Drought stress is one of the most important environmental stresses which limit plants growth andproductions in different regions of the world. An experiment was performed to investigate the effects of drought stress and differenttemperatureregimeson germination and seedling growth of Tanacetumpolycephalum. Temperatures included 5, 10, 15, 20,25, 30 and 35 °C and for each temperature six level of osmotic potentials (0, -2, -4, -6, -8 and -10 bar) imposed by polyethylene glycol) simulating drought conditions. The results showed that, the effects of osmotic stress and temperature was significant on total germination percentage, normal germinationpercentage,mean germination time, rootlength,shoot length and vigor index. At all temperatures germination percentage and other parameters decreased by increasing stress level. At 5 and 10°C drought tolerance was not considerableandseedswere germinated in -2 bar of PEG only. The highest drought tolerance was observed at 25°C which reached to 100% in control (0 bar PEG) and 14.66% in -10 bar of PEG at this temperature. Germination percentage and rate decreased under temperature of 35°C, and it reached to 79.33% in control seeds. In conclusion,25°C was determined as the optimum temperature of germination for this plant. This isdue to exhibition of the highest germination parameters under different water potentials.Also, this herb can tolerate osmotic potential, up to -10bar. Therefore, it is a semi drought tolerant plant species.

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