Heterotic Patterns of IITA and CIMMYT Early-Maturing Yellow Maize Inbreds under Contrasting Environments

1321 Promotion and wide adoption of early-maturing cultivars developed by IITA and partners have signifi cantly contributed to the rapid spread of maize into the savannas of WA, making it the most important cereal crop aft er rice (Oryza sativa L.). However, production in the savanna agro-ecology is severely constrained by low-N and recurrent drought. Drought and low-N stresses constitute the most important factors frequently limiting maize production, food security, and economic growth in sub-Saharan Africa (Banziger et al., 2006). Edmeades et al. (1995) reported an annual maize yield loss of 15% from drought stress in the savanna of West and central Africa (WCA) and indicated that localized losses might be much higher in the marginal areas where the annual rainfall is below 500 mm and soils are sandy or shallow. However, the grain yield losses could be higher if drought occurs at the fl owering and grain-fi lling periods (NeSmith and Ritchie, 1992). Estimated yield losses from low-N stress alone vary from 10 to 50% (Wolfe et al., 1988) in WA and are attributable to inadequate or no application of inorganic fertilizer by farmers and rapid mineralization of organic matter in the soil (McCown et al., 1992; Banziger and Lafi tte, 1997). In addition to drought and low-N stresses, infestation by a parasitic weed, Striga hermonthica (Del.) Benth is a major constraint to maize production in the savannas of WA. In the farmer’s fi eld, drought, Striga infestation, and soil nutrient defi ciency can occur simultaneously, with a devastating combined eff ect (Cechin and Press, 1993; Kim and Adetimirin, 1997; Badu-Apraku et al., 2011b). Th erefore, maize varieties targeted to the Striga-prone areas of WCA must also be resistant or at least tolerant to drought and low-N. Heterotic Patterns of IITA and CIMMYT Early-Maturing Yellow Maize Inbreds under Contrasting Environments