Effects of Gibberellic Acid Treatments and Testa Removal on Seed Germination and Seedling Vigor in Hydnocarpus pentandrus (Buch.-Ham.) Oken

Hydnocarpus pentandrus (Buch.-Ham.) Oken is an endemic tree species whose large-scale propagation is limited by poor and inconsistent seed germination caused by dormancy. The present study investigated the effects of seed coat removal and gibberellic acid (GA₃) treatments on seed germination and seedling vigor on H. pentandrus. Seeds with intact seed coats exhibited very low germination under control and cold-water treatments, indicating that the hard, impermeable seed coat imposes strong physical dormancy. Application of GA₃ improved germination in intact seeds, particularly at higher concentrations and longer soaking periods, suggesting partial alleviation of physiological dormancy; however, germination remained limited by the presence of the seed coat. In contrast, mechanical removal of the seed coat significantly enhanced germination percentage, speed and uniformity and promoted vigorous seedling development. Seeds without seed coats responded positively even to lower concentrations of GA₃, highlighting the importance of removing physical constraints to enable effective hormonal action. The combined use of seed coat removal and GA₃ treatment produced the best overall germination and seedling performance. These results confirm that seed coat– imposed physical dormancy is the primary factor restricting germination in H. pentandrus and it demonstrates that integrated mechanical and hormonal treatments are essential for successful propagation, nursery production and conservation of this species.