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Key message: Genetic mapping of some key plant architectural traits in a vegetable type and an oleiferous B. juncea cross revealed QTL and candidate genes for breeding more productive ideotypes. Brassica juncea (AABB, 2n = 36), commonly called mustard, is an allopolyploid crop of recent origin but contains considerable morphological and genetic variation. An F1-derived doubled haploid population developed from a cross between an Indian oleiferous line, Varuna, and a Chinese stem type vegetable mustard, Tumida showed significant variability for some key plant architectural traits—four stem strength-related traits, stem diameter (Dia), plant height (Plht), branch initiation height (Bih), number of primary branches (Pbr), and days to flowering (Df). Multi-environment QTL analysis identified twenty Stable QTL for the above-mentioned nine plant architectural traits. Though Tumida is ill-adapted to the Indian growing conditions, it was found to contribute favorable alleles in Stable QTL for five architectural traits—press force, Dia, Plht, Bih, and Pbr; these QTL could be used to breed superior ideotypes in the oleiferous mustard lines. A QTL cluster on LG A10 contained Stable QTL for seven architectural traits that included major QTL (phenotypic variance ≥ 10%) for Df and Pbr, with Tumida contributing the trait-enhancing alleles for both. Since early flowering is critical for the cultivation of mustard in the Indian subcontinent, this QTL cannot be used for the improvement of Pbr in the Indian gene pool lines. Conditional QTL analysis for Pbr, however, identified other QTL which could be used for the improvement of Pbr without affecting Df. The Stable QTL intervals were mapped on the genome assemblies of Tumida and Varuna for the identification of candidate genes. [ABSTRACT FROM AUTHOR]

Key message: BjuWRR1, a CNL-type R gene, was identified from an east European gene pool line of Brassica juncea and validated for conferring resistance to white rust by genetic transformation. White rust caused by the oomycete pathogen Albugo candida is a significant disease of crucifer crops including Brassica juncea (mustard), a major oilseed crop of the Indian subcontinent. Earlier, a resistance-conferring locus named AcB1-A5.1 was mapped in an east European gene pool line of B. juncea—Donskaja-IV. This line was tested along with some other lines of B. juncea (AABB), B. rapa (AA) and B. nigra (BB) for resistance to six isolates of A. candida collected from different mustard growing regions of India. Donskaja-IV was found to be completely resistant to all the tested isolates. Sequencing of a BAC spanning the locus AcB1-A5.1 showed the presence of a single CC-NB-LRR protein encoding R gene. The genomic sequence of the putative R gene with its native promoter and terminator was used for the genetic transformation of a susceptible Indian gene pool line Varuna and was found to confer complete resistance to all the isolates. This is the first white rust resistance-conferring gene described from Brassica species and has been named BjuWRR1. Allelic variants of the gene in B. juncea germplasm and orthologues in the Brassicaceae genomes were studied to understand the evolutionary dynamics of the BjuWRR1 gene. [ABSTRACT FROM AUTHOR]

Key message: Seed weight QTL identified in different populations were synthesized into consensus QTL which were shown to harbor candidate genes by in silico mapping. Allelic variation inferred would be useful in breeding B. juncea lines with high seed weight. Abstract: Seed weight is an important yield influencing trait in oilseed Brassicas and is a multigenic trait. Among the oilseed Brassicas, Brassica juncea harbors the maximum phenotypic variation wherein thousand seed weight varies from around 2.0 g to more than 7.0 g. In this study, we have undertaken quantitative trait locus/quantitative trait loci (QTL) analysis of seed weight in B. juncea using four bi-parental doubled-haploid populations. These four populations were derived from six lines (three Indian and three east European lines) with parental phenotypic values for thousand seed weight ranging from 2.0 to 7.6 g in different environments. Multi-environment QTL analysis of the four populations identified a total of 65 QTL ranging from 10 to 25 in each population. Meta-analysis of these component QTL of the four populations identified six 'consensus' QTL ( C- QTL) in A3, A7, A10 and B3 by merging 33 of the 65 component Tsw QTL from different bi-parental populations. Allelic diversity analysis of these six C- QTL showed that Indian lines, Pusajaikisan and Varuna, hold the most positive allele in all the six C- QTL. In silico mapping of candidate genes with the consensus QTL localized 11 genes known to influence seed weight in Arabidopsis thaliana and also showed conserved crucifer blocks harboring seed weight QTL between the A subgenomes of B. juncea and B. rapa. These findings pave the way for a better understanding of the genetics of seed weight in the oilseed crop B. juncea and reveal the scope available for improvement of seed weight through marker-assisted breeding. [ABSTRACT FROM AUTHOR]

Key message: QTL mapping by two DH mapping populations deciphered allelic variations for five different seed glucosinolate traits in B. juncea. Abstract: Allelic variations for five different seed glucosinolate (GS) traits, namely % propyl, % butyl, % pentyl, aliphatics and total GS content were studied through QTL analysis using two doubled haploid (DH) mapping populations. While the high GS parents in two populations differed in their profiles of seed aliphatic GS, the low GS parents were similar. Phenotypic data of seed GS traits from three environments of the two populations were subjected to QTL analysis. The first population (referred to as DE population) detected a total of 60 QTL from three environments which upon intra-population meta-QTL analysis were merged to 17 S- QTL (Stable QTL) and 15 E- QTL (Environment QTL). The second population (referred to as VH population) detected 58 QTL from the three environments that were merged to 15 S- QTL and 16 E- QTL. In both the populations, majority of S- QTL were detected as major QTL. Inter-population meta-analysis identified three C- QTL (consensus QTL) formed by merging major QTL from the two populations. Candidate genes of GS pathway were co-localized to the QTL regions either through genetic mapping or through in silico comparative analysis. Parental allelic variants of QTL or of the co-mapped candidate gene(s) were determined on the basis of the significantly different R values of the component QTL from the two populations which were merged to form C- QTL. The results of the study are significant for marker-assisted transfer of the low GS trait and also for developing lines with lower GS than are present in Brassica juncea. [ABSTRACT FROM AUTHOR]

Key message: Genetic locus for tetralocular ovary ( tet - o ) in Brassica rapa was identified and it was shown that the number of locules and width of silique are associated. Abstract: Brassica rapa is a highly polymorphic species containing many vegetables and oleiferous types. An interesting group of oleiferous types is the yellow sarson group (subspecies trilocularis) grown mostly in eastern India. This group contains lines that have bilocular ovaries, a defining trait of Brassicaceae, but also lines that have tetralocular ovaries. Yellow sarson lines commonly have high silique width which is further enhanced in the tetralocular types. We mapped the locus influencing tetralocular ovary in B. rapa using three mapping populations (F, F and F) derived from a cross between Chiifu (subspecies pekinensis, having bilocular ovary) and Tetralocular (having tetralocular ovary). QTL mapping of silique width was undertaken using the three mapping populations and a F population derived from a cross between Chiifu and YSPB-24 (a bilocular line belonging to yellow sarson group). Qualitative mapping of the trait governing locule number ( tet- o) in B. rapa mapped the locus to linkage group A4. QTL mapping for silique width detected a major QTL on LG A4, co-mapping with the tet- o locus in bilocular/tetralocular cross. This QTL was not detected in the bilocular/bilocular cross. Saturation mapping of the tet- o region with SNP markers identified Bra034340, a homologue of CLAVATA3 of Arabidopsis thaliana, as the candidate gene for locule number. A C → T transition at position 176 of the coding sequence of Bra034340 revealed co-segregation with the tetralocular phenotype. The study of silique related traits is of interest both for understanding evolution under artificial selection and for breeding of cultivated Brassica species. [ABSTRACT FROM AUTHOR]

Identification of the candidate gene responsible for the seed coat colour variation in Brassica juncea was undertaken following an earlier study where two independent loci ( BjSc1 and BjSc2) were mapped to two linkage groups, LG A9 and B3 (Padmaja et al. in Theor Appl Genet 111:8-14, ). The genome search from BRAD data for the presence of flavonoid genes in B. rapa identified three candidate genes namely, DFR, TT1 and TT8 in the LG A9. Quantitative real-time PCR revealed absence of transcript for the late biosynthetic genes (LBGs) and showed significant reduction of transcript in the TT8 from the developing seeds of yellow-seeded line. While mapping of two DFR genes, the BjuA.DFR and BjuB.DFR did not show perfect co-segregation with the seed coat colour loci, that of the two TT8 genes, BjuA.TT8 and BjuB.TT8 showed perfect co-segregation with the seed coat colour phenotype. The BjuA.TT8 allele from the yellow-seeded line revealed the presence of an insertion of 1,279 bp in the exon 7 and did not produce any transcript as revealed by reverse transcriptase PCR. The BjuB.TT8 allele from the yellow-seeded line revealed the presence of an SNP (C→T) in the exon 7 resulting in a stop codon predicting a truncated protein lacking the C-terminal 8 amino acid residues and produced significantly low level of transcript than its wild-type counterpart. Hence, it is hypothesized that the mutations in both the TT8 genes are required for inhibiting the transcription of LBGs in the yellow-seeded mutant of B. juncea. [ABSTRACT FROM AUTHOR]

Genetic analysis of 12 yield-associated traits was undertaken by dissection of quantitative trait loci (QTL) through meta-analysis and epistatic interaction studies in Brassica juncea. A consensus (integrated) map in B. juncea was constructed using two maps. These were VH map, developed earlier in the laboratory by using a DH population from the cross between Varuna and Heera (Pradhan et al. in Theor Appl Genet 106:607-614, ; Ramchiary et al. in Theor Appl Genet. 115:807-817, ; Panjabi et al. in BMC Genomics 9:113, ), and the TD map, developed in the present study using a DH population of 100 lines from the cross between TM-4 and Donskaja-IV. The TD map was constructed with 911 markers consisting of 585 AFLP, 8 SSR and 318 IP markers covering a total genome length of 1,629.9 cM. The consensus map constructed by using the common markers between the two maps contained a total of 2,662 markers and covered a total genome length of 1,927.1 cM. Firstly, QTL analysis of 12 yield-associated traits was undertaken for the TD population based on three-environment phenotypic data. Secondly, the three-environment phenotypic data for the same 12 quantitative traits generated by Ramchiary et al. () were re-analyzed for the QTL detection in the VH map. Comparative analysis identified both common and population-specific QTL. The study revealed the presence of QTL clusters on LG A7, A8 and A10 in both TD and VH maps. Meta-analyses resolved 187 QTL distributed over nine linkage groups of TD and VH maps into 20 meta-QTL. Maximum resolution was recorded for the LG A10 wherein all the 54 QTL were mapped to a single meta-QTL within a confidence interval of 3.0 cM. Digenic epistatic interactions of QTL in both TD and VH maps revealed substantial additive × additive interactions showing a higher frequency of Type 1 and Type 2 interactions than Type 3 interactions. Some of the loci interacted with more than one locus indicating the presence of higher order epistatic interactions. These findings provided some detailed insight into the genetic architecture of the yield-associated traits in B. juncea. [ABSTRACT FROM AUTHOR]

Oil content and oil quality fractions (viz., oleic, linoleic and linolenic acid) are strongly influenced by the erucic acid pathway in oilseed Brassicas. Low levels of erucic acid in seed oil increases oleic acid content to nutritionally desirable levels, but also increases the linoleic and linolenic acid fractions and reduces oil content in Indian mustard ( Brassica juncea). Analysis of phenotypic variability for oil quality fractions among a high-erucic Indian variety (Varuna), a low-erucic east-European variety (Heera) and a zero-erucic Indian variety (ZE-Varuna) developed by backcross breeding in this study indicated that lower levels of linoleic and linolenic acid in Varuna are due to substrate limitation caused by an active erucic acid pathway and not due to weaker alleles or enzyme limitation. To identify compensatory loci that could be used to increase oil content and maintain desirable levels of oil quality fractions under zero-erucic conditions, we performed Quantitative Trait Loci (QTL) mapping for the above traits on two independent F1 doubled haploid (F1DH) mapping populations developed from a cross between Varuna and Heera. One of the populations comprised plants segregating for erucic acid content (SE) and was used earlier for construction of a linkage map and QTL mapping of several yield-influencing traits in B. juncea. The second population consisted of zero-erucic acid individuals (ZE) for which, an Amplified Fragment Length Polymorphism (AFLP)-based framework linkage map was constructed in the present study. By QTL mapping for oil quality fractions and oil content in the ZE population, we detected novel loci contributing to the above traits. These loci did not co-localize with mapped locations of the fatty acid desaturase 2 ( FAD2), fatty acid desaturase 3 ( FAD3) or fatty acid elongase ( FAE) genes unlike those of the SE population wherein major QTL were found to coincide with mapped locations of the FAE genes. Some of the new loci identified in the ZE population could be detected as 'weak' contributors (with LOD < 2.5) in the SE population in which their contribution to the traits was 'masked' due to pleiotropic effects of erucic acid genes. The novel loci identified in this study could now be used to improve oil quality parameters and oil content in B. juncea under zero-erucic conditions. [ABSTRACT FROM AUTHOR]

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]

The construction and characterization of two genome-specific recombinant DNA clones from B. nigra are described. Southern analysis showed that the two clones belong to a dispersed repeat family. They differ from each other in their length, distribution and sequence, though the average GC content is nearly the same (45%). These B genome-specific repeats have been used to analyse the phylogenetic relationships between cultivated and wild species of the family Brassicaceae. [ABSTRACT FROM AUTHOR]