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found to be salt-sensitive whereas genotypes Jahongir,
Uzbekistan-32, Xalima, Miroz, Xisor 32 and Flip 06-102
were found to be salt-tolerant at 10 dS/m salinity level.
There was a significant interaction between salt and
shoot and root growth (
P
< 0.05) (Table 9.2).
However, other genotypes remained intermediate in
their salt tolerance with respect to seedling shoot and
root length. This would suggest the possibility of exploit-
ing genotypic variation in chickpea for tolerance to
specific concentrations of salts. The present observations
are in line with earlier reports in bean (Kaymakanova,
2009), ground nut (Mensah
et al.,
2006) and chickpea
(Al-Mutawa, 2003), where increased salinity also led to
decreased radicle lengths.
Salinity also affects uptake by plants of nutrients such as
phosphorus, nitrogen and potassium (Egamberdiyeva &
Hoflich 2004). According to Van Hoorn
et al.
(2001)
salinity strongly reduced soil nitrogen content, probably
through inhibiting nitrogen fixation and soil biological
activity responsible for transformation of organic
nitrogen. Salehi
et al.
(2008) reported that salt stress
reduced plant dry weight, nitrogen content and the
number of active nodules in alfalfa cultivars.
0 mM
50 mM
75 mM
100 mM
Figure 9.1
The effect of NaCl concentration on the colonization
of
Mezorhizobium
sp. in the rhizosphere of
Glycyrrhiza uralensis
.
a salt concentration of 100 mM NaCl totally inhibited
bacterial survival (Figure 9.1).
However, the species vary in tolerance to environ-
mental stresses (Sridhar
et al.,
2005; Wei
et al.,
2008;
Biswas
et al.,
2008). The rhizobial strains from various
grain legumes may tolerate 100-300 mM concentrations
of NaCl (Predeepa & Ravindran, 2010). Leguminous
plants growing in saline environments require both the
rhizobia and the host to be tolerant to salt. The salt toler-
ance of rhizobia is important for improved symbiotic
performance of legumes under stress conditions, where
they may enhance the nodulation and nitrogen fixation
ability of plants (Shamseldin & Werner, 2005; Ali
et al.,
2009). Salt-tolerant strains of rhizobia improved the salt
tolerance of host plants (Zou
et al.,
1995; Hashem
et al.,
1998; Shamseldin & Werner, 2005). Zahran (1999)
reported that rhizobia use distinct mechanisms for osmotic
adaptation to salt stress. Rüberg
et al.
(2003) reported the
accumulation of low-molecular-weight organic solutes
(osmolytes) by rhizobia to equilibrate internal and
external osmotic concentrations under salt stress.
9.2.2 rhizobia-legume symbiosis
and stress
It has been reported that the colonization and infection
of root hairs by rhizobial cells is sensitive to environ-
mental stresses (Zahran, 1999; Räsänen
et al.,
2003).
Several environmental stresses, including salinity,
drought, extreme temperature and nutrient deficiency,
are known to decrease survival and proliferation of rhi-
zobia in the rhizosphere, and inhibit the infection process
leading to symbiotic association with their plant host
(Biswas
et al.,
2008; Ali
et al.,
2009). Salt inhibits the
absorption of Ca, which reduces the growth of roots, root
tips and root hairs, thereby decreasing sites for potential
rhizobial infection and further nodule development
(Bouhmouch
et al.,
2005). The number of rhizobial cells
was found to be reduced in the root of soybean, common
bean and chickpea grown under salt stress conditions
(Zahran & Sprent, 1986; Bouhmouch
et al.,
2005).
We have also observed that increased salt content
decreased the ability of
Rhizobium galegae
sv.
officinalis
cells to colonize goat's rue roots (Egamberdieva
et al.,
2013b). Similar observations were made about the
decrease of root colonization of liquorice (
Glycyrrhiza
uralensis
) by
Mesorhizobium
sp. under salt stress, where
9.3 Improving legume yield by
inoculation with rhizobacteria
The utilization of root-associated bacteria that interact
with plants to mitigate the effects of various stresses
opens a novel, inexpensive and advanced technology for
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