Determination of cardinal germination temperatures of invasive weeds of Euphorbia (Euphorbia maculata) and its germination hydrothermal model.
In order to quantify the germination characteristics and determine the cardinal temperature of germination of Euphorbia maculata, seeds were placed at constant temperatures (2- 45°C) in Randomized Complete Design with four replications at Science Research Branch, Islamic Azad University in 2018. Seed of E.maculata had no germination at temperatures of 2, 5, 10 and 45°C, and the temperature of 30° C was the best temperature for germination seeds (91% Germination percentage). Three models of intersected-line, dent-like segmented and quadratic polynomials were used to estimate the cardinal temperatures. The best model for estimating the cardinal temperatures in E.maculata was intersected-line model with respect to coefficient of determination and mean square error. According to the intersected-line the minimum, optimum and maximum temperatures were calculated 9.8, 28.33 and 43.16°C. In order to investigate water potential on germination percentage, seeds treated with water potentials (0, -0.2, -0.4, -0.6 and -0.8 MPa) at optimum temperature of 28°C. Baesd on the three-parameter sigmoid method, the value of x50 for speed, root length, stem length, seedling fresh weight and dry weight were estimated to be -0.53, -0.48, -0.51, -0.48, -0.52 Mpa respectively. According to the hydro-time model based on normal distribution, the hydro-time constant and the base-water potential (which is a threshold for germination beginning) of E.maculata degree were 291.32 (MPa/h) and -1.2 (MPa) at 28°C, respectively. Thus, this weed species has a great potential for distribution to other areas such as provinces with a dryer climate than Golestan, and the necessary measures to prevent its distribution is necessary.