oleracea

 The genus Brassica consists of several hundreds of diploid and amphidiploid species. Most of the diploid species have eight, nine or ten pairs of chromosomes, known respectively as the B, C, and A genomes. Genetic maps were constructed for both B. napus and B. oleracea using mostly RFLP and RAPD markers. For the B. napus linkage map, 274 RFLPs, 66 RAPDs, and two STS loci were arranged in 19 major linkage groups and ten smaller unassigned segments, covering a genetic distance of 2125 cM. A genetic map of B. oleracea was constructed using the same set of RFLP probes and RAPD primers. The B. oleracea map consisted of 270 RFLPs, 31 RAPDs, one STS, three SCARs, one phenotypic and four isozyme marker loci, arranged into nine major linkage groups and four smaller unassigned segments, covering a genetic distance of 1606 cM. Comparison of the B. napus and B. oleracea linkage maps showed that eight out of nine B. oleracea linkage groups were conserved in the B. napus map. There were also regions in the B. oleracea map showing homoeologies with more than one linkage group in the B. napus map. These results provided molecular evidence for B. oleracea, or a closely related 2n=18 Brassica species, as the C-genome progenitor, and also reflected on the homoeology between the A and C genomes in B. napus. Received: 14 June 1996 / Accepted: 11 October 1996     

SNP markers‐based map construction and genome‐wide linkage analysis in Brassica napus

An Illumina Infinium array comprising 5306 single nucleotide polymorphism (SNP) markers was used to genotype 175 individuals of a doubled haploid population derived from a cross between Skipton and Ag‐Spectrum, two Australian cultivars of rapeseed (Brassica napus L.). A genetic linkage map based on 613 SNP and 228 non‐SNP (DArT, SSR, SRAP and candidate gene markers) covering 2514.8 cM was constructed and further utilized to identify loci associated with flowering time and resistance to blackleg, a disease caused by the fungus Leptosphaeria maculans. Comparison between genetic map positions of SNP markers and the sequenced Brassica rapa (A) and Brassica oleracea (C) genome scaffolds showed several genomic rearrangements in the B. napus genome. A major locus controlling resistance to L. maculans was identified at both seedling and adult plant stages on chromosome A07. QTL analyses revealed that up to 40.2% of genetic variation for flowering time was accounted for by loci having quantitative effects. Comparative mapping showed Arabidopsis and Brassica flowering genes such as Phytochrome A/D, Flowering Locus C and agamous‐Like MADS box gene AGL1 map within marker intervals associated with flowering time in a DH population from Skipton/Ag‐Spectrum. Genomic regions associated with flowering time and resistance to L. maculans had several SNP markers mapped within 10 cM. Our results suggest that SNP markers will be suitable for various applications such as trait introgression, comparative mapping and high‐resolution mapping of loci in B. napus.     

Mapping and validation of chromosome regions conferring a new boron-efficient locus in <Emphasis Type="Italic">Brassica napus</Emphasis>

Considerable genotypic variation exists in the response of different cultivars of rapeseed (Brassica napus) to B deficiency. This raises the possibility of genetic improvement of a B nutrition trait that will make the plant more tolerant to low B stress. The results of our study showed that B-efficient backcross plants had lower B concentration and more dry matter when grown at low levels of B when compared with the recurrent parent. Accordingly, we proposed that the improved B efficiency was attributed to either a high B utilization efficiency or less demand for B. The results of the genetic analysis showed that B efficiency is a dominant trait that is controlled by a single locus, namely BnBE2. By using bulked segregant analysis (BSA) in combination with amplified fragment length polymorphism (AFLP) and sequence related amplified polymorphism (SRAP) techniques, five SRAP markers and one converted single strand conformation polymorphism (SSCP) marker were identified to be linked to BnBE2 after screening 1,800 primer combinations. The six markers together with BnBE2 were mapped in a region that covered a genetic distance of 6.9 cM on a linkage group using a BC₆ population. This region was located on linkage group N14 after mapping these markers in two doubled haploid (DH) populations (TNDH and BQDH). The SRAP and AFLP markers were sequenced and found to be homologous to a BAC sequence from Brassica oleracea (CC). This finding suggested that the segment containing BnBE2 locus originated from the C genome of Brassica oleracea. Three SSR markers were identified to be linked to BnBE2 through comparative mapping. All these markers might have potential value for facilitating the pyramiding of the BnBE2 gene with other B efficient genes in order to improve the B efficiency trait and for further fine mapping of the BnBE2 gene in Brassica napus.     

Development and genetic mapping of microsatellite markers from whole genome shotgun sequences in <Emphasis Type="Italic">Brassica oleracea</Emphasis>

The availability of whole genome shotgun sequences (WGSs) in Brassica oleracea provides an unprecedented opportunity for development of microsatellite or simple sequence repeat (SSR) markers for genome analysis and genetic improvement in Brassica species. In this study, a total of 56,465 non-redundant SSRs were identified from the WGSs in B. oleracea, with dinucleotide repeats being the most abundant, followed by tri-, tetra- and pentanucleotide repeats. From these, 1,398 new SSR markers (designated as BoGMS) with repeat length ≥25 bp were developed and used to survey polymorphisms with a panel of six rapeseed varieties, which is the largest number of SSR markers developed for the C genome in a single study. Of these SSR markers, 752 (69.5%) showed polymorphism among the six varieties. Of these, 266 markers that showed clear scorable polymorphisms between B. napus varieties No. 2127 and ZY821 were integrated into an existing B. napus genetic linkage map. These new markers are preferentially distributed on the linkage groups in the C genome, and significantly increased the number of SSR markers in the C genome. These SSR markers will be very useful for gene mapping and marker-assisted selection of important agronomic traits in Brassica species.     

Development of a core set of single-locus SSR markers for allotetraploid rapeseed (Brassica napus L.)

Brassica napus (AACC) is a recent allotetraploid species evolved through hybridization between two diploids, B. rapa (AA) and B. oleracea (CC). Due to extensive genome duplication and homoeology within and between the A and C genomes of B. napus, most SSR markers display multiple fragments or loci, which limit their application in genetics and breeding studies of this economically important crop. In this study, we collected 3,890 SSR markers from previous studies and also developed 5,968 SSR markers from genomic sequences of B. rapa, B. oleracea and B. napus. Of these, 2,701 markers that produced single amplicons were putative single-locus markers in the B. napus genome. Finally, a set of 230 high-quality single-locus SSR markers were established and assigned to the 19 linkage groups of B. napus using a segregating population with 154 DH individuals. A subset of 78 selected single-locus SSR markers was proved to be highly stable and could successfully discriminate each of the 45 inbred lines and hybrids. In addition, most of the 230 SSR markers showed the single-locus nature in at least one of the Brassica species of the U’s triangle besides B. napus. These results indicated that this set of single-locus SSR markers has a wide range of coverage with excellent stability and would be useful for gene tagging, sequence scaffold assignment, comparative mapping, diversity analysis, variety identification and association mapping in Brassica species.     

An integrated AFLP and RFLP Brassica oleracea linkage map from two morphologically distinct doubled-haploid mapping populations

Genetical maps of molecular markers in two very different F₁-derived doubled-haploid populations of Brassica oleracea are compared and the first integrated map described. The F₁ crosses were: Chinese kale×calabrese (var. alboglabra×var. italica) and cauliflower×Brussels sprout (var. botrytis×var. gemmifera). Integration of the two component maps using Joinmap v.2.0 was based on 105 common loci including RFLPs, AFLPs and microsatellites. This provided an effective method of producing a high-density consensus linkage map of the B. oleracea genome. Based on 547 markers mapping to nine linkage groups, the integrated map covers a total map length of 893 cM, with an average locus interval of 2.6 cM. Comparisons back to the component linkage maps revealed similar sequences of common markers, although significant differences in recombination frequency were observed between some pairs of homologous markers. Map integration resulted in an increased locus density and effective population size, providing a stronger framework for subsequent physical mapping and for precision mapping of QTLs using substitution lines. Received: 5 February 1999 / Accepted: 16 June 1999     

Efficient large-scale development of microsatellites for marker and mapping applications in<Emphasis Type="Italic"> Brassica</Emphasis> crop species

A set of 398 simple sequence repeat markers (SSRs) have been developed and characterised for use with genetic studies of Brassica species. Small-insert (250–900 bp) genomic libraries from Brassica rapa, B. nigra, B. oleracea and B. napus, highly enriched for dinucleotide and trinucleotide SSR motifs, were constructed. Screening the clones with a mixture of oligonucleotide repeat probes revealed positive hybridisation to between 75% and 90% of the clones. Of these, 1,230 were sequenced. Primer pairs were designed for 398 SSR clones, and of these, 270 (67.8%) amplified a PCR product of the expected size in their focal and/or closely related species. A further screen of 138 primers pairs that produced a PCR product in B. napus germplasm found that 86 (62.3%) revealed length polymorphisms within at least one line of a test array representing the four Brassica species. The results of this screen were used to identify 56 SSRs and were combined with 41 SSRs that had previously shown polymorphism between the parents of a B. napus mapping population. These 97 SSR markers were mapped relative to a framework of RFLP markers and detected 136 loci over all 19 linkage groups of the oilseed rape genome.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by O. Savolainen     

In silico integration of quantitative trait loci for seed yield and yield-related traits in Brassica napus

Mapping quantitative trait loci (QTLs) is a foundation for molecular marker-assisted selection and map-based gene cloning. During the past decade, numerous QTLs for seed yield (SY) and yield-related traits in Brassica napus L. have been identified. However, integration of these results in order to compare QTLs from different mapping populations has not been undertaken, due to the lack of common molecular markers between studies. Using previously reported Brassica rapa and Brassica oleracea genome sequences, we carried out in silico integration of 1,960 QTLs associated with 13 SY and yield-related traits from 15 B. napus mapping experiments over the last decade. A total of 736 SY and yield-related QTLs were mapped onto 283 loci in the A and C genomes of B. napus. These QTLs were unevenly distributed across the 19 B. napus chromosomes, with the most on chromosome A3 and the least on chromosome C6. Our integrated QTL map identified 142 loci where the conserved QTLs were detected and 25 multifunctional loci, mostly for the traits of flowering time (FT), plant height, 1,000-seed weight, maturity time and SY. These conserved QTLs and multifunctional loci may result from pleiotropism or clustered genes. At the same time, a total of 146 genes underlying the QTLs for FT and other yield-related traits were identified by comparative mapping with the Arabidopsis genome. These results facilitate the retrieval of B. napus SY and yield-related QTLs for research communities, increase the density of targeted QTL-linked markers, validate the existence of QTLs across different populations, and advance the fine mapping of genes.     

From Arabidopsis thaliana to Brassica napus: development of amplified consensus genetic markers (ACGM) for construction of a gene map

The evolution of genomes can be studied by comparing maps of homologous genes which show changes in nucleic acid sequences and chromosome rearrangements. In this study, we developed a set of 32 amplified consensus gene markers (ACGMs) that amplified gene sequences from Arabidopsis thaliana and Brassica napus. Our methodology, based on PCR, facilitated the rapid sequencing of homologous genes from various species of the same phylogenetic family and the detection of intragenic polymorphism. We found that such polymorphism principally concerned intron sequences and we used it to attribute a Brassica oleracea or Brassica rapa origin to the B. napus sequences and to map 43 rapeseed genes. We confirm that the genetic position of homologous genes varied between B. napus and A. thaliana. ACGMs are a useful tool for genome evolution studies and for the further development of single nucleotide polymorphism suitable for use in genetic mapping and genetic diversity analyses.     

Linkage arrangement of restriction fragment length polymorphism loci in Brassica oleracea

Summary A detailed genetic linkage map of Brassica oleracea was constructed based on the segregation of 258 restriction fragment length polymorphism loci in a broccoli × cabbage F₂ population. The genetic markers defined nine linkage groups, covering 820 recombination units. A majority of the informative genomic DNA probes hybridized to more than two restriction fragments in the F₂ population. Duplicate sequences having restriction fragment length polymorphism were generally found to be unlinked for any given probe. Many of these duplicated loci were clustered non-randomly on certain pairs of linkage groups, and conservation of the relative linkage arrangement of the loci between linkage groups was observed. While these data support previous cytological evidence for the existence of duplicated regions and the evolution of B. oleracea from a lower chromosome number progenitor, no evidence was provided for the current existence of blocks of homoeology spanning entire pairs of linkage groups. The arrangement of the analyzed duplicated loci suggests that a fairly high degree of genetic rearrangement has occurred in the evolution of B. oleracea. Several probes used in this study were useful in detecting rearrangements between the B. oleracea accessions used as parents, indicating that genetic rearrangements have occurred in the relatively recent evolution of this species.     

Identifying the chromosomes of the A- and C-genome diploid Brassica species B. rapa (syn. campestris) and B. oleracea in their amphidiploid B. napus

Oilseed rape (Brassica napus L.) is an amphidiploid species that originated from a spontaneous hybridisation of Brassica rapa L. (syn. campestris) and Brassica oleracea L., and contains the complete diploid chromosome sets of both parental genomes. The metaphase chromosomes of the highly homoeologous A genome of B. rapa and the C genome of B. oleracea cannot be reliably distinguished in B. napus because of their morphological similarity. Fluorescence in situ hybridisation (FISH) with 5S and 25S ribosomal DNA probes to prometaphase chromosomes, in combination with DAPI staining, allows more dependable identification of Brassica chromosomes. By comparing rDNA hybridisation and DAPI staining patterns from B. rapa and B. oleracea prometaphase chromosomes with those from B. napus, we were able to identify the putative homologues of B. napus chromosomes in the diploid chromosome sets of B. rapa and B. oleracea, respectively. In some cases, differences were observed between the rDNA hybridisation patterns of chromosomes in the diploid species and their putative homologue in B. napus, indicating locus losses or alterations in rDNA copy number. The ability to reliably identify A and C genome chromosomes in B. napus is discussed with respect to evolutionary and breeding aspects. Received: 13 July 2001 / Accepted: 23 August 2001     

Alignment of the conserved C genomes of Brassica oleracea and Brassica napus

A population of 169 microspore-derived doubled-haploid lines was produced from a highly polymorphic Brassica oleracea cross. A dense genetic linkage map of B. oleracea was then developed based on the segregation of 303 RFLP-defined loci. It is hoped that these lines will be used by other geneticists to facilitate the construction of a unified genetic map of B. oleracea. When the B. oleracea map was compared to one ofB. napus (Parkin et al. 1995), based on the same RFLP probes (Sharpe et al. 1995), good collinearity between the C-genome linkage groups of the two species was observed.     

A review of sources of resistance to turnip yellows virus (TuYV) in Brassica species

Turnip yellows virus (TuYV; previously known as beet western yellows virus) causes major diseases of Brassica species worldwide resulting in severe yield-losses in arable and vegetable crops. It has also been shown to reduce the quality of vegetables, particularly cabbage where it causes tip burn. Incidences of 100% have been recorded in commercial crops of winter oilseed rape (Brassica napus) and vegetable crops (particularly Brassica oleracea) in Europe. This review summarises the known sources of resistance to TuYV in B. napus (AACC genome), Brassica rapa (AA genome) and B. oleracea (CC genome). It also proposes names for the quantitative trait loci (QTLs) responsible for the resistances, Tu rnip Y ellows virus R esistance (TuYR), that have been mapped to at least the chromosome level in the different Brassica species. There is currently only one known source of resistance deployed commercially (TuYR1). This resistance is said to have originated in B. rapa and was introgressed into the A genome of oilseed rape via hybridisation with B. oleracea to produce allotetraploid (AACC) plants that were then backcrossed into oilseed rape. It has been utilised in the majority of known TuYV-resistant oilseed rape varieties. This has placed significant selection pressure for resistance-breaking mutations arising in TuYV. Further QTLs for resistance to TuYV (TuYR2-TuYR9) have been mapped in the genomes of B. napus, B. rapa and B. oleracea and are described here. QTLs from the latter two species have been introgressed into allotetraploid plants, providing for the first time, combined resistance from both the A and the C genomes for deployment in oilseed rape. Introgression of these new resistances into commercial oilseed rape and vegetable brassicas can be accelerated using the molecular markers that have been developed. The deployment of these resistances should lessen selection pressure for resistance-breaking isolates of TuYV and thereby prolong the effectiveness of each other and extant resistance.     

An ultradense genetic recombination map for <Emphasis Type="Italic">Brassica napus</Emphasis>, consisting of 13551 SRAP markers

Sequence related amplified polymorphism (SRAP) was used to construct an ultradense genetic recombination map for a doubled haploid (DH) population in B. napus. A total of 1,634 primer combinations including 12 fluorescently labeled primers and 442 unlabeled ones produced 13,551 mapped SRAP markers. All these SRAPs were assembled in 1,055 bins that were placed onto 19 linkage groups. Ten of the nineteen linkage groups were assigned to the A genome and the remaining nine to the C genome on the basis of the differential SRAP PCR amplification in two DH lines of B. rapa and B. oleracea. Furthermore, all 19 linkage groups were assigned to their corresponding N1–N19 groups of B. napus by comparison with 55 SSR markers used to construct previous maps in this species. In total, 1,663 crossovers were detected, resulting in a map length span of 1604.8 cM. The marker density is 8.45 SRAPs per cM, and there could be more than one marker in 100 kb physical distance. There are four linkage groups in the A genome with more than 800 SRAP markers each, and three linkage groups in the C genome with more 1,000 SRAP markers each. Our studies suggest that a single SRAP map might be applicable to the three Brassica species, B. napus, B. oleracea and B. rapa. The use of this ultra high-density genetic recombination map in marker development and map-based gene cloning is discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Abundance, marker development and genetic mapping of microsatellites from unigenes in Brassica napus

Rapeseed (Brassica napus) is the second most important oil crop in the world after soybean. The repertoire of simple sequence repeat (SSR) markers for rapeseed is limited and warrants a search for a larger number of polymorphic SSRs for germplasm characterization and breeding applications. In this study, a total of 5,310 SSR-containing unigenes were identified from a set of 46,038 B. napus unigenes with an average density of one SSR every 5.75?kb. A set of 1,000 expressed sequence tag (EST)-SSR markers with repeat length ??18?bp were developed and tested for their ability to detect polymorphism among a panel of six rapeseed varieties. Of these SSR markers, 776 markers detected clear amplification products, and 511 displayed polymorphisms among the six varieties. Of these polymorphic markers, 195 EST-SSR markers, corresponding to 233 loci, were integrated into an existing B. napus linkage map. These EST-SSRs were randomly distributed on the 19 linkage groups of B. napus. Of the mapped loci, 166 showed significant homology to Arabidopsis genes. Based on the homology, 44 conserved syntenic blocks were identified between B. napus and Arabidopsis genomes. Most of the syntenic blocks were consistent with the duplication and rearrangement events identified previously. In addition, we also identified three previously unreported blocks in B. napus. A subset of 40 SSRs was used to assess genetic diversity in a collection of 192 rapeseed accessions. The polymorphism information content of these markers ranged from 0.0357 to 0.6753 with an average value of 0.3373. These results indicated that the EST-SSR markers developed in this study are useful for genetic mapping, molecular marker-assisted selection and comparative genomics.     

Molecular-mapping analysis in Brassica napus using isozyme, RAPD and RFLP markers on a doubled-haploid progeny

We have undertaken the construction of a Brassica napus genetic map with isozyme (4%), RFLP (26.5%) and RAPD (68%) markers on a 152 lines of a doubled-haploid population. The map covers 1765 cM and comprises 254 markers including three PCR-specific markers and a morphological marker. They are assembled into 19 linkage groups, covering approximatively 71% of the rapeseed genome. Thirty five percent of the studied markers did not segregate according to the expected Mendelian ratio and tended to cluster in eight specific linkage groups. In this paper, the structure of the genetic map is described and the existence of non-Mendelian segregations in linkage analysis as well as the origins of the observed distortions, are discussed. The mapped RFLP loci corresponded to the cDNAs already used to construct B. napus maps. The first results of intraspecific comparative mapping are presented.     

Desaturase multigene families of Brassica napus arose through genome duplication

 This paper reports the estimated gene copy number and restriction fragment length polymorphism (RFLP) map locations of five different desaturase cDNA clones from Brassica napus (oilseed rape). The desaturase enzymes encoded by four of these genes catalyze successive reactions that insert double bonds into lipid-linked fatty acid residues. Delta-12 (e2) and delta-15 (e3) desaturases are active in the endoplasmic reticulum, while omega-6 (p2) and omega-3 (p3) desaturases catalyze analogous desaturation reactions via a parallel pathway located in plastids. The fifth cDNA clone (b5) contains a desaturase-like domain bound to a cytochrome b₅ segment. Estimates of gene copy number based on Southern blot analysis of 16 oilseed rape varieties and three different resynthesized Brassica napus lines indicated that e2 had 4–6 gene copies and e3, p2, p3 and b5 each had 6–8 gene copies per haploid genome. Estimates of the gene copy number for the two progenitor species, Brassica oleracea and Brassica rapa, supported the premise that all these genes were at least duplicated or triplicated in the two progenitor species before they combined to form B. napus. RFLP mapping results showed that the e2 probe detected 4 distinct loci, the e3 probe 6 loci and p2, p3 and b5 each detected 8 loci, with pairs of loci often mapping to homoeologous regions on 2 different linkage groups. The 28 mappable loci were distributed across 12 linkage groups of the B. napus map (Parkin et al. 1995) and were usually represented by single RFLP fragments. A collinear segment containing the e2 and p3 loci was positioned on B. napus linkage groups N1, N11, N3, N13, N5 and N15. This segment was collinear with a 30-cM region of Arabidopsis thaliana chromosome 3 that contains the homologous fad2 (e2) and fad7(p3) genes. This suggests that the desaturase multigene families arose as the result of duplication of large chromosome segments rather than duplication of individual genes. Received: 14 August 1996 / Accepted: 18 October 1996     

Patterns of molecular variation in a species-wide germplasm set of <Emphasis Type="Italic">Brassica napus</Emphasis>

Rapeseed (Brassica napus L.) is the leading European oilseed crop serving as source for edible oil and renewable energy. The objectives of our study were to (i) examine the population structure of a large and diverse set of B. napus inbred lines, (ii) investigate patterns of genetic diversity within and among different germplasm types, (iii) compare the two genomes of B. napus with regard to genetic diversity, and (iv) assess the extent of linkage disequilibrium (LD) between simple sequence repeat (SSR) markers. Our study was based on 509 B. napus inbred lines genotyped with 89 genome-specific SSR primer combinations. Both a principal coordinate analysis and software STRUCTURE revealed that winter types, spring types, and swedes were assigned to three major clusters. The genetic diversity of winter oilseed rape was lower than the diversity found in other germplasm types. Within winter oilseed rape types, a decay of genetic diversity with more recent release dates and reduced levels of erucic acid and glucosinolates was observed. The percentage of linked SSR loci pairs in significant (r ² > Q _{95 unlinked loci pairs}) LD was 6.29% for the entire germplasm set. Furthermore, LD decayed rapidly with distance, which will allow a relatively high mapping resolution in genome-wide association studies using our germplasm set, but, on the other hand, will require a high number of markers.