Heterosis and Combining Ability for Striga Tolerance in Maize (Zea mays L.)

Background: Maize is a major staple in sub-Saharan Africa, but its production is severely constrained by Striga hermonthica, which causes significant yield and economic losses. Developing tolerant varieties remains the most sustainable control strategy. Aims: To evaluate 45 F1 hybrids from a 10×10 diallel cross of maize inbred lines for Striga (Striga hermonthica) tolerance, estimate combining ability parameters, and identify the best hybrid combinations for infested zones in Côte d'Ivoire. Study Design: Randomised complete block design with two replications per environment. Place and Duration of Study: CNRA research station, Ferkessédougou, northern Côte d'Ivoire, 2024. Methodology: Fifty-five genotypes (45 hybrids + 10 parents) were evaluated under non-infested and artificially Striga-infested conditions (5,000 germinable seeds m⁻²). Combining ability was estimated using Griffing’s (1956) Method 4 with a fixed-effects model, focusing specifically on the 45 F1 hybrids to determine GCA and SCA effects. Mid-parent (MPH) and better-parent (BPH) heterosis were computed. Pearson correlations were calculated among measured agronomic traits. Results: Combined ANOVA showed highly significant effects (**) of genotype, environment and G×E interaction for all traits. Mean yield reduction due to Striga was 62.8% in parents and 45.3% in hybrids. Using Griffing’s Method 4, genetic analysis revealed that non-additive effects predominated in tolerance expression, as indicated by a σ2SCA/σ2GCA ratio of 4.32 under infested conditions versus 3.17 in non-infested environments. Lines P8 (TZMI 20672) and P10 (TZMI 1262) showed the highest GCA effects under stress (0.92 and 0.88, respectively). Hybrids P5×P10, P2×P8 and P8×P10 yielded above 6.5 t ha⁻¹ under infestation with reductions below 35% and highly significant SCA effects. Conclusion: Heterosis exploitation offers substantial gains in Striga tolerance. Lines P8 and P10 are major tolerance sources for breeding programmes. Hybrids P8×P10, P5×P10 and P2×P8 are priority candidates for national catalogue registration; however, their stability across diverse environments remains to be confirmed through multi-location validation before broad commercial recommendation.