Matching physiological traits and ion concentrations associated with salt stress in cowpea genotypes

The salt tolerance of 25 cowpea genotypes (Vigna unguiculata L. Walp.) was studied during early vegetative growth. Salinity treatments were applied by irrigating with a nutrient solution containing 0, 85, and 170 mmol NaCl/L. Seedling survival decreased linearly as salinity increased, but this enabled cowpea genotypes to be ranked for salinity tolerance according to the magnitudes of slopes of regression of survival percentage on salinity. Sodium concentration was higher in roots than in shoots in all genotypes, and increased significantly in both roots and shoots as salinity increased. Chloride concentration in both roots and shoots increased with increasing salinity in all genotypes, and was higher in shoots than in roots at 85 and 170 mmol NaCl/L. In some cases, Ca, Mg, K, and P concentrations were reduced by an increase in salinity, but none of the genotypes appeared to suffer any nutrient deficiency. We observed wide differences in responses to salinity, and our results suggest that during the growth stage studied, 7 of the 25 genotppes tested could be classified as tolerant or relatively tolerant to salinity (Sonorense, CB3, CB27, Cuarenteno, CB46, Paceno, and IT82D-889).