Selection for contrasting tocopherol content and profile in Ethiopian mustard

Abstract

Tocopherols are compounds present in oilseeds with major effect on nutritional and technological properties of seed oils. Brassica spp. mainly contain varying concentrations of a-tocopherol, with high vitamin E value, and c-tocopherol, which contributes to oil stability. The objective of this research was to select for contrasting tocopherol content and profile in Ethiopian mustard (Brassica carinata A. Braun). A collection of 211 F 4:5 lines was evaluated for tocopherol content and profile, and divergent selection was conducted till the S 3:4 generation. Selection resulted in two lines with increased tocopherol content (244 and 243 mg/ kg seed as average of four environments), one line with reduced tocopherol content (117 mg/kg), two lines with reduced a/c-tocopherol ratio (0.22 and 0.28) and two lines with increased a/c-tocopherol ratio (3.74 and 3.34). Control line C-101 averaged 196 mg/kg with a/c-tocopherol ratio of 1.10. Reduced a/c-tocopherol ratio was controlled by recessive alleles at a single locus. Seed to plant correlation was high (r = 0.92), which suggests the feasibility of selecting at the single-seed level.

Genetic Analysis of Reducedγ-Tocopherol Content in Ethiopian Mustard Seeds

“…In the present research, heritability was not estimated because the line with reduced γ -tocopherol content had been selected for this trait during several generations. It was selected from individual plants that exhibited the mutant trait within a germplasm accession with an average tocopherol profile close to the wild type [ 11 ]. The estimation of the minimum number of genes suggested that the trait is likely to be controlled by only two genes which, together with the absence of epistatic effects, may anticipate good response to selection.…”

“…Ethiopian mustard line BCT-6 is characterized by a reduced accumulation of γ -tocopherol, which results in an increased relative concentration of α -tocopherol and a reduced total tocopherol content [ 11 ]. The authors reported a tocopherol content of 127 mg kg −1 and α -/ γ -tocopherol ratio of 3.07 in BCT-6 compared to 185 mg kg −1 and α -/ γ -tocopherol ratio of 1.17 in the control line C-101.…”

“…The tocopherol fraction in seeds of the genus Brassica , which includes the major oilseed crop rapeseed/canola ( Brassica napus L.), is predominantly made up of varying proportions of α - and γ -tocopherol, with the latter being in general the predominant tocopherol form [ 9 , 10 ]. Only in a few cases has germplasm with predominance of α -tocopherol been reported, for example, in B. rapa [ 9 ] and B. carinata [ 9 , 11 ]. The relative concentrations of α - and γ -tocopherol are mainly determined by a γ -tocopherol methyltransferase ( γ -TMT), which catalyses a methylation step from γ -tocopherol to α -tocopherol [ 12 ].…”

“…75% of total tocopherols compared to 44% in conventional germplasm) was identified. The trait was found to be controlled by partially recessive alleles at a single locus [ 11 ]. Germplasm with increased relative concentration of α -tocopherol, around 70% of total tocopherols, was also reported in the same research.…”

“…Such a high concentration of α -tocopherol has not been identified in other Brassica spp., including transgenic B. juncea lines that had a maximum concentration of α -tocopherol around 60% [ 13 ]. Increased α -tocopherol concentration in Ethiopian mustard was the result of reduced γ -tocopherol content rather than an increase in α -tocopherol accumulation [ 11 ].…”