Effect of indole-3-butyric acid concentration and cutting type on the propagation of Osmanthus fragrans

Osmanthus fragrans Lour. (sweet olive) is an evergreen shrub or small tree in the Oleaceae family with small and fragrant flowers. Stem cutting is the most commonly used asexual method for propagating O. fragrans. Different cutting types of O. fragrans respond differently to formulations and concentrations of plant growth regulators (PGRs) in terms of propagation success. This study evaluated the effects of seven formulations/rates of indole-3-butyric acid (IBA) (1,000, 3,000, and 8,000 mg/L of a potassium IBA [K-IBA] solution; 1,000, 3,000, and 8,000 mg/L of IBA powder; and 3,100 mg/L IBA rooting gel) on O. fragrans 'Beni Kin Mokusei' semi-hardwood cuttings collected in August and hardwood cuttings collected in October 2024. Water dipping was used as the control. Propagation parameters, including survival percent (%), rooting percentage (%), number of roots per cutting, total root length (cm), longest root length (cm), average root length (cm), root index, and cutting biomass (g) were measured. The results showed that the semi-hardwood cuttings treated with 3,100 mg/L IBA rooting gel produced the highest rooting percentage (87.50%), the most roots per cutting (6.50), and the longest total and individual root lengths (18.36 and 4.74 cm, respectively). In conclusion, under August collection conditions and a mist greenhouse environment, treating cuttings with 3,100 mg/L IBA rooting gel is the most effective method for propagating O. fragrans by cutting. Further research should be conducted to test different collection times, longer experiment durations, and the conditions of stem-cutting propagation for other O. fragrans cultivars.