IONIC CONCENTRATIONS AND WATER RELATIONS OF ALFALFA SEEDLINGS DIFFERING IN SALT TOLERANCE

There is great variability within alfalfa (Medicago sativa L.) populations in response to salinity stress. This study was conducted to investigate the physiological basis of that variability. Growth performance and physiology were compared in two groups of a population of alfalfa seedlings that differ in vigor when grown under - 0.7 MPa salinity. The experiments were conducted in a greenhouse using a system designed to screen seedlings for salt tolerance. Plant height, internode length, leaf area, number of leaves, dry weight, ion concentration, percent water, and water potential were measured. Shoot parts of the more vigorous group contained lower concentrations of Na and Cl. Roots of the vigorous group contained higher Na concentrations. The vigorous group contained more total ions (Na + Cl + K) per plant but fewer total ions on a dry weight basis. Water potentials of both shoots and roots were greater in the vigorous seedling group; there were no differences in percent water. Salt tolerance appeared to be related to the ability of the vigorous plants to maintain lower ion concentrations, particularly in the leaves, and to their greater growth rates, which may have served to dilute ions.