Breeding for colored quality protein popcorn with improved amino acid composition

Popcorn is deficient in essential lysine due to the high abundance of lysine-devoid zein storage proteins in the endosperm. Opaque-2 (o2) mutants reduce zein accumulation, resulting in increased lysine-containing non-zein proteins. By introgressing o2 along with modifier genes into dent corn and popcorn germplasm, high-lysine varieties called Quality Protein Maize (QPM) and Quality Protein Popcorn (QPP) have been created. While previous QPP studies used proprietary yellow popcorn germplasm, we employed publicly available, highly open-pollinated, and diversely colored popcorn germplasm. The objective of this project was to breed high-lysine, diversely colored popcorn inbreds with improved protein quality, which can then be used to produce QPP hybrids with diverse flake taste, aroma, and texture, along with robust agronomics. QPM lines were crossed with colored popcorns to generate novel colored QPP lines. Segregating F₂ ears were used for selection of diverse color, popcorn kernel size and shape, and o2 phenotypes. Using recurrent backcrossing and selection to the BC₃ generation, followed by five generations of selfing and selection, nine BC₃F₅ colored QPP inbreds were selected for analysis and hybrid crossing. SDS-PAGE analysis confirmed the reduction of the 22-kDa alpha zeins, and despite the low alpha zeins, protein concentrations remained equivalent to the parental popcorns. Analysis of the amino acids revealed a significant increase in protein-bound lysine (up to twofold), free lysine (up to 10-fold), and variable increases in free tryptophan in popped QPP inbreds. The inbreds exhibited variability in popping performance, with five of the nine exhibiting significant reductions in pop volume, while four inbreds produced popping values similar to parental popcorn lines and were selected for ongoing production of QPP hybrids. This study highlights the potential to address popcorn's incomplete protein profile by increasing essential lysine content, thereby expanding its nutritional potential. Superior colored QPP genotypes bearing both normal popcorn endosperm vitreousness and high-lysine trait characteristics are currently being used in the development of various colored QPP hybrids.