Quantification of germination response of two sugar beet cultivars to temperature and salinity: nonlinear regression models

This study was conducted with the aim of investigating the effect of salinity stress and different temperatures on germination and determining the cardinal temperatures of germination (basic, optimal and ceiling germination temperatures) of two sugar beet cultivars. Experimental treatments included different levels of salinity stress (0, 40, 80, 120 and 160 mM) and different temperatures (5, 10, 15, 20, 25, 30, 35 and 40 °C). The three-parameter sigmoidal model was used to determine the time to reach 50% germination. The results showed that temperature and salinity stress had an effect on germination percentage and germination rate. In addition, the results showed that with increasing temperature up to optimum temperature, the germination percentage and germination rate increased, and with increasing salinity stress, the germination percentage and also the germination rate decreased. The germination percentage and germination rate in Brigitta variety was higher than that of Shokofa variety. According to the RMSE, CV, R2Adj, SE parameters, the beta model was the most suitable model for both sugar beet cultivars. In the Brigitta variety, the base temperature is between 3.67 and 5 °C, the optimal temperature is between 16.67 and 26.35 °C, and the roof temperature is between 40.10 and 40.89 °C, and in the shokofa variety, the base temperature is between 2.88 and 2.80 °C. 5.65, the optimum temperature varied between 16.11 and 26.47 °C and the ceiling temperature between 39.94 and 42.94 °C. The obtained results showed that the percentage and speed of germination in Brigitta variety under salinity stress conditions and different temperatures was higher than that of Shokofa variety, but there was no significant difference between the two varieties in terms of cardinal temperatures. Therefore, by using the output of these models at different temperatures, it is possible to predict the germination speed at different potentials.