Seedling-derived split internode and leaf explants as efficient alternatives for callus induction in tropical maize

The development of effective callogenesis and regeneration protocols remains a major challenge for tropical maize genotypes, which are often recalcitrant to in vitro culture techniques. This study evaluates the callus-forming potential of two explants derived from young seedlings split internodes and leaf pieces in four local varieties (ATP, CHH, CHABA, and KASSAI), grown on five hormone-based media containing 2,4-D combined with cytokinins. Measured parameters include callus induction percentage and relative fresh weight growth rate (RFWGR). Results reveal a strong genotype dependence, with CHABA showing the best performance, while split internodes consistently outperform leaves in proliferation. Induction media containing 2–2.5 mg/L of 2,4-D combined with BAP or kinetin proved most effective. These results demonstrate that seedling-derived explants provide a robust alternative to immature embryos and offer a solid basis for optimizing tropical maize transformation and regeneration protocols.