Cardinal Temperatures for Germination of Ziziphora clinopodioides. Lam.

In order to study the cardinal temperatures of seed germination for Ziziphora clinopodioides. Lam., an experiment was conducted in Special Plants Research Laboratory, Faculty of Agriculture, Ferdowsi University of Mashhad in 2008. The experiment was a completely randomized design with 8 treatments and four replications. Treatments consisted of 8 constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40 °C) with 50- 60 percent relative humidity and constant light radiation (12 h lightness / 12 h darkness) during germination for 21 days. Cardinal temperatures of seed germination for Z. clinopodioides. Lam. were calculated with three models (Intersected-lines Model (ISL), Five-Parameters Beta Model (FPB) and Quadratic Polynomial Model). Results showed that there was no dormancy of seeds of Z. clinopodioides. Lam. Effect of temperature on rate, percentage and average time of seed germination for Z. clinopodioides. Lam. was significant (p ≤ 0.01). Maximum germination percentage and rate of germination at 20°C were 29.6 and 6.37 per day and minimum average time of seed germination was 0.006 per day. Maximum germination rate at 20°C was 0.4. According to three models cardinal temperatures including base temperature (Tb), optimum temperature (To) and ceiling temperature (Tc) for Z. clinopodioides. Lam. were varied between 5 - 5.8, 22 – 22.6 and 39.5 – 40.5 °C respectively and their differences was lower than 1 °C., among models