Salinity stress, its physiological response and mitigating effects of microbial bio inoculants and organic compounds

Abstract

Around 20% of irrigated land globally affected due to salinity stress. This condition is more severe in some states where the effect is more than 35%. Salinity stress caused mainly due to two reasons one of them is the poor quality of irrigated water and other is the excess concentration of salts present in the soil. There are two different mechanisms in plants in response to salt stress, which further provides signals to various parts of plants and enacts according to that response. Based on the ability to tolerate the stress plants classified as glycophytes, which can tolerate a low level of saline stress while others are halophytes, which can tolerate more level of saline stress. Halophytes like mustard can cope up with the situation of salinity stress because they have a special mechanism for it. There many ill effects of salinity stress on mustard plants, which leads to its lower productivity and a lower economic benefit. This saline stress has adverse effects in all around the world along with India, especially in arid regions. There are various mitigation methods to cope with this salt stress and thus preventing its negative effects on production and reduce our economic loss. The application of microbial bio inoculants that are trichoderma, mycorrhiza, rhizobium, and organic compounds that are cycocel and benzyl adenine reviewed in this paper. It also involves various mitigating effects of them, which is, observed by application of them in Mustard plants. Introduction The Brassica juncea L. that is usually named, as Indian mustard is a plant of Brassicaceae family and used in various purposes. The chief component of the mustard plant is its oil, which is famous for its comestible nature and medicinal usefulness in not only India but also whole over the world. It has some other purposes also like biofuels, feed for cattle and fertilizer for the land. It is widely cultivated in arid and many semi-arid zones of the world. India positioned second in all over the earth in terms of cultivation of Brassica as well as contributes to 7 per cent of edible oil's supply in all countries but still, its cultivation is not fulfilling the needs of the population of the country and also not sufficient for export. The reason behind very less production is highly susceptible to nature to various stresses. In among all of them; saline stress is a major concern. Soil is considered to be saline if its electrical conductivity is more than 4 dS/m which is equivalent to 4 mmhos/m. The salinity stress is of two major types one of the natural salinity is due to the number of salts present naturally in soil and other is induced salinity, which is due to the accumulation of salt due to various human activities. The plant characterized into two ways based on the tolerance of their salt stress. One of them is a halophyte, which could easily tolerate this salt stress, and others are Glycophytes, which are sensitive to saline conditions and unable to grow under salinity stress. Halophytes like mustard can cope up with the situation of salinity stress because they have a special mechanism for it. The first step it includes is Exclusion in which the entry of toxic ions at root level 2 nd is compartmentation at plant level in which toxic ions transferred to older leaf sheath and older plant tissues. The third includes the excretion of toxic salt through salt hairs, salt glands and or bladders. The fourth step includes cell level compartmentation in which sequestration of toxic ions to vacuoles and cell wall. Salinity stress causes types of stress one of them is Ionic and other is Osmotic. In ionic stress plant, there is an accumulation of Na ions and K deficiency, which leads to Na toxicity which results in plant senescence. In response to its plants to avoid this stress plant, maintain ion homeostasis and Na extrusion. While on other stress i.e. osmotic stress it leads to dehydration and low leaf development. The salt stress has also been found responsible for an increased respiration rate, ion toxicity, changes in C and N metabolism,