The interaction between salinity stress and seed vigour during germination of soyabean seeds

Seeds of six soyabean (Glycine max (L.) Merr.) cultivars were germinated between paper towels moistened with a range of solutions of both NaCI (32.2 to 421.1 mmolal NaCI) and polyethylene glycol (PEG, 5-30% w/v). The solutions of NaCI and PEG used had the same water potentials within the range -0.23 to -1.9 MPa. After 8d the ungerminated seeds were transferred to towels moistened with deionised water for 7d. Cultivars differed in their response to salinity and failure of seeds to recover from high salinity when transferred to deionised water, revealed the toxicity of NaCl. In contrast, the increase in germination during the recovery period after exposure to PEG suggested that PEG was not toxic. At the same external water potential, the lower mean germination time (MGT) and higher final germination in NaCl than in PEG could be explained by the more rapid imbibition in NaCl solutions and achievement of a moisture content that allowed germination. The influence of seed vigour on the response of soyabean to stress was examined using seeds having high percentage germination but a range of seed vigour, produced by rapid ageing at 15% moisture content (MC) and 45°C for up to 9h. The germination of aged seeds having reduced vigour fell with increased salinity (330, 421 mmolal NaCI) but there was no significant interaction between salinity and seed ageing. Transfer of unaged and aged seeds to 0 MPa after exposure to NaCI resulted in a greater increase in the germination of unaged seeds. The negative correlation of seed leachate conductivity and MGT with the increase percentage germination after transfer to 0 MPa suggested that seed vigour influences the ability of seeds to recover from saline conditions.