Evaluation of germination characteristics and determination of cardinal temperatures of poppy (Papaver somniferum) seed

The aim of this study was to quantify the response of germination rate to temperature and to find cardinal temperatures required for different germination percentiles in Papaver somniferum. Four models of non-linear regression [Quadratic, Segmented, Beta and Dent-like] were evaluated to describe the relationships between germination rate and temperature of P. somniferum over 7 constant temperatures (3, 5, 10, 15, 20, 25 and 30 ˚C). Different statistical indices [Root Mean Squares of Error (RMSE) and coefficient of determination (R2)] were used to compare models performance. The Dent-like was found to be the best model to predict germination rate (RMSE=000.35, R2=0.87). The base, sub optimum, supra optimum and the ceiling temperatures for P.somniferum  seed germination were estimated 3, 7, 20 and 31˚C, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, Dent-like was better suited than the other models to estimate the cardinal temperatures for germination of P. somniferum seed. The highest germination percentage (72) and germination rate (0.86) was observed in 10 and 15 ˚C, respectively.