In order to study the response of Isabgol (Plantago ovata) and Psyllium (Plantago psyllium) seed germination under salinity and drought stresses, a factorial experiment based on completely randomized design with three replications was conducted. The first factor was plant species (Isabgol and Psyllium), the second factor was different salinity and drought treatments (NaCl, Na2SO4, KCl , K2SO4 , NaCl + Na2SO4 , KCl + K2SO4 and PEG 6000) and finally the third factor was different osmotic potentials (0,-0.4, - 0.8 , -1.2, -1.6 and -2 MPa). The seed germination percentage and rate and also seedling growth were investigated during the study. The results showed that Isabgol and Psyllium seed germination was significantly different under salinity and drought stresses, as Isabgol germination percentage and rate was more than Psyllium but Psyllium seedling growth was better than Isabgol. The results also indicated that germination characteristics decreased with increasing the osmotic potentials, especially in -1.6 and -2 MPa. Salinity and drought treatments also showed different inhibitory effects on germination so that KCl/ PEG600 had the least and the most effects on reducing the investigated characteristics, respectively. In this study it was observed that sodium salts was more toxic compare to potassium salts and similarly SO4 ⎯ pointed out more toxicity compare to Cl⎯. Therefore, osmotic potential was not the only effectiv agent on germination and there existed specific ionic effects.
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