Genetic and Molecular Analysis of High Gamma-Tocopherol Content in Sunflower

Sunflower (Helianthus annuus L.) seeds contain alpha-tocopherol as the major tocopherol derivative, which accounts for more than 900 g kg⁻¹ total tocopherols. However, four sources of high gamma-tocopherol content (>850 g kg⁻¹) have been developed. First studies on the lines LG-17 and T2100 concluded that the trait in both lines was determined by recessive alleles at the Tph2 locus. The objectives of the present research were (i) to conduct an allelic study on the other two lines, IAST-1 and IAST-540, (ii) to identify markers linked to the Tph2 gene, and (iii) to map this gene. Plants of T2100 were crossed with plants of the other three lines, which resulted in F₁ and F₂ populations with uniformly high gamma-tocopherol content in the seeds, indicating the presence of tph2 alleles in the four lines. Genetic mapping of the Tph2 gene was conducted with an F₂ population from the cross between CAS-12, with standard tocopherol profile, and IAST-540. F₂ seeds segregated following a 3 low to 1 high gamma-tocopherol ratio. Bulked segregant analysis identified two simple sequence repeats (SSR) markers on linkage group (LG) 8 linked to Tph2. A large linkage group was constructed by genotyping additional markers. Tph2 mapped between markers ORS312 (3.6 cM proximal) and ORS599 (1.9 cM distal). The availability of closely linked PCR-based markers and the location of the Tph2 gene on the sunflower genetic map will be useful for marker-assisted selection and further characterization of tocopherol biosynthesis in sunflower seeds.