Germination and Early Seedling Vigor of Pentadesma butyracea under Abiotic Constraints: Implications for the Domestication of a Threatened Wild Oilseed Species in Benin

Abstract

Pentadesma butyracea is a vulnerable multipurpose tree whose propagation by seed is limited by poor and heterogeneous germination. This study evaluated the effects of seed source, temperature, seed coat removal, gibberellic acid (GA₃) and substrate on germination and early seedling growth. Seeds from eight mother trees (four per zone) collected in the Sudano-Guinean and Sudanian zones of Benin were incubated at five constant temperatures (20-40 °C). In the greenhouse, a factorial experiment combined seed type (dehusked and intact), GA₃ (0, 10 and 20 mg/L) and substrate (poorly developed soil, vertisol and ferralitic soil). Germination varied strongly with mother tree, temperature and their interaction (P < 0.0001). Only one tree (ZSGP1) germinated well at 40 °C (70%). The higher mean germination of Sudano-Guinean seeds (24.5% vs. 11.5%) was largely driven by this single tree, so ecotypic differentiation between zones could not be demonstrated. Seed coat removal shortened the latency period (7 vs. 14 days), concentrated germination (peak at 28 days vs. spread over 70 days) and increased final germination (99.2% vs. 82.5%) and seedling growth (height: 32.4 vs. 24.8 cm; root-collar diameter: 0.66 vs. 0.52 cm). GA₃ brought no benefit to germination and reduced seedling height at the tested concentrations, and substrate type had no significant (P > 0.05) main effect, although it interacted with seed type for seedling growth. Seed weight was positively related to seedling size but explained at most 20% of its variation. Seed coat removal is recommended for nursery propagation, and seed collection should be spread across many mother trees; ZSGP1 deserves further evaluation for heat-tolerant germination. Results are preliminary given the small number of mother trees per zone and the controlled conditions, but these crucial findings provide strategic guidelines for accelerating high-quality plant stock production in forest nurseries.