Evaluation of Drought Tolerance in Complete Diallel Among Maize (Zea mays L.) Inbred Lines in Zuru, Kebbi State

Abstract

Maize (Zea mays L.) production in the Sudan Savanna agroecological zone of Nigeria is severely constrained by terminal drought stress, resulting in grain yield losses of 25–70% annually. Identifying drought-tolerant hybrids through combining ability analysis is essential to improve productivity under reduced water availability. This study evaluated six tropical maize inbred lines and their 15 F₁ crosses generated through a complete diallel mating design for drought tolerance using Griffing's Method 2, Model I. The 21 genotypes (6 parents + 15 crosses) were evaluated under drought-stressed (DS) and well-watered (WW) conditions in Zuru, Kebbi State (11°26'N, 5°13'E; altitude 265 m a.s.l.) during the 2025 late cropping season using a Randomized Complete Block Design (RCBD) with three replications. Traits evaluated included grain yield (GY), days to silking (DTS), days to anthesis (DTA), anthesis-silking interval (ASI), plant height (PH), ear height (EH), leaf rolling score (LRS), leaf senescence score (LSS), and husk cover rating (HCR). Drought tolerance was assessed using stress tolerance index (STI), geometric mean productivity (GMP), mean productivity (MP), tolerance (TOL), and stress susceptibility index (SSI). Analysis of variance revealed significant (p ≤ 0.01) effects of general combining ability (GCA) and specific combining ability (SCA) for all traits under both moisture regimes. The GCA: SCA variance ratio exceeded unity for grain yield, days to silking, and plant height, suggesting predominance of additive gene action. Parental lines L2 (TZEI 23) and L4 (TZEI 41) consistently exhibited the highest positive GCA effects for grain yield and negative GCA effects for ASI under drought stress, indicating their superior general combining ability. The cross L2 × L4 produced the highest GY under DS (3.47 t ha⁻¹), the shortest ASI (2.4 days), and the highest STI (0.842), followed by L1 × L2 and L1 × L4. Lines L2 and L4 are recommended as promising parents for drought-tolerant hybrid development. The cross L2 × L4 is a candidate for advancement to multi-location trials targeting the Sudan Savanna zone of Northwestern Nigeria.