Baffour Badu-Apraku, Maize Improvement Unit, International Institute of Tropical Agriculture-Nigeria, Ibadan, Nigeria, Talabi Abidemi, Maize Improvement Unit, IITA, Ibadan, Nigeria and Michael Aderounmu, Maize Improvement Unit, International Institute of Tropical Agriculture, Ibadan, Nigeria
Maize (Zea mays L.) has a critical nutritional role to play in sub-Saharan Africa (SSA) as the most important staple food crop with kernels containing vitamins, carbohydrates, essential minerals and proteins. The white endosperm maize varieties which are the most preferred types for human consumption in SSA are deficient in provitamin A while the yellow varieties contain less than 2 μg g−1 of provitamin A. Besides the problem of lack of provitamin A, maize production is constrained by Strigahermonthica parasitism, drought and low soil nitrogen (low-N). Therefore, the development and commercialization of stress tolerant provitamin A maize is crucial to the fight against malnutrition in SSA. One hundred and thirty-two extra-early provitamin A maize hybrids derived from crosses between 33 extra-early provitamin A inbreds and four extra-early inbred testers were evaluated under multiple stress (Striga infestation, drought and low-N) and non-stress environments in Nigeria, 2015-2016. The objectives of the study were to: (i) estimate general combining ability (GCA) and specific combining ability (SCA) effects of grain yield and other traits of the extra-early maturing provitamin A inbreds (ii) classify the inbreds into heterotic groups using the general combining ability of multiple traits (HGCAMT) method (iii) identify provitamin A inbred testers and (iv) assess the performance of the extra-early maturing F1 provitamin A hybrids under multiple stress and non-stress environments. Results revealed preponderance of additive genetic variance over the non additive for grain yield and other traits under multiple stress, optimal and across environments. The inbreds TZEEIOR 30, TZEEIOR 41, TZEEIOR 42, TZEEIOR 97, TZEEIOR 109 and TZEEIOR 140 possessed genes for multiple stress tolerance and Provitamin A and could be used to develop stress tolerant hybrids with high provitamin A and also could be introgressed into tropical maize populations to improve the levels of provitamin A. The HGCAMT method classified the inbreds into five groups under multiple stresses and three groups each under optimal and across environments. The inbreds TZEEIOR 197 and TZEEIOR 30 were identified as testers for heterotic groups 1 and 2, while no tester was identified for heterotic group 3. The hybrids TZEIOR 197 x TZdEEI 12 and TZEIOR 123 x TZdEEI 7 were the most stable and high yielding across multiple stress and non-stress environments and should be tested on-farm to confirm consistency of performance and commercialized in SSA.