Improvement of Seed Germination in Three Medicinal Plant Species by Plant Growth Regulators

Peppermint (Mentha piperita), sweet basil (Ocimum basilicum), and coriander (Coriandrum sativum) are important medicinal plants in the pharmacological industry. These plants are produced in commercial scale but their seeds exhibit low germination percentages under favorable germination conditions. Enhancing seed germination is thus crucial for improving the production of these plants. The influence of gibberellic acid (GA(3)), indole-3-acetic acid (IAA), indol-3-butyric acid (IBA), and naphthalene acetic acid (NAA) on seed germination of the three plants were investigated. The seeds were soaked in each plant growth regulator at 50, 100, and 150 mg.L-1 for 24 hours at 25 +/- 2 degrees C. Seed germination was checked daily for 20 days and germination parameters including final germination percentage (FGP), corrected germination rate (CGRI), and number of days lapsed to reach 50% of FGP (GT(50)) were recorded. The phosphorus and protein contents were determined in germinated seedlings on day 21 of culture. All plant growth regulators enhanced seed germination as compared with control. However, GA(3) improved seed germination more than IAA, IBA, and NAA. GA(3) at 100 mg.L-1 significantly increased the FGP from 22.3% and 33.3% (control) to 74% and 65.6% for peppermint and sweet basil, respectively. Low concentration of GA(3) at 50 mg.L-1 increased the FGP for coriander from 27% to 52.3%. GA(3) also increased CGRI, GT(50), phosphorus, and protein contents in germinated seedlings as compared with control. Seeds of peppermint, sweet basil, and coriander possess a physiological dormancy that could be elevated by GA(3) presowing treatment. This study established a successful methodology for optimizing seed germination to satisfy the demand for the medicinal parts of these plants in the pharmacological industry.