Breeding Insights Into <scp> <i>Curvularia</i> </scp> Leaf Spot Resistance and Agronomic‐Nutritional Resilience in Extra‐Early Provitamin A‐Quality Protein Maize ( <scp> <i>Zea mays</i> </scp> L.) Testcrosses

Abstract

ABSTRACT Extra‐early provitamin A‐quality protein maize (PVA‐QPM) represents a sustainable breeding strategy to address food and nutritional insecurity in sub‐Saharan Africa by simultaneously enhancing grain yield and nutritional quality. In this study, 10 extra‐early PVA‐QPM inbred lines, 45 hybrids, and two commercial checks were evaluated for agronomic performance, nutritional traits, and resistance to Curvularia leaf spot (CLS) under natural infection supplemented with artificial inoculation across the 2023 and 2024 cropping seasons at Oke‐Oyi, Nigeria. Trials were conducted in a randomised complete block design with three replications per year. Significant genetic variation was observed among genotypes for yield, nutritional, and disease‐resistance traits, with several hybrids outperforming parental lines and checks. The hybrid TZEEIORQ 55 × TZEEIOR 65 achieved the highest grain yield (5.28 t ha −1 ), surpassing the best check by 19.2%, while TZEEI 79 × TZEEIORQ 55 recorded superior β‐carotene (8.3 μg g −1 ) and tryptophan (1.03%). Resistant hybrids exhibited reduced CLS severity and lower area under disease progress curve (AUDPC), confirming their potential for durable resistance. Variance analysis revealed predominance of additive gene action, with general combining ability exceeding specific combining ability, though non‐additive effects were also relevant. Broad‐sense heritability was highest for days to 50% anthesis, plant height, and β‐carotene content, suggesting reliable selection for these traits. Grain yield correlated positively with β‐carotene, tryptophan, stay‐green index, and plant height, but negatively with disease severity and AUDPC. The identified superior hybrids constitute valuable genetic resources for breeding programmes targeting yield, nutritional quality, and CLS resistance in extra‐early PVA‐QPM maize.