EVALUATION OF CARDINAL TEMPERATURES AND THERMAL TIME REQUIREMENT FOR GERMINATION OF SCROPHULARIA STRIATA AND TANACETUM POLYCEPHALUM (SCHULTZ BIP. SSP. HETEROPHYLLUM)
Abstract
Scrophularia striata and Tanacetum polycephalum are important medicinal plants in Iran which are rich in
essential oils, bitter substances, and sesquiterpene lactones. The present study was conducted to compare four
non-linear regression models (segmented, beta, beta modified and Dent-like) to describe the germination ratetemperature
relationships of Scrophularia striata and Tanacetum polycephalum over eight and seven constant
temperatures, respectively, to find cardinal temperatures and thermal time requirements to reach different
germination percentiles. An iterative optimization method was used to calibrate the models and different
statistical indices including RMSE, coefficient of determination (R2), and AICc were applied to compare their
performance. The beta model was found to be the best model to predict germination rate of Scrophularia
striata at D10, D50 and D90 (R2 = 0.96, R2 = 0.97, R2 = 0.95; RMSE = 0.005, 0.001 and 0.001, respectively).
According to this model outputs, the base, optimum, and the maximum temperatures for germination were
estimated as 1.21 ± 0.39, 25.91 ± 0.33 and 46.35 ± 4.12 °C, respectively. Also the segmented model was
found to be the best model to predict germination rate of Tanacetum polycephalum at D10, D50 and D90 (R2
= 0.98, R2 = 0.98, R2 = 0.98; RMSE = 0.067, 0.59 and 0.56, respectively). According to the model outputs, the
base, optimum, and the maximum temperatures for germination were estimated as 0.44±1.15, 26.95±0.75 and
38.33±0.98 oC, respectively. It seems these two medicinal plants need moderate optimum temperature for seed
germination.
Keywords
Cardinal temperatures,; Seed germination rate,; Thermal time,; modeling
Department of Agronomy and Plant breeding, College of Agriculture & Natural Resouces, University of Tehran, Karaj, Iran; Iran, Islamic Republic of
Department of Agronomy and Plant Breeding, College of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran; Iran, Islamic Republic of
Department of Agronomy and Plant breeding, College of Agriculture & Natural Resouces, University of Tehran, Karaj, Iran; Iran, Islamic Republic of
Department of Agronomy, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran; Iran, Islamic Republic of
Department of Agronomy, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran; Iran, Islamic Republic of
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