7.2
Salt Stress Tolerance
Several countries all over the world still depend on agriculture for its economic
growth and even per capita income depends on agriculture produce. In such situation, several issues are bothering agriculture which hampers the economy of the
nation. One such bothering issue in agriculture is the soil salinity. It is considered as
a major threat to agriculture and Ashraf (1994) and Vinocur and Altman (2005)
report that by 2050, 50% of all agriculture soils will be affected by increased salinity.
The stress induced in the soil due to the presence of different salt ions soluble in
water in excess creates salt stress. It may be because of carbonate (CO 3
2À ), bicarbonate (HCO 3
À ), calcium (Ca
2+ ), sodium (Na
+
), magnesium (Mg
2+ ), chloride (Cl
À ),
sulfate (SO 4
2À
), and potassium (K
+
) ions which leads to salinization. Even among
these, sodium chloride is considered to be a major contributor to salinity and the
chloride ions associated with it are toxic to many living organisms including plants.
Accumulation of these ions may also be a result of poor drainage of these ions from
the agricultural field through irrigation. They finally enter plant cells and lead to
bioaccumulation. High amount of these ions are detrimental for plant growth (Liu
and Zhu 1998; Zhu et al. 2005; Hasegawa 2013).
The vigor of the plant depends on several biochemical and physiological and
molecular approaches of the plant to the environment. High salt concentration is
known to disturb all these processes at various stages of its growth. The major
parameters altered during high salt concentration are membrane integrity, protein
synthesis, stomatal function, glandular trichome density, mineral nutrition, volatile
exudation, rate of photosynthesis, antioxidant capacity, and metabolism of lipids and
carbon (Parida and Das 2005; Zhou et al. 2018).
In an attempt to create a natural soil management strategy in sustainable agriculture, it is imperative to search for new strains of microorganisms which involve
along with the plants to alleviate the salinity induced stress, finally leading to plant
growth promotion and yield (Grover et al. 2011; Singh et al. 2011). To prove the
efficiency of microorganisms in the field, several researchers isolated the
microorganisms from the saline environment and attempted to prove their ability
in plant growth promotion. Goswamia et al. (2014) reported the isolation of
85 isolates from the rhizosphere of the halotolerant plant Suaeda fruticosa located
in the saline desert of the Little Rann of Kutch, Gujarat, India. Along with its ability
to survive and support plant growth in a saline environment, these isolates were also
screened for their additional ability to solubilize phosphate and production of indole
acetic acid (IAA). Among 85 isolates, 23 were found phosphate solubilizers, 11 were
reported to produce IAA, and 7 isolates were found to have both the activities. The
research also revealed the growth promoting activity of Bacillus licheniformis even
in the soil supplemented with 50 mM NaCl concentration used for testing the treated
plants. Highly promising result on significant increase in fresh biomass, root length,
and total length compared to control was also observed. These parameters of growth
enhancement are found even more significant in treated plants compared to control
in absence of sodium chloride.
230
M. P. Raghavendra
Salt Stress Tolerance
Several countries all over the world still depend on agriculture for its economic
growth and even per capita income depends on agriculture produce. In such situation, several issues are bothering agriculture which hampers the economy of the
nation. One such bothering issue in agriculture is the soil salinity. It is considered as
a major threat to agriculture and Ashraf (1994) and Vinocur and Altman (2005)
report that by 2050, 50% of all agriculture soils will be affected by increased salinity.
The stress induced in the soil due to the presence of different salt ions soluble in
water in excess creates salt stress. It may be because of carbonate (CO 3
2À ), bicarbonate (HCO 3
À ), calcium (Ca
2+ ), sodium (Na
+
), magnesium (Mg
2+ ), chloride (Cl
À ),
sulfate (SO 4
2À
), and potassium (K
+
) ions which leads to salinization. Even among
these, sodium chloride is considered to be a major contributor to salinity and the
chloride ions associated with it are toxic to many living organisms including plants.
Accumulation of these ions may also be a result of poor drainage of these ions from
the agricultural field through irrigation. They finally enter plant cells and lead to
bioaccumulation. High amount of these ions are detrimental for plant growth (Liu
and Zhu 1998; Zhu et al. 2005; Hasegawa 2013).
The vigor of the plant depends on several biochemical and physiological and
molecular approaches of the plant to the environment. High salt concentration is
known to disturb all these processes at various stages of its growth. The major
parameters altered during high salt concentration are membrane integrity, protein
synthesis, stomatal function, glandular trichome density, mineral nutrition, volatile
exudation, rate of photosynthesis, antioxidant capacity, and metabolism of lipids and
carbon (Parida and Das 2005; Zhou et al. 2018).
In an attempt to create a natural soil management strategy in sustainable agriculture, it is imperative to search for new strains of microorganisms which involve
along with the plants to alleviate the salinity induced stress, finally leading to plant
growth promotion and yield (Grover et al. 2011; Singh et al. 2011). To prove the
efficiency of microorganisms in the field, several researchers isolated the
microorganisms from the saline environment and attempted to prove their ability
in plant growth promotion. Goswamia et al. (2014) reported the isolation of
85 isolates from the rhizosphere of the halotolerant plant Suaeda fruticosa located
in the saline desert of the Little Rann of Kutch, Gujarat, India. Along with its ability
to survive and support plant growth in a saline environment, these isolates were also
screened for their additional ability to solubilize phosphate and production of indole
acetic acid (IAA). Among 85 isolates, 23 were found phosphate solubilizers, 11 were
reported to produce IAA, and 7 isolates were found to have both the activities. The
research also revealed the growth promoting activity of Bacillus licheniformis even
in the soil supplemented with 50 mM NaCl concentration used for testing the treated
plants. Highly promising result on significant increase in fresh biomass, root length,
and total length compared to control was also observed. These parameters of growth
enhancement are found even more significant in treated plants compared to control
in absence of sodium chloride.
230
M. P. Raghavendra