Combining Ability and Heterosis for Endosperm Carotenoids and Agronomic Traits in Tropical Maize Lines.

Girum Azmach,Charles Spillane,Abebe Menkir,Melaku Gedil

doi:10.3389/fpls.2021.674089

Abstract

Provitamin A enrichment of staple crops through biofortification breeding is a powerful approach to mitigate the public health problem of vitamin A deficiency in developing countries. Twenty-four genetically diverse yellow and orange endosperm maize inbred lines with differing levels of provitamin A content were used for the analysis of their combining ability. Each inbred line was developed from crosses and backcrosses between temperate and tropical germplasm. The inbred lines were grouped into different sets according to their provitamin A levels and were then intercrossed in a factorial mating scheme to generate 80 different single-cross hybrids. The hybrids were evaluated in field trials across a range of agroecological zones in Nigeria. The effect of hybrids was significant on all the measured provitamin A and non-provitamin A carotenoids and agronomic traits. While the effect of genotype-by-environment (GxE) interaction was significant for almost all traits, it was a non-crossover-type interaction for carotenoid content. Partitioning of the variances associated with the carotenoid and agronomic traits into their respective components revealed the presence of significant positive and negative estimates of general combining ability (GCA) and specific combining ability (SCA) effects for both carotenoid content and agronomic traits. The preponderance of GCA effects indicates the importance of additive gene effects in the inheritance of carotenoid content. We found F1 hybrids displaying high parent heterosis for both provitamin A content and agronomic performance. Our study demonstrates that provitamin A biofortification can be effectively implemented in maize breeding programs without adverse effects on important agronomic traits, including grain yield.

Highlights

Hidden hunger or micronutrient deficiency remains a serious global public health problem
Spearman’s rank correlation analysis showed significant (p < 0.0001) positive pairwise correlations between pairs of environments for the concentration of each carotenoid, indicating that the environment-by-F1 hybrid interaction for carotenoids was not of the cross-over type, which means that genotypes did not differ in their relative carotenoid content with environmental changes
The strong impact of genetic effects on carotenoid variability was further confirmed by our estimates of heritability, which ranged from 57% for αcarotene to 95% for lutein in the parent trial, and 57% for αcarotene to 92% for β-cryptoxanthin in the F1 hybrid trial

Summary

Introduction

Hidden hunger or micronutrient deficiency remains a serious global public health problem. Biofortification of staple crops can be used to reduce the micronutrient deficiency burden in poorer communities. Biofortification is the application of conventional breeding and modern biotechnology to develop staple food crops with increased concentrations of bioavailable micronutrients in the edible parts of crops (Nestel et al, 2006; Miller and Welch, 2013). Maize Combining Ability for Carotenoid & Agronomic Traits people in the developing world. Maize is naturally endowed with the ability to accumulate carotenoids in the endosperm, the widely cultivated maize that is used for human consumption is deficient in provitamin A (Ranum et al, 2014). A range of maize biofortification breeding initiatives have developed and used maize inbred lines with high level of endosperm provitamin A to develop hybrids (Azmach et al, 2013; Babu et al, 2013; Pixley et al, 2013)

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