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Development of Maize Hybrids With Enhanced Vitamin-E, Vitamin-A, Lysine, and Tryptophan Through Molecular Breeding.

ABSTRACT: Malnutrition is a widespread problem that affects human health, society, and the economy. Traditional maize that serves as an important source of human nutrition is deficient in vitamin-E, vitamin-A, lysine, and tryptophan. Here, favorable alleles of vte4 (α-tocopherol methyl transferase), crtRB1 (β-carotene hydroxylase), lcyE (lycopene ε-cyclase), and o2 (opaque2) genes were combined in parental lines of four popular hybrids using marker-assisted selection (MAS). BC₁F₁, BC₂F₁, and BC₂F₂ populations were genotyped using gene-based markers of vte4, crtRB1, lcyE, and o2. Background selection using 81-103 simple sequence repeats (SSRs) markers led to the recovery of recurrent parent genome (RPG) up to 95.45%. Alpha (α)-tocopherol was significantly enhanced among introgressed progenies (16.13 μg/g) as compared to original inbreds (7.90 μg/g). Provitamin-A (proA) (10.42 μg/g), lysine (0.352%), and tryptophan (0.086%) were also high in the introgressed progenies. The reconstituted hybrids showed a 2-fold enhancement in α-tocopherol (16.83 μg/g) over original hybrids (8.06 μg/g). Improved hybrids also possessed high proA (11.48 μg/g), lysine (0.367%), and tryptophan (0.084%) when compared with traditional hybrids. The reconstituted hybrids recorded the mean grain yield of 8,066 kg/ha, which was at par with original hybrids (mean: 7,846 kg/ha). The MAS-derived genotypes resembled their corresponding original hybrids for the majority of agronomic and yield-related traits, besides characteristics related to distinctness, uniformity, and stability (DUS). This is the first report for the development of maize with enhanced vitamin-E, vitamin-A, lysine, and tryptophan.

SUBMITTER: Das AK

PROVIDER: S-EPMC8335160 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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 F1, BC1F1-BC3F1, and ICF1-ICF3), 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 BC3F1 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 ICF1-ICF3 generations. Further, these gene pyramided lines were examined for agronomic performance and the β-carotene, lysine, and tryptophan contents. Six ICF3 lines (DBT-IC-β1σ4-4-8-8, DBT-IC-β1σ4-9-21-21, DBT-IC-β1σ4-10-1-1, DBT-IC-β2σ5-9-51-51, DBT-IC-β2σ5-9-52-52 and DBT-IC-β2σ5-9-53-53) possessing crtRB1 and o2 genes showed better agronomic performance (77.78-99.31% for DBT-IC-β1σ4 population and 85.71-99.51% for DBT-IC-β2σ5 population) like the recurrent parents and β-carotene (14.21-14.35 μg/g for DBT-IC-β1σ4 and 13.28-13.62 μg/g for DBT-IC-β2σ5), lysine (0.31-0.33% for DBT-IC-β1σ4 and 0.31-0.34% for DBT-IC-β2σ5), and tryptophan (0.079-0.082% for DBT-IC-β1σ4 and 0.078-0.083% for DBT-IC-β2σ5) 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.

Project description:Traditional yellow maize though contains high kernel carotenoids, the concentration of provitamin A (proA) is quite low (<2 μg/g), compared to recommended level (15 μg/g). It also possesses poor endosperm protein quality due to low concentration of lysine and tryptophan. Natural variant of crtRB1 (β-carotene hydroxylase) and lcyE (lycopene-ε-cyclase) cause significant enhancement of proA concentration, while recessive allele, opaque2 (o2) enhances the level of these amino acids. Development of biofortified maize enriched in proA, lysine and tryptophan thus holds significance in alleviation of micronutrient malnutrition. In the present study, marker-assisted stacking of crtRB1, lcyE and o2 was undertaken in the genetic background of four maize hybrids (HQPM1, HQPM4, HQPM5, and HQPM7) popularly grown in India. HP704-22 and HP704-23 were used as donors, while four elite QPM parents viz., HKI161, HKI163, HKI193-1, and HKI193-2 were used as recipients. CrtRB1 showed severe segregation distortion, while lcyE segregated as per the expectation. Recovery of recurrent parent genome (RPG) among selected backcross progenies ranged from 89 to 93%. Introgressed progenies possessed high concentration of proA (7.38-13.59 μg/g), compared to 1.65-2.04 μg/g in the recurrent parents. The reconstituted hybrids showed an average of 4.5-fold increase in proA with a range of 9.25-12.88 μg/g, compared to original hybrids (2.14-2.48 μg/g). Similar plant-, ear-, and grain- characteristics of improved versions of both inbreds and hybrids were observed when evaluated with their respective original versions. Mean lysine (0.334%) and tryptophan (0.080%) of the improved hybrids were at par with the original versions (lysine: 0.340%, tryptophan: 0.083%). Improved hybrids also possessed similar grain yield potential (6,301-8,545 kg/ha) with their original versions (6,135-8,479 kg/ha) evaluated at two locations. This is the first study of staking crtRB1-, lcyE-, and o2-, favorable alleles in single genetic background. The improved inbreds can be effectively used as potential donor for independent and/or simultaneous introgression of crtRB1, lcyE, and o2 in the future breeding programme. These biofortified maize hybrids, rich in proA, lysine and tryptophan will hold great promise for nutritional security.

Project description:Genomic selection predicts the genomic estimated breeding values (GEBVs) of individuals not previously phenotyped. Several studies have investigated the accuracy of genomic predictions in maize but there is little empirical evidence on the practical performance of lines selected based on phenotype in comparison with those selected solely on GEBVs in advanced testcross yield trials. The main objectives of this study were to (1) empirically compare the performance of tropical maize hybrids selected through phenotypic selection (PS) and genomic selection (GS) under well-watered (WW) and managed drought stress (WS) conditions in Kenya, and (2) compare the cost-benefit analysis of GS and PS. For this study, we used two experimental maize data sets (stage I and stage II yield trials). The stage I data set consisted of 1492 doubled haploid (DH) lines genotyped with rAmpSeq SNPs. A subset of these lines (855) representing various DH populations within the stage I cohort was crossed with an individual single-cross tester chosen to complement each population. These testcross hybrids were evaluated in replicated trials under WW and WS conditions for grain yield and other agronomic traits, while the remaining 637 DH lines were predicted using the 855 lines as a training set. The second data set (stage II) consists of 348 DH lines from the first data set. Among these 348 best DH lines, 172 lines selected were solely based on GEBVs, and 176 lines were selected based on phenotypic performance. Each of the 348 DH lines were crossed with three common testers from complementary heterotic groups, and the resulting 1042 testcross hybrids and six commercial checks were evaluated in four to five WW locations and one WS condition in Kenya. For stage I trials, the cross-validated prediction accuracy for grain yield was 0.67 and 0.65 under WW and WS conditions, respectively. We found similar responses to selection using PS and GS for grain yield other agronomic traits under WW and WS conditions. The top 15% of hybrids advanced through GS and PS gave 21%-23% higher grain yield under WW and 51%-52% more grain yield under WS than the mean of the checks. The GS reduced the cost by 32% over the PS with similar selection gains. We concluded that the use of GS for yield under WW and WS conditions in maize can produce selection candidates with similar performance as those generated from conventional PS, but at a lower cost, and therefore, should be incorporated into maize breeding pipelines to increase breeding program efficiency.

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Development of Maize Hybrids With Enhanced Vitamin-E, Vitamin-A, Lysine, and Tryptophan Through Molecular Breeding.

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