Effect of Explant Type and Developmental Stage on In Vitro Regeneration Efficiency of Tropical Tree Species

A three-species factorial in vitro regeneration experiment was conducted using Tectona grandis, Khaya senegalensis, and Milicia excelsa. The experimental dataset comprised 3,240 inoculated explants arranged as three species × three donor developmental stages × four explant types × 30 explants × three independent runs. Juvenile tissues achieved 83.33% establishment, 81.78% shoot induction, 4.46 usable shoots per responding explant, 81.54% rooting, and 89.09% survival at 12 weeks, compared with 41.85%, 30.97%, 1.82, 46.67%, and 65.55%, respectively, for mature tissues. Shoot tips produced the highest shoot-induction rate (75.43%) and mean usable shoot number (4.30), whereas nodal segments provided the highest overall establishment among explant classes (68.52%) and the highest acclimatization survival (87.57%). T. grandis recorded the strongest species-level performance, with 67.13% establishment, 68.83% shoot induction, 80.15% rooting, and 87.12% acclimatization survival. The highest normalized regeneration-efficiency index was obtained from juvenile T. grandis shoot tips, closely followed by juvenile T. grandis nodal segments. Generalized linear modelling showed strong developmental-stage effects across the major outcomes and a significant developmental stage × explant type interaction for shoot induction (Wald χ² = 16.45, p = 0.012). The findings demonstrate that complete regeneration efficiency depends on the joint effects of physiological age, tissue identity, species, rooting capacity, and ex vitro survival rather than shoot production alone.