effect of temperature on germination rate of russianthistle (salsola kali l.) based on regression models

salsola kali l. is a summer annual broad-leaved weed and c4, salt and drought-tolerant species belonging to chenopodiaceae family. it is a prolific seed-producing weed. in order to investigate the germination cardinal temperatures of salsola kali l., seeds were collected from north khorasan (faroj) and razavi khorasan (mashhad) and a laboratory experiment was conducted at constant temperatures including, 5, 10, 20, 30, 35, 40 and 45 °c with a daily alternating photoperiod (12 h light/12 h dark) in a completely randomized design with four replications in ferdowsi university of mashhad. to determine the cardinal temperatures for seed germination, nonlinear regression methods of quadratic polynomial (qpn), intersected-lines (isl) and five-parameter beta (fpb) models have been used. the highest germination percentage was within the range of 10-40 °c, while the highest germination rate occurred in the 20-40°c range. fpb and isl models showed most suitable fit based on highest r2adj for razavi khorasan and north khorasan, respectively. the cardinal temperatures for north khorasan seeds were 2.35, 34.8 and 48.35 °c and for razavi khorasan were 2.63, 32.55 and 45.42 °c. by these results, the broad temperature range of germination and invasion ability for this weed would be indicated.