Progressive introgression between Brassica napus (oilseed rape) and B. rapa

We have earlier shown extensive introgression between oilseed rape (Brassica napus) and B. rapa in a weedy population using AFLP markers specific for the nuclear genomes. In order to describe the progress of this introgression, we examined 117 offspring from 12 maternal plants from the introgressed population with the same AFLP-markers; AFLP data were supported by chromosome counting. We also analysed the offspring with a species-specific chloroplast marker and finally evaluated the reproductive system in selected maternal plants. Our results indicated a high outcrossing rate of the introgressed maternal plants. It seemed that B. rapa most often functioned as the maternal plant in the introgression process and that the amount of oilseed rape DNA was highly diminished in the offspring compared to their introgressed maternal plants. However, our analysis of plants from the weedy population indicated that introgression can lead to both (1) exchange of chloroplast DNA between species producing B. rapa-like plants with B. napus chloroplasts and (2) incorporation of B. napus C-genome DNA into the B. rapa genome. Therefore, we question whether it can be regarded as containment to position transgenes in the chloroplast or in specific parts of the nuclear genome of B. napus.     

RGA- and RAPD-derived SCAR markers for a Brassica B-genome introgression conferring resistance to blackleg in oilseed rape

An introgression derived from the B genome of Brassica juncea in spring-type oilseed rape (B. napus) conferring recessively inherited cotyledon resistance against several pathotypes of the blackleg fungus Leptosphaeria maculans was mapped using PCR-based molecular markers. Resistance-associated B-genome-specific randomly amplified (RAPD) and resistance gene analog (RGA) DNA polymorphisms were converted into three sequence-specific markers (SCARs; B5-1520, C5-1000, RGALm). The flanking sequence of the RGALm locus was determined by genomic walking, leading to a 1,610-bp EcoRV fragment which showed extensive homology to known and putative resistance genes of a cluster on Arabidopsis chromosome 5. Partial sequence analysis of the genomic RAPD segment OPC-05-1700 revealed strong homology to the gibberellin 2-oxidase gene of Arabidopsis. The SCAR markers were analyzed in two segregating populations and were found to be linked in coupling to each other, and in repulsion to the resistance locus. In both populations, markers deviated significantly from a monogenic 3:1 segregation ratio, with plants lacking the markers being more frequent than expected. Although the mode of introgression is yet unknown, the recombinant individuals observed among susceptible progeny suggest homeology between the B-genome-specific segment and its B. napus counterpart. This would offer prospects for reducing the size of the introgression and further fine mapping of the resistance locus.     

Molecular markers linked to white rust resistance in mustard Brassica juncea

 White rust, caused by Albugo candida (Pers.) Kuntze, is an economically important disease of Brassica juncea (L.) Czern. and Coss mustard, particularly in India. The most efficient and cost-effective way of protecting mustard plants from white rust disease is through genetic resistance. The objective of this study was to identify RAPD markers for white rust resistance in an F₁-derived doubled-haploid (DH) population originating from a cross between white rust-susceptible and white rust-resistant breeding lines of B. juncea from the canola-quality B. juncea breeding project of the Agriculture and Agri-Food Canada-Saskatoon Research Centre. The DH population was used to screen for RAPD markers associated with white rust resistance/susceptibility using bulked segregant analysis. Two markers, WR2 and WR3, linked to white rust resistance, flanked the resistance locus Ac2 ₁ and were highly effective in identifying the presence or absence of the resistance gene in the DH population. These two markers were shown to be specific to the Russian source of white rust resistance utilized in this project. It is concluded that the availability of these RAPD markers will enhance the breeding for white rust resistance in B. juncea. Received: 17 December 1997 / Accepted: 7 April 1998     

Linkage mapping of genes controlling resistance to white rust (Albugo candida) in Brassica rapa (syn. campestris) and comparative mapping to Brassica napus and Arabidopsis thaliana.

Genes for resistance to white rust (Albugo candida) in oilseed Brassica rapa were mapped using a recombinant inbred (RI) population and a genetic linkage map consisting of 144 restriction fragment length polymorphism (RFLP) markers and 3 phenotypic markers. Young seedlings were evaluated by inoculating cotyledons with A. candida race 2 (AC2) and race 7 (AC7) and scoring the interaction phenotype (IP) on a 0-9 scale. The IP of each line was nearly identical for the two races and the population showed bimodal distributions, suggesting that a single major gene (or tightly linked genes) controlled resistance to the two races. The IP scores were converted to categorical resistant and susceptible scores, and these data were used to map a single Mendelian gene controlling resistance to both races on linkage group 4 where resistance to race 2 had been mapped previously. A quantitative trait loci (QTL) mapping approach using the IP scores detected the same major resistance locus for both races, plus a second minor QTL effect for AC2 on linkage group 2. These results indicate that either a dominant allele at a single locus (Acal) or two tightly linked loci control seedling resistance to both races of white rust in the biennial turnip rape cultivar Per. The map positions of white rust resistance genes in B. rapa and Brassica napus were compared and the results indicate where additional loci that have not been mapped may be located. Alignment of these maps to the physical map of the Arabidopsis genome identified regions to target for comparative fine mapping using this model organism.     

Fine mapping of the yellow seed locus in Brassica juncea L

The yellow mustard plant in Northern Shaanxi is a precious germplasm, and the yellow seed trait is controlled by a single recessive gene. In this report, amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) techniques were used to identify markers linked to the brown seed locus in an F(2) population consisting of 1258 plants. After screening 256 AFLP primer combinations and 456 pairs of SSR primers, we found 14 AFLP and 2 SSR markers that were closely linked to the brown seed locus. Among these markers, the SSR marker CB1022 showed codominant inheritance. By integrating markers previously found to be linked to the brown seed locus into the genetic map of the F(2) population, 23 markers were linked to the brown seed locus. The two closest markers, EA02MC08 and P03MC08, were located on either side of the brown seed locus at a distance of 0.3 and 0.5 cM, respectively. To use the markers for the breeding of yellow-seeded mustard plants, two AFLP markers (EA06MC11 and EA08MC13) were converted into sequence-characterized amplified region (SCAR) markers, SC1 and SC2, with the latter as the codominant marker. The two SSR markers were subsequently mapped to the A9/N9 linkage group of Brassica napus L. by comparing common SSR markers with the published genetic map of B. napus. A BLAST analysis indicated that the sequences of seven markers showed good colinearity with those of Arabidopsis chromosome 3 and that the homolog of the brown seed locus might exist between At3g14120 and At3g29615 on this same chromosome. To develop closer markers, we could make use of the sequence information of this region to design primers for future studies. Regardless, the close markers obtained in the present study will lay a solid foundation for cloning the yellow seed gene using a map-based cloning strategy.     

与甘蓝型油菜重要经济性状有关的DNA克隆在拟南芥遗传图谱中的整合

拟南芥与油菜同属十字花科植物芸寡族,亲缘关系很近,基因组间的同源性很高,在用拟南芥EST克隆和油菜DNA克隆作探针定位了甘蓝型油菜一系列重要性状的基础上,对25个与油菜雄性不育恢复基因,硼高效利用基因,抗菌核病QTL及油菜种间杂种营养优势相关联的克隆进行了测序,在拟南芥基因组数据库中寻找到与这25个克隆高度同源的序列,根据这些高度同源序列在拟南芥染色体上的相位位置,将油菜DNA克隆整合到了拟南芥遗传图谱上,其中油菜硼高效基因BE1两侧的标记克隆整合在拟南芥第一染色体长臂一个较小的区段内,以该目标区段内的拟南芥EST克隆PA24为探针对甘蓝型油菜基因组比较作图,将该克隆定位在油菜连锁图BE1两侧标记之间,表明了利用基因组间的相互比较作图来精细定位芸薹属作物重要基因的可能性。     

Identification and mapping of a third blackleg resistance locus in Brassica napus derived from B. rapa subsp. sylvestris.

The spectrum of resistance to isolates of Leptosphaeria maculans and the map location of a new blackleg resistance gene found in the canola cultivar Brassica napus 'Surpass 400' are described. Two blackleg resistance genes, LepR1 and LepR2, from B. rapa subsp. sylvestris and introgressed in B. napus were identified previously. 'Surpass 400' also has blackleg resistance introgressed from B. rapa subsp. sylvestris. Using 31 diverse isolates of L. maculans, the disease reaction of 'Surpass 400' was compared with those of the resistant breeding lines AD9 (which contains LepR1), AD49 (which contains LepR2), and MC1-8 (which contains both LepR1 and LepR2). The disease reaction on 'Surpass 400' was different from those observed on AD9 and MC1-8, indicating that 'Surpass 400' carries neither LepR1 nor both LepR1 and LepR2 in combination. Disease reactions of 'Surpass 400' to most of the isolates tested were indistinguishable from those of AD49, which suggested 'Surpass 400' might contain LepR2 or a similar resistance gene. Classical genetic analysis of F1 and BC1 plants showed that a dominant allele conferred resistance to isolates of L. maculans in 'Surpass 400'. The resistance gene, which mapped to B. napus linkage group N10 in an interval of 2.9 cM flanked by microsatellite markers sR12281a and sN2428Rb and 11.7 cM below LepR2, was designated LepR3. A 9 cM region of the B. napus genome containing LepR3 was found to be syntenic with a segment of Arabidopsis chromosome 5.     

甘蓝型油菜花瓣缺失基因的图谱定位

在无花瓣品系APT02和正常有花瓣品种中双4号构建的的F2分离群体中,运用AFLP和SRAP两种标记技术对甘蓝型油菜花瓣缺失基因进行分子标记和图谱定位。在两亲本间筛选20对AFLP引物和170对SRAP 引物,进一步通过BSA法筛选,获得了与甘蓝型油菜花瓣缺失基因WHB连锁的1个SRAP标记e8m3_4（600bp）和1个AFLP标记E3247_15（150bp）,标记与基因WHB之间的遗传距离分别为5 cM和13.5cM;构建了一个甘蓝型油菜(Brassica napus.L )的分子标记遗传连锁图谱,该图谱共包含213个AFLP标记、56个SRAP标记和1个形态标记,分布于17个主要连锁群、两个三联体和4个连锁对中,遗传图距总长2487.1cM,标记间平均距离为10.09 cM。通过图谱定位,控制花瓣缺失性状的基因WHB被定位到第4连锁群(LG4)上。     

Development and validation of CAPS and AFLP markers for white rust resistance gene in<Emphasis Type="Italic"> Brassica juncea</Emphasis>

White rust, caused by Albugo candida, is a very serious disease in crucifers. In Indian mustard (Brassica juncea), it can cause a yield loss to the extent of 89.9%. The locus Ac2(t) controlling resistance to white rust in BEC-144, an exotic accession of mustard, was mapped using RAPD markers. In the present study, we developed: (1) a more tightly linked marker for the white rust resistance gene, using AFLP in conjunction with bulk segregant analysis, and (2) a PCR-based cleaved amplified polymorphic sequence (CAPS) marker for the closely linked RAPD marker, OPB06₁₀₀₀. The data obtained on 94 RILs revealed that the CAPS marker for OPB06₁₀₀₀ and the AFLP marker E-ACC/M-CAA₃₅₀ flank the Ac2(t) gene at 3.8 cM and 6.7 cM, respectively. Validation of the CAPS marker in two different F₂ populations of crosses Varuna × BEC-144 and Varuna × BEC-286 was also undertaken, which established its utility in marker-assisted selection (MAS) for white rust resistance. The use of both flanking markers in MAS would allow only 0.25% misclassification and thus provide greater efficiency to selection.Communicated by C. Möllers     

WRR4, a broad-spectrum TIR-NB-LRR gene from Arabidopsis thaliana that confers white rust resistance in transgenic oilseed brassica crops

White blister rust caused by Albugo candida (Pers.) Kuntze is a common and often devastating disease of oilseed and vegetable brassica crops worldwide. Physiological races of the parasite have been described, including races 2, 7 and 9 from Brassica juncea , B. rapa and B. oleracea , respectively, and race 4 from Capsella bursa-pastoris (the type host). A gene named WRR4 has been characterized recently from polygenic resistance in the wild brassica relative Arabidopsis thaliana (accession Columbia) that confers broad-spectrum white rust resistance ( WRR ) to all four of the above Al. candida races. This gene encodes a TIR-NB-LRR (Toll-like/interleukin-1 receptor-nucleotide binding-leucine-rich repeat) protein which, as with other known functional members in this subclass of intracellular receptor-like proteins, requires the expression of the lipase-like defence regulator, enhanced disease susceptibility 1 ( EDS1 ). Thus, we used RNA interference-mediated suppression of EDS1 in a white rust-resistant breeding line of B. napus (transformed with a construct designed from the A. thaliana EDS1 gene) to determine whether defence signalling via EDS1 is functionally intact in this oilseed brassica. The eds1-suppressed lines were fully susceptible following inoculation with either race 2 or 7 isolates of Al. candida. We then transformed white rust-susceptible cultivars of B. juncea (susceptible to race 2) and B. napus (susceptible to race 7) with the WRR4 gene from A. thaliana . The WRR4-transformed lines were resistant to the corresponding Al. candida race for each host species. The combined data indicate that WRR4 could potentially provide a novel source of white rust resistance in oilseed and vegetable brassica crops.     

Association mapping of seed oil content in Brassica napus and comparison with quantitative trait loci identified from linkage mapping

Association mapping has been used increasingly in natural populations with rich genetic diversity to detect DNA-based markers that are associated with important agronomic traits. Brassica napus is an important oil crop with limited genetic diversity. "New-type" B. napus that is introgressed with subgenomic components from related species has been developed to broaden the genetic basis of "traditional" B. napus. In this study, new-type B. napus lines and a collection of traditional B. napus varieties from different countries were used as two different populations to evaluate seed oil content and to determine the efficacy of association mapping by comparison with previous study of linkage mapping. Relatively rich genetic diversity, but a higher level of linkage disequilibrium was observed in the new-type B. napus as compared with the traditional B. napus. Similarly, a larger variation in oil content and a greater number of associated markers were detected in the population of new-type B. napus. Meanwhile, more than half of the genetic loci, to which the associated markers corresponded, were located within the quantitative trait loci intervals identified previously in linkage mapping experiments, which demonstrated the power of association mapping in B. napus.     

Free amino acid content of phloem sap from Brassica plants in relation to performance of Lipaphis erysimi (Hemiptera: Aphididae)

Cultivars of Brassica juncea, B. napus and B. campestris, differing in host-suitability to the mustard aphid (Lipaphis erysimi pseudobrassicae Kalt.), were analysed for their phloem sap content of free amino acids. Sap was collected from excised mustard aphid stylets and analysed by means of high performance liquid chromatography. Aspartic and glutamic acid were, together with glutamine, the dominating amino acids. All plants had very little glycine, γ-aminobutyric acid (GABA), methionine and tryptophan in their sap. This amino acid pattern closely resembled that of cereals. The total concentration and the individual composition of amino acids were not found to be related to the level of aphid resistance previously found in the investigated Brassica species. However, one B. campestris cultivar, yellow sarson YSB-9, on which the aphids were shown to grow more slowly, had less amino acid content than other B. campestris varieties. The slow population growth of aphids on B. juncea, compared to that on B. campestris, is probably due to other than nutritional factors.     

Complexities of chromosome landing in a highly duplicated genome: toward map-based cloning of a gene controlling blackleg resistance in Brassica napus

The LmR1 locus, which controls seedling resistance to the blackleg fungus Leptosphaeria maculans in the Brassica napus cultivar Shiralee, was positioned on linkage group N7. Fine genetic mapping in a population of 2500 backcross lines identified three molecular markers that cosegregated with LmR1. Additional linkage mapping in a second population colocalized a seedling resistance gene, ClmR1, from the cultivar Cresor to the same genetic interval on N7 as LmR1. Both genes were located in a region that showed extensive inter- and intragenomic duplications as well as intrachromosomal tandem duplications. The tandem duplications seem to have occurred in the Brassica lineage before the divergence of B. rapa and B. oleracea but after the separation of Brassica and Arabidopsis from a common ancestor. Microsynteny was found between the region on N7 carrying the resistance gene and the end of Arabidopsis chromosome 1, interrupted by a single inversion close to the resistance locus. The collinear region in Arabidopsis was assayed for the presence of possible candidate genes for blackleg resistance. These data provided novel insights into the genomic structure and evolution of plant resistance loci and an evaluation of the candidate gene approach using comparative mapping with a model organism.     

Exploiting comparative mapping among Brassica species to accelerate the physical delimitation of a genic male-sterile locus (BnRf) in Brassica napus

The recessive genic male sterility (RGMS) line 9012AB has been used as an important pollination control system for rapeseed hybrid production in China. Here, we report our study on physical mapping of one male-sterile locus (BnRf) in 9012AB by exploiting the comparative genomics among Brassica species. The genetic maps around BnRf from previous reports were integrated and enriched with markers from the Brassica A7 chromosome. Subsequent collinearity analysis of these markers contributed to the identification of a novel ancestral karyotype block F that possibly encompasses BnRf. Fourteen insertion/deletion markers were further developed from this conserved block and genotyped in three large backcross populations, leading to the construction of high-resolution local genetic maps where the BnRf locus was restricted to a less than 0.1-cM region. Moreover, it was observed that the target region in Brassica napus shares a high collinearity relationship with a region from the Brassica rapa A7 chromosome. A BnRf-cosegregated marker (AT3G23870) was then used to screen a B. napus bacterial artificial chromosome (BAC) library. From the resulting 16 positive BAC clones, one (JBnB089D05) was identified to most possibly contain the BnRf (c) allele. With the assistance of the genome sequence from the Brassica rapa homolog, the 13.8-kb DNA fragment covering both closest flanking markers from the BAC clone was isolated. Gene annotation based on the comparison of microcollinear regions among Brassica napus, B. rapa and Arabidopsis showed that five potential open reading frames reside in this fragment. These results provide a foundation for the characterization of the BnRf locus and allow a better understanding of the chromosome evolution around BnRf.     

Cloning of dehydrin coding sequences from Brassica juncea and Brassica napus and their low temperature-inducible expression in germinating seeds.

A novel subclass of dehydrin genes, homologous to the Raphanus sativus late embryogenesis-abundant (LEA) protein (RsLEA2) and the Arabidopsis thaliana dehydrin, was isolated from Brassica juncea and Brassica napus, here designated BjDHN1 and BnDHN1, respectively. The cDNA of BjDHN1 and BnDHN1 genes share 100% nucleotide identity. The encoded protein is predicted to consist of 183 amino acid residues (molecular mass of 19.2 kDa and pI of 7.0). It shares 85.3% and 65.4% amino acid sequence identity with the RsLEA2 and Arabidopsis dehydrin, respectively. This Brassica dehydrin also features a "Y(3)SK(2)" plant dehydrin structure. Expression analysis indicated that the Brassica dehydrin gene is expressed at the late stages of developing siliques, suggesting that the gene expression may be inducible by water-deficit. Analysis of gene expression also indicated that in germinating seeds the gene expression was inducible by low temperature. Seed germination under low temperature was compared between B. juncea and B. napus. The results showed that B. juncea seeds germinated faster than B. napus seeds. Expression of Brassica dehydrin gene was also examined as a function of seed germination under low temperature.     

Basic compatibility of Albugo candida in Arabidopsis thaliana and Brassica juncea causes broad-spectrum suppression of innate immunity

A biotrophic parasite often depends on an intrinsic ability to suppress host defenses in a manner that will enable it to infect and successfully colonize a susceptible host. If the suppressed defenses otherwise would have been effective against alternative pathogens, it follows that primary infection by the "suppressive" biotroph potentially could enhance susceptibility of the host to secondary infection by avirulent pathogens. This phenomenon previously has been attributed to true fungi such as rust (basidiomycete) and powdery mildew (ascomycete) pathogens. In our study, we observed broad-spectrum suppression of host defense by the oomycete Albugo candida (white blister rust) in the wild crucifer Arabidopsis thaliana and a domesticated relative, Brassica juncea. A. candida subsp. arabidopsis suppressed the "runaway cell death" phenotype of the lesion mimic mutant lsd1 in Arabidopsis thaliana in a sustained manner even after subsequent inoculation with avirulent Hyaloperonospora arabidopsis (Arabidopsis thaliana downy mildew). In sequential inoculation experiments, we show that preinfection by virulent Albugo candida can suppress disease resistance in cotyledons to several downy mildew pathogens, including contrasting examples of genotype resistance to H. arabidopsis in Arabidopsis thaliana that differ in the R protein and modes of defense signaling used to confer the resistance; genotype specific resistance in B. juncea to H. parasitica (Brassica downy mildew; isolates derived from B. juncea); species level (nonhost) resistance in both crucifers to Bremia lactucae (lettuce downy mildew) and an isolate of the H. parasitica race derived from Brassica oleracea; and nonhost resistance in B. juncea to H. arabidopsis. Broad-spectrum powdery mildew resistance conferred by RPW8 also was suppressed in Arabidopsis thaliana to two morphotypes of Erysiphe spp. following pre-infection with A. candida subsp. arabidopsis.     

油菜硫甙性状QTL 区间的加密和整合

目的:加密油菜控制硫甙性状QTL区间,并进行QTL整合预测候选基因。方法:利用生物信息学方法根据已知测序的白菜BAC序列信息设计引物,在油菜TN DH群体中进行多态性扩增和定位,并根据加密后构建的遗传连锁图重新检测QTL,进行QTL整合。结果:将根据白菜BAC设计的3对多态性标记成功定位到油菜控制硫甙性状QTL区间,进行QTL整合后将QTL置信区间进一步缩小,并判定了初步的候选基因。结论:充分利用白菜已测序的BAC或者基因组信息,将能加快油菜基础研究的步伐。     

A high-density linkage map in <Emphasis Type="Italic">Brassica juncea</Emphasis> (Indian mustard) using AFLP and RFLP markers

A high-density genetic linkage map of Brassica juncea (2n = 36) was constructed with 996 AFLP (amplified fragment length polymorphism) and 33 RFLP (restriction fragment length polymorphism) markers using a F1-derived doubled-haploid (DH) population of 123 individuals. This mapping population was developed by crossing a well-adapted, extensively grown Indian variety Varuna and a canola quality line Heera. The two lines are highly divergent and contain a number of contrasting qualitative and quantitative traits of high agronomic value. AFLPs were generated by the use of restriction enzymes EcoRI or PstI in combination with either MseI or TaqI. Using 91 primer pairs, a total of 1,576 parental polymorphic bands were detected of which 996 were used for mapping. In addition, 33 RFLP markers, developed from genomic clones of B. napus, were added to the map. The segregation of each marker and linkage analysis was performed using the program JoinMap version 2.0. The 1,029 mapped-markers were aligned in 18 linkage groups, which is the haploid chromosome number of the species, at LOD values ranging from 5 to 8. The total map length was 1,629 cM with an average marker interval of 3.5 cM. AFLP markers generated by EcoRI were more clustered, whereas PstI markers showed more extensive distribution. A set of 26 primer pairs (9 EcoRI/ MseI, 6 EcoRI/ TaqI, 6 PstI/ MseI and 5 PstI/ TaqI) generating 385 markers were identified for AFLP-based whole-genome selection as these markers covered 96% of the genome mapped with the 91 primer pairs. The map developed in the present study could be used for dissection and the transfer of agronomically important traits and favourable QTLs from ill-adapted exotic germplasm to cultivated Indian varieties.     

Development of an AFLP-based linkage map and localization of QTLs for seed fatty acid content in condiment mustard (Brassica juncea).

A genetic linkage map of Brassica juncea based on AFLP and RAPD markers was constructed using 131 F1-derived doubled-haploid (DH) plants from a cross between two mustard lines. The map included 273 markers (264 AFLP, 9 RAPD) arranged on 18 linkage groups, and covered a total genetic distance of 1641 cM; 18.3% of the AFLP markers showed a segregation distortion (P < 0.01). The markers with biased segregation were clustered on seven linkage groups. QTLs for oil contents, palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), linolenic acid (18:3), eicosenoic acid (20:1), and erucic acid (22:1), were mapped on the AFLP linkage map. Correlation studies among fatty acids in the DH population and the localization of QTLs involved in their control indicated that a major gene located on linkage group (LG) 2 controlled the elongation step of erucic acid.     

Mapping genes for resistance to Leptosphaeria maculans in Brassica juncea.

Blackleg disease of crucifers, caused by the fungus Leptosphaeria maculans, is a major concern to oilseed rape producers worldwide. Brassica species containing the B genome have high levels of resistance to blackleg. Brassica juncea F2 and first-backcross (B1) populations segregating for resistance to a PG2 isolate of L. maculans were created. Segregation for resistance to L. maculans in these populations suggested that resistance was controlled by two independent genes, one dominant and one recessive in nature. A map of the B. juncea genome was constructed using segregation in the F2 population of a combination of restriction fragment length polymorphism (RFLP) and microsatel lite markers. The B. juncea map consisted of 325 loci and was aligned with previous maps of the Brassica A and B genomes. The gene controlling dominant resistance to L. maculans was positioned on linkage group J13 based on segregation for resistance in the F2 population. This position was confirmed in the B1 population in which the resistance gene was definitively mapped in the interval flanked by pN199RV and sB31143F. The provisional location of the recessive gene controlling resistance to L. maculans on linkage group J18 was identified using a subset of informative F2 individuals.