The role of light and Gibberellic Acid on cardinal temperatures and thermal time required for germination of Charnushka (Nigella sativa) seed

Abstract

The response of seed germination to environmental factors can be estimated by nonlinear regression. This study was performed to compare four nonlinear regression models (segmented, beta, beta-modified, and dent-like) for describing the germination rate and temperature relationships of Charnushka seeds under light and utilizing seed-priming treatments at six constant temperatures. Its aim was to identify the cardinal temperatures and thermal times required to reach different germination percentiles. Models and statistical indices were calibrated using an iterative optimization method, and their performance was compared by the root mean square error (RMSE), coefficient of determination (R2), and Akaike information criterion correction (AICc). The beta model under dark conditions was found to be the best model for predicting the required time to reach 50% germination (D50) (R2, 0.99; RMSE, 0.0004; AICc, 19.17). Based on the model outputs, the base, optimum, and maximum temperatures of seed germination under dark conditions were 0.10 ± 0.2, 19.2 ± 0.28, and 35.0 ± 0.19 °C, respectively. However, hydropriming resulted in a higher base temperature of approximately 5 °C. The thermal times required for 50% and 90% of seed germination under dark conditions were 1130.4 and 1543.5 degree days, respectively. Seed priming using GA3 exhibited lower thermal time requirements for the 50% fraction (923.0) and the 90% fraction (1384.5) of total seed germination.