Abstract

This study aimed to evaluate the effects of plant growth regulators and growing substrates on the germination rate and seedling growth of noni (Morinda citrifolia) during the early growth stage. Noni is a medicinal plant of high biological and economic value; however, its propagation via seeds remains challenging due to low germination rates and weak seedling vigor. In this experiment, selected seeds were pre-treated with plant growth regulators such as gibberellic acid (GA₃) and alpha-naphthaleneacetic acid (α-NAA) prior to sowing. The seedlings were then grown in four different substrate formulations composed of clean soil, coir dust, rice husk ash, decomposed manure, biochar, phosphate fertilizer, and NPK compound fertilizer. Results showed that treating fresh seeds with GA₃ significantly increased the germination rate up to 90% and shortened germination time to 6–7 days. Among the substrate treatments, the NT3 formulation (30% clean soil, 30% coir dust, 10% rice husk ash, 20% manure, 5% phosphate fertilizer, and 5% NPK) outperformed others in terms of seedling growth, with an average of 27.7 leaves per plant, 4.75 branches, and a height of 64.3 cm after 8 weeks of cultivation. These findings suggest that combining seed pretreatment with plant growth regulators and using nutrient-rich growing media offers an effective technical solution to enhance noni seedling quality and support the sustainable development of medicinal plant cultivation.