Genetic Analysis of Grain Yield and Other Traits of Extra-Early Yellow Maize Inbreds and Hybrid Performance Under Contrasting Environments.

Maize (Zea mays L.) is a major staple crop in West and Central Africa (WCA) but production is constrained by Striga hermonthica parasitism and recurrent drought in the savannas where maize yield potential is highest due to low night temperatures, high solar radiation and low incidence of diseases. Total yield loss may result from severe Striga infestation while yield reduction from drought stress at flowering and grain filling may be as high as 40-90%. The two stresses occur simultaneously; therefore, the International Institute of Tropical Agriculture (IITA), Nigeria has developed extra-early Striga resistant and drought tolerant populations, inbreds, and varieties to combat the threats posed by the two stresses. Two studies were conducted for 2 yr at 5 locations in Nigeria to determine the combining ability of seven extra-early yellow-grained inbreds, place them into heterotic groups, identify best testers and superior single-cross hybrids under Striga-infested, drought stress at flowering and grain filling, optimal and across environments. Results showed that general combining ability (GCA) and specific combining ability (SCA) mean squares were significant for grain yield and most other traits across research environments. Similarly, The GCA mean squares were larger than those of SCA in all environments, indicating that additive gene action is more important in inheritance of traits. Three testers (TZEEI 79, TZEEI 76 and TZEEI 63) and opposing heterotic groups were identified across environments. TZEEI 79 had the highest positive GCA effects across environments. The best extra-early hybrid  TZEEI 79 x TZEEI 63  under drought stress and  TZEEI 82 x TZEEI 79 under Striga infestation,  out-yielded the best open-pollinated early checks by 3%  and 12%, respectively. TZEEI 79 x TZEEI 76 was the highest yielding and most stable hybrid across environments. In conclusion, the available extra-early maize germplasm are not only drought escaping but also possess drought tolerant genes.