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combating the problems of salinity (Egamberdiyeva &
Hoflich, 2003; Berg
et al.,
2010; Pliego
et al.,
2011;
Lugtenberg
et al.,
2013). In our previous work, we
reported increased dry matter yield, nodulation, seed
yield and protein content of soybean seeds grown under
saline soil after inoculation with salt-tolerant strains of
Bradyrhizobium
spp. (Egamberdiyeva
et al.,
2004).
Similar results were observed for chickpea, where shoot,
root length and dry matter increased after inoculation
of PGPR strain under stressful soil conditions (Mishra
et al.,
2010).
The tripartite bacterial-mycorrhizal-legume symbi-
osis also showed improvement in legume growth and
development under stressful conditions. For example,
Estévez
et al.
(2009) observed that co-inoculation of
Rhizobium tropici
CIAT899 with
Chryseobacterium balusti-
num
Aur9 improved growth and symbiotic performance
of salt-stressed soybeans compared with the single
inoculation (CIAT899). Molla
et al.
(2001) also showed
that total root length, root number, dry matter, root
hair development, number of nodules and shoot dry
matter of soybean were significantly increased by
Azospirillum lipoferum
and
Bradyrhizobium japonicum
.
Dardanelli
et al.
(2008) also observed improved rhizo-
bia-legume symbioses under saline conditions by
co-inoculation of common bean with
Rhizobium
and
Azospirillum
strains.
Dual inoculation of
Rhizobium
with
Azotobacter
showed
increased nodulation and plant growth of faba bean
under drought conditions (Dashadi
et al.,
2011). Han
and Lee (2005) also observed alleviation of induced
stress in plants and improvement in root and shoot
growth of soybean by dual inoculation with
Bacillus sub-
tilis
and
Bradyrhizobium japonicum
.
There are also several reports on the improvement of
nodulation and plant growth of legumes by phosphate-
solubilizing bacteria. For example, Rosas
et al.
(2006)
reported on the positive effect of phosphate-solubilizing
bacteria
Bradyrhizobium japonicum
and
Pseudomonas putida
on the root and shoot growth of soybean. Similar results
were observed by Kumar and Chandra (2008), who
showed that phosphate-solubilizing bacteria improved
the symbiotic performance of introduced rhizobia in
field-grown lentils. In another study,
Pseudomonas
spp.
inoculated together with rhizobia significantly increased
the number of pods per plant, number of seeds per pod
per plant and seed yield per hectare of soybean (Argaw,
2012). Phosphate-solubilizing bacteria (PSB) are known
to help plants to acquire more phosphorus from soil,
thus stimulating P uptake by plants and also improving
nodulation and nitrogen fixation (Elkoca
et al.,
2008).
El-Azouni (2008) observed significant increases of dry
matter, N and P uptake and yield of soybean grown in
Egyptian soil inoculated with the phosphate-solubilizing
fungi
Aspergillus niger
and
Penicillium italicum.
In another
study, the sulphur-oxidizing bacteria
Thiobacillus
sp.
stimulated nodule number, plant biomass and yield of
groundnut, and increased soil available S (Anandham
et al.,
2007).
Rabie and Almadini (2005) observed that the dual
inoculation of faba bean (
Vicia faba
) with nitrogen-fixing
bacteria (NFB)
Azospirillum brasilense
and the arbuscular
mycorrhizal (AM) fungus
Glomus clarum
increased salt
tolerance of plants and improved growth and development
under saline conditions. In their study significant effects
of inoculation were reported in the plants for salinity tol-
erance, mycorrhizal dependency, phosphorus level,
phosphatase enzymes, nodule number, nitrogen uptake,
protein content and nitrogenase enzymes.
A greenhouse experiment demonstrated that the salt
tolerance of goat's rue was clearly improved when the
plant was inoculated with its own specific symbiont
Rhizobium galegae
sv.
officinalis
and
Pseudomonas extre-
morientalis
TSAU20 (Egamberdieva
et al.,
2013). Dual
inoculation with
Rhizobium
and plant growth-promoting
rhizobacteria (PGPR)
Pseudomonas
could also enhance
formation of nodules on soybean grown in salinized
potting soil. In recent studies, Aamir
et al.
(2013) dem-
onstrated that combined inoculation of mung bean
enhanced nodulation, grain yield (up to 30%) and pro-
tein content (up to 48%) compared to an individually
inoculated control.
The survival of introduced PGPR strains in the roots
of legumes is important, as bacteria may deliver biolog-
ically active compounds directly to the rhizosphere of
plants. We have investigated the effect of salinity on the
colonization of two selected plant-growth-promoting
bacteria
P. extremorientalis
TSAU20 and
P. chlororaphis
TSAU13 in the rhizosphere of common bean, using a
gnotobiotic sand system, and determined their survival
on the plant roots in pot experiments under salinated
soil conditions (Egamberdieva, 2011). Results showed
that bacterial strains were able to colonize the rhizo-
sphere of bean at the highest salinity (12.5 dS/m) and
were also able to survive in the root of bean grown in
saline soil.
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