Rhizobium and Phosphate Solubilizing Bacteria Improve the Yield and Phosphorus Uptake in Wheat (Triticum aestivum)

Abstract

Rhizobium and phosphorus (P) solubilizing bacteria are important to plant nutrition. These microbes also play a significant role as plant growth-promoting rhizobacteria (PGPR) in the biofertilization of crops. A study was conducted in order to investigate the effects of a rhizobial strain (Thal 8) and a P solubilizer strain (54RB) in single and dual combination with and without P 2 O 5 on wheat in a P deficient natural non-sterilized sandy loam soil. The results of this pot experiment revealed that single and dual inoculation with fertilizer (P 2 O 5) significantly increased root and shoot weight, plant height, spike length, grain yield, seed P content, leaf protein and leaf sugar content of the test crop. It is concluded that single and dual inoculation along with P fertilizer is 30-40% better than only P fertilizer for improving grain yield of wheat and dual inoculation without fertilizer (P) improved grain yield up to 20% as compared to P application.

Full text

INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY
ISSN Print: 1560–8530; ISSN Online: 1814–9596
07-092/MFA/2008/10–1–85–88
http://www.fspublishers.org
Full Length Article
To cite this paper: Afzal, A. and B. Asghari, 2008. Rhizobium and phosphate solubilizing bacteria improve the yield and phosphorus uptake in wheat
(Triticum aestivum L.). Int. J. Agri. Biol., 10: 85–88
Rhizobium and Phosphate Solubilizing Bacteria Improve the
Yield and Phosphorus Uptake in Wheat (Triticum aestivum)
AFTAB AFZAL AND ASGHARI BANO
1
Department of Plant Sciences, Faculty of Biological Sciences, Quaid-i-Azam University Islamabad, Pakistan
1
Corresponding author’s e-mail: asgharibano@yahoo.com
ABSTRACT
Rhizobium and phosphorus (P) solubilizing bacteria are important to plant nutrition. These microbes also play a significant role
as plant growth-promoting rhizobacteria (PGPR) in the biofertilization of crops. A study was conducted in order to investigate
the effects of a rhizobial strain (Thal 8) and a P solubilizer strain (54RB) in single and dual combination with and without P
2
O
5
on wheat in a P deficient natural non-sterilized sandy loam soil. The results of this pot experiment revealed that single and dual
inoculation with fertilizer (P
2
O
5
) significantly increased root and shoot weight, plant height, spike length, grain yield, seed P
content, leaf protein and leaf sugar content of the test crop. It is concluded that single and dual inoculation along with P
fertilizer is 30-40% better than only P fertilizer for improving grain yield of wheat and dual inoculation without fertilizer (P)
improved grain yield up to 20% as compared to P application.
Key Words: Phosphate solubilizing bacteria; P uptake; Rhizobium; Wheat yield
INTRODUCTION
Soil-plant-microbe interaction has got much
importance in recent decades. Many types of
microorganisms are known to inhabit soil, especially
rhizosphere and play important role in plant growth and
development. Phosphate solubilizing bacteria (PSB) are
used as biofertilizer since 1950’s (Kudashev, 1956;
Krasilinikov, 1957). These microorganisms secrete different
types of organic acids e.g., carboxylic acid (Deubel &
Merbach, 2005) thus lowering the pH in the rhizosphere (He
& Zhu, 1988) and consequently dissociate the bound forms
of phosphate like Ca
3
(PO
4
)
2
in calcareous soils.
Use of these microorganisms as environment friendly
biofertilizer helps to reduce the much expensive phosphatic
fertilizers. Phosphorus biofertilizers could help increase the
availability of accumulated phosphate (by solubilization),
efficiency of biological nitrogen fixation and increase the
availability of Fe, Zn etc., through production of plant
growth promoting substances (Kucey et al., 1989). Trials
with PSB indicated yield increases in rice (Tiwari et al.,
1989), maize (Pal, 1999) and other cereals (Afzal et al.,
2005; Ozturk et al., 2003).
Rhizobium previously well known as a symbiotic N
fixer is reported as asymbiotic (associative & endophytic)
microorganisms in recent years (Biswas et al., 2000a, b).
The most inoculation studies have focused on free living
diazotrophs, although a few reports indicate rhizobia can act
as plant growth promoting rhizobacteria (PGPR) (Hoflich et
al., 1995; Noel et al., 1996; Yanni et al., 1997). The PGPR
influence the crop growth and development by releasing
plant growth regulators (Glick & Bashan, 1997; Volpin &
Philips, 1998) and improving morphological characteristics
of inoculated roots (Biswas, 1998), which favored nutrient
uptake (Okon & Kapulnik, 1986). The growth promoting
effects of rhizobacteria may include phytohormone
production (Chabot et al., 1996), N
2
fixation (Urquiaga et
al., 1992) and more efficient use of nutrients (Chabot et al.,
1996). Yanni et al. (1997) and Biswas (1998) reported
increased N uptake in rice plants inoculated with rhizobia.
Combined inoculation with N
2
fixing and phosphate
solubilizing bacteria was more effective than single
microorganism for providing a more balanced nutrition for
plants (Belimov et al., 1995). Dual inoculation increased
yields in sorghum (Algawadi & Gaur, 1992), barley
(Belimov et al., 1995), black gram (Tanwar et al., 2002),
soybean (Abdalla & Omar, 2001) and wheat (Galal, 2003).
Reports regarding co-inoculation of Rhizobium and P
solubilizing bacteria on wheat are rare, especially in
Pakistan very little work has been done on these lines. The
objective of present investigation was to explore the effect
of single and dual inoculations with N
2
-fixing and P-
soulbilizing bacterial species on wheat yield and P uptake
and to explore the hidden potential of Rhizobium as a PGPR
for this important non-legume.
MATERIALS AND METHODS
A pot experiment was carried out in experimental area
of Quaid-i-Azam University Islamabad, Pakistan, to
investigate the effects of single and dual inoculations with
N-fixing bacteria (Rhizobium leguminismarum Thal-8/SK8)
and phosphorus solubilizing bacteria (Pseudomonas sp.
strain 54RB) on yield and yield components of wheat
(Triticum aestivum) variety Margalla 99. The bacterial
strains, Thal-8 originally isolated from Thal area and 54RB
isolated from rice, were obtained from Soil Biology and

AFZAL AND BANO / Int. J. Agri. Biol., Vol. 10, No. 1, 2008
Biochemistry Lab. National Agricultural Research Centre
(NARC) Islamabad, Pakistan. Wheat seeds were obtained
from Institute of Field Crops (wheat section), NARC
Islamabad. Clay pots (10 kg soil capacity) were used for
trial. Sandy loam soil having organic matter 0.65%, pH 7.9,
P content 8 ppm and NO
3
-N 10 ppm collected from farmer
field was used. Urea and single super phosphate (SSP) were
applied as source of N and P respectively.
Un-sterilized soil was air dried and mixed with sand in
1:1 ratio and filled in pots. Composite soil samples were
collected and analyzed (analysis given above). These pots
were placed under natural conditions. Urea was mixed in
upper soil (0-10 cm) @ 1.8 g pot
-1
before sowing. Similarly
SSP was applied as treatment in respective pots @ 2 g per
pot. Eight seeds were sown in each pot. With average
minimum temperature of 9
o
C and average maximum
temperature of 25
o
C, a total rainfall of 430 mm, relative
humidity of 80% and day length ranging from 10-13 h, plant
growth in the region is restricted to the period between
November and May. The experimental design for the study
was completely randomized block design with six
replicates. Treatments were: T0 control (without inoculation
& with N) T1 (P
2
O
5
), T2 (Rhizobium @10 mL broth culture
per plant), T3 (PSB @10 mL broth culture per plant), T4
(PSB+Rhizobium), T5 (P
2
O
5
+Rhizobium), T6 (P
2
O
5
+PSB)
and T7 (P
2
O
5
+PSB+Rhizobium).
Inoculum for Rhizobium was prepared in yeast
mannitol (YM) broth (Somasegaran & Hoben, 1985) by
inoculating autoclaved YM with Rhizobia (1 mL) and
placed in shaker at 28
o
C. Inoculum for PSB was prepared in
Pikovskaya medium by the same
procedure. Inoculation
@10 mL per
seedling was done at log phase i.e., about 10
8
cells mL
-1
at the base of plant. Five plants per pot were kept
after thinning and grown until maturity to get final yield.
During the growing period, leaf samples were
collected (at 108 days after sowing) for sugar and protein
analysis before heading. The analyses were done according
to Johnson et al. (1966) and Lowry et al. (1951)
respectively. At maturity, data regarding plants height, spike
length, root weight, shoots weight and grain yield were
recorded using standard procedures. Soil samples from each
treatment were collected and analyzed for phosphorus
content according to Soltanpur and Workman (1979). Seed
P content was measured according to Cottenie (1980). In the
present study, P solubilizing ability of 54RB and Thal-8 was
demonstrated based on the qualitative methods (Metha &
Nautiyal, 2001) under the laboratory condition. Indole acetic
acid (IAA) and gibberellic acid (GA) production for both
the strains was also determined using HPLC (Table I).
Phosphate solubilization was determined using following
formula:
SI = colony diameter + halozone diameter
Colony diameter
Statistical analysis. The data obtained in the study were
subjected to analysis of variance using MSTATC, computer
software (Bricker, 1991) and means were compared by
Duncan’s Multiple Range Test (Duncan, 1955).
Correlations between growth parameter (s) were also
calculated (Bricker, 1991).
RESULTS AND DISCUSSION
In this study generally all the parameters were
significantly affected by inoculation treatments over control
(Table II). Root weight and seed P content (%), however,
were non-significantly affected by dual inoculation without
fertilizer P (Table II). The highest shoot weight was
obtained in pots, which received Rhizobium inoculation
along with fertilizer that was statistically similar to pots,
which received PSB with fertilizer and dual inoculation
(Rhizobium + PSB) with fertilizer (Table II). Single
inoculation of Rhizobium and PSB behaved similar to that
of control for root and shoot weight (Table II). Dual
inoculation with fertilizer yielded maximum root weight
followed by single inoculation of Rhizobium with P and
single inoculation of PSB along with P. Control and other
treatments had similar root weight (Table II). Increased root,
shoot weight with dual inoculation have been reported by
Höflich et al. (1994) in barley, Yanni et al. (1997) in rice,
Chabot et al. (1993) in maize. Our results are also in line
with similar previous findings. We also found a highly
positive correlation (r = 0.79) between root and shoot
weight (Table III). Better root development may be due to
synergistic relationship of the inoculated bacteria for
improving root length and weight by producing growth
regulators (Okon, 1985) like IAA and GA (Table I) that
along with P fertilizer favored better root development,
which enhanced water and nutrient uptake and ultimately
helped better shoot development. Single inoculation of
either PSB or Rhizobium showed no statistical difference
over control (Höflich, 2000). However, dual inoculation was
the most effective in increasing root/shoot weight.
According to Bashan (1998) soil microbial cultures with
statistically similar or different functions might express
beneficial actions in a soil or rhizosphere.
All inoculations with fertilizer P and dual inoculation
without P had significantly greater plant height than other
treatments. Single inoculation of Rhizobium/PSB, without
fertilizer P did not increase plant height over control. Spike
length was increased by fertilizer P, dual inoculation and
combined application of inoculants + P. Fertilizer P alone
and in combinations with inoculations and dual inoculation
all significantly increased the grain yield over control as
well as single inoculations. These results confirmed the
previous findings (Khalid et al., 1997; Biswas et al., 2000a,
b; Hilali et al., 2000, 2001), who reported increased plant
height and spikelets per spike of various crop plants by
microbial inoculation. Plant height and spike length were
significantly correlated (r = 0.80 & r = 0.94) with shoot
weight and with each other (r = 0.80) (Table III).
Highest grain yield (3.19 g pot
-1
) was obtained with
PSB+P
2
O
5
but it was similar to P
2
O
5
and combination of
86

IMPROVING YIELD AND PHOSPHORUS UPTAKE IN WHEAT / Int. J. Agri. Biol., Vol. 10, No. 1, 2008
Table I. Some important biochemical features of microbial strains tested during this investigation. Bacterial cultures were grown
in respective media incubated for one week. Production of IAA and GA was determined in cell free medium
Bacterial strains IAA production µg/ml GA production µg/ml P solubilization index Gram reaction
Rhizobium leguminosarum (Thal 8) 65.90 833.7 2.5 Negative
Pseudomonas sp. (54RB) 8.034 1766 4.1 Negative
Table I1. Effect of Rhizobium and phosphate solubilizing bacteria (PSB) on agronomic traits, yield components, seed and soil P
content, leaf sugar and protein content in wheat
Treatments Shoot wt.
(g pot
-1
)
Root wt.
(g pot
-1
)
Plant height
(cm)
Spike
length (cm)
Grain yield
(g pot
-1
)
Seed P
content (%)
Soil P content
(ppm)
Leaf sugar
(µg g
-1
)
Leaf protein
(µg g
-1
)
Control (T0) 3.10 c 0.10 c 55.30 b 7.30 c 1.22 b 0.30d 4.10 21.40 c 3767 c
P
2
O
5
(T1) 6.22 b 0.30 c 64.00 ab 8.80 bc 2.28 a 0.36c 4.33 70.20 b 3930 bc
Rhizobium (T2) 4.10 c 0.20 c 56.70 b 7.50 c 1.15 b 0.31d 4.67 65.30 b 4474 a
PSB (T3) 4.05 c 0.12 c 55.50 b 7.20 c 1.25 b 0.38c 4.57 25.80 c 3966 bc
Rhizobium + PSB (T4) 6.41 b 0.33 c 68.30 a 9.70 ab 2.85 a 0.29d 4.53 64.50 b 4419 a
Rhizobium + P
2
O
5
(T5) 10.3 a 0.68 b 69.30 a 11.00 a 2.31 a 0.45b 4.10 73.70 b 3826 bc
PSB + P
2
O
5
(T6) 8.93 a 0.65 b 71.70 a 10.50 ab 3.19 a 0.45b 4.87 66.70 b 4188 ab
Rhizobium + PSB + P
2
O
5
(T7) 9.20 a 0.93 a 67.30 a 10.00 ab 2.93 a 0.49a 5.00 94.50 a 4448 a
LSD values 2.075 0.235 9.044 1.551 0.881 0.25 NS 19.31 376.4
Values followed by different letters in a column were significantly different (P < 0.05), using Duncan’s multiple range test. NS, not significant..PSB,
Phosphate Solubilizing Bacteria (Pseudomonas sp.) rhizobium (Rhizobium leguminosarum), P
2
O
5
@ 0.38 g pot
-1
Table III. Correlation effects of Rhizobium and phosphate solubilizing bacteria on wheat yield and yield traits (per plant basis)
Variable Shoot wt Root wt Plant height Spike length Grain yield Flag leaf Sugar Soil P
Root wt. 0.796243**
Plant height 0.803548** 0.65216**
Spike length 0.944879** 0.707167** 0.815159**
Grain yield 0.786934** 0.655576** 0.768131** 0.78742**
Flag leaf Sugar 0.671061** 0.608289** 0.627023** 0.623612** 0.569902**
Soil P 0.718864** 0.690239** 0.614421** 0.620678** 0.630866** 0.625122**
Seed P 0.619352** 0.741055** 0.398551
NS
0.471929* 0.34184
NS
0.521501** 0.692944**
** = Highly significant at 1% level of probability, * = Significant at 5% level of probability, NS= Non-significant
P
2
O
5
and inoculations. Rhizobium and PSB alone did not
increase the grain yield. Dual inoculation with P
2
O
5
had
highest seed P content of 0.49%. The Rhizobium alone did
not increase seed P content. However, PSB alone increase P
content as compared to control. Many researchers reported
increased seed P content by phosphate solubilizing
microorganisms (Kucey, 1987; Mehana & Wahid, 2002;
Zaidi et al., 2004), our study revealed the same effect. But
dual inoculation without fertilizer could not improve seed P
concentration. This may be due to competition of the
microbes for P (Azcon-Aguillar et al., 1986). Soil P were
not affected by any of the treatment significantly.
Leaf sugar content was significantly increased by
Rhizobium inoculation and fertilizer treatments. Highest
value of leaf sugar content (49.5 μg g
-1
) was recorded in
dual inoculation with fertilizer treated plants. Leaf protein
was significantly affected by rhizobial treatments and best
treatment in this case was Rhizobium along with P
2
O
5
. This
may be due to increased N uptake by a larger root surface
area
associated with additional root hairs and lateral root
development and/or to BNF, either directly by the
inoculants strains or indirectly by stimulating BNF activity
of the associated rhizosphere community
(Ladha et al.,
1998)
. Maximum sugar was accumulated in dual inoculated
and fertilized plants. Sahin et al. (2004) documented
increased sugar content in sugar beet by co-inoculation of
N-fixing and P solubilizing bacteria.
The present study indicated that single inoculations
with Rhizobium could not increase grain yield as compared
to control. Inoculation with PSB alone increased yield by
2.5% over control (Table II). Dual inoculation of Rhizobium
and PSB gave yield increases of 29% and 25% with and
without fertilizer respectively. Fertilizer P application,
however gave yield increases up to 80%. It is concluded that
mixed culturing is better than single inoculation. Reduced
fertilization (up to 50%) is required with inoculations.
Rhizobial and/or PSB inoculaton without fertilization is not
effective. Rhizobium with non-legumes could act as
phosphate solubilizer, hormone producer and to some extent
as N-fixer. Addition of Azospirillum or other diazotrophs
(for N fixation) with present combination would give
promising results, which will reduce the N fertilizer use for
the profit of farmer and prove environment-friendly.
REFERENCES
Abdalla, M.H. and S.A. Omer, 2001. Survival of Rhizobia/Bradirhizobia
and a rock phosphate solubilizing fungus Aspergillus nigeron various
carriers from some agroindustrial wastes and their effect on
nodulation
and growth of fababean and soybean. J. Plant Nut., 24: 261–
72
Afzal, A., M. Ashraf, S.A. Asad and M. Farooq, 2005. Effect of phosphate
solubilizing microorganisms on phosphorus uptake, yield and yield
traits of wheat (Triticum aestivum L.) in rainfed area. Int. J. Agric.
Biol., 7: 207–9
Alagawadi, A.R. and A.C. Gaur, 1992. Inoculation of Azospirillum
brasilense and phosphate-solubilizing bacteria on yield of sorghum
(Sorghum bicolor L. Moench) in dry land. Trop. Agric., 69: 347–50
87

AFZAL AND BANO / Int. J. Agri. Biol., Vol. 10, No. 1, 2008
Azcon-Aguillar, C., V. Gianinazzi-Pearson and J.C. Fardeau, 1986. Effect
of vesicular-arbuscular mycorrhizal fungi and phosphate-solubilizing
bacteria on growth and nutrition of soybean in a neutral calcareous
soil
amended with 32P-45Ca tricalcium phosphate. Plant Soil, 96: 3–15
Bashan, Y., 1998. Inoculations of plant growth-promoting bacteria for use
in agriculture. Biotehnol. Adv., 16: 729–70
Belimov, A.A., P.A. Kojemiakov and C.V. Chuvarliyeva, 1995. Interaction
between barley and mixed cultures of nitrogen fixing and phosphate-
solubilizing bacteria. Plant Soil, 17: 29–37
Biswas, J.C., J.K. Ladha and F.B. Dazzo, 2000a. Rhizobia inoculation
improves nutrient uptake and growth of lowland rice. Soil Sci. Soc.
America J., l 64: 1644–50
Biswas, J.C., J.K. Ladha, F.B. Dazzo, Y.G. Yanni and B.G. Rolfe, 2000b.
Rhizobial inoculation influences seedling vigor and yield of rice.
Agron. J., 92: 880–6
Biswas, J.C., 1998. Effect of Nitrogen Fixing Bacteria on Growth
Promotion of Lowland Rice (Oryza sativa L.). Ph. D Thesis,
Department of Soil Science University of Phillipines, Los Banos
Bricker, B., 1991. A Micro Computer Programme for the Design, Manage
and Analysis of Agronomic Research Expt. Crop and Science
Department, AUS, Lansin USA
Çakmakçi, R., F. Kantar and F. Sahin, 2001. Effect of N
2
-fixing bacterial
inoculations on yield of sugar beet and barley. J. Plant Nutr. Soil
Sci., 164: 527–31
Chabot, R., H. Antoun and M.P. Cescas, 1993. Stimulation de la croissance
du maïs et de la laitue romaine par des microorganismes dissolvant le
phosphore inorganique. Canadian J. Microbiol., 39: 941–7
Chabot, R., H. Antoun and M.P. Cescas, 1996. Growth promotion of maize
and lettuce by phosphate-solubilizing Rhizobium leguminosarum
biovar phaseoli. Plant Soil, 184: 311–21
Cottenie, A., 1980. Soil and Plant testing as a basis of fertilizer
recommendations. FAO. Soil’s Bulletin, 38: 64–5
Deubel, A. and W. Merbach, 2005. Influence of microorganisms on
phosphorus bioavailability in soils. In: Buscot, F. and A. Varma
(eds.), Microorganisms in Soils: Roles in Genesis and Functions, pp:
177–91. Springer-Verlag, Berlin Heidelberg, Germany
Duncan,
D.B., 1955. Multiple range and multiple F- test. Biometrics, 11: 1–42
Galal, Y.G.M., 2003. Assessment of nitrogen availability to wheat (Triticum
aestivum L.) from inorganic and organic N sources as affected by
Azospirillum brasilense and Rhizobium leguminosarum inoculation.
Egyptian J. Microbiol., 38: 57–73
Glick, B.R. and Y. Bashan, 1997. Genetic manipulation of plant growth
promoting bacteria to enhance biocontrol of phytopathogens.
Biotechnol. Adv., 15: 353–78
He, Z. and J. Zhu, 1988. Microbial utilization and transformation of
phosphate adsorbed by variable charged minerals. Soil Biol.
Biochem., 30: 917–23
Hilali, A., D. Przvost, W.J. Broughton and H. Antoun, 2000. Potential use
of Rhizobium leguminosarum bv. trifolii as plant growth promoting
rhizobacteria with wheat Abstract. 17
th
North American Conference
on Symbiotic Nitrogen Fixation, Laval University, Quebec, Canada
23-28 July 2000
Hilali, A., D. Przvost, W.J. Broughton and H. Antoun, 2001. Effects de
I’inoculation avec des souches de Rhizobium leguminosarum bv.
trifolii sur la croissance du bl’e dans deux sols du Marco. Canadian
J. Microbiol., 47: 590–3
Höflich, G., 2000. Colonization and growth promotion of non-legumes by
Rhizobium bacteria. Microbial Biosystems: New Frontiers. In: Bell,
C.R., M. Brylinsky and P. Johnson-Green (eds.), Proceedings of the
8
th
International Symposium on Microbial Ecology, pp: 827–30.
Atlantic Canada Society for Microbial Ecology, Halifax, Canada
Höflich, G., W. Wiehe and G. Köhn, 1994. Plant growth stimulation by
inoculation with Symbiotic and associative rhizosphere
microorganisms. Experienca, 50: 897–905
Johnson, R.R., T.L. Balwani, L.J. Johnson, K.E. Meclure and B.A.
Denority, 1966. Corn plant maturity II. Effect on in-vitro cellular
digestibility and soluble carbohydrate content. J. Anim. Sci., 25: 617
Khalid, A., M. Arshad, Z.A. Zahir and A. Khaliq, 1997. Potential of plant
growth promoting rhizobacteria for enhancing wheat yield. J. Anim.
Plant Sci., 7: 53–6
Krasilinikov, N.A., 1957. On the role of soil micro-organism in plant
nutrition. Microbiologiya, 26: 659–72
Kudashev, I.S., 1956. The effect of phosphobacterin on the yield and protein
content in grains of Autumm wheat, maize and soybean. Doki. Akad.
Skh. Nauk, 8: 20–3
Kucey, R.M.N., H.H. Janzen and M.E. Leggett, 1989. Microbially mediated
increases in plant-available phosphorus. Ad. Agron., 42: 199–228
Kucey, R.M.N., 1987. Increased phosphorus uptake by wheat and field
beans inoculated with a phosphorus-solubilizing Penicillium bilaji
strain and with vesicular-arbuscular mycorrhizal fungi. Appl.
Environ. Microbiol., 53: 2699–703
Ladha, J.K., G.J.D. Kirk, J. Bennett, C.K. Reddy, P.M. Reddy and U. Singh,
1998. Opportunities for increased nitrogen use efficiency from
improved lowland rice germplasm. Field Crops Res., 56: 36–69
Lowry, O.H., N.J. Rosbrough, A.L. Farr and R.J. Randall, 1951.
J. Biol.
Chem., 193:
265
Mehana, T.A. and O.A. Wahid, 2002. Associative effect of phosphate
dissolving fungi, Rhizobium and phosphate fertilizer on some soil
properties, yield components and the phosphorus and nitrogen
concentration and uptake by Vicia faba L. under field conditions.
Pakistan J. Biol. Sci., 5: 1226–31
Methaa, S. and C.S. Nautiyal, 2001. An efficient method for qualitative
screening of phosphate-solubilizing bacteria. Curr. Microbiol., 43:
51–6
Noel, T.C., C. Sheng, C.K. Yost, R.P. Pharis and M.F. Hynes, 1996.
Rhizobium leguminosarum as a plant growth-promoting
rhizobacterium: direct growth promotion of canola and lettuce.
Canadian J. Microbiol., 42: 279–83
Okon, Y., 1985. Azospirillum as a potential inoculant for agriculture. Trends
Biotechnol., 3: 223–8
Okon, Y. and Y. Kapulnik, 1986. Development and function of
Azospirillum inoculated roots. Plant Soil, 90: 3–16
Öztürk, A., O. Caˇglar and F. Sahin, 2003. Yield response of wheat and
barley to inoculation of plant growth promoting rhizobacteria at
various levels of nitrogen fertilization. J. Plant Nutr. Soil Sci., 166:
1–5
Pal, S.S., 1999. Interaction of an acid tolerant strain of phosphate
solubilizing bacteria with a few acid tolerant crops. Plant Soil, 213:
221–30
Sahin, F., R. Cakmakci and F. Kantar, 2004. Sugar beet and barley yields in
relation to inoculation with N2-fixing and phosphate solubilizing
bacteria. Plant Soil, 265: 123–9
Soltanpur, P.N. and S. Workman, 1979. Modification of the NH4CO3-
DTPA soil test to omit carbon black. Commun. Soil Sci. Plant Annl.,
10: 1411–20
Somasegaran, P. and H.J. Hoben, 1985. Methods in Legume-rhizobium
Technology. NifTAL project and MIRCEN. Department of
Agronomy, 2
nd
Soil Science Hawaii Institute Tropical Agriculture
Human research, Univ Hawaii Manoa
Tanwar, S.P.S., G.L. Sharma and M.S. Chahar, 2002. Effect of phosphorus
and biefertilizers on the growth and productivity of black gram. Annl.
Agric. Res., 23: 491–3
Tiwari, V.N., L.K. Lehri and A.N. Pathak, 1989. Effect of inoculating crops
with phospho-microbes. Exp. Agric., 25: 47–50
Urquiaga, S., K.H.S. Cruz and R.M. Boddey, 1992. Contribution of nitrogen
fixation to sugar cane: nitrogen-15 and nitrogen-balance estimates.
Soil Sci. Soc. America Proc., 56: 105–14
Volpin, H. and D.A. Philips, 1998. Respiratory elicitors from Rhizobium
meliloti effect intact alfalfa roots. Plant Physiol., 116: 777–83
Yanni, Y.G., R.Y. Rizk, V. Corich, A. Squartini, K. Ninke, S. Philip-
Hollingsworth, G. Orgambide, F. De Bruijn, J. Stoltzfus, D. Buckley,
T.M. Schmidt, P.F. Mateos, J.K. Ladha and F.B. Dazzo, 1997.
Natural endophytic association between Rhizobium leguminosarum
bv. trifolii and rice roots and assessment of its potential to promote
rice growth. Plant Soil, 194: 99–114
Zaidi, A., M.S. Khan and M. Aamil, 2004. Bioassociative effect of
rhizospheric microorganisms on growth, yield, and nutrient uptake of
greengram. J. Plant Nut., 27: 601–12
(Received 29 May 2007; Accepted 05 October 2007)
88