Maize (Zea mays L.) is the most important cereal crop on which many smallholder farmers in sub-Sahara Africa (SSA) depend on as a sole source of calories, proteins, and vitamins. However, conventional maize is deficient in two essential amino acids, lysine, and tryptophan. Thereafter, Quality Protein Maize (QPM) developed to combat protein malnutrition. In SSA low soil nitrogen is also the most limiting factor in maize production and productivity. To determine the combining ability of QPM inbred lines for grain yield and other agronomic traits under low and optimum N environments, 121 genotypes generated using 11 QPM inbred lines in a complete diallel mating design with 5 checks were evaluated under both low and optimum N environments at 3 locations in the 2018 cropping season. Significant differences were observed among the genotypes for major characters under both low and optimum N environments. Under low and optimum N environments, non-additive gene actions were more important than additive gene action for grain yield, number of ears per plant, plant and ear height, ear length and diameter. Under low N environments, more contributions of reciprocal effects than GCA effects were observed for number of ears per plant, plant aspect, ear diameter. Parental lines TL156579, TL156583, and TL148288 were considered as a good general combiner for grain yield under low N environments. Parental line TL156612 showed higher positive GCA effects when used as female while parental line TL156612 showed higher negative GCA effects when used as a male parent for grain yield under low N environments.
Key words: Complete diallel, general combining ability, low soil nitrogen, lysine, optimum soil nitrogen, quality Protein maize, reciprocal effect, tryptophan.
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