Abstract
Maize is the predominant food source for the world population, but lack of lysine and tryptophan in maize endosperm cannot fulfill the nutritional requirements of humans. Hence, the improvement of lysine and tryptophan content is the ultimate goal of maize biofortification programs. In the present study, the marker-assisted backcross (MABC) breeding strategy was used to enhance the lysine and tryptophan content of the elite maize inbred line UMI1230 by introgressing opaque 2 (o2) gene from the VQL1. During the transfer of the gene into UMI1230, SSR marker umc1066 tightly associated with o2 used for foreground selection. Background recovery was estimated using 168 SSR markers. Phenotype screening for morphological traits was adopted to choose plants parallel to UMI1230. As a result, four BC(2)F(3) improved lines (DBT5-1-14/25-5/25-8/25-8/25, DBT5-1-14/25-5/25-8/25-7/25, DBT5-1-14/25-5/25-8/25-10/25 and DBT5-1-14/25-5/25-8/25-12/25) with o2 were developed. The improved line's background genome recovery varied between 90.60 and 94.80%. Also, the improved lines had better agronomic performance along with increased lysine (0.311-0.331%) and tryptophan (0.040-0.048%) contents. In summary, the MABC breeding strategy has successfully improved the levels of lysine and tryptophan in UMI1230 without affecting agronomic performance. The improved line's hold great potential as donors in biofortification programs in maize.