Effect of drought stress on germination characteristics of Tanacetum polycephalum subsp. Heterophyllum under different temperature regimes

Drought stress is one of the most important environmental stresses which limit plants growth and productions in different regions of the world. An experiment was performed to investigate the effects of drought stress and different temperature regimes on germination and seedling growth of Tanacetum polycephalum. 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 germination percentage, mean germination time, root length, 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 considerable and seeds were 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 is due 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.