Genotype and environmental effects on maize grain yield, nutritional value and milling quality
Khajoane, Tsietso Jeanett
University of the Free State
In sub-Saharan Africa and other regions in the world, many people rely on maize as their primary food. To guarantee food security, high yielding and nutritious maize hybrids must be bred. Breeding for increased maize grain yield, nutritional quality traits and milling quality allows diversification and an increase in maize production. It also helps in the alleviation of malnutrition in countries that rely on maize as their dietary source. This research was conducted in order to: 1) determine the genotype and environmental effects on maize grain yield, nutritional quality traits, and milling quality, 2) determine the interrelationship among grain yield, nutritional quality traits and milling quality in maize genotypes and 3) to evaluate genotype by environment interaction for grain yield and to determine the grain yield stability of maize hybrids. Eighteen maize genotypes (nine commercial and nine experimental hybrids) were planted using a randomized complete block design (RCBD), replicated six times at seven sites representing the diverse agro-ecologies where maize is predominantly grown in South Africa. Genotype and genotype by environment interaction effects were highly significant (P ≤ 0.001) for all traits, indicating the existence of variability in the maize breeding populations. On average, broad sense heritability (H²) of nutritional quality traits, milling quality and defective grain (DEFG) ranged from 30.86 to 82.50%, which indicated that the phenotypic differences were mostly attributed to genotypic effects. Low H² (17.63%) for grain yield was observed, which indicated that phenotypic differences observed were mostly attributed to environmental factors. High performing genotypes were identified, such as G15-Ex (grain yield, fat and milling quality), G16-Ex (protein and low moisture), G11-Ex (starch) and G14-Ex (fibre). Genotype G2-C and G4-Ex had low mean values for DEFG. The findings in this study provided variation that can be exploited in breeding programmes to improve maize. Significant and positive correlation was found for protein content with grain yield, indicating that these traits could be selected and improved simultaneously. Milling quality was positively correlated with grain yield, protein, fat and low moisture, indicating that multiple trait selection would be possible. Starch was negatively associated with protein content and grain yield, suggesting that the improvement of starch will have a negative effect on maize grain yield and protein content. The clustered heat map identified three clusters of maize hybrids, which were 1) G1-C, G7-C, G9-C, G13-Ex, G14-Ex, G16-Ex and G17-Ex, associated with high protein and fibre content, 2) G4-Ex, G5-C, G6-C, G8-C and G11-Ex, associated with high grain yield, fat, moisture and fibre content and 3) G3-C, G10-C, G12-Ex, G15-Ex and G18-Ex, associated with high milling quality and fat content. Additive main effects and multiplicative interaction analysis (AMMI) identified experimental genotypes G4-Ex, G15-Ex and G17-Ex as high yielding and the most stable genotypes, which suggested that these genotypes have broad adaptation. Genotypes G8-C and G11-Ex were high yielding but unstable. The GGE scatter plot identified high yielding genotypes that showed specific (G2-C, G7-C, G8-C, G16-Ex and G17-Ex) and broad (G1-C, G4-Ex, G13-Ex and G15-Ex) adaptation in test environments and revealed two mega environments. Therefore, testing maize genotypes in different environments is important to determine their adaptability and stability before cultivar release and recommendation for commercial production. Maize hybrids with improved grain yield and nutritional quality may be used to alleviate challenges associated with malnutrition.
Dissertation (M.Sc.(Plant Breeding))--University of the Free State, 2022
Maize, grain yield, nutritional quality traits, milling quality, broad sense heritability, variability, correlations, stability, adaptation, genotypes by environment interaction