Quality Protein Maize Germplasm Characterized for Amino Acid Profiles and Endosperm Opacity

Abstract

<p>Quality protein maize (QPM) is improved over normal (non-QPM) maize in grain concentrations of the essential amino acids lysine and tryptophan. Quality protein maize has a long history as tropical adapted germplasm, but little effort has been made to incorporate temperate or sub-tropical germplasm for temperate adaptation and interactions between different modifier loci in these backgrounds are poorly understood. A design-II mating scheme including new temperate and subtropical lines produced 69 hybrids. Large hybrid genetic variation components resulted in substantial broad-sense heritability H² estimates, specifically tryptophan (0.46) and endosperm opacity (0.82). A microbial assay for amino acid estimation proved robust across diverse environments with minimal genotype × environment (G×E) effects. Endosperm opacity had no G×E effects across both Texas and Iowa locations demonstrating stability for this trait. Endosperm opacity primarily followed an additive, midparent trend, with a few hybrids deviating from the trend (36%) suggesting a complex nature of multiple modifier loci across diverse germplasm. The top QPM hybrid outperformed the top commercial hybrid by 35 and 30% for lysine and tryptophan as a proportion of grain, respectively. QPM line Tx832 was a parent of top hybrids for lysine and tryptophan, and the highest noncommercial hybrids for methionine. Minimal correlations with yield and other traits suggest that future breeding should result in QPM hybrids with increasingly competitive yields.</p>