Incorporation of opaque-2 into ‘UMI 1200’, an elite maize inbred line, through marker-assisted backcross breeding

Maize is an important agricultural plant valued for its productivity and nutritive qualities. However, a deficiency of two essential amino acids (lysine and tryptophan) significantly reduces the nutritional quality of maize proteins. The recessive opaque-2 (o2) mutant has a greater content of lysine and tryptophan in their endosperm proteins and their bioavailability is better. Therefore, marker-assisted backcross breeding (MABB) was attempted to incorporate the o2 allele from the donor line VQL 1 into the genetic background of UMI 1200 to develop quality protein maize (QPM) lines. Foreground selection for the gene o2 was effected using tightly linked molecular marker umc1066, in UMI 1200 x VQL 1 backcross series. Further, background selection was done together with stringent phenotypic selection for agronomic traits, to accelerate recurrent parent phenome recovery. As a result, three advanced QPM maize lines (DBT 4-1-1/25-10/25-10/25-16, DBT 4-1-1/25-10/25-17/25-11 and DBT 4-1-1/25-10/25-17/25-13) carrying the opaque-2 allele in a homozygous state, similar to VQL 1 were developed. The lysine and tryptophan content of these lines ranged from 0.35% to 0.40% and 0.03 to 0.05%, respectively, which is on par with the VQL 1. Background analysis using 250 simple sequence repeats (SSRs) revealed up to 97% recurrent parent genome recovery. In conclusion, the newly developed QPM lines can be used in future maize breeding programmes to improve the nutritional traits.