Maize Ideotypes for Sub-Saharan Africa.

Maize (Zea mays L.), the most important cereal crop for human food, livestock feed and industrial raw material in Africa, receives quality research attention from CIMMYT and IITA scientists in sub-Saharan Africa (SSA). The crop is adapted to a wide range of environments although its production is constrained by many abiotic and biotic stresses, some of which are cross-cutting while others are limited to specific niches. For optimum productivity, therefore, breeders must develop maize ideotypes targeted to specific environmental conditions. However, an ideotype for all environments in sub-Saharan Africa must be tolerant of (i) moisture stress occurring at any growth stage, (ii) low soil nutrient, particularly nitrogen, and (iii) relatively high plant density. Studies conducted in southern, eastern, central and west Africa consistently showed that genotypes selected under stress conditions such as low soil N and drought had value addition when evaluated under non-stress conditions. Selections under non-stress evaluated under stress conditions were not desirable. Some other important traits for SSA maize ideotype are vigorous growth at the seedling and early vegetative growth stages, synchronized nicking of anthesis and silking, relatively long grain-filling period, delayed senescence, and upright orientation of leaves, especially above the top ear. Ideotypes for specific niches may require additional traits. For example, varieties for all ecologies in west Africa must be resistant to the streak virus whereas those for some savanna ecology need to be resistant or tolerant to Striga hermonthica (Del.) Benth. For the east African region, maize lethal necrosis (MLN) disease is a new challenge to maize production, and appreciable levels of resistance to the disease is an added requirement for new varieties to be released. Maize breeders in national programs may exploit the available germplasm at IITA-Ibadan, Nigeria and CIMMYT-Nairobi, Kenya to develop ideotypes for the niches of their operation.