Salt tolerance in two soybean cultivars

Experiments were conducted in an environmentally controlled growth chamber to evaluate the role of the root system in the salt tolerance of two soybean (Glycine max (L.) Merr.) cultivars, Tachiyutaka and Dare, that differ in salt tolerance. Young plants were submitted to 0 (control), 40, 80, and 120 mM NaCl treatments for 3, 23, and 30 days in three experiments, respectively. The most significant differences between the two cultivars were obtained in 40 mM NaCl. Under this condition, compared with salt sensitive cv. Tachiyutaka, tolerant cv. Dare showed a higher relative shoot and root growth (Dare: 70 and 63%, Tachiyutaka: 42 and 42%, respectively), water extraction ability (Dare: 0.18g cm^-2d^-1 for transpiration and 0.98gm^-1d^-1 for water uptake, Tachiyutaka: 0.13 g cm^-2d^-1 and 0.81 gm^-1d^-1 respectively), root pressure (Dare: 5.68mg g^-1 for root exudate, Tachiyutaka: 0.32mg g^-1), better root osmotic adjustment (Dare: -0.61MPa for osmotic potential, Tachiyutaka: -0.59MPa), and less sodium (Na⁺) accumulation in plant tissue (Dare: 0.1, 0.4, and 9.2mg g^-1 in leaf, stem, and root, respectively, Tachiyutaka: 1.4, 3.5, and 11.6mg g^-1). The difference in salt tolerance between the two cultivars is attributed to the root system. The salt tolerance of cv. Dare is associated with high water uptake, and Na⁺ and chloride (Cl^-) exclusion of the roots.