The evaluation response of onion (Allium cepa) seed germination to temperature by Thermal-time analysis and determine cardinal temperatures by using nonlinear regression

This study was conducted to quantify germination response of onion (Allium cepa) to temperature. For this purpose, seeds were exposed to Various constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40ºC) treatments in seed lab, the university of Tehran, in 2015. The effects of temperatures on rate and percentage of germination was significant. With temperature increasing from 5 to 30ºC, both germination percentage and rate increased, while it decreased with increasing temperature from 30 to 35ºC. Cardinal temperatures of seed germination were estimated by using four regression models including dent-like, segmented, beta modified and beta Models. The best model for estimating cardinal temperatures was dent-like and beta modified models that by used dent-like model The base, under optimal, upper optimal and ceiling temperatures were 0.3, 24.99, 33 and 35.89 °C, respectively, and following beta modified model, The base, optimal and ceiling temperature were 0.2, 26.87 and 35.51°C. For predicting time of germination at different constant temperatures used Thermal-time that constant coefficient of Thermal-time was 3191.43 (°Cd).