Salt Tolerance

Abstract

AbstractSalinity has adversely affected irrigated agriculture for thousands of years. The salt tolerance of a plant defined as the plant's capacity to endure the effects of excess salts in the m,edium of plant growth has a major role in managing salt affected lands found both under irrigated and non‐irrigated agriculture. Plants show both inter and intragenic differences in tolerance to salts. Absolute tolerance to salinity cannot be expressed explicitly because many edaphic and environmental factors influence salt tolerance in plants. Even the growth stage at which salt stress is experienced has a profound effect on salt tolerance. Although data are not sufficient to conclude but one would tend to agree to a statement that many crops and plants show increased tolerance with age. Amongst many criteria evolved to date to characterize relative salt tolerance of plants such as survival of the plants, vegetative growth, absolute yield and relative yield, the last one seems to be the most promising. A piecewise linear model proposed by Maas and Hoffman has been extensively used to prepare relative salt tolerance tables for most kind of crops such as herbaceous crops, vegetable and fruit crops, woody crops, ornamental shrubs, trees and ground cover crops. Salt tolerance characteristic of plants have played and would continue to play a role in the management of poor quality land and water resources for the benefit of mankind. It has been illustrated with the help of an example of sequential concentration model to manage poor quality water resource. Although attempts to make a headway in developing salt tolerant crops have been made but still many teething troubles are being experienced. The complexity of these problems rule out any major breakthrough on this front in a near future yet efforts in this direction seems to be well focused.The literal meaning of tolerance is to endure, sustain, or put up with. Thus, the salt tolerance of a plant could be defined as the plant's capacity to endure the effects of excess salt in the medium of root growth. That plants can withstand a fair amount of salts without adverse effects is implicit in this definition. In fact, a fair proportion of salts in the growing medium is needed for good growth. There are instances where plant growth is stimulated at low concentrations of salts, and only thereafter, the yield starts declining. Apparently, the problem of soil salinity develops only when the salts accumulate in the root zone to an extent that it becomes harmful to the plants. The salt tolerance of a plant is also expressed in terms of the yield decrease expected for a given level of salinity compared to the yield under nonsaline conditions. Many times, salt tolerance and salt resistance have been used synonymously although, the two do not convey the same meaning. Salt resistance is a plant's ability to decrease or prevent the stress from penetrating into its tissues, but tolerance is the ability of the plant to eliminate, reduce, or repair the stress once it has already penetrated.