511 (Sri Wida - Potency).cdr
POTENCY OF RHIZOSPHERE BACTERIA TO PROMOTE
RICE GROWTH UNDER SALINE CONDITION
*
SRI WIDAWATI and I MADE SUDIANA
Research Center for Biology, Indonesian Institute of Sciences CSC-LIPI, Bogor 16911, Indonesia
Received: 8 July 2015/Accepted: 25 July 2016
ABSTRACT
Saline soil is a common problem in coastal paddy field, especially in Indonesia. Salinity affects rice growth and the
activities of soil functional microbes, including functional bacteria, which play roles in plant growth. Some of these
microbes are associated with rice plants and are able to survive under saline condition. The presence of functional
microbes is also important to improve soil quality. Nitrogen and phosphate are essential soil nutrients and is available in
soil due to the activities of nitrogen-fixing bacteria and free-living plant-associated bacteria. The objective of the
present study was to obtain nitrogen-fixing, phosphate solubilizing and Indole Acetic Acid (IAA)-producing bacteria
that are able to survive and promote the growth of rice under saline conditions. From rice and peanut rhizosphere, Ca-
phosphate (Ca-P) solubilizing and nitrogen-fixing bacteria were isolated separately using specific media. Then, the Ca-
P solubilizing ability, phosphomonoesterase activity and IAA-producing ability were quantitatively examined. Based
on the abilities, 20 strains were selected and identified as Burkholderia cepacia-complex, Burkholderia anthina, Burkholderia
cenocepacia, Bacillus cereus-complex (three strains), Achromobacter spanius, Azospirillum sp. (four strains), Azotobacter sp.
(three strains), Rhizobium leguminosarum, Rhizobium sp. (two strains), and Pseudomonas sp. (three strains). The inoculation
of several single strains or the mixture of the selected strains promoted the growth of rice under saline conditions.
These inoculants could be potential as biofertilizer in saline paddy fields.
Keywords: Indole Acetic Acid production, phosphate solubilization, plant growth promoting bacteria, nitrogen
fixation, rhizosphere, rice
INTRODUCTION
Most of the fertile paddy fields in Indonesia
are located in coastal area and experiences soil
salinization due to seawater intrusion (Djufry et al.
2011). Salinity affects not only the growth of rice
(Oryza sativa Linn.), but also the activities of
functional soil microbes, including bacteria, that
play roles in mineralization of macro and
microelements for plant growth (Balser et al.
2006). Some of these bacteria are associated with
rice plants and are able to survive under saline
condition. The activity of soil microbes is an
important aspect of biogeochemical cycles of
carbon, nitrogen, sulfur, phosphorus, etc. (Banig
et al. 2008). The presence of functional microbes
is also important to improve the quality of soil
(Wijebandara et al. 2009). Nitrogen and phosphate
are essential nutrients and are available in soil due
to the activities of nitrogen-fixing bacteria and
free-living plant-associated bacteria (Steenhoudt
& Vanderleyden 2000). Several bacteria belonging
to the genera Rhizobium, Azotobacter and
Azospirillum are able to fix nitrogen and solubilize
phosphate (Nosrati et al. 2014). Some members
of these genera also produce plant growth
promoting hormone such as Indole Acetic Acid
(IAA), gibberellins and cytokinins (Bhattacharyya
& Jha 2012). Therefore, these genera are regarded
as important components of biofertilizer (Rao
1994; Bhattacharjee & Dey 2014). Introduction
of growth promoting bacteria can increase
nitrogen availability for plants and enhance crop
productivity. However, very little information is
available for the effect of salinity on bacteria that
have beneficial functions, such as nitrogen
fixation, phosphate solubilization and the
production of plant growth hormone (Pliego et al.
2011; Lugtenberg et al. 2013; Nakbanpote et al.
2014). The purpose of this study is to obtain
nitrogen-fixing, phosphate solubilizing and IAA
producing bacteria that are able to survive and
BIOTROPIA 3 2 6 116 123 Vol. 2 No. , 201 : - DOI: 10.11598/btb.2016.2 . .3 2 511
* Corresponding author: widadomon@yahoo.com
116
promote the growth of rice under saline
conditions.
MATERIALS AND METHODS
Bacterial Sources
Bacterial sources were obtained from collected
rhizosphere of rice (Oryza sativa) and peanut
(Arachis hypogaea) cultivated in the research field of
Cibinong Science Center, West Java Province,
Indonesia. The physical and chemical properties
of this research field indicated that the soil is
infertile soil (Table 1).
Isolation of Bacteria
Phosphate solubilizing bacteria were screened
following the method of Park et al. (2011). Halo
zone formation around colonies after 7 day-
cultivation at 30 °C on Pikovskaya medium was
used as an indicator of Ca-Phosphate (Ca-P)
solubilization (Nguyen et al. 1992). Nitrogen-
fixing bacteria were isolated targeting the genera
Rhizobium, Azopirillum and Azotobacter according
to Mubarik et al. (2011) and Salamone et al. (2012)
as well as Aquilanti and Clementi (2004),
respectively.
Determination of Ca-P Solubilization
Ca-P solubilizing ability of the isolated strains
was quantitatively determined according to Chen
et al. (2006) by measuring orthophosphate in the
culture fluid after 7 days of cultivation.
Orthosphosphate determination was conducted
according to Vassileva et al. (2000).
Determination of Phosphatase Activity
Extracellular phosphomonoesterase (PMEase)
activity of the strains was determined following
the method of Tabatabai and Bremner (1969)
using p-nitrophenyl phosphate. The unit of the
PMEase activity was defined as µmol/hof p-
nitrophenol released in 1 mL of extracellular
enzyme solution that was fractioned from 1.0 mL
of the culture fluid after 7 days of cultivation.
Determination of IAA Production
The IAA production of the strains was
investigated after 7 days of cultivation, following
the methods of Crozier et al. (1988) and Gravel et
al. (2007).
Selection and Identification of Bacteria
Based on the Ca-P solubilization, PMEase
activity and IAA production abilities, a total of
20 strains were selected from the above strains
for rice growth assays. Identification of the 20
strains was performed following the method
of Otsuka et al. (2008) based on the 16S rRNA
g e n e s e q u e n c e w i t h 1 6 S - 9 F ( 5 -
GAGTTTGATCCTGGCTCAG-3) and 16S-
1 5 1 0 R ( 5 - G G C T AC C T T G T T AC G A - 3 )
primers.
Rice Growth Assay at the Stage of
Germination under Saline Condition
One strain out of 10 taxonomic groups was
selected and subjected to a root and shoot growth
assay of rice at the stage of germination based on
Zaller (2007) and Cerabolini et al. (2004). Briefly,
ten seeds of three rice cultivars, INPARA-3,
INPARI-13 and INPARA-6 were soaked in sterile
water for 5 hours in their respective containers.
These 10 rice seeds were then arranged based on
their respective cultivars on top of filter paper
which was put inside a Petridish (20 cm in
diameter). Fifteen milliliter of 4.0 g/L NaCl
solution was poured onto the filter paper inside
Table 1 Physical and chemical properties of soils in the research field
Parameter
P
(%)
K
(%)
C
(%)
N
(%)
C/N
ratio
Ca
(%)
Exchangable
Mg
(%)
Exchangable
Na
(%)
Exchangable
Al dd
(%)
Soil
pH
Amount
of
bacteria
population
Characteristic
0.173
0.045 1.303
0.36
3.61
11.41
0.57 0.30 0.04
5.8
10
4
-10
5
Determined
accoding to
Rowell (1994)
Very
low
Very
low
Low
Moderate
Very
low
High
Low
Low
Low
Acid Infertile
117
Promoting rice growth using rhizosphere – Widawati and Sudiana
each Petridish, on which 10 rice seeds were lined
up, followed by 1.0 mL of bacterial inoculant
9
suspension containing 10 cells/mL. Root and
shoot lengths were measured at 7 days after
germination. This experiment was set up using
Complete Randomized Design with three
replications.
Rice Growth Assay at 45 Days after Planting
under Saline and Non-Saline Conditions
Ten strains out of 20 isolates tested on
germination test were then subjected to rice
growth assay for 45 days under saline condition
with 0.4% NaCl. The number of cells for each
7
treatment was adjusted to about 3.2 x 10 . This
value was selected based on the number of
bacteria commonly found in paddy field soil.
In a preliminary test (rice growth assay at the stage
of germination), INPARI-13 and INPARA-6
could not grow well under the same saline
condition. Therefore, only INPARA-3 was used
in this assay. Four seeds of INPARA-3 were
planted to experimental pots (0.5 gallon pots)
containing sterile sands (1.5 kg) flooded with
water(field capacity of sands = 24% or 360 mL ).
Treatments applied were: 1. Saline condition
(adding 360 mL of 0.4% NaCl (6 g NaCl) to the
0.5 gallon pots) and 2. non-saline condition
(without 0.4% NaCl). Into each pot, 5 mL of
bacterial inoculant suspension was added. The
result of experiment is shown in Table 5. After 7
days, the second inoculation with the same
amount of bacterial suspension was conducted.
The water level in pot was regulated by adding
sterile water to compensate water decrease
due to evaporation. The electrical conductivity
(EC) value of the assay media under saline
condition was kept at 7.5 mS/cm. At 45 days
after planting the growth of rice was evaluated.
This experiment was set as complete randomized
design performed with three replications.
RESULTS AND DISCUSSION
Composition of the Strains
The selected 20 strains, originated from the
rhizosphere of rice and peanut, belonged to the
genera Burkholderia, Bacillus, Achromobacter,
Pseudomonas, Azospirillum, Rhizobium and
Azotobacter (Table 2). The selected strains were
originated from non-saline soil. The reason for
the selection was to compare the physiological
characteristics of microbes isolated from saline
and non-saline soil. The result of this study
showed that the functional microbes for
Table 2 List of bacteria isolated from rice and peanut rhizosphere
Isolate
code*
Phylum/class** Taxon Source
(rhizosphere)
CSC P1
CSC P2
CSC P3
CSC P4
CSC P5
CSC P6
CSC P7
CSC P8
CSC P9
CSC P10
CSC P11
CSC P12
CSC N1
CSC N2
CSC N3
CSC N7
CSC N8
CSC N9
CSC N10
CSC N11
Proteobacteria/Beta-
Proteobacteria/Beta-
Firmicutes/Bacilli
Proteobacteria/Beta-
Firmicutes/Bacilli
Proteobacteria/Gamma-
Proteobacteria/Alpha-
Proteobacteria/Alpha-
Proteobacteria/Alpha-
Proteobacteria/Gamma-
Proteobacteria/Gamma-
Proteobacteria/Beta-
Proteobacteria/Alpha-
Proteobacteria/Gamma-
Proteobacteria/Alpha-
Proteobacteria/Alpha-
Firmicutes/Bacilli
Proteobacteria/Gamma-
Proteobacteria/Gamma-
Proteobacteria/Alpha-
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Rice
Peanut
Peanut
Peanut
Peanut
Peanut
Peanut
Peanut
Peanut
Notes: * = A Strain with P in its code were isolated as Ca-P solubilizing bacteria, and that with N were isolated as nitrogen fixing bacteria
** = Alpha-, Beta- and Gamma- denote the classes Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria, respectively
Burkholderia cepacia-complex
Burkholderia cenocepacia
Bacillus cereus-complex
Achromobacter spanius
Bacillus cereus-complex
Pseudomonas sp.
Azospirillum sp.
Azospirillum sp.
Rhizobium sp.
Azotobacter sp.
Azotobacter sp.
Burkholderia anthina
Rhizobium sp.
Pseudomonas sp.
Rhizobium leguminosarum
Azospirillum sp.
Bacillus cereus-complex
Azotobacter sp.
Pseudomonas sp.
Azospirillum sp.
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BIOTROPIA Vol. 23 No. 2, 2016
promoting rice growth were not different from
that reported by Susilowati et al. (2015).
Phosphate Solubilizing Ability of the Strains
Ca-P solubilizing ability of the strains is shown
in Table 3. The difference in the strength of Ca-P
solubilizing ability was not related to the
taxonomic property. All strains formed halo zone
around colonies, and the area ratio of the halo
zone to a colony was variable (data not shown)
indicating the ability to solubilize Ca-P differed
among the strains. This was reflected in the Ca-P
solubilizing ability which was quantitatively
determined (Table 3). The highest Ca-P
solubilization ability was shown by Pseudomonas sp.
CSC N2 and the lowest was shown by
Achromobacter spanius CSC P4. The activity of
PMEase is shown in Table 3. Pseudomonas sp.
CSCN2 again showed the highest PMEase
activity, and Achromobacter spanius CSC P4 seemed
to have no extracellular PMEase activity.
Nitrogen-Fixing Ability of the Strains
All strains belonging to Rhizobium, Azotobacter
and Azospirillum genera were able to grow on
nitrogen-limited media implying that these strains
were able to fix nitrogen (Chien et al. 1992).
IAA Production of the Strains
IAA production of the strains is shown in
Table 3. The amount of IAA produced varied
depending on strains. The highest production was
achieved by Azospirillum sp. CSC P8 and
Azospirillum sp. CSC P7. The lowest IAA
production was detected in Achromobacter spanius
CSC P4.
Effect of Bacterial Inoculation on the Rice
During the 7-day germination assay with 0.4%
NaCl, the effect of bacterial inoculation varied
depending on the strains (Table 4). The best
growth was obtained by the mixture of strains on
INPARA-3, with 7.46 cm and 6.5 cm in shoot and
root length, respectively. Medium level effect was
observed in Burkholderia cepacia-complex, Bacillus
cereus-complex, Pseudomonas sp., Azospirillum sp.
and Azotobacter sp. However, inoculation of
Burkholderia cenocepacia, Achromobacter spanius,
Rhizobium sp., Burkholderia anthina and Rhizobium
leguminosarum had no effect on shoot and root
length. Cultivars INPARA-6 and INPARI-13
could not grow without any inoculant (control) or
with five single-strain-inoculants.
In the 45-day growth assay (Table 5), the
growth of rice cultivar INPARA-3 under saline
Burkholderia cepacia-complex
Burkholderia cenocepacia
Bacillus cereus-complex
Achromobacter spanius
Bacillus cereus-complex
Pseudomonas sp.
Azospirillum sp.
Azospirillum sp.
Rhizobium sp.
Azotobacter sp.
Azotobacter sp.
Burkholderia anthina
Rhizobium sp.
Pseudomonas sp.
Rhizobium leguminosarum
Azospirillum sp.
Bacillus cereus-complex
Azotobacter sp.
Pseudomonas sp.
Azospirillum sp.
Table 3 Ca (PO ) solubilization ability, PMEase activity and IAA production of the strains3 4 2
Isolate
code
Taxon
Phosphate
Solubilization
(mg/L)*
PMEase
(Unit)*
IAA
Production
(mg/L)*
CSC P1
CSC P2
CSC P3
CSC P4
CSC P5
CSC P6
CSC P7
CSC P8
CSC P9
CSC P10
CSC P11
CSC P12
CSC N1
CSC N2
CSC N3
CSC N7
CSC N8
CSC N9
CSCN10
CSCN11
8.72 ± 0.89
1.06 ± 0.16
10.54 ± 0.16
0.30 ± 0.68
1.51 ± 0.11
11.26 ± 0.58
7.39 ± 0.42
6.68 ± 0.37
2.28 ± 0.63
5.71 ± 0.53
1.57 ± 0.95
0.47 ± 0.47
1.18 ± 0.05
11.39 ± 0.53
4.94 ± 0.32
2.00 ± 0.32
0.89 ± 0.95
0.83 ± 0.89
10.08 ± 0.26
1.86 ± 0.47
0.63 ± 0.71
0.13 ± 0.52
0.82 ± 0.85
0.01 ± 0.04
0.10 ± 0.86
0.75 ± 0.26
0.60 ± 0.86
0.68 ± 0.10
0.51 ± 0.70
1.27 ± 0.68
0.49 ± 0.67
0.10 ± 0.12
2.01 ± 0.34
2.22 ± 0.93
0.31 ± 0.27
0.47 ± 0.03
0.12 ± 0.88
0.45 ± 0.09
0.85 ± 0.89
0.14 ± 0.59
8.67 ± 0.92
2.63 ± 0.16
8.16 ± 0.90
1.94 ± 0.21
5.46 ± 0.58
8.27 ± 0.67
9.45 ± 0.06
9.56 ± 0.16
6.08 ± 0.42
8.75 ± 0.98
6.21 ± 0.32
2.13 ± 0.16
3.82 ± 0.89
8.16 ± 0.90
8.61 ± 0.10
7.61 ± 0.39
2.73 ± 0.68
8.39 ± 0.06
8.33 ± 0.84
8.09 ± 0.22
Note: Values represent mean±standard deviation (n = 3)
119
Promoting rice growth using rhizosphere – Widawati and Sudiana
Table 4 The effect of bacterial inoculants on root and shoot length of rice (three cultivars) at the stage of seed germination
Isolate code Taxon Rice cultivar
Shoot length
(cm)*
Root length
(cm)*
Control
CSC P1
CSC P2
CSC P3
CSC P4
CSC P6
CSC P8
CSC N1
CSC N9
CSC N12
CSC N3
Mix
(Control: no inoculation)
Burkholderia cepacia-complex
Burkholderia cenocepacia
Bacillus cereus-complex
Achromobacter spanius
Pseudomonas sp.
Azospirillum
sp.
Rhizobium
sp.
Azotobacter
sp.
Burkholderia anthina
Rhizobium leguminosarum
Mixture of strain
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
INPARA -3
INPARI -13
INPARA -6
4.03 a
dead
dead
5.55 de
4.23 ab
4.37 ab
4.16 ab
dead
dead
5.54 de
4.51 abcd
4.59 abcd
4.09 a
dead
dead
5.58 de
4.55 abcd
4.79 abcd
6.10 e
4.80 abcd
4.94 abcd
4.30 ab
dead
dead
5.56 de
4.82 abcd
4.31 ab
4.03 a
dead
dead
4.34
dead
dead
7.46 f
4.98 abcd
4.96 abcd
0.51 a
dead
dead
4.43 ghi
2,00 bcde
1.39 abc
1.47 abcd
dead
dead
4.24 ghi
2.99 defg
2.04 bcde
2.90 cdefg
dead
dead
4.70 hi
3.41 efgh
3.22 efgh
5.00 i
3.65 fghi
3.11 efgh
3.95 fghi
dead
dead
4.44 ghi
2.83 cdefg
2.39 bcdef
1.25 ab
dead
dead
3.62
dead
dead
6.50 j
4.01 ghi
4.13 ghi
Note: Values followed by the same letter in the same column are not significantly different based on Duncan's multiple range test at
5% level
condition was less than that under no saline
condition. Under saline condition, rice cultivar
INPARA-3 inoculated with the mixture of strains
showed the best growth with 29 cm in plant height
and 5.5 cm in root length. As a single isolate
inoculation, Pseudomonas sp. CSC N6 showed the
best effect.
Twenty strains with Ca-P solubilizing,
extracellular PMEase producing and IAA
producing abilities were successfully obtained,
with an exception of A. spanius CSC P4 that did
not show clear PMEase activity. These strains did
not lean to a specific taxonomic lineage and
composed of members of the phyla Proteobacteria
(the classes Alphaproteobacteria, Betaproteobacteria
and Gammaproteobacteria) and Fermicutes. The fact
that the strains were isolated as nitrogen-fixing
bacteria including Ca-P solubilizing members
indicated that Ca-P solubilizing ability was
common among bacteria, at least among those
living in the rhizosphere. It was also possible that
P M E a s e a c t iv i t y wa s c o m m o n a m o n g
120
BIOTROPIA Vol. 23 No. 2, 2016
Table 5 The effect of bacterial inoculants on the growth of rice cultivar INPARA-3, in sterile sand media under saline and
non-saline conditions 45 days after planting
Isolate
code
Inoculant Salinity
condition
Total dry
biomass
(g)
Plant
height
(cm)
Root
length
(cm)
–
CSC P1
CSC P2
CSC P3
CSCP4
CSC P6
CSC P8
CSC N1
CSC N9
CSCN12
CSC N3
–
No bacteria
Burkholderia cepacia-complex
Burkholderia cenocepacia
Bacillus cereus-complex
Achromobacter spanius
Pseudomonas sp.
Azospirillum
sp.
Rhizobium
sp.
Azotobacter
sp.
Burkholderia anthina
Rhizobium leguminosarum
Mixture of all the isolates
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
Non-saline
Saline
0.02 a
0.01 a
0.09 cde
0.07 abcd
0.06 abcd
0.04 abc
0.09 cde
0.08 bcd
0.04 abc
0.02 a
0.13 e
0.09 cde
0.09 cde
0.07 abcd
0.07 abcd
0.04 abc
0.08 bcd
0.07 abcd
0.06 abc
0.02 a
0.05 abc
0.02 abc
0.14 e
0.12 de
14.25 ab
13.00 a
27.50 ghi
26.25 ghi
26.00 fgh
22.75 cdefg
27.30 ghi
26.00 fgh
25.50 efgh
17.00 abc
29.50 hi
26.88 ghi
27.50 ghi
26.25 ghi
24.50 defgh
20.75 cde
26.50 ghi
26.25 ghi
21.00 cdef
17.15 abc
23.00 defg
19.00 bcd
31.00 i
29.00 hi
1.50 ab
1.00 a
5.00 jk
4.00 hij
3.50 fgh
2.65 de
4.50 ij
3.75 ghi
3.50 fgh
3.00 ef
6.15 l
5.00 jk
4.25 ij
4.00 hij
3.25 fg
2.25 cd
4.50 ij
3.75 ghi
3.50 fgh
2.25 cd
3.25 fg
2.00 bc
6.50 l
5.50 k
rhizosphere bacteria. Interestingly, the strains with
higher Ca-P solubilizing ability generally showed
higher PMEase activity. IAA production was also
reported as common among soil bacteria (Hasan
2002; Xin et al. 2009), which was supported by the
present study.
Saline environment inhibits rice growth. This is
because rice is a saline sensitive plant (Ashraf &
+ +
Harris 2004); also because the uptake of Ca , K 2
and inorganic N and P are disrupted under high
Na concentration (Ashraf & Harris 2004). In
addition, the salinity also affected soil enzyme
activities (Siddikee et al. 2011), which could
indirectly affect rice growth. The inoculation of
the selected strains affected germination of rice
under saline condition (Table 4). The inoculation
of mixture of the strains resulted in the best rice
growth. As single strain, Azospirillum sp. CSC P8
and Pseudomonas sp. CSC P6 provided the best and
the second best rice growth support, respectively.
It was possible that the inoculants supported the
growth of rice by supplying phosphate and IAA.
Azospirillum sp. is a potential nitrogen fixer and the
mixture of the strains also includes nitrogen
fixers. Therefore, it was possible that nitrogen
fixed by the inoculants might also promote rice
growth. Rice cultivars INPARI-13 and INPARA-
6 did not grow without the existence of
inoculants. The present study showed that the
inoculation of five strains and the mixture of
strains enabled these cultivars to grow. This
indicated that the inoculation not only promoted
rice growth by supplying nutrient and IAA, but
also enhanced rice tolerance towards salinity. It
was interesting that some strains isolated from
peanut rhizosphere could promote and support
rice growth.
Among the rice cultivars tested in the present
study, only INPARA-3 grew in saline condition
without inoculation of the strains. Therefore,
INPARA-3 was then subjected to rice growth
assay with 0.4% NaCl. In this assay, the
inoculation of the mixture of strains, Pseudomonas
sp. CSC P6 and Azospirillum sp. CSC P8 provided
Notes: Values followed by the same letter in the same column are not significantly different by Duncan's multiple range test at 5% level.
Non-saline condition = 360 mL freshwater in 0.5 gallon pots.
Saline condition = 360 mL freshwater in 0.5 gallon pots was added with 0.4% NaCl (6 g NaCl).
121
Promoting rice growth using rhizosphere – Widawati and Sudiana
the best, the second best, and the third best rice
growth support, respectively. These inoculants
may be promising as biofertilizer to support rice
growth in saline paddy fields.
CONCLUSIONS
Twenty strains of rhizosphere bacteria with
Ca-P solubilizing ability and IAA production were
successfully obtained in this study. Those bacteria
mainly belonged to Burkholderia cepacia-complex,
Burkholderia anthina, Burkholderia cenocepacia,
Bacillus cereus-complex, Achromobacter spanius,
Azospirillum sp., Azotobacter sp., Rhizobium
leguminosarum, Rhizobium sp. and Pseudomonas sp.
Potential nitrogen fixing bacteria are
Azospirillum sp., Azotobacter sp., Rhizobium
leguminosarum and Rhizobium sp. Most strains had
PMEase activity. Some strains showed growth-
promoting effect on rice under saline conditions
and produced plant growth hormone. These
strains could be candidates for biofertilizer for rice
in saline paddy field. It is also important to
consider using combination of inoculants and
rice cultivars to obtain maximum result.
ACKNOWLEDGEMENTS
This work was funded by JICA-JST SATREP
2011-2016. We thank Dr Shigeto Otsuka from
University of Tokyo for research guidance. We
are grateful to Senlie Oktavitana, Anis Mutirani
and Rinatu Siwi for their assistance in laboratory
works.
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