Quinoa (Chenepodium quinoa Willd.) is a grain-like crop which has a high potential of crop yield under arid environments. The objective of this study was to evaluate the responses of seed germination rate and percentage to temperatures and estimate cardinal temperatures in three quinoa cultivars (i.e., Sajama, Titicaca and Santamaria). Germination of quinoa seeds were daily counted at the temperatures ranging from 5.0 to 40.0°C (5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0 and 40.0 °C). Four relevant regression models of segmented, beta, dent-like and modified beta were fit to germination rates with temperatures and subsequently the parameters including base temperature, optimum temperature, ceiling temperature and maximum germination rate were estimated. The accuracy of the model was measured by using RMSE (root mean square of error) and Aikaik Information Criteria (AIC). The interaction between temperature and cultivars effect was significant (p≤0.0001). For Sajama and Santamaria, the highest germination percentage occurred between 15-35 °C, while for Titicaca the highest germination was taken place between 5-35 °C. The beta and beta modified models for Santamaria and Sajama and the dent-like model for Titicaca were found to be the best models for predicting the thermal parameters of germination. Optimum thermal range for germination of Sajama was estimated at a wider ranges (i.e., 18-36 °C) rather than the other two cultivars of Santamaria (i.e., 23-35°C) or Titicaca (i.e., 22-35°C). The results of current study showed that quinoa is capable enough to germinate over a wide range of temperatures from 1.0 °C (Tb) to 54.0 °C (Tc).

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