Combining ability of maize inbred lines for productivity, agronomics, and nutritional content under different nitrogen fertilizer regimes.

Abstract

Maize is a staple crop in sub-Saharan Africa with an average per capita consumption of 100 kg per annum. Despite its importance, maize is rich in starch but deficient in other nutrients leading to malnutrition in many people that heavily depend on maize without other nutrient-rich complementary sources of food. The objectives of this study were to (i) assess genetic variation for agronomic traits, yield and nutritional content among maize inbred lines and hybrids under high and low soil nitrogen availability (ii) determine the combining ability of maize inbred lines and their crosses for agronomic traits, grain yield, and nutritional content, and (iii) deduce the gene action controlling the inheritance of these traits under low and high input conditions. Ten maize inbred lines consisting of five quality protein maize (QPM) and five normalendosperm maize (non-QPM) inbred lines were crossed using the Griffing’s diallel mating design. The resultant hybrids, their parental lines and three control varieties were evaluated under low and high soil nitrogen treatments across two seasons at two locations in South Africa. The hybrids and their inbred line parents exhibited significant genetic variation for plant height, ear height, anthesis days, silking days, anthesis to silking interval, grain moisture, shelling percentage, grain yield, protein, oil and starch content. There were significant genotype x environment interaction effects on grain yield, shelling percentage, grain moisture and anthesis to silking interval. On average, yield and agronomic performances were lower in QPM hybrids under low nitrogen conditions confirming their less adaptation to the low input conditions compared to their normal maize endosperm counterparts. The protein, oil and starch contents of maize decreased under low nitrogen conditions. Both the general (GCA) and specific (SCA) combining ability effects for grain yield, protein and oil contents were significant across nitrogen management conditions. The significance of GCA and SCA effects suggested that both additive and non-additive gene action were involved in the inheritance of grain yield, agronomic traits, protein, and oil content.