Soil water supply is an important environmental factor controlling seed germination. In order to study the impact of different water potential levels on germination characteristics and preliminary growth on fleawort (Plantago ovata L.) and purple coneflower (Echinacea purpurea L.), a laboratory experiment was conducted based on completely randomized design with four replications at the Special Crop Laboratory, College of Agriculture, Ferdowsi University of Mashhad during year of 2011. Water potential levels were zero, -3, -5 and -7 bar. For water potential and zero potential were used Polyethylene Glycol-6000 and deionized water, respectively. The results showed that the effect of different drought stress levels was significant (p≤0.01) on final germination, germination rate (GR), plumule length and radicle length and seed vigor index of fleawort and purple coneflower. Drought stress reduced water absorption and then disordered germination of both species. By increasing water potential from zero to -7 bar decreased GR up to 100%. It concluded that purple coneflower is more sensitive medicinal plant than fleawort to drought stress.

Keywords