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

Abstract

Vitamin A deficiency (VAD) is a serious problem in sub-Saharan Africa (SSA) and other parts of the world. Understanding the effect of marker-based improvement (MARS) of two maize synthetics (HGA and HGB) representing different heterotic groups on their agronomic performance, carotenoid content, and combining abilities could help identify suitable sources to develop divergent inbred lines for optimizing heterosis. This study involved three selection cycles each of the two synthetics and their nine varietal-cross hybrids together with a released check variety was conducted across four diverse locations in Nigeria in 2018 and 2019. Environment and hybrid effects were significant on grain yield and other agronomic traits as well as provitamin A content and other carotenoids. Genetic improvement per cycle of MARS in the parental synthetics was 15% for provitamin A, 25% for β-carotene and 26% for lutein in HGA and 4% for grain yield, 3% for zeaxanthin and 5% for α-carotene in HGB. Grain yield and agronomic traits of the two maize synthetics were controlled by additive and non-additive gene effects, while provitamin A content and other carotenoids were mainly controlled by additive gene effects. Some selection cycles which were high in grain yield and provitamin A content were identified as potential sources of new and divergent maize inbred lines in maize breeding programs. Some varietal-cross hybrids expressed significant mid-parent heterosis for grain yield and moderate mid-parent heterosis for provitamin A, β-carotene and xanthophylls. These hybrids could be commercialized at reasonable prices to small-scale farmers in rural areas that are most affected by vitamin A deficiency.

Improving the Carotenoid Content in Maize by Using Isonuclear Lines

“…Maize with a high carotenoid content is an ideal source for carotenoid consumption in human and animal nutrition, as it usually contains lutein and zeaxanthin as major pigments [6]. Yellow and orange maize grains accumulate several carotenoids (α-carotene, β-carotene and β-cryptoxanthin) which can be transformed into vitamin A in the human body [7,8]. Lutein and zeaxanthin have antioxidant properties, and they accumulate in the retinal macula as they are also involved in vision process [9]; these carotenoids may help reduce the risk of certain types of cancer, particularly those of the breast and lung, and have a potential contribution to the prevention of heart disease and stroke [10], UV-induced skin damage, coronary heart disease [11], cataracts and macular degeneration [9,12,13].…”

“…Marker-assisted selection was also used in order to improve the carotenoid content of some maize genotypes, by identifying the presence of favorable alleles crtRB1 and lcyE, followed by introgression of the genes through backcrosses [8,[34][35][36][37][38][39][40][41]. These studies used the backcross method, but for a smaller number of generations than were used in the present study.…”

Effects of drought stress on grain yield, agronomic performance, and heterosis of marker-based improved provitamin-A maize synthetics and their hybrids

“…The rapid change in weather patterns, the projected rising temperatures and uncertainties in rainfall patterns associated with the current trend of climate change will further heighten the intensity and frequency of drought in many parts of Africa, including the corn belt of Nigeria (Badu-Apraku et al 2011a;FAO 2013;Masih et al 2014;Shiferaw et al 2014). Therefore, enhancing food security and farmers' livelihoods in SSA require an improvement in the resilience of crops to drought (Menkir et al 2020).…”

“…To promote farmers' adoption of biofortified maize, varieties with enhanced provitamin A content should combine high yield potential with stable performance across a broad range of growing conditions (Mengesha et al 2019). Maize breeders at the International Institute of Tropical Agriculture (IITA), Ibadan, have developed two marker-based provitamin A-enriched maize synthetics (HGA and HGB) belonging to different heterotic groups (Astatke 2018;Iseghohi et al 2020). The maize synthetics, their selection cycles and varietal-cross hybrids were evaluated across eight environments in Nigeria and were found to be stable in grain yield and content of major carotenoids (Iseghohi et al 2020).…”

“…Maize breeders at the International Institute of Tropical Agriculture (IITA), Ibadan, have developed two marker-based provitamin A-enriched maize synthetics (HGA and HGB) belonging to different heterotic groups (Astatke 2018;Iseghohi et al 2020). The maize synthetics, their selection cycles and varietal-cross hybrids were evaluated across eight environments in Nigeria and were found to be stable in grain yield and content of major carotenoids (Iseghohi et al 2020). However, their responses under drought stress have not been evaluated.…”