Genetic analysis of visually scored orange kernel color in maize

Increasing levels of provitamin A carotenoids in maize (Zea mays L.) grain through plant breeding has potential to help humans suffering from vitamin A deficiency. In parts of Africa where this deficiency is prevalent, there is a consumer preference for white maize grain and an avoidance of yellow maize grain. White grain has minimal levels of carotenoids whereas yellow grain can have appreciable levels of carotenoids. There is a new effort to introduce orange maize that contains high levels of provitamin A, which appears to be a more acceptable color than yellow to consumers in Africa. The implementation of this program requires backcross selection to convert Africanadapted germplasm with white grain to orange. We conducted a study to assess the heritability of visual scores for relative intensity of orange kernel color and identify genetic markers associated with orange color across and within 10 families of the maize nested association mapping population. We found visually scored kernel color to have a moderately high heritability and identified five common quantitative trait loci (QTL) and six rare QTL for intensity of orange color. Notably, half of them coincided with carotenoid biosynthetic genes. Our results indicate that breeders in Africa, Asia, and throughout the world would have flexibility to select for orange kernel color visually and/or with gene-specific markers. Such selection can be combined with marker-assisted selection efforts to increase provitamin A levels in maize grain.