Effects of salinity and drought stress on seed germination of common purslane Portulaca oleracea

Common purslane (Portulaca oleracea) is a halophyte cultivated for use that is not only as an edible vegetable, but also as a traditional medicine. This purslane can adapt to extreme salinity and drought, and the effects of these stresses on its growth, yield and quality were understood; but that on seed germination is still unclear. Seed germination is an important stage for establishing P. oleracea seedlings that will contribute to their plant yield and productivity. Thus, the aim of the present study was to examine individual effects of different stress levels of NaCl - induced salinity (50, 100, 200, 400 mM) and PEG - induced drought (0.22, 0.45, 0.89, 1.78 MPa), which imposed equivalent osmotic pressures between the stresses at each level, on germination characteristics of seeds. The seeds sowed in petri dishes containing filter paper layers that wetted with NaCl and PEG-6000 solutions for the treatments, and the germination parameters including final germina-tion percentage (GP), germination rate (GR), germination energy GE), and mean germination time (MGT) were determined every day in test duration of 15 days. Data analysis showed germination capacity of seeds were decreased with increasing salinity and drought levels, and there was a different response in seed germination between salinity and drought stresses. The seeds only maintained germination under 50 mM NaCl - induced salinity, but it germinated under 0.45 MPa PEG - induced drought that imposed a higher osmotic pressure, suggested that the ion toxicity effect on germination may be higher than the osmotic effect.