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White rust caused by Albugo candida (Pers.) Kuntze is a major disease of the oilseed mustard Brassica juncea. Almost all the released varieties of B. juncea in India are highly susceptible to the disease. This causes major yield losses. Hence, there is an urgent need to identify genes for resistance to white rust and transfer these to the existing commercial varieties through marker-assisted breeding. While the germplasm belonging to the Indian gene pool is highly susceptible to the disease, the east European germplasm of B. juncea is highly resistant. In the present study, we have tagged two independent loci governing resistance to A. candida race 2V in two east European lines, Heera and Donskaja-IV. Two doubled haploid populations were used; the first population was derived from a cross between Varuna (susceptible Indian type) and Heera (partially resistant east European line) and the second from a cross between TM-4 (susceptible Indian type) and Donskaja-IV (fully resistant east European line). In both the resistant lines, a single major locus was identified to confer resistance to white rust. In Heera, the resistance locus AcB1-A4.1 was mapped to linkage group A4, while in Donskaja-IV, the resistant locus AcB1-A5.1 was mapped to linkage group A5. In both the cases, closely linked flanking markers were developed based on synteny between Arabidopsis and B. juncea. These flanking markers will assist introgression of resistance-conferring loci in the susceptible varieties. [ABSTRACT FROM AUTHOR]

Fine mapping of six seed glucosinolate QTL ( J2Gsl1, J3Gsl2, J9Gsl3, J16Gsl4, J17Gsl5 and J3Gsl6) (Ramchiary et al. in Theor Appl Genet 116:77–85, ) was undertaken by the candidate gene approach. Based on the DNA sequences from Arabidopsis and Brassica oleracea for the different genes involved in the aliphatic glucosinolate biosynthesis, candidate genes were amplified and sequenced from high to low glucosinolate Brassica juncea lines Varuna and Heera, respectively. Of the 20 paralogues identified, 17 paralogues belonging to six gene families were mapped to 12 of the 18 linkage groups of B. juncea genome. Co-mapping of candidate genes with glucosinolate QTL revealed that the candidate gene BjuA.GSL-ELONG.a mapped to the QTL interval of J2Gsl1, BjuA.GSL-ELONG.c, BjuA.GSL-ELONG.d and BjuA.Myb28.a mapped to the QTL interval of J3Gsl2, BjuA.GSL-ALK.a mapped to the QTL interval of J3Gsl6 and BjuB.Myb28.a mapped to the QTL interval of J17Gsl5. The QTL J9Gsl3 and J16Gsl4 did not correspond to any of the mapped candidate genes. The functionality and contribution of different candidate genes/QTL was assessed by allelic variation study using phenotypic data of 785 BC4DH lines. It was observed that BjuA.Myb28.a and J9Gsl3 contributed significantly to the base level glucosinolate production while J16Gsl4, probably GSL-PRO, BjuA.GSL-ELONG.a and BjuA.GSL-ELONG.c contributed to the C3, C4 and C5 elongation pathways, respectively. Three A genome QTL: J2Gsl1harbouring BjuA.GSL-ELONG.a, J3Gsl2 harbouring both BjuA.GSL-ELONG.c and BjuA.Myb28.a and J9Gsl3, possibly the ‘Bronowski genes’, were identified as most important loci for breeding low glucosinolate B. juncea. We observed two-step genetic control of seed glucosinolate in B. juncea mainly effected by these three A genome QTL. This study, therefore, provides clues to the genetic mechanism of ‘Bronowski genes’ controlling the glucosinolate trait and also provides efficient markers for marker-assisted introgression of low glucosinolate trait in B. juncea. [ABSTRACT FROM AUTHOR]

Seed glucosinolate content in Brassica juncea is a complex quantitative trait. A recurrent selection backcross (RSB) method with a doubled haploid (DH) generation interspersing backcross generations was used for the introgression of low glucosinolate alleles from an east European gene pool B. juncea line, Heera into an Indian gene pool variety, Varuna. Phenotypic comparisons among the DH populations derived from early to advanced backcrosses revealed a shift in the mean values for various glucosinolates with the advancement of backcrossing, indicating a change in the selective values of the alleles with change in the genetic background due to the existence of epistasis and context dependencies. QTL mapping for various seed glucosinolates from early (F1DH) and advanced generation (BC4DH) populations confirmed the presence of epistasis and context dependency. The common QTL detected in both F1DH and BC4DH changed their R 2 values from the former to the later generation. Some of the QTL detected in the F1DH became irrelevant in the BC4DH population. Further, new QTL were detected in the BC4DH population for various glucosinolates. A validation study on a population of low glucosinolate DH lines derived from all the backcross generations of the RSB breeding programme revealed that the QTL detected in BC4DH were the ‘true’ QTL. Using glucosinolate as an example, the study provides strong evidence for the importance of the RSB method for the identification of the ‘true’ QTL which would be significant for marker assisted introgression of a complex quantitative trait whose expression is influenced by epistatic interactions. [ABSTRACT FROM AUTHOR]

Microsatellite marker technology in combination with three doubled haploid mapping populations of Brassica juncea were used to map and tag two independent loci controlling seed coat colour in B. juncea. One of the populations, derived from a cross between a brown-seeded Indian cultivar, Varuna, and a Canadian yellow-seeded line, Heera, segregated for two genes coding for seed coat colour; the other two populations segregated for one gene each. Microsatellite markers were obtained from related Brassica species. Three microsatellite markers (Ra2-A11, Na10-A08 and Ni4-F11) showing strong association with seed coat colour were identified through bulk segregant analysis. Subsequent mapping placed Ra2-A11 and Na10-A08 on linkage group (LG) 1 at an interval of 0.6 cM from each other and marker Ni4-F11 on LG 2 of the linkage map of B. juncea published previously (Pradhan et al., Theor Appl Genet 106:607–614, 2003). The two seed coat colour genes were placed with markers Ra2-A11 and Na10-A08 on LG 1 and Ni4-F11 on LG 2 based on marker genotyping data derived from the two mapping populations segregating for one gene each. One of the genes ( BjSC1) co-segregated with marker Na10-A08 in LG 1 and the other gene ( BjSC2) with Ni4-F11 in LG 2, without any recombination in the respective mapping populations of 130 and 103 segregating plants. The identified microsatellite markers were studied for their length polymorphism in a number of yellow-seeded eastern European and brown-seeded Indian germplasm of B. juncea and were found to be useful for the diversification of yellow seed coat colour from a variety of sources into Indian germplasm. [ABSTRACT FROM AUTHOR]

Molecular mapping and tagging of the erucic acid trait (C22:1) in Brassica juncea was done by a candidate gene approach. Two QTLs underlying the variation of seed erucic acid content were assigned to two linkage groups of a B. juncea map using a doubled haploid (DH) mapping population derived from high × low erucic acid F1 hybrid. Two consensus primers corresponding to the full-length Fatty Acid Elongase 1 (FAE1) gene, reported to be involved in the elongation of C18:1 to C22:1, were designed. PCR amplification and subsequent cloning and sequencing identified two FAE1 genes (FAE1.1 and FAE1.2) in both high and low erucic acid mustard lines. Sequence alignment of corresponding FAE1 genes between high and low erucic acid mustard lines identified four substitution type single nucleotide polymorphisms (SNPs) in FAE1.1 and three in FAE1.2. Using the SNuPE method of SNP genotyping, these two genes were mapped to two independent loci that co-segregated with the two QTLs governing the erucic acid trait. Association of wild (E1E2) and mutant (e1e2) haplotypes of two FAE1 genes with erucic acid variation in two segregating populations revealed that the e1e1e2e2 genotype identified low erucic acid individuals (<2%) and E1E1E2E2 identified individuals with highest erucic acid content (>40%). The E1e1E2e2 heterozygote was found to be intermediate in phenotype. The applicability of these SNPs in marker-assisted manipulation of the erucic acid trait was verified by genotyping a set of contrasting germplasm of B. juncea belonging to two distinct gene pools (Indian and east European) and other oil-yielding Brassica species. [ABSTRACT FROM AUTHOR]

AFLP markers were employed to assess the genetic diversity amongst 21 established natural and nine synthetic varietes and lines of Brassica juncea originating from Asia, Australia, Canada, Eastern Europe and Russia. Six of the synthetics used for diversity studies have been developed recently. Twenty one EcoRI/MseI-based AFLP primer pairs generated a total of 1251 scorable fragments among the 30 genotypes studied, of which 778 bands were polymorphic with an average of 37 polymorphic bands per primer pair. On the basis of the similarity coefficients (F value), cluster analysis was performed using the UPGMA method. The 30 B. juncea lines could be grouped into three distinct clusters. All the Indian, Chinese and previously developed synthetics formed one cluster (cluster A), the recently developed synthetics formed a separate cluster (cluster B) and the lines from Australia, Canada, Eastern Europe and Russia formed the third cluster (cluster C). A majority of the lines were uniquely identified by one or more primer pairs due to the presence or absence of variety specific band(s). Four primer pairs were found to be most informative, since these uniquely identified all the genotypes assayed. These four primer pairs, could therefore be used as fingerprinting primers for varietal identification. [ABSTRACT FROM AUTHOR]

Alloplasmic lines of cultivated Brassica species with B. oxyrrhina cytoplasm are male-sterile and suffer from severe chlorosis. We developed male-sterile lines corrected for chlorosis by fusing protoplasts of CMS B. juncea (AABB) with ’oxy’ cytoplasm and normal B. oleracea (CC). A large number of male-sterile AABBCC somatic hybrids with desirable organelle combinations, i.e. chloroplasts of B. oleracea and mitochondria with recombinant genomes, were recovered. While no recombination was observed in the chloroplast genome, the mitochondrial genome showed extensive recombination that resulted in the appearance of totally novel banding patterns in some of the hybrids. Hybrids with a parental-type mitochondrial genome as well as recombinant patterns close to either of the parental types were also obtained. Using AABBCC somatic hybrids as bridging material, we transferred the desirable organelle combinations to B. juncea (AABB), B. napus (AACC), and B. carinata (BBCC). Many of these lines are now at advanced stages of backcrossing and show stable inheritance of the CMS character and do not suffer from chlorosis. [ABSTRACT FROM AUTHOR]