Development of tryptophan rich maize lines through simple sequence repeat marker aided introgression of opaque2 trait

Maize is the main staple food of the world but it is nutritional deficient due to the scarcity of two essential amino acids viz., lysine and tryptophan. Under this study, opaque2 gene from QPM donor (CML-169) was transferred into normal maize (BAJIM-08-26) through marker aided backcross breeding method. The opaque2 specific SSR marker (phi057) was used for foreground selection in BC1 F1 and BC2 F1 generations. The heterozygous offspring were self-pollinated to produce the BC2 F2 generation. Further plants on the basis of 25% opaqueness were selected and selfed to develop BC2 F3 and BC2 F4 progenies. The background selection using a series of SSR markers showed 97% recovery in the recurrent parent genome of backcrossed generation. Tryptophan content and total protein in the endosperm of BC2 F4 progenies were  found to be ranged from 0.75 to 0.93% and 7.0 to 9.6 %, respectively. As an outcome, three promising MAS derived QPM lines viz., B76-22-2, B70-5-8 and B42-3-1 were developed that showed a high percentage of tryptophan, grain yield and recovery of recurrent parent genome. The  worldwide problem of protein malnutrition could be improved by adopting a molecular breeding approach for the development of nutritionally rich maize over the normal maize.