| Summary: | Low soil nitrogen is one of the principal abiotic stresses affecting maize productivity in Sub-saharan Africa. Field studies were conducted at the International Institute of Tropical Agriculture (IITA), Ibadan during the cropping seasons for three years, from 2010 to 2012, with ten open pollinated maize varieties (OPVs) derived from two breeding eras (1 and 2). The ten OPVs and their crosses were evaluated under high-N and low-N conditions. The aim was to identify superior populations that may be useful sources genes for inbred line extraction and hybrid development for grain yield. Under low-N condition, mid and high parent heterosis for grain yield were low indicating the suitability of the hybrids for cultivation only in environments with high productivity index. Hybrid DMR-LSR-W (Era 1) × TZSR-Y-I (Era 2) had greatest mid and high-parent heterosis for grain yield under high-N and across the other four test environments. Parent AMATZBR-WC2B with higher general combining ability effects and mean values for grain yield, and cross combinations DMR-LSR-W (Era 1) x BR9928DMRSR (Era 2) and BR9922DMRSR (Era 2) x TZBRELD-4C0W (Era 2) with higher specific combining ability for grain yield under low-N environment are promising candidates for the development of nitrogen use efficient varieties for cultivation in low-N environments.
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