TISSUE CULTURE AND RADICLE EXCISION TECHNIQUES FOR EVALUATION OF SALT TOLERANT ALFALFA (MEDICAGO SATIVA L.).

Tissue culture and radicle excision techniques were employed to evaluate salt tolerance in alfalfa (Medicago sativa L.). Plant suspension cultures of either seedling root or shoot origin were studied in media with or without supplemental NaCl (3.54 g liter⁻¹). In most cases, the growth rates of root-derived cultures were stimulated by this low level of supplemental NaCl while most shoot-derived cultures were not stimulated by NaCl. Excised radicles of three populations of alfalfa which possessed widely differing ranges of germination salt tolerance were screened in four salts (NaCl, KCl, Na₂SO₄, and K₂SO₄) at six varying concentrations. As was observed in the tissue culture experiments, low levels of NaCl (7.09 g liter⁻¹) stimulated radicle elongation of all populations as compared to the elongation levels of the control solutions (no supplemental salts). In general, for NaCl, the population that posessed the highest degree of germination salt tolerance (Az-St 1982) also displayed the greatest rates of radicle elongation especially in the highest salt concentrations. Additionally, this population along with the moderately germination salt tolerant population (Az-ST 1979) maintained higher rates of elongation in KCl, K₂SO₄ and Na₂SO₄ than did the control germplasm which has little germination salt tolerance (Mesa Sirsa Control). Examinations of each individual population in all four salts simultaneously, indicated that the sulfate salts reduced radicle elongation to a greater extent than did the chloride salts. Evaluation of both osmotic effects and specific ion effects showed that the specific ion effects attributed to the anions were more detrimental to radicle elongation than were the osmotic effects.