Investigations on the cardinal temperatures for germination of Plantago ovata and Plantago psyllium

A laboratory study was conducted to investigate the effect of different temperatures on seed germination of two species of Plantago namely P. ovata and P. psyllium in a completely randomized design with four replications. Various constant temperature (5, 7, 10, 15, 20, 25, 30 and 35 ◦C) were considered. According to the results, the effect of temperature on rate and percentage of seed germination in both species was significant. The highest germination rates were in 20 and 25 ◦C for P. ovata and P. psyllium, respectively. Maximum seed germination occurred for P. ovata (100%) and P. psyllium (99%) in 15 and 25 ◦C, respectively. Optimum thermal range for seed germination of P. ovata was (10-20◦C) and for P. psyllium was (15-25◦C). By increasing or decreasing temperature beyond the optimal thermal range, percentage of seed germination was decreased significantly. Based on linear regression between germination rate and temperature in both species, the cardinal temperatures: minimum(Tmin), optimum(To) and maximum (Tmax) were determined which were: 4.4, 19.0 and 25.5 ◦C for P.ovata and 9.4, 28.8 and 35.0◦C for P. psyllium, respectively.