The Estimation of cardinal temperatures in common Marigold (Calendula officinalis L.)

Temperature is one of the most effective and important environmental agents on seed germination, thus interaction effect of germination with temperature is very important in prediction of germination time and modeling especially. A completely randomized design experiment performed in seed research laboratory of Islamic Azad University, Mahabad Branch with four replications which temperature treatment were 11 levels as: 3, 5, 7, 10, 15, 20, 25, 30, 35, 40 and 45 0C. Three nonlinear regression models as Beta, 5-Parametric Beta and Segmented functions tested. Results revealed that temperature had a significant effects of rate, uniformity and germination percent. The highest uniformity and germination percentage were detected in 15 0C, but the highest value of rate of germination obtained in 20 0C.  Although, there was no significant difference between practiced models in estimation of cardinal temperatures, however, the segmented model which had the less RMSE, CV and the more R2 and correlation coefficients than the others, was a better model and thus, cardinal temperatures including base, optimum and ceiling temperatures were 3.35, 20.84 and 40.94 0C, respectively. Also, the maximum germination rate (rmax ) was  0.010 h-1.