Applications and benefits of marker-assisted introgression of the opaque-2 gene in quality protein maize breeding

Maize (Zea mays) is a crucial crop in Africa serving as one of the chief carbohydrate sources used as food and feed. However, maize is deficient in essential amino acids, lysine and tryptophan. Protein malnutrition is a major challenge as a result, especially in developing countries where maize is a staple crop. The discovery of the opaque-2 maize mutant, high in lysine and tryptophan, has offered an avenue for maize protein quality improvement. Quality protein maize (QPM) is a product of the extensive development of the opaque-2 mutant. It stands as an affordable and viable option to overcome the scourge of protein malnutrition in humans and monogastric livestock. The conventional QPM breeding methods are based on phenotypic selection to identify materials carrying two copies of the recessive opaque-2 allele. However, phenotypic selection in QPM breeding programs is influenced by the environment and has huge drain on resources such as time, money and labour with low genetic gains. Marker assisted introgression of the opaque-2 gene with simple sequence repeat markers for foreground selection is a molecular technology based methodology of accelerating the Quality protein maize breeding process. Colorimetric tryptophan analysis stands as a crucial step in the QPM breeding process as it validates the elevated levels of tryptophan and the action amino acid modifier loci. Knowledge of the combining ability of the genetic materials used in the crosses made is pivotal in any QPM breeding programme.