Mung bean (Vignaradiata L.) belongs to family Papilionaceae. It is an important pulse crop in South and Southeast Asia and is widely used due to its nutritional value. It is used in various forms such as cooked foods, mixed with different vegetables and meat as well as different types of cakes and noodles is also formed by using mung bean. In Pakistan, mung bean is grown on an area of 218,000 ha with annual production of 138.46 thousand tons. Mung bean has a high nutritional value. There are 22-28per cent protein, 60-65 per cent carbohydrates, 1-1.5per cent fat and 3.5-4.5 per cent fibers in the seeds of mung bean. It is the richest source of proteins. Nearly 50 per cent production of mung bean is reduced by the salinity. This decline in production was due to the accumulation of high concentrations of toxic ions like Na+ and Mg2+ and low concentration of Ca2+ and K+ ions in plant body under salt stress. Pulses are a richest source of protein, but under salt stress condition production of protein is significantly decreased. Particularly in mung bean, legume production is severely affected under salt stress condition due to increased necrosis and chlorosis as well as reduction in photosynthetic pigments in leaves.
Pakistan has mostly arid and semi-arid areas resulting in more rates of evapotranspiration and low precipitation. Large quantity of the surface water is penetrating in the ground and very low amount of water is available to the cultivators for the irrigation purpose. Due to these factors, different salt ions have been accumulating in soil to alarming situation and causing the more salinity level in the soil. According to an estimate, soils in Pakistan have very high ionic profiles mainly of cultivable land. Soil salinity has a remarkable effect on various physiological and yield parameters and causes deficiency of essential nutrients.
Soil salinity is a common problem in various parts of the world and has adverse effect on all the crop plants. It is a usual problem for the irrigated agriculture. Problem of soil salinity during the last few decades has emerged as a major global issue, which stands true for Pakistan as well. Salinity is the global crisis now a day. Soil salinity is widespread mainly in those regions of the world which have arid and semi-arid land. Production of the most crops was abruptly decreased from last few decades due to the salt stress. Soil salinity interrupts the various essential processes of plants. As a result of this, growth of the different crops was significantly reduced. Soil salinity is a major concern to the agriculture in the different areas of the world.
The growth and productivity of the several crops are significantly reduced by the increasing salinization. A lot of work has been done in relation to impact of salinity on crop plants. Soil salinity is the major problem in the world and causing a huge loss of crop production worldwide. Problem of the salinity is more severe on the lands that have low precipitation rate as well as more cutting of vegetation. Extensive irrigation of the cultivated land also results in accumulation of various salts. The world wide area affected by the salinity is about 953 million ha, which consist of 8 percent of the land surface. In Pakistan, 10.0 Mha area is salt affected, which consists of 12.9per cent of the total land area of Pakistan (FAO, 2008).
The balance of different ions in plants is disturbed by the salt stress. This ion distribution is effected by the salinity at the cell level as well as in the entire plant. Due to this disturbance of ions, different types of stresses in plants are produced like osmotic stress and oxidative damage, which ultimately cause the death of the plant.During the salt stress condition, various metabolic changes occurred due to high amount of NaCl. These change including the distruption the process of photosynthesis, inhibition the functions of some enzymes as well as production of reactive oxygen species. Division and expansion of the cells is reduced due to these metabolic changes and probably the cells are more likely to be dead.
Various activated oxygen species are produced under salt stress condition. These species severely affect the structure of proteins, DNA as well as reduction in photosynthetic pigments. Due to the activated oxygen species, chlorophyll contents are decreased in the plants, which are exposed to salinity stress. Under the salinity stress, amount of proline is significantly increased. The enhanced proline is the source of energy for plants, which they used against the salt stress tolerance.
Salt stress also significantly affects the anatomical attributes of root and stem. The water conducting tissue is curtained by the increasing amounts of salt stress, in particular the number of xylem vessels decreased. Size of some parenchymatous tissues like cortex and pith is also reduced under salt stress. Different anatomical changes are observed in the root and shoot under salt stress condition.
The diameter and the length of the root become decreased due to salinity stress. Some other changes like reduction in the mass of vascular cylinder, cortex layer and apical meristems. Moreover, some layers like endodermis and exodermises become more lignified and suberized.Soil salinity has a significant effect on the pulses. When the pulses are exposed to salt stress environment, their ability for ion uptake is reduced and concentrations of the different dangerous salts increase in plants, whereas the amounts of some important ions like K+ and Ca2+ decrease during salt stress. Accumulation of some ions like Na+ and Cl- in pulses disturbed the functioning of certain enzymes.