Combined Effects of Mechanical Scarification, Hormonal Treatments, and Hydration Optimization on Germination and Early Seedling Growth of Argania spinosa under Plastic Tunnel Conditions

Argania spinosa (L.) is an ecologically and economically important tree species native to North Africa; however, its large-scale propagation is constrained by low and irregular germination due primarily to strong physical dormancy imposed by a hard, impermeable seed coat. This study aimed to systematically evaluate and optimize dormancy-breaking treatments to enhance germination and early seedling growth under plastic tunnel conditions. Two successive experiments were conducted using mechanically scarified seeds to eliminate physical dormancy. In Experiment I, scarified seeds were soaked for a fixed duration in different plant growth regulators (PGRs) including gibberellic acid (GA₃), naphthalene acetic acid (NAA), and indole-3-acetic acid (IAA), alongside hot water and tap water treatments. Based on the most promising treatment, Experiment II further optimized soaking duration and germination substrate. Germination percentage, plant height, and leaf number were assessed at 30 and 60 days after sowing. The results indicate that, in Experiment I, PGRs did not significantly improve germination compared with simple tap water soaking, which achieved the highest germination percentage (33.30%). However, higher concentrations of GA ₃ significantly enhanced vegetative growth. In Experiment II, extending soaking duration from 10 minutes to 3 hours dramatically increased germination to 100% and significantly improved seedling development. Substrate type also affected emergence, with cardboard-based media achieving 73.30% germination compared to 13.30% in sawdust. These indicate that prolonged hydration following mechanical scarification is more effective for maximizing germination than short-duration hormonal treatments. The optimized protocol including mechanical scarification followed by prolonged soaking in tap water and sowing in a well-aerated substrate, offers a simple, low-cost, and scalable strategy for argan nursery production and restoration programs in arid and semi-arid regions.