Genetic dissection of seed weight by QTL analysis and detection of allelic variation in Indian and east European gene pool lines of Brassica juncea.

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. 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.

Deciphering allelic variations for seed glucosinolate traits in oilseed mustard (Brassica juncea) using two bi-parental mapping populations.

KEY MESSAGE: QTL mapping by two DH mapping populations deciphered allelic variations for five different seed glucosinolate traits in B. juncea. 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 15S-QTL and 16E-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 (2) 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.

QTL Landscape for Oil Content in Brassica juncea: Analysis in Multiple Bi-Parental Populations in High and "0" Erucic Background.

Increasing oil content in oilseed mustard (Brassica juncea) is a major breeding objective-more so, in the lines that have "0" erucic acid content (< 2% of the seed oil) as earlier studies have shown negative pleiotropic effect of erucic acid loci on the oil content, both in oilseed mustard and rapeseed. We report here QTL analysis of oil content in eight different mapping populations involving seven different parents-including a high oil content line J8 (~49%). The parental lines of the mapping populations contained wide variation in oil content and erucic acid content. The eight mapping populations were categorized into two sets-five populations with individuals segregating for erucic acid (SE populations) and the remaining three with zero erucic acid segregants (ZE populations). Meta-analysis of QTL mapped in individual SE populations identified nine significant C-QTL, with two of these merging most of the major oil QTL that colocalized with the erucic acid loci on the linkage groups A08 and B07. QTL analysis of oil content in ZE populations revealed a change in the landscape of the oil QTL compared to the SE populations, in terms of altered allelic effects and phenotypic variance explained by ZE QTL at the "common" QTL and observation of "novel" QTL in the ZE background. The important loci contributing to oil content variation, identified in the present study could be used in the breeding programmes for increasing the oil content in high erucic and "0" erucic backgrounds.