tBasil has many applications in industrial, cosmetic, pharmacy, foods, perfumery and culinary. Therefore,understanding of its temperature needs is necessary for its appropriate germination, growth and devel-opment. In present study three regression models (Intersected-lines model, Quadratic Polynomial modeland Five-Parameters Beta model) were used for describing the relationships between germination rateand temperature in green and purple cultivars of basil. Temperature treatments were included of nineconstant temperatures including 0, 5, 10, 15, 20, 25, 30, 35 and 40◦C. The experiment was conducted atseed research laboratory of University of Birjand, based on a completely randomized design with fourreplications. Germination of purple basil started from 10◦C (6%), reached to maximum at 20◦C (73%)and then decreased with increasing temperature until reached to 0% at 40◦C. The highest amount ofgermination rate was obtained at 25◦C (10 seed day−1), followed by 20◦C treatment. Intersected-linesmodel was found to be the best model to predict germination rate of purple basil (R2= 0.9). Based onmodel output, the amounts of base temperature (Tb), optimum temperature (To) and maximum temper-ature (Tm) for germination of purple basil were 7, 24.97 and 41.84◦C, respectively. Germination of greenbasil was started from 10◦C (15%), followed by 60–67% in 15-30◦C and finally decreased to 7% in 40◦C.The highest values of germination rate were obtained at 25–30◦C (9.4–9.65 seed day−1). Intersected-linesmodel showed most suitable fitness in the case of green basil (R2= 0.91). Based on the regression betweengermination rate and temperature, the cardinal temperatures (Tb, Toand Tm) for green basil were 6.11,28.97 and 43.58◦C, respectively. In addition, temperature range (Tm–Tb) for purple and green basil wasobtained 34.84 and 37.47◦C, respectively. Totally, the use of the three models confirms the generallyknown fact that basil needs higher temperatures for germination.

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