Physiological Traits Underlying Differences in Salt Tolerance among Glycine Species.

Salinity is an important abiotic factor that can drastically reduce crop yields by limiting water uptake and causing ion-specific stress. Soybean [Glycine max (L.) Merr.] is sensitive to soil salinity. Previous studies, however, have shown that there is variability among genotypes and Glycine species for salt tolerance, which suggests that genetic improvement may be possible. The objective of this study was to identify physiological traits underlying differences in salt tolerance among four Glycine species. Four NaCl (salt) treatments, 0mM, 50mM, 75mM and 100mM, were imposed at the V2-V3 growth stage (Fehr et.al., 1971) on G. max, G. soja, G. tomentella and G. argyrea accessions with different levels of salinity tolerance. Fourteen days after initial NaCl treatments, each of the genotypes was evaluated for leaf scorch, chlorophyll content, leaf, stem and root dry weights and ion content, and stem and root lengths. Significant differences in leaf scorch scores were observed across accessions. Also, significant and positive correlations between leaf injury (scorching) and leaf Cl^- and Na⁺ concentrations were discovered. Regression analyses indicated that tolerant genotypes have a greater capacity to prevent Na⁺ and Cl^- transport from the soil solution to the leaves than sensitive genotypes. Moreover, the magnitude of leaf injury was lower in tolerant accessions per unit increase in Na⁺ or Cl^- concentrations in leaves than in susceptible ones. In addition, salt tolerant accessions had significantly greater chlorophyll-meter readings than sensitive ones at all NaCl concentrations. G. argyrea and G. tomentella accessions possessed higher salt tolerance than G. soja and G. max genotypes. Identification and understanding of traits differentially expressed in salt tolerant and sensitive genotypes and their inclusion in the breeder’s toolbox will allow further improvement in breeding salt tolerant soybean.