Na+ and/or Cl- Toxicities Determine Salt Sensitivity in Soybean (Glycine max (L.) Merr.), Mungbean (Vigna radiata (L.) R. Wilczek), Cowpea (Vigna unguiculata (L.) Walp.), and Common Bean (Phaseolus vulgaris L.)

Grain legumes are important crops, but they are salt sensitive. This research dissected the responses of four (sub)tropical grain legumes to ionic components (Na+ and/or Cl-) of salt stress. Soybean, mungbean, cowpea, and common bean were subjected to NaCl, Na salts (without Cl-), Cl- salts (without Na+), and a high cation negative control for 57 days. Growth, leaf gas exchange, and tissue ion concentrations were assessed at different growing stages. For soybean, NaCl and Na+ salts impaired seed dry mass (30% of control), more so than Cl- salts (60% of control). All treatments impaired mungbean growth, with NaCl and Cl- salt treatments affecting seed dry mass the most (2% of control). For cowpea, NaCl had the greatest adverse impact on seed dry mass (20% of control), while Nat salts and Cl- salts had similar intermediate effects (similar to 45% of control). For common bean, NaCl had the greatest adverse effect on seed dry mass (4% of control), while Nat salts and Cl- salts impaired seed dry mass to a lesser extent (similar to 45% of control). NaCl and Na+ salts (without Cl-) affected the photosynthesis (P-n) of soybean more than Cl- salts (without Nat) (50% of control), while the reverse was true for mungbean. Na(+ )salts (without Cl-), Cl- salts (without Nat), and NaCl had similar adverse effects on P a of cowpea and common bean (similar to 70% of control). In conclusion, salt sensitivity is predominantly determined by Nat toxicity in soybean, Cl- toxicity in mungbean, and both Na+ and Cl- toxicity in cowpea and common bean.

Automated summary

Soybean is mainly affected by Na+ toxicity, mungbean is mainly affected by Cl- toxicity, and cowpea and common bean are affected by both Na+ and Cl- toxicity.