Seed germination is one of the most critical plant growth stages regulated by temperature (T) and water potential (Ψ). This experiment was conducted to quantify the seed germination response of two quinoa (Chenopodium quinoa) cultivars (Sajama and Titicaca) to T and Ψ using hydro time (HT) and hydrothermal time (HTT) models. The results showed that T, Ψ, and their interaction significantly affected the maximum germination percentage (MGP) of both cultivars. Based on the results of the segmented model fit at Ψ = 0 MPa, the minimum (Tb\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{b}}$$\end{document}), optimum (To\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{o}}$$\end{document}), and maximum T (Tc\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{c}}$$\end{document}) in Sajama was estimated at 6.9, 21.9 and 34.9 °C, respectively and in Titicaca were estimated 8.0, 21.8 and 33.6 °C, respectively. While using the HTT model at different T and ѱ the Tb\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{b}}$$\end{document} was estimated by 8.28 and 8.39 °C for Sajama and Titicaca, respectively, the To\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{o}}$$\end{document} also estimated 26.96 for Sajama and 27.21 °C for Titicaca. Also, using the modified HTT model, the To\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{o}}$$\end{document} estimated 27.46 for Sajama and 27.31 °C for Titicaca. There was an increase in hydro time constant (θH\documentclass[12pt]{minimal}
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\begin{document}$${\theta }_{\mathrm{H}}$$\end{document}) when T increased at supra-optimal Ts (from 17 to 70 MPa h−1) as well as when the T decreased at sub-optimal Ts (from 17 to 79 MPa h−1). Also, it was observed that change of the T from To\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{o}}$$\end{document} to Tb\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{b}}$$\end{document} and Tc\documentclass[12pt]{minimal}
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\begin{document}$${T}_{\mathrm{c}}$$\end{document} increased base Ψ (ψb) so that for each degree Celsius decrease of T at sub-optimal Ts, the ψb increased by 0.032 and 0.034 MPa in Sajama and Titicaca, respectively. Each degree Celsius increase of T at supra-optimal Ts also increased ψb by 0.021 MPa in Sajama and 0.020 MPa in Titicaca. Using HT and HTT to predict germination rate for the 50% of germination (GR50) revealed that they had acceptable accuracy (HT, R2 = 0.97, and = 0.99 for Sajama and Titicaca, respectively; HTT, R2 = 0.87 for Sajama and = 0.90 for Titicaca). The results of this experiment provide data for future simulating models of quinoa growth and development.
