QTL mapping for the tocopherols at milk stage of kernel development in sweet corn

Tocopherols have several beneficial effects in plants, and are indispensable micronutrients for humans. Sweet corn is a major source of tocopherols in high concentrations. In this investigation, tocopherol compounds in sweet corn were analyzed by high performance liquid chromatography. To detect quantitative trait loci (QTL) controlling accumulation of tocopherols at the milk stage in sweet corn, a F-2 population consisting of 229 F-2:3 lines was created from the cross between a high-total tocopherols line (A6) and a low-total tocopherols line (A57). A genetic map was constructed using 136 polymorphic molecular markers including one gene-targeted marker based on the tocopherol biosynthesis pathway (HPPD). Eleven putative QTLs for tocopherol content and composition were detected by composite interval mapping and located on Chr. 1, Chr. 2, Chr. 5, Chr. 6 and Chr. 10. Phenotypic variance explained by each QTL ranged from 4.74 to 41.16 %. Eight mapped QTLs were co-localized, suggesting that the same QTL affected the amounts of more than one tocopherol compound. One candidate gene-targeted marker (HPPD) showed co-localization with the major QTL for gamma-tocopherol and total tocopherols. Only one interval (umc1177-bnlg1429) on chromosome one exhibited a QTL for alpha, delta, gamma, and total tocopherols with high LOD and R-2 values. The primary conclusion of this work is that two major QTLs located on Chr. 1 and Chr. 5 can be used for improvement of sweet corn nutrition quality by marker-assisted selection.