Mahan, Adam Lyle (2012-08). Genetic Combining Analysis of Food-Grade Maize: Colored and Quality Protein. Master's Thesis.
Maize genetic diversity includes an array of kernel colors (red, blue, purple) with blue concentrated in the aleurone and red primarily in the pericarp. Quality protein maize (QPM) is improved over normal maize in regards to grain concentration of the essential amino acids lysine and tryptophan but has not been widely adapted in part due to lower than conventional yields. These are minimally-utilized specialty corns when compared to the yellows and whites commonly grown. Red, blue, and purple pigments are antioxidant phytochemicals produced by the plant as secondary metabolites. Antioxidants have been linked to anti-cancer and other anti-inflammatory health benefits. QPM hybrids are desirable in developing countries where subsistent agriculture is commonly practiced and quality protein cereals are non-existent. These two diverse maize categories have been the subject of little breeding research compared to normal maize and the potential for high phenolic content as well as the characterization of these QPM hybrids has not been previously investigated. We evaluated 153 maize hybrids (84 colored, 69 QPM) across three locations. High heritability estimates were found for phenolic content (0.80), tryptophan (0.46), and endosperm opacity (0.82). It was encouraging that all three traits observed little genotype by environment (GxE) interaction across diverse environments. This proved the trait analysis procedure to be robust in detecting and separating genotypes for both total phenolic content in colored maize, and amino acids in QPM. Top combiners for phenolics were the purple maize "maize morado" and red lines, with blue, yellow and white maize performing in descending order. Within the tested hybrids, high per kernel antioxidants (measured by total phenolics) may be the answer for producing the most total phenolics, with the top hybrid yielding greater than twice the total phenolics as the top yielding yellow hybrid. The top QPM hybrid out yielded the top normal hybrid by 35 and 30% for lysine and tryptophan. Additionally, QPM endosperm opacity primarily followed an additive, mid-parent trend, with some hybrids (20%) from diverse germplasm backgrounds deviating from that trend displaying the complexity and recessive nature of multiple modifier loci. Additional agronomic and composition traits were minimally correlated with phenolics.