www.tropicalplantresearch.com 145 Received: 07 December 2016 Published online: 30 April 2017 https://doi.org/10.22271/tpr.2017.v4.i1.021 ISSN (E): 2349 – 1183 ISSN (P): 2349 – 9265 4(1): 145–152, 2017 DOI: 10.22271/tpr.2017.v4.i1.021 Review article Quality protein maize (QPM): Genetic basis and breeding perspective Swapan K. Tripathy*, Dinesh M. Ithape, Manasmita Maharana and A. M. Prusty Department of Agricultural Biotechnology, College of Agriculture, OUAT, Bhubaneswar, Odisha, India *Corresponding Author: swapankumartripathy@gmail.com [Accepted: 10 April 2017] Abstract: Major fraction (60%) of seed storage protein in maize is zein which determines the quality of food and feed. Zeins comprise four subfamilies e.g., α , β, γ and δ zeins. Among these, α- zeins are the major prolamin subunits in maize. α-zeins are rich in glutamine, leucine and proline but, deficient in essential amino acids like lysine and tryptophan causing malnutrition. The opaque-2 (o2)-a natural recessive mutation in maize led to nearly double the lysine and tryptophan content in endosperm due to a decrease in the synthesis of zein proteins and increase in the other seed protein bound lysine and tryptophan. RNAi studies proved down regulation of 22kD zeins than the 19kD component as the biochemical basis of QPM phenotype. However, the opaque-2 mutation made the endosperm chalky and soft resulting damaged kernel while harvesting, poor germination, increased susceptibility to pest and diseases, inferior for food processing and in general reduced yield. Later, combining opaque-2 allele with its desirable genetic modifiers made it possible to breed QPM genotypes having hard kernel with high lysine and tryptophan content. Since, opaque-2 is a recessive mutation and endosperm specific, and biochemical analysis of lysine and tryptophan content is expensive; conventional backcross breeding alone is inefficient for the nutritional enrichment of maize. However, use of opaque-2 gene specific markers provided excellent opportunities for conversion of elite normal inbreds to homozygous o2/o2 forms through marker assisted selection (MAS). In India, Vivek QPM-9: a hybrid of two QPM introgression lines is being widely used for commercial cultivation. Keywords: Quality protein maize (QPM) - Opaque-2 - Nutritional value - Introgression lines - QPM hybrids. [Cite as: Tripathy SK, Ithape DM, Maharana M & Prusty AM (2017) Quality protein maize (QPM): Genetic basis and breeding perspective. Tropical Plant Research 4(1): 145–152] INTRODUCTION Maize is the queen of cereal crops with highest grain yield potential. Endosperm is the store house of seed storage proteins. Maize grains contain around 9% protein. The major fraction (60%) of seed protein in maize is zeins (a prolamin group-alcohol soluble) (Leite et al. 1999) followed by glutelin (34%), while albumin and globulin occur in traces (3% each). A balanced protein is required to assist body building process and therefore, amino acid balance seems to be a determining factor for quality of any food and feed. Daily protein requirement for average Indian adult is 52 gm as against the availability of merely 26–30 gm in the daily diet. To alleviate malnutrition, protein content can be increased to as high as 18% by increasing the prolamine (zein) fraction in maize endosperm (Dudley & Lambert 1969), but unfortunately it consequently led to lysine and tryptophan deficiency. Many researchers around the globe have tried to address the problem using quality protein maize (QPM). In this pursuit, we focus on the genetic basis and prospects of quality protein maize for amino acid amelioration and enhancing the productivity of maize through the development of heterotic hybrids using elite QPM introgression lines. GENETIC BASIS Zein seed proteins are the products of multigene families (Lending & Larkins 1989) and located within protein bodies on the rough endoplasmic reticulum (Larkins et al 1993). Each of the zein polypeptide is a product of a differential structural gene (Zp). These Zp genes are simply inherited and are members of a large