Superior salt tolerance in wild soybean (G. soja) is associated with better ion ‘exclusion’ ability from leaves and mesophyll cells than cultivated soybean genotypes (G. max)

Soybean (Glycine max) is a salt-sensitive crop. However, wild soybean (Glycine soja) is a potential source of germplasm to improve salt tolerance in G. max. This study evaluated the response of cultivated soybean (G. max cv. Bunya and Lee) and wild soybean (G. soja) to ionic components of salt stress to test the hypothesis that wild and cultivated soybean genotypes differ in leaf tissue tolerance to Na⁺ and/or Cl^–. The soybean genotypes were subjected to NaCl, Na⁺ salts, and Cl^– salts at 50, 75 and 100 mM, and a non-saline control to analyse the effect of salts/ions on growth, tissue ion concentrations and photosynthesis. Cryo-SEM X-ray microanalysis was used to evaluate cellular [Na], [Cl] and [K] in various cell types within leaflets. NaCl and Na⁺ salts reduced shoot and root dry mass more than Cl^– salts in the three genotypes. Soja maintained higher photosynthetic rates (84 % of control) than Lee (70 % of control) and Bunya (60 % of control) in the 75 mM treatments. Soja had lower [Na⁺] in leaves and mesophyll cells than Lee and Bunya. G. soja had greater tolerance to salinity than G. max due to better ‘ion exclusion’ from leaves and photosynthetically active mesophyll cells.