Bahman Jafari - Department of Agronomy and Plant Breeding, Faculty of Agricultural Sciences, University of Guilan, P.O. Box: ۴۱۶۳۵-۱۳۱۴, Rasht, Iran.
Mojtaba Kordrostami - Nuclear Agriculture Research School, Nuclear Science and Technology Research Institute (NSTRI), Karaj, Iran
Ali Akbar Ghasemi-Soloklui - Nuclear Agriculture Research School, Nuclear Science and Technology Research Institute (NSTRI), Karaj, P.O. Box ۳۱۴۸۵۴۹۸, Iran

Seed germination is a crucial stage in the life cycle of plants, as it determines their growth and reproduction success. Thus, to estimate the cardinal temperatures and the thermal time requirement for seed germination, as well as evaluate the effect of different temperature levels on the germination characteristics of tomatoes (Lycopersicon esculentum cv. Early CH), an experiment was conducted using a completely randomized design with four replications and seven determinate temperature levels (۵, ۱۰, ۱۵, ۲۰, ۲۵, ۳۰, and ۳۵ degrees Celsius). To describe the relationship between germination rate and temperature and calculate the cardinal temperatures for tomato (cv. EARLY CH) seed germination, four types of regression models were used: segmented, dent-like, original beta, and modified beta. The highest germination percentage (۸۱-۸۶%) and vigor index (۴.۰۴-۵.۴۷ cm) were similarly obtained in the ۲۰-۳۰°C range. The highest germination rate (۵/۷ seeds per day) was observed at ۲۵°C, and the lowest mean germination time (۴.۵-۴.۸۴ days) occurred in the ۲۰-۲۵°C range. Germination characteristics were significantly different when the temperature increased above ۳۰°C. Based on the parameters for measuring regression models, the best model for estimating the cardinal temperature of this cultivar was segmented. In general, the study's results showed that the cardinal temperatures for seed germination were estimated using a superior regression model for minimum (۰.۵-۳°C), optimal (۲۵-۲۶°C), and maximum (۳۵.۴-۴۰°C) temperatures. Additionally, our thermal time model accurately predicted the seed germination process (R۲=۰.۹۰), and the thermal time amount for ۵۰% germination of this cultivar was estimated at ۱۸۴۸.۲۹-degree hours.

Base temperature, germination parameters, Germination rate, Regression models, Thermal time