Cardinal temperatures for germination of Salvia leriifolia Benth.
The focus of this study is based on the examination of the germination traits and the development of thermal models of the medicinal plant Salvia leriifolia Benth. A laboratory experiment was carried out at constant temperatures ranging from 0 to 35°C, at 5°C intervals in a completely randomized design with eight replications. To describe the germination rate response to temperature, three regression models, namely Intersected-Lines (ISL), Quadratic Polynomial (QPN) and Five-Parameters Beta (FPB) were used. The highest Germination Percentage (GP) (92.8%) occurred in 15°C, but GP in the range of 10–25°C was not significant (p≤0.05). The germination process stopped at 0°C and at above 30°C. The results indicated that the highest Germination Rate (GR), the lowest Mean Germination Time (MGT) and also times to 50% germination (D50) were obtained at 20°C. Seeds did not reach to their 50% germination level in temperatures higher than 25°C. The FPB model had the best realistic estimation for cardinal temperatures. Based on models estimation, Base (Tb), Optimum (To) and Ceiling (Tc) temperatures were in the ranges of (1–1.9°C), (18.1–20.8°C) and (34.5–38.7°C), respectively.