Development of β-carotene, lysine, and tryptophan-rich maize (Zea mays) inbreds through marker-assisted gene pyramiding

Maize (Zea mays L.) is the leading cereal crop and staple food in many parts of the world. This study aims to develop nutrient-rich maize genotypes by incorporating crtRB1 and o2 genes associated with increased β-carotene, lysine, and tryptophan levels. UMI1200 and UMI1230, high quality maize inbreds, are well-adapted to tropical and semi-arid regions in India. However, they are deficient in β-carotene, lysine, and tryptophan. We used the concurrent stepwise transfer of genes by marker-assisted backcross breeding (MABB) scheme to introgress crtRB1 and o2 genes. In each generation (from F(1), BC(1)F(1)–BC(3)F(1), and ICF(1)–ICF(3)), foreground and background selections were carried out using gene-linked (crtRB1 3′TE and umc1066) and genome-wide simple sequence repeats (SSR) markers. Four independent BC(3)F(1) lines of UMI1200 × CE477 (Cross-1), UMI1200 × VQL1 (Cross-2), UMI1230 × CE477 (Cross-3), and UMI1230 × VQL1 (Cross-4) having crtRB1 and o2 genes and 87.45–88.41% of recurrent parent genome recovery (RPGR) were intercrossed to generate the ICF(1)-ICF(3) generations. Further, these gene pyramided lines were examined for agronomic performance and the β-carotene, lysine, and tryptophan contents. Six ICF(3) lines (DBT-IC-β(1)σ(4)-4-8-8, DBT-IC-β(1)σ(4)-9-21-21, DBT-IC-β(1)σ(4)-10-1-1, DBT-IC-β(2)σ(5)-9-51-51, DBT-IC-β(2)σ(5)-9-52-52 and DBT-IC-β(2)σ(5)-9-53-53) possessing crtRB1 and o2 genes showed better agronomic performance (77.78–99.31% for DBT-IC-β(1)σ(4) population and 85.71–99.51% for DBT-IC-β(2)σ(5) population) like the recurrent parents and β-carotene (14.21–14.35 μg/g for DBT-IC-β(1)σ(4) and 13.28–13.62 μg/g for DBT-IC-β(2)σ(5)), lysine (0.31–0.33% for DBT-IC-β(1)σ(4) and 0.31–0.34% for DBT-IC-β(2)σ(5)), and tryptophan (0.079–0.082% for DBT-IC-β(1)σ(4) and 0.078–0.083% for DBT-IC-β(2)σ(5)) levels on par with that of the donor parents. In the future, these improved lines could be developed as a cultivar for various agro-climatic zones and also as good genetic materials for maize nutritional breeding programs.