Effect of osmotic and salinity stresses on germination and seedling growth indices of artichoke (Cynara scoolymus) and purple coneflower (Echinacea purpurea)

In order to study the effects of osmotic and salinity stresses on germination and seedlinggrowth indices of Artichoke and Purple coneflower, four separate laboratory experimentswere conducted as completely randomized design with four replications at Crop PhysiologyLaboratory of Ferdowsi University of Mashhad during 2009. Treatments were eight levels of osmotic stress (0, -2, -4, -6, -8, -10, -12 and -14 bar) using PEG 6000 for first and second experiments and six levels of salinity stress using NaCl (0, -1, -3, -5, -7 and -9 bar) for third and fourth experiments. Results showed that Artichoke was more resistant than Purple coneflower to osmotic and salinity stresses. Germination percentages of Artichoke and Purple coneflower were 72 and 5% in -10 bar osmotic stress, respectively; while germination percentages of Artichoke and Purple coneflower were 75 and 8% in -5 bar salinity stress, respectively. Increasing osmotic stress severity increased mean germination time of Artichoke, while the effect of different osmotic stress levels was not significant on mean germination time of Purple coneflower. Radicle / plumule length ratio was increased by increasing osmotic and salinity levels in Artichoke, while this ratio was not varied by osmotic stress and was decreased by salinity stress in Purple Coneflower. Moreover, seedling dry weight was decreased by increasing osmotic and salinity stress in both medicinal plants. Overall, it seems that germination indices and seedling growth in Artichoke were superior to Purple coneflower under stress conditions.