Genetic analysis of grain yield and related traits of extra-early orange maize inbred lines and their hybrids under drought and rain-fed conditions

Abstract

Background: Orange maize genotypes are sources of provitamin A (PVA) carotenoids, which are precursors of vitamin A. PVA deficiency and drought constitute major challenges causing increasing food and nutritional insecurity in sub-Saharan Africa (SSA). Breeding of drought-tolerant provitamin A hybrid maize can mitigate these challenges. This study was undertaken to determine the combining ability of newly developed extra-early orange inbreds for grain yield and related traits under managed drought stress and rain-fed conditions, determine the mode of gene action conditioning the inheritance of the traits, and classify the inbreds into heterotic groups.

Methodology: One hundred and ninety-six extra-early orange hybrids comprising 180 testcrosses, 10 single crosses, and 6 commercial checks were evaluated under managed drought and rain-fed conditions at Ikenne. In addition, 41 inbreds comprising 36 orange lines and 5 PVA testers involved in the hybrid development were assessed under drought and rain-fed conditions.

Results: The means square for general combining ability (GCA) and specific combining ability (SCA) were significant for grain yield and most other traits under both growing conditions. The contributions of GCA to performance were larger than SCA in each growing condition. Broad-sense and narrow-sense heritability estimates for grain yield were 66% and 37% under managed drought and 88% and 32% under rain-fed conditions, respectively. Mid-parent heterosis and better-parent heterosis for grain yield were 338% and 247% under managed drought, while 173% and 137% under rain-fed conditions. Significant positive correlations existed among grain yield of hybrids, heterosis, and specific combining ability under managed drought. The 41 inbred lines were classified into three heterotic groups under both growing conditions. Sixteen testcross hybrids out-yielded the best commercial check under managed drought.

Conclusion: The testcross hybrids have great potential for commercialization to address the problem of drought and PVA deficiency in SSA. Inbred TZEEIOR 510 showed desirable GCA effects for grain yield and 04 other traits under drought.

Keywords: drought stress; general combining ability; genetic distance; heterosis; specific combining ability.

Figure 1

Proportion of additive (GCA) and non-additive (SCA) genetic variances for grain yield and other agronomic traits under managed drought and rain-fed conditions. GCA, general combining ability; SCA, specific combining ability, MD, managed drought; WW, well-watered=rain-fed; GY, grain yield; ASI, anthesis-silking interval; PHT, plant height; EHT, ear height; PASP, plant aspect; EASP, ear aspect; EPP, ear per plant; HCV, husk cover; DP, days to 50% pollen shed; DS, days to 50% silking; STGC, stay green characteristic.

Figure 2

Heterotic group of 41 inbreds comprised 36 inbreds and 5 standard inbred testers under managed drought stress using the HGCAMT grouping method. Cluster 1 (Red), Cluster 2 (Blue), and Cluster 3 (Green).

Figure 3

Heterotic group of 41 inbreds comprised 36 inbreds and 5 standard inbred testers under rain-fed conditions using the HGCAMT method. Cluster 1 (Red), Cluster 2 (Green), and Cluster 3 (Blue).

Figure 4

Comparison of heterotic groups of inbred lines using HGCAMT method under rain-fed and managed drought stress conditions. The black line in between the two dendrograms represent mismatched inbred lines while the red line are inbreds in the same position (perfect alignment) across both clusters and the green represent good a matched of inbred lines._: TZEEIOR; Well-watered=rain-fed.