Modeling seed germination of quinoa (Chenopodium quinoa Willd.) at different temperatures and water potentials

Seed germination is one of the most critical plant growth stages regulated by temperature (T) and water potential (Psi). This experiment was conducted to quantify the seed germination response of two quinoa (Chenopodium quinoa) cultivars (Sajama and Titicaca) to T and Psi using hydro time (HT) and hydrothermal time (HTT) models. The results showed that T, Psi, and their interaction significantly affected the maximum germination percentage (MGP) of both cultivars. Based on the results of the segmented model fit at Psi=0 MPa, the minimum (T-b), optimum (T-o), and maximum T (T-c) in Sajama was estimated at 6.9, 21.9 and 34.9 degrees C, respectively and in Titicaca were estimated 8.0, 21.8 and 33.6 degrees C, respectively. While using the HTT model at different T and psi the T-b was estimated by 8.28 and 8.39 degrees C for Sajama and Titicaca, respectively, the T-o also estimated 26.96 for Sajama and 27.21 degrees C for Titicaca. Also, using the modified HTT model, the T-o estimated 27.46 for Sajama and 27.31 degrees C for Titicaca. There was an increase in hydro time constant (theta(H)) when T increased at supra-optimal T-s (from 17 to 70 MPa h(-1)) as well as when the T decreased at sub-optimal T-s (from 17 to 79 MPa h(-1)). Also, it was observed that change of the T from T-o to T-b and T-c increased base Psi (psi(b)) so that for each degree Celsius decrease of T at sub-optimal T-s, the psi(b) increased by 0.032 and 0.034 MPa in Sajama and Titicaca, respectively. Each degree Celsius increase of T at supraoptimal T-s also increased psi(b) 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, R-2 =0.97, and =0.99 for Sajama and Titicaca, respectively; HTT, R-2 =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.