Growth Indices and Grain Yield Attributes in Six Maize Cultivars Representing Two Era of Maize Breeding in Nigeria

Growth parameters such as seedling germination attributes, crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) as well as yield parameters were investigated in six maizecultivars representing two era of maize breeding in Nigeria during the 2005 late and 2006 early cropping seasons. Differences between maize breeding era were significant for seedling emergence (E %) and emergence index (EI) while genotypes within a particular breeding era (G/E) differed significantly for E% and emergence rate index (ERI). Seasonal (S) variation in seedling parameters was also significant for E % and ERI with a 15% higherseedling emergence in 2006 early season. CGR in the genotypes in breeding era 1 was higher by seven percent (7%) during vegetative growth phase but lower by 14% at flowering phase compared to genotypes in breedingera 2. NAR on the other hand was consistently higher in varieties developed in 1970’s by 15.2 and 13.8%compared to varieties developed in 1990’s. Regardless of the breeding era, varieties with higher values for LARat flowering (except var. TZPB-SR) were higher yielding than those with lower LAR. Overall, varietiesdeveloped in era 2 were superior to those developed in era 1 for E% and also had six percent (6%) higher valuesfor LAR at vegetative growth phase than those developed in era 1 but decreased by two percent (2%) atflowering phase. E% in the genotypes ranged from 48.56 in ACR 9943 DMRSR to 79.33 in ACR99TZLCOMP4 DMRSR, while EI and ERI ranged from 0.86 and 0.010 in TZB-SR to 0.96 and 0.014 in ACR 97 TZLCOMP1-W. Grain yield was significantly higher in 2006 early cropping season by 0.3t/ha-1 translating to14.78% than in late season and it ranged from 1.64t/ha-1 in TZPB-SR (era 1) to 2.94t/ha-1 inACR99TZLCOMP4DMRSR (era 2). Var. ACR99TZL COMP4DMRSR with the lowest values for CGR, RGRand NAR at vegetative phase had the highest grain yield (2.94t/ha-1) indicating that genotypic superiority forgrain yield is not particularly related to differences in any of these traits but rather dependent on the inherentgenetic potential of the varieties themselves