Research Brief: Akintunde Adewole
Advancing Pro-Vitamin A Maize for Higher Yield and Nutritional Security in Southwest Nigeria
Background
Maize (Zea mays L.) is a major staple and industrial crop in Nigeria and an important source of food, income, and raw materials. However, increasing demand for maize requires varieties that combine high productivity with improved nutritional quality and reliable performance across diverse production environments. Pro-vitamin A (PVA) maize offers an opportunity to address both challenges by increasing dietary intake of carotenoids that can contribute to vitamin A nutrition while maintaining the agronomic attributes required by farmers.
What the Study Investigated
This study focused on the genetic improvement of tropical-adapted PVA maize through an integrated assessment of genetic diversity, combining ability, heterosis, and genotype × environment interaction. Thirty-one maize inbred lines obtained from the International Institute of Tropical Agriculture (IITA) were initially evaluated at the Institute of Agricultural Research and Training, Ibadan, during the 2021 cropping season. The lines were assessed for agronomic performance, yield, and disease responses, while functional molecular markers were used to identify lines carrying favourable alleles associated with PVA. Six selected inbred lines were subsequently crossed with ten elite open-pollinated varieties using a line × tester mating design, producing 60 topcross hybrids. The hybrids, together with their parents and checks, were evaluated at four locations; Ibadan, Ilora, Kishi, and Orin-Ekiti in the 2023 cropping season. Statistical and genetic analyses were used to determine the extent of genetic variation, parental combining ability, heterosis, and hybrid stability across environments.
Key Findings
The study revealed substantial genetic diversity among the 31 PVA maize inbred lines. Grain yield ranged from 0.15 to 2.73 t ha⁻¹, with several inbred lines averaging more than 100 t ha-1 among the highest-yielding inbreds. Molecular marker analysis identified six lines carrying favourable alleles for PVA, while morphological and SSR-based analyses grouped the germplasm into four clusters, confirming useful genetic differentiation for breeding.
The 60 topcross hybrids showed considerably greater productivity, with grain yield ranging from 4.44 to 8.53 t ha⁻¹. F₈ × M₆, F₂ × M₆, F₁ × M₅, F₂ × M₃, and F₈ × M₂ were among the most promising hybrids for grain yield. Two male parent lines were identified as superior general combiners, while F₆ × M₂ and F₈ × M₂ expressed high specific combining ability. Substantial heterosis was also recorded, with F₄ × M₄ and F₃ × M₄ exhibiting the highest mid-parent and better-parent heterosis, respectively.
Significant genotype × environment interaction demonstrated that hybrid performance varied across locations. AMMI and GGE biplot analyses identified hybrids with favourable combinations of yield and stability, while Ilora emerged as the most discriminating test environment. The analyses also showed that some hybrids had broader adaptation, whereas others exhibited stronger responses to particular environments.
Implications for Maize Improvement
The findings demonstrate the value of integrating molecular selection for provitamin A, genetic diversity analysis, combining ability, heterosis exploitation, and multi-environment testing in maize improvement. The study identifies promising parental materials and hybrids that can serve as candidates for further breeding and evaluation. Based on their combined yield performance and stability, G28 (F₈ × M₂), G37 (F₇ × M₃), G45 (F₅ × M₄), G49 (F₉ × M₄), G29 (F₉ × M₂) and G50 (F₁₀ × M₅) are recommended for further multi-location and multi-season testing. Their continued evaluation could contribute to the development of productive, nutritionally enhanced, and environmentally adaptable PVA maize hybrids for Southwest Nigeria and similar tropical production environments.
