Determination of cardinal temperatures for seed germination in Thymus kotschyanus, T. daenensis, and T. lancifolius

To evaluate the germination characteristics and determine the cardinal germination temperatures of Thymus kotschyanus Boiss. & Hohen, T. daenensis Celak., and T. lancifolius Celak., a factorial experiment was conducted in ۲۰۲۳, at the Seed Technology Research Laboratory of the Natural Resources Gene Bank of Iran. This experiment, designed in a completely randomized format with three replications, aimed to evaluate the germination characteristics and determine the cardinal temperatures of germination of three thyme species: Thymus kotschyanus, Thymus daenensis, and T. lancifolius. The seeds were exposed to a range of temperatures from ۵ to ۴۰ °C, a crucial step in understanding their germination behavior. Three non-linear regression models, including dent-like, segmented, and beta, were employed to characterize the germination rate response of three thyme species across eight temperature levels. Statistical indices such as root mean squared error (RMSE) and coefficient of determination (R²) were utilized to compare the models. Results from this experiment demonstrated that the studied thyme species exhibited similar germination peaks due to similar initial growth rates. Based on the results, the dent-like model provided the best fit for T. lancifolius with a basic temperature of ۷.۵۸ °C, a lower optimum temperature of ۱۵.۱۰ °C, an upper optimum temperature of ۱۵.۶۵ °C, and a ceiling temperature of ۳۶.۱۹ °C, with R² and RMSE values of ۰.۹۷ and ۰.۱۵, respectively. For T. kotschyanus, the dent-like model with a basic temperature of ۵ °C, lower optimum temperature of ۱۷.۴۷ °C, upper optimum temperature of ۱۹.۷۳ °C, and a ceiling temperature of ۳۴.۲۴ °C, and R² and RMSE values of ۰.۹۲ and ۰.۰۸, respectively, also showed a good fit. However, for T. daenensis, the segmented model with an essential temperature of ۶ °C, optimum temperature of ۲۰ °C, and ceiling temperature of ۳۶ °C, and R² and RMSE values of ۰.۹۹ and ۰.۰۶, respectively, provided the most reliable fit. Conclusively, the germination temperature range for all three thyme species was ۱۰ to ۳۵ °C, with an optimal germination temperature of ۱۵ to ۲۰ °C. These results emphasized the high adaptability and promising cultivation potential of the three thyme species in temperate natural resource areas, offering a significant implication for future agricultural practices.

کلیدواژه ها:

Basic temperature ، Ceiling temperature ، Optimal temperature ، Thyme