Univrsity of Tehran PressIranian Journal of Field Crop Science2008-481148120170522Cardinal temperatures, response to temperature and range of thermal tolerance for seed germination in Okra (Abelmoschus esculentus)Cardinal temperatures, response to temperature and range of thermal tolerance for seed germination in Okra (Abelmoschus esculentus)1992056238610.22059/ijfcs.2017.134346.653963FAVahid Amiri MonfaredFormer M.Sc. Student, Seed Science and Technology, Agriculture and Natural Resources, University of Tehran, Karaj, IranMohammad FatholahiFormer M.Sc. Student, Seed Science and Technology, University of Guilan, IranReza Tavakkol AfshariProfessor, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran0000-0003-0073-8665Journal Article20151017The aim of this study was to quantify the response of germination rate to temperature and determining cardinal temperatures for different germination percentiles in <em>Abelmoschus esculentus</em>. Three models of non-linear regression [Quadratic, segmented and beta] were investigated to describe the temperature response of germination rate of <em>A</em>. <em>esculentus</em> over seven constant temperatures (10, 15, 20, 25, 30, 35 and 40 ˚C). Different statistical indices [Root Mean of Squares of Error (RMSE) and coefficient of determination (R<sup>2</sup>)] were used to compare models. The estimated model parameters using by beta models were more confidence than others (RMSE=0.0019, R2=0.90). The base, the optimum and the ceiling temperatures for the germination of <em>A</em>. <em>esculentus</em> were estimated to be 9.84, 30.31 and 40.63<sup>˚C</sup>, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, the beta model was better suited than the other models to estimate the cardinal temperatures for the germination of <em>A</em>. <em>esculentus</em>. The greatest germination percentage (98.7) and germination rate (0.0207) was observed in 25 and 30 <sup>˚C</sup>, respectively.The aim of this study was to quantify the response of germination rate to temperature and determining cardinal temperatures for different germination percentiles in <em>Abelmoschus esculentus</em>. Three models of non-linear regression [Quadratic, segmented and beta] were investigated to describe the temperature response of germination rate of <em>A</em>. <em>esculentus</em> over seven constant temperatures (10, 15, 20, 25, 30, 35 and 40 ˚C). Different statistical indices [Root Mean of Squares of Error (RMSE) and coefficient of determination (R<sup>2</sup>)] were used to compare models. The estimated model parameters using by beta models were more confidence than others (RMSE=0.0019, R2=0.90). The base, the optimum and the ceiling temperatures for the germination of <em>A</em>. <em>esculentus</em> were estimated to be 9.84, 30.31 and 40.63<sup>˚C</sup>, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, the beta model was better suited than the other models to estimate the cardinal temperatures for the germination of <em>A</em>. <em>esculentus</em>. The greatest germination percentage (98.7) and germination rate (0.0207) was observed in 25 and 30 <sup>˚C</sup>, respectively.https://ijfcs.ut.ac.ir/article_62386_b5c75b0f1cb312bc84bce4c472e5f0dc.pdf