Evaluation of Maize Genotypes for Northern Leaf Blight Resistance and Yield in Ethiopian Hotspots

Northern leaf blight (NLB), caused by Exserohilum turcicum, is a major constraint to maize production in Ethiopia's mid-altitude and transitional-highland agro-ecologies. This study evaluated 30 maize genotypes (24 commercial hybrids released 1988-2020 and six female parent lines) at two NLB hotspot locations (Arsi Negele, 1960 m a.s.l.; Wondo Genet, 1720 m a.s.l.) during the 2022 and 2023 main cropping seasons. Artificial inoculation using ground-infected leaf tissue combined with BH543 spreader rows ensured uniform disease pressure. A randomized complete block design with three replications was used at each location. Disease parameters (NLB severity, AUDPC, apparent infection rate, lesion size) and grain yield were assessed. Combined analysis of variance revealed significant genotype × year × location interactions (p < 0.001) for all traits, justifying location-specific analyses. Final NLB severity (NLB6) ranged from 25.1% (F-BH661) to 53.5% (F-BH543). Obsolete varieties BH140 (released 1988) and BH540 (released 1995) showed high susceptibility (48.7%-48.8% NLB6), statistically similar to the susceptible check BH543 (51.3%), suggesting possible erosion of resistance effectiveness over 17-27 years, though pathogen race characterization is required for confirmation. Grain yield ranged from 3.2 to 7.9 t ha^-1, with BH549 achieving the highest yield (6.80 t ha^-1). Female-parent relative heterosis analysis revealed contrasting male parent effects: BH661 maintained resistance near the female-parent level (+6.7% heterosis for NLB6, indicating a marginal increase in susceptibility), while BH546 exhibited substantially increased susceptibility (+53.4%). NLB6 correlated negatively with yield (r = -0.40, p < 0.01) and positively with AUDPC (r = 0.78) and infection rate (r = 0.90). F-BH661 was identified as the most resistant genotype, contributing differentially to BH661 and BH546 resistance. These findings provide critical insights for breeding durable NLB resistance and developing location-specific variety recommendations for Ethiopian maize production systems.