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

Comparative Analysis of Fruit Metabolites and Pungency Candidate Genes Expression between Bhut Jolokia and Other <i>Capsicum</i> Species

<div><p>Bhut jolokia, commonly known as Ghost chili, a native <i>Capsicum</i> species found in North East India was recorded as the naturally occurring hottest chili in the world by the Guinness Book of World Records in 2006. Although few studies have reported variation in pungency content of this particular species, no study till date has reported detailed expression analysis of candidate genes involved in capsaicinoids (pungency) biosynthesis pathway and other fruit metabolites. Therefore, the present study was designed to evaluate the diversity of fruit morphology, fruiting habit, capsaicinoids and other metabolite contents in 136 different genotypes mainly collected from North East India. Significant intra and inter-specific variations for fruit morphological traits, fruiting habits and 65 fruit metabolites were observed in the collected <i>Capsicum</i> germplasm belonging to three <i>Capsicum</i> species i.e., <i>Capsicum chinense</i> (Bhut jolokia, 63 accessions), <i>C</i>. <i>frutescens</i> (17 accessions) and <i>C</i>. <i>annuum</i> (56 accessions). The pungency level, measured in Scoville Heat Unit (SHU) and antioxidant activity measured by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay showed maximum levels in <i>C</i>. <i>chinense</i> accessions followed by <i>C</i>. <i>frutescens</i> accessions, while <i>C</i>. <i>annuum</i> accessions showed the lowest value for both the traits. The number of different fruit metabolites detected did not vary significantly among the different species but the metabolite such as benzoic acid hydroxyl esters identified in large percentage in majority of <i>C</i>. <i>annuum</i> genotypes was totally absent in the <i>C</i>. <i>chinense</i> genotypes and sparingly present in few genotypes of <i>C</i>. <i>frutescens</i>. Significant correlations were observed between fruit metabolites capsaicin, dihydrocapsaicin, hexadecanoic acid, cyclopentane, α-tocopherol and antioxidant activity. Furthermore, comparative expression analysis (through qRT-PCR) of candidate genes involved in capsaicinoid biosynthesis pathway revealed many fold higher expression of majority of the genes in <i>C</i>. <i>chinense</i> compared to <i>C</i>. <i>frutescens</i> and <i>C</i>. <i>annuum</i> suggesting that the possible reason for extremely high pungency might be due to the higher level of candidate gene(s) expression although nucleotide variation in pungency related genes may also be involved in imparting variations in level of pungency.</p></div

Morphological diversity of <i>Capsicum</i> species.

<p>Selected <i>Capsicum</i> germplasm from North East India showing contrasting phenotypes for fruit morphology, color, and fruiting habits. Accessions in 1-3^rd rows are contrasting Bhut jolokia genotypes (<i>C</i>. <i>chinense</i>), 4^th and 5^th row contains <i>C</i>. <i>chinense</i>, <i>C</i>. <i>frutescens</i> and <i>C</i>. <i>annuum</i> accessions.</p

Range of antioxidant activity of different <i>Capsicum</i> species.

<p>Anti-oxidant activity using DPPH assay obtained for <i>C</i>. <i>chinense</i>, <i>C</i>. <i>frutescens</i> and <i>C</i>. <i>annuum</i> varieties and represented in 25mg/ml dilutions.</p

Metabolite range of different <i>Capsicum</i> species.

<p>Metabolite range of <i>C</i>. <i>chinense</i>, <i>C</i>. <i>frutescens</i> and <i>C</i>. <i>annuum</i> varieties.</p

Principal component analysis of metabolites identified using gas chromatography–mass spectrometry (GC–MS) analysis.

<p>For GC–MS, different genotypes of <i>C</i>. <i>chinense</i> [Acc 1–63 (major accession formed red circle)], <i>C</i>. <i>frutescens</i> [Acc 64–80 (major accession formed blue circle)] and <i>C</i>. <i>annuum</i> [Acc 81–136 (major accession formed brown circle)] were analysed and the correlation variances explained by the PC1 and PC2 components are 51% and 11%, respectively.</p

Morphological characteristics of <i>Capsicum</i> fruits.

<p>Morphological characteristics of <i>Capsicum</i> fruits.</p

SHU range of different <i>Capsicum</i> species.

<p>Total capsaicinoids content observed in <i>C</i>. <i>chinense</i> (63 accessions), <i>C</i>. <i>frutescens</i> (17 accessions) and <i>C</i>. <i>annuum</i> (56 accessions) accessions in Scoville Heat Unit (SHU).</p

Pungency and capsaicinoid biosynthesis gene expression analysis.

<p><b>(A)</b> Pungency analysis of selected <i>Capsicum</i> genotypes <b>(B)</b> Quantitative real time PCR analysis to analyze the expression of candidate genes involved in capsaicinoid biosynthesis pathway in highly pungent Bhut jolokia (Acc 23 and Acc 50), moderately pungent <i>C</i>. <i>frutescens</i> (Acc 65) and low pungent <i>C</i>. <i>annuum</i> (Acc 93 and Acc 95) accessions. The expression analysis was done in leaf, flowers, and three different stages of fruit developmental i.e. green (20 days after anthesis), Breaker (30–45 days after anthesis) and Mature stage of each genotype. The majority of the important genes involved in the capsaicinoid biosynthesis pathway (<i>Pun 1</i>, <i>AMT</i>, <i>ACS</i>, <i>ACL</i>, <i>KAS</i> and <i>BCAT</i>) were expressed very high in <i>C</i>. <i>chinense</i> accessions followed by <i>C</i>. <i>frutescens</i>. The low pungent <i>C</i>. <i>annuum</i> accessions showed very low expression of these genes. The other genes (<i>PAL</i>, <i>COMT</i>, <i>FatA</i> and <i>C4H</i>) were expressed variably among the three species. ***<i>P</i><0.001</p

Molecular mapping reveals two independent loci conferring resistance to Albugo candida in the east European germplasm of oilseed mustard Brassica juncea

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