Three treatments consisting of 0%,15%,and 30%seawater were investigated to analyse the ecotypic variabilities among five populations of Jerusalem artichoke(Helianthus tuberosus)regarding their responses to seawater stress under a hydroponic culture system.Analyses were done 2,4,and 6 days after treatments.The 15%and 30%seawater treatments reduced the growth rates of roots and shoots of H.tuberosus populations.The activities of superoxide dismutase, peroxidase,and catalase majored in the leaves were stimulated under the seawater stress.The electrolyte leakage and malondialdehyde contents of the leaves were also stimulated owing to seawater stress.The contents of proline and soluble- sugars in the leaves increased significantly with increasing seawater concentrations.The concentrations of Na+,K+,and Cl-in the aerial parts and roots increased with an increase in the seawater concentration throughout the experimental period.There were ecotypic differences among the five populations of H.tuberosus as evidenced by the analyses of the above items in both aerial parts and roots under seawater treatment.The magnitude of the ecotypic variance components indicated that a substantial proportion of the total variation for these physiological and biochemical responses were owing to ecotype,indicating the possibility of improvement through hybridization and selection. Three conditioning consisting of 0%, 15%, and 30% seawater were investigated to analyze the ecotypic variabilities among five populations of Jerusalem artichoke (Helianthus tuberosus) regarding their responses to seawater stress under a hydroponic culture system. Assays were done 2,4, and 6 days after treatments. The 15% and 30% seawater treatments reduced the growth rates of roots and shoots of H. tuberosus populations. The activities of superoxide dismutase, peroxidase, and catalase majored in the leaves were stimulated under the seawater stress. electrolyte leakage and malondialdehyde contents of the leaves were also stimulated due to seawater stress. The contents of proline and soluble- sugars in the leaves increased significantly with increasing seawater concentrations. concentrations of Na +, K +, and Cl-in the aerial parts and roots increased with an increase in the seawater concentration throughout the experimental period.There were ecotypic differences among the five populations of H.tu berosus as evidenced by the analyzes of the above items in both aerial parts and roots under seawater treatment.The magnitude of the ecotypic variance components indicated that a substantial proportion of the total variation for these physiological and biochemical responses were due to ecotype, indicating likely of improvement through hybridization and selection.