Physiological Response of Salt‐Tolerant and Nontolerant Alfalfa to Salinity during Germination1

Abstract

Identification of the physiological processes involved in salt tolerance is required to develop appropriate selection criteria for breeding salt‐tolerant crops. For this purpose selected physiological characteristics were evaluated in five alfalfa (Medicago sativa L.) populations selected for NaCl tolerance during seed germination and the source population, 'Mesa‐Sirsa'. Seed of the populations (Syn‐1) was germinated in distilled water and solutions of NaCl, NaNO3, KC1, KNO3, and mannitol ranging from −1.0 to −1.6 MPa osmotic potential. The mean difference in percent germination between Mesa‐ Sirsa and ‘AZST1982’, the most salt‐tolerant population, was greater in the NaCl solutions than the other salt solutions (P < 0.01). Seed from AZST 1982 also had higher percent germination than Mesa‐Sirsa in mannitol solutions (90.6 and 2.8%, respectively, at −1.6 MPa osmotic potential). Mesa‐Sirsa had higher (P < 0.01) average seed respiration rate than AZST 1982 between 3 and 24 h of germination in NaCl solutions of −0.6 to −3.0 MPa osmotic potential. There was no significant difference between Mesa‐Sirsa and AZST 1982 for Na+ or Cl− accumulation after 48 h of germination in NaCl solutions of −0.6 to −1.8 MPa osmotic potential, or absorption of tritiated water after 6 and 12 h of germination in NaCl solutions of −1.3 and −2.0 MPa osmotic potential. Selection for NaCl tolerance in germinating alfalfa seed results in two separate types of tolerance: tolerance of an inhibitory effect specific to NaCl and tolerance of lowered water potential. Selection for NaCl tolerance of alfalfa during germination does not appear to influence ion accumulation or the rate of imbibitional water uptake.