Introgression of the crtRB1 gene into quality protein maize inbred lines using molecular markers

Quality protein maize (QPM; Zea mays L.) has effectively enhanced levels of the amino acids, lysine, and tryptophan, over normal maize and provided balanced dietary protein for the health and development of monogastric animals and humans. However, as in normal maize, QPM varieties are low in provitamin A (ProVA), a precursor of vitamin A, which can lead to vitamin A deficiency in humans when maize is a significant part of their diet. In this study, maize inbred Hp321-1 carrying the favorable alleles crtRB1-5'TE-2 and crtRB1-3'TE-1 that can enhance levels of ProVA, was used as donor for improving ProVA in QPM inbred lines CML161 and CML171. Functional markers for identifying the favorable alleles crtRB1-5'TE-2 and crtRB1-3'TE-1 were used in foreground selection, and simple sequence repeat markers were used in background selection for the BC₁F₁, BC₂F₁, and BC₂F₂ generations. The background recovery rates were 77.4 and 84.5 % for CML161 and CML171 populations, respectively, in the BC₁F₁ generation, and 89.9 and 92.1 % in the BC₂F₂ generation. With foreground and background selection, the mean ProVA concentration has been improved from 1.60 µg g^-1 in the parent of CML161 to 5.25 µg g^-1 in its BC₂F₃ offspring, from 1.80 µg g^-1 in the parent of CML171 to 8.14 µg g^-1 in its BC₂F₃ offspring while maintaining similar QPM characteristics of the recurrent parents. The success from this study offers maize breeders a procedure for increasing ProVA in QPM lines, which will greatly mitigate vitamin A deficiency and protein-energy malnutrition in developing countries.