Molecular Breeding for Nutritionally Enriched Maize: Status and Prospects

Abstract

Maize is a major source of food security and economic development in sub-Saharan Africa (SSA), Latin America, and the Caribbean, and is among the top three cereal crops in Asia. Yet, maize is deficient in certain essential amino acids, vitamins, and minerals. Biofortified maize cultivars enriched with essential minerals and vitamins could be particularly impactful in rural areas with limited access to diversified diet, dietary supplements, and fortified foods. Significant progress has been made in developing, testing, and deploying maize cultivars biofortified with quality protein maize (QPM), provitamin A, and kernel zinc. In this review, we outline the status and prospects of developing nutritionally enriched maize by successfully harnessing conventional and molecular marker-assisted breeding, highlighting the need for intensification of efforts to create greater impacts on malnutrition in maize-consuming populations, especially in the low-and middle-income countries. Molecular marker-assisted selection methods are particularly useful for improving nutritional traits since conventional breeding methods are relatively constrained by the cost and throughput of nutritional trait phenotyping.

Assessing Effect of Marker-Based Improvement of Maize Synthetics on Agronomic Performance, Carotenoid Content, Combining Ability and Heterosis

“…Although the genetic basis of heterosis is yet to be unraveled [54], [33] attributed heterosis for maize carotenoids to being influenced by QTLs' affecting the total flux through the carotenoid biosynthesis pathway as well as QTLs that favor flux to one branch of the pathway over the other branch. Based on the results of the current study, continuous selection for favorable alleles of β-carotene, β-cryptoxanthin of the β-branch of the pathway with corresponding reduction of flux into the α-branch could further increase heterosis of provitamin A in the maize varietal-cross hybrids [2,8,55].…”

“…Maize is the second most widely grown cereal in the world next to wheat, with an estimated total production of over one billion tons per annum [1]. Maize and its products constitute 30% of the food supply in the Americas, 38% in Africa and 6.5% in Asia [2]. It is the most important staple crop widely consumed in sub-Saharan Africa (SSA) supplying daily energy, protein and mineral nutrients.…”

Eleven biosynthetic genes explain the majority of natural variation for carotenoid levels in maize grain

“…This finding is reinforced by the positive pleiotropy observed at lcyE, dxs2, and psy1 for the two traits. Given that only crtRB1 and in some cases lcyE are currently in use in marker-assisted selection efforts for βcarotene/provitamin A (BABU et al 2013, PRASANNA et al 2020, incorporating this set of additional major-effect genes in selection decisions is likely to provide substantial gains for both β-carotene and β-cryptoxanthin. While higher heritability was observed for α-carotene in this study than in a smaller inbred diversity panel (OWENS et al 2014), only two large-effect QTL, lcyE and dxs2, were detected that explained 63.9% of variation attributed to QTL for α-carotene.…”

The Application of Metabolomics for the Study of Cereal Corn (Zea mays L.)

“…In contrast to the observations on corn phenolic compounds, several investigations from different continents have focused their attention on the characterization of carotenoids in worldwide corn biodiversity. Corn has been targeted as one of the major crops for provitamin A enrichment, and important global initiatives such as the HarvestPlus and CYMMIT programs have focused on obtaining high-provitamin-A corn cultivars through conventional and molecular breeding strategies [99,100]. The main objective of the HarvestPlus program (2003-2016) was to develop high-yielding provitamin-A-enriched corn cultivars with proven efficiency in reducing vitamin A deficiency that is profitable to farmers and acceptable to the consumers [100,101].…”

“…Corn has been targeted as one of the major crops for provitamin A enrichment, and important global initiatives such as the HarvestPlus and CYMMIT programs have focused on obtaining high-provitamin-A corn cultivars through conventional and molecular breeding strategies [99,100]. The main objective of the HarvestPlus program (2003-2016) was to develop high-yielding provitamin-A-enriched corn cultivars with proven efficiency in reducing vitamin A deficiency that is profitable to farmers and acceptable to the consumers [100,101]. Targeted metabolomics have revealed that carotenoids are mostly concentrated in the endosperm and that overall orange-pigmented varieties show the highest carotenoids levels (Table 4).…”