Determination of Cardinal Temperatures and Response to Temperature for Seed Germination in Basil (Ocimum basilicum L.) Ecotypes

Response of seed germination crops to temperature is important in aspect of fast and uniformity germination. In order to determination the cardinal temperatures and the effect of different levels of temperature on germination indices in basil ecotypes an experiment was carried out in completely randomized design with 4 replications in factorial experimental arrangement. The first factor was 7 basil ecotypes (Includes: Purple Bandar Abbas, Kerman Purple, Dezfol Green, Yazd green, Mahallat green, Shiraz green and Isfahan green) and second factor was 8 levels of temperatures (5, 10, 15, 20, 25, 30, 35 and 40 °C). Results showed that the effect of temperature and basil ecotypes were significant difference on seed germination indices. The highest germination indices (speed and percent of germination, seedling vigor index, radicle and plumule length, radicle to plumule ratio) were obtain from of 20 °C. All of basil ecotypes had the highest germination percent (GP) and germination rate (GR) at 25 °C. The maximum germination rate with 39.1 seed per day was found in Yazd green ecotype at 25 °C and the lowest of this trait was also obtain from Isfehan green ecotype with 13.2 seed per day in this temperature (25°C). With increasing temperature above 25 °C, all of germination indices were reduced and when temperature was higher than 35 °C all germination indices were declined very sharply. With increasing temperature from 15 °C was considerable increased GP and GR. Based on linear regression between germination rate and temperature, the cardinal temperatures in all basil ecotypes: minimum (Tmin), optimum (To) and maximum (Tmax) were determined in the range 3.5-7.1, 24-27.8 and 42.5-45.7 ° C respectively.