Strategies for Crop Improvement in Saline Soils

Abstract

With increasing salinization and desertification of previously productive land, new sources of salt tolerance are needed for crops grown in areas with saline sub-soils, or with rising water tables that bring salts to the surface. Salt tolerance is needed in perennial species that might be used to lower the water tables and so control salinization, and also for annual crops providing food and forage.

Salts in the soil water inhibit plant growth for two reasons. First, the presence of salt in the soil solution reduces the ability of the plant to take up water, and this leads to reductions in the growth rate. This is the osmotic or water-deficit effect of salinity. Second, if excessive amounts of salt enter the plant in the transpiration stream there will be injury to cells in the transpiring leaves and this may cause further reductions in growth. This is the salt-specific or toxic effect of salinity. As salinity is often caused by rising water tables, it can be accompanied by waterlogging. Waterlogging itself inhibits plant growth and also reduces the ability of the roots to exclude salt, thus increasing the uptake rate of salt and its accumulation in shoots.

Vast natural variation exists within crop species and their close relatives which is largely unexplored. This biodiversity could provide improved germplasm for salt-affected land. However, screening large germplasm collections is difficult and more targeted and feasible selection techniques are required. Knowledge of the target environment and understanding of the genetic basis for improvement will help to choose the most appropriate screening method. Towards this end, the different types of salinity and the physiological and molecular mechanisms for salt tolerance are briefly summarised in this review. There is great scope for improving the tolerance of important food and feed crops.