Quality protein maize (QPM): Importance, genetics, timeline of different events, breeding strategies and varietal adoption

Abstract

Lysine and tryptophan are two essential amino acids and these are deficit in maize grain thus posing the problem of nutritional deficiencies in the consumers. A wide range of deficiency symptoms like cognitive disorder, kwashiorkor disease, reduced appetite, impaired skeleton development, delayed growth and aberrant behaviour are associated with lysine and tryptophan deficiency. These amino acids are also important to cure the Pellagra disease. Researchers identified several mutants in maize especially opaque-2 which are responsible for higher lysine and tryptophan contents. Few years later, it was observed that opaque-2 mutant has several pleiotropic effects on maize grain and plant. Efforts of researchers are spanning over the period of four decades to develop quality protein maize (QPM). QPM is described as nutritionally superior maize with high lysine and tryptophan contents and desired kernel characteristics as compared to its normal maize counterparts. Biological value of QPM was almost equivalent to egg protein. Breeding of maize for quality protein is based on three genetic systems like opaque-2 genetic system, endosperm modifier genetic system and associated gene systems. Keeping in view the importance of QPM, current review article is compiled to discuss the genetic basis, genetic systems and breeding strategies. Timeline for various events is also drafted like discovery of various mutants, several conventional and modern approaches for development and deployment of QPM varieties across the world. Despite its nutritional benefits, the rate of adoption of QPM is generally at low pace in the developing world and this review article discuss the challenges and potential opportunities for QPM adoption.