ABSTRACT
Salt tolerance is generally defined as the degree to which a plant endures salinity as a stressor. The components of salinity include the composition of the ions in the salt, e.g., sodium, chloride, calcium, and sulfate, and their concentrations. A plant may be exposed to salt continuously or intermittently and salt ions may affect the plant through their effects in the root zone as a component of the soil water or as a salt spray on leaf surfaces. Different plant species, and even sometimes varieties within a species, differ in salt tolerance. In addition, plants differ in their tolerance to salinity exposure depending on their stage of growth and different plant measurements can be taken as an index of salt tolerance. If salt stress becomes too severe, the plant may exhibit varying types of leaf burn and necrosis and will eventually die, but under moderately saline conditions it is very difficult to identify a salt-stunted plant from visual symptoms. Although scientists have studied the effects of salinity on plant growth, metabolism, and biochemistry, only a few genetic markers have been identified that have helped to improve salt tolerance in crops.
