Effect of Phosphate Solubilizing Bacteria on Seed Germination and Seedling Growth of Faba Bean (Vicia faba L.)
The aim of this study was to evaluate effect of phosphate solubilizing bacteria on seed germination and seedling growth of Faba bean (Vicia faba L.) under lath-house condition. Phosphorous is an essential macronutrient next to nitrogen required by the plants for vital biosynthesis. But often unavailable for plants because of adsorbed by Ca2+, Mg2+, Fe2+ and Al3+ ions through legend exchange. Although there is mounting information that phosphorus solubilizing bacteria as inoculants increases P uptake of plants. This was not yet tested on Faba bean in Ethiopia. A total of 183 phosphate solubilizing bacteria were isolated from 150 samples collected from rhizosphere soil and root nodules. From these isolates based on their solublization index and mobilization efficacy, two isolates (JURB48 and JURMB69) were selected and tested on Faba bean. The co-inoculants (JURB48+JURMB69) increased the percentage of seed germination (21.4%), vigor index (46.2%), radicle (25.3%) and plumule (50%) lengths of germinated seeds of Faba bean over the non-inoculated. Faba bean shoot fresh, root weight, leaf number, flower number, root dry weight and total dry matter were significantly increased compared to non-inoculated as a result of co-inoculants (JURB48+JURMB69). Plant height, root length, phosphorus content, P uptake and Nodule number and weight were enhanced due to inoculation with JURB48 and JURMB69, respectively, compared to non-inoculated either in the presence or absence of phosphate sources. The present study suggests the potential of JURB48 and JURMB69 isolates as biofertilizers for Faba bean cultivation.
Received: April 02, 2013;
Accepted: July 30, 2013;
Published: September 07, 2013
Faba bean (Vicia faba L.) is commonly named as broad, field and bell
bean among most of the world population (Duc et al.,
2010). Even if the exact origin of the Faba bean is not known, central Asia,
Mediterranean basin and South America were reported as the possible centers
of diversity (Muehlauer and Tullu, 1997). Faba bean is
widely cultivated in Ethiopia following China in the world (Yirga
et al., 2010), in Ethiopia, especially within the range of 1800-2400
m above sea level (Telaye, 1985). It was the third-largest
export crop of Ethiopia following coffee and oil seed, between the years 1998-2000.
Nearly, Ethiopia exported 88 tons of Faba bean each year to Djibouti, Yemen
and Israel (Rashid et al., 2010).
Faba bean is considered as multipurpose crops for its use as human food in
developing countries and as animal feed in industrialized countries (Mulualem
et al., 2012). It plays a great role in agricultural production as
a driver for economic growth and food security by contributing to smallholder
income, as a high value crop compared to cereals and to diet as a cost-effective
(affordable for smallholders) source of protein, fat, carbohydrate, fibre and
minerals like iron, magnesium, potassium, zinc, copper, selenium and various
vitamins (Haciseferogullari et al., 2003). In
addition, Faba bean contains a chemical called Levodopa which is used for controlling
the Parkinsons symptoms disease (brain neurons disease that affects body
movement) (Holden, 2009).
In addition to play a great role in food consumption and therapeutic value,
Faba bean is flourish soil fertility due to fixing atmospheric nitrogen which
is contribute for decreasing fertilizer expenditure and environmental costs
of chemical fertilizers because of the efficacy of Faba bean form association
with potential nitrogen fixing bacteria such as Rhizobium leguminosarum biovar
viciae (Danso, 1992). Particularly, the augmentation
of soil fertility because of Faba bean and Rhizobial association is more significance
in extensive area of farming land to boost agronomical product (Habtegebrial
and Singh, 2006). Moreover, crop rotation that incorporates the Faba bean
will decrease soil-borne disease such as wheat and barley diseases because of
Faba bean association with various types of phytobeneficial microorganisms (Agegnehu
et al., 2006). In addition to hosting nitrogen fixing bacteria, Faba
bean also have a potential to form association with Phosphate Solubilizing Bacteria
(PSB) (Keneni et al., 2010). Potent PSB including
Pseudomonas spp., Rhizobium spp. and Bacillus spp. are mainly
solubilized phosphate pool by production of organic acid which is easily uptake
by the plant (Khan et al., 2007; Awasthi
et al., 2011).
Currently, the productivity of Faba bean in Ethiopia is far below the expected
potential because of low input usage, natural disasters like snowstorm, depletion
of macronutrient from cultivable land and unavailability of essential nutrients
such as phosphorus. To solve this problem the Ethiopia government has been promoting
the practice of using chemical (inorganic) and organic fertilizers with less
emphasis to bio-inoculums (Zelleke et al., 2010).
However, bio-inoculums are the most important fertilizers that building organic
and sustainable agriculture unlike to chemical fertilizers which affect human
health and cause environmental pollution (Savci, 2012).
Hence, the side effects of chemical fertilizers and problem of low soil fertility
could be averted by use of bio-inoculums. Among these, PSB are great gear to
pace the turnover of phosphorus from various pools of phosphate to enhance growth
and development of crop under question (Khan et al.,
2009). However, the potential of PSB inoculation in simultaneous increase
of phosphorus uptake and growth of Faba bean is not yet evaluated. To this effect,
the present study was designed to evaluate the effects of selected PSB on in
vitro seed germination of Faba bean under laboratory condition and seedling
growth of Faba bean under lath house condition.
MATERIALS AND METHODS
Description of the study area: The study was carried out at Jimma University, located at 353 km to the southwest of Addis Ababa the capital city of Ethiopia. The microbial analysis and seed germination were conducted in Postgraduate and Research Laboratory of the Department of Biology, Jimma University. The lath house experiment was conducted at Jimma University College of Agriculture and Veterinary Medicine (JUCAVM), Jimma, Ethiopia, the study area is located at 7°, 33N and 36°, 57E at an altitude of 1710 m.
Sample size and collection: The rhizosphere soil sample and root nodule
were collected from Mana district, Oromia regional state, Ethiopia. We sampled
rhizosphere soil and nodule from roots of five plant species; Vicia faba
(Faba bean), Pisum sativum (Pea), Phaseolus vulgaris (Haricoat
bean), Medicago sativa (Alfalfa) and Sasbania spp. we sampled
30 plants from each of the five plants species. The plant samples were uprooted
along with non-rhizosphere soil using shovel. Intact roots along with adhered
soil from all of the 5 host plants were transferred to polythene bag and transported
to Postgraduate and Research Laboratory, Department of Biology, Jimma University
and stored at low (4°C) temperature for further analysis.
Isolation of phosphate solubilizing bacteria: The loosely adherent soil
was removed by gentle shaking and the roots were cut into 1-2 cm pieces with
strongly adhering soil using sterile scissors. Ten grams of each sample was
placed in flasks containing 90 mL of saline solution and kept on rotary shaker
at 125 rpm for 30 min. A ten-fold serial dilution was made to obtain appropriate
dilution factor. From appropriate serial dilution, a 0.1 mL aliquots was spread
on the petriplates containing Pikovskayas Agar Medium (PVK) (Glucose 10
g; Ca3 (PO4)2 5 g; NH4(SO4)2
0.5 g; Yeast extract 0.5 g; MgSO4.7H2O 0.1 g; NaCl
0.2 g; KCl 0.2 g; MnSO4 0.002 g; FeSO4 0.002 g; Agar 15
g; distilled water 1000 mL) (Pikovskaya, 1948). The
petri plates were incubated at 32°C for 2-7 days. The isolates that showed
discrete halo zone around colonies were assumed to be phosphate solubilizers.
Determination of phosphate solubilization index (SI): Phosphate solubilization
index (SI) was calculated using the formula outlined in Premono
et al. (1996). A loopful of 24 h old cultures was spotted at two
point of equidistant on Pikovskayas agar plate and incubated at 30±2°C
for 2-7 days. The diameter of colony and halo zone was measured using transparent
Quantification of mobilized phosphate: From 24 h old culture of potent
PSB, two loopful of bacterial suspension were inoculated into 200 mL of sterilized
National Botanical Research Institute's phosphate growth medium broth (10 g
of Glucose, 5 g of Ca3 (PO4)2, 5 g of MgCl2.6H2O,
0.25 g of MgSO4.7H2O, 0.2 g of KCl, 0.1 g of (NH4)2SO4)
in 250 mL capacity of Erlenmeyer flask (Nautiyal, 1999).
All the inoculated flasks were placed on rotary shaker at 150 rpm for 8 h within
days and incubated at 30±2°C. The amount of mobilized phosphate in
the broth was estimated from triplicate flasks at 0, 5, 10, 15 and 20 days of
incubation with a set of uninoculated control using phosphomolybdic blue color
method (Yasmin and Bano, 2011).
Experiment 1 Seed germination bioassay: Twenty one seeds of Faba bean
(either single or co-inoculants) were dipped into nutrient broth culture for
Pseudomonas sp. (JURB48) and yeast extract mannitol broth for Rhizobium
(JURMB69) for 5 h, which contain the bacterial suspension (108 CFU
mL-1) while 21 seeds were dipped in distilled water served as control.
Seven seeds per plate of inoculated Faba beans were placed in Petri dishes with
one layer of Whatman No. 1 filter paper and moist cotton. Both treated and untreated
plate containing Faba bean seeds were arranged in Complete Randomized Design
(CRD) in triplicate and incubated at 30±2°C for 3-7 days. Then, the
percent of germinated seeds for 1-3 days, radicle and plumule length of geminated
seeds were taken up to 7 days (Gholami et al., 2009).
The vigor index of germinating seeds was also determined using the formula:
Experiment 2 pot experiment: A pot experiment was carried out to investigate the effects of phosphate solubilizing bacteria (JURMB69 and JURB48) with single and dual inoculations in the presence or absence of phosphate sources (Orga and RP) on the Faba bean vegetative growth under lath house condition.
The experiment was performed according to Kucey (1987).
Unsterilized soil samples were collected from research site of JUCAVM with no
history of Faba bean cultivation for the last 20 years. The soil samples were
air dried and busted down to small size. The Bikilal Rock phosphate (BRP) which
was brought from western Ethiopia (Wollega) incorporated as source of inorganic
phosphate was crushed using hammer. First, the soil and BRP was sieved using
2 mm mesh-size sieve. Second, the sieved soil was filled into 4 kg capacity
plastic pots. Then, 2 mm mesh-size of 22 g BRP and 4.4 g of Orga phosphate fertilizer
which is made up of bones, stomach paunch, horns and hooves by the action of
PSB that contains mainly 1% nitrogen, 23% P2O5, 20.98%
organic matter and 21% calcium oxide per 100 kg were added per pot and placed
under lath conditions (NAFMAC, 2002). Faba bean variety
Dagaga obtained from Holeta Research Center, Ethiopia were used.
The inoculants in yeast extract mannitol and nutrient broth were mixed with
gum arabic in 1:3 ratios and coated onto the seeds (Anonymous,
2012). Sixty seeds of Faba bean for each (JURB48, JURMB69 and JURB48+JURMB69)
soaked separately in 60 mL of inoculants-gum arabic mixed suspension for 5 h
and pelleting was done by CaCO3. The treated seeds were kept overnight
in the laminar flow hood for drying but 60 seeds were sown without inoculants
(control). After seed inoculation, 5 seeds were sown into each pot and thinned
to three per pot after 7 days of emergence. Three plants per pot were kept upto
45 days. After 15 days of emergence, each seedling of Faba bean was inoculated
with 1 mL (about 108 cells mL-1) of their respective inoculants
and watered every 2 days until 45 days. The experimental design for the study
was Randomized Completely Blocks Design (RCBD) having sixteen treatments replicated
Data collected: Faba bean plants were harvested after 45 days of sowing
and the data on plant height, root length, number of nodules and leaves, plant
biomass and phosphorus content were recorded following standard procedures (Tennakoon,
Biomass measurements: At the end of the experiments the root length of Faba bean was carefully uprooted and washed to remove soil. Then, the root length was recorded by measuring the length from base of stem to the tip of longest root. The fresh weight (g) of root and nodules were also measured. Moreover, the fresh weight (g), height (cm), leaves and flower numbers were recorded. Nodules, roots and shoot portions were separated from plants and air dried. The air dried plant samples further oven dried at 72°C for 72 h. The nodule, root and shoot dry weights were measured separately and expressed in g per plant.
Phosphorus content: The oven dried plant samples were ground to fine
powder for estimation of phosphorus contents. To 500 mg of plant sample, 10
mL of conc. HNO3 was added in a 250 mL conical flask. The flask was
swirled to moisten the entire sample and placed on a hot sand bath for 30 min
on the electric hot plate at 180-200°C. The suspension was boiled until
nearly to dryness. Five milliliter of tri acid mixture (Conc. HNO3,
H2SO4 and 60% HClO4 (10:1:4 ratio)) was added
to pre-digested sample and further digested at 180-200°C on a digestion
mantle until the residue in the flask became clear white. Ten milliliter of
6 N HCl was added to residue and swirled well. The acid digest was transferred
to 50 mL volumetric flask and the volume was adjusted to 50 mL with distilled
water. Then, 5 mL of wet oxidized digested sample was taken in a 50 mL of volumetric
flask and 10 mL of vanadomolybdate reagent was added. The volume was topped
up to 50 mL with distilled water and allowed to react for 30 min. The development
of yellow color was read at 490 nm using spectrophotometer.
The P content was obtained by standard curve. To prepare a standard curve,
0.439 g of KH2PO4 oven dried was dissolved in distilled
water and adjusted to 1000 mL in a volumetric flask (100 ppm P-solution). Aliquots
of 1-10 mL were transferred to 50 mL volumetric flask and 10 mL vanadomolybdate
reagent was added to each flask including blank. The volume was made up to 50
mL with distilled water. The development of yellow color was read at 490 nm
using spectrophotometer. The standard curve was obtained by plotting a graph
as concentration along X-axis and corresponding absorbance along Y-axis (Jackson,
Phosphorus uptake: Phosphorus uptake in plants was calculated according
to Tennakoon (2007):
Statistical analysis: For each of the response variables, the validity of model assumption was verified by examining the residuals. The data of seed germination, fresh and dry biomasses of Faba bean were analyzed using SAS version 9.0. Moreover, the data of radicle and plumule length of germinated seeds didnt meet model assumption and transformed using Arcsine x. while vigor index of seed germination was transformed by square root. Means separation were performed for significant parameters at p<0.05 using Tukeys test.
Isolation of phosphate solubilizing bacteria: A total of 183 PSB were isolated from 150 rhizosphere samples and root nodules. Based on their SI and phosphate mobilization efficiency the two isolates namely JURB48 (Pseudomonas sp.) and JURMB69 (Rhizobium sp.) were selected for seed germination and pot experiment.
Effect of PSB inoculation on seed germination: The results of germination percentage, radicle and plumule length of Faba bean inoculation with co-inoculants (JURB48+JURMB69), JURMB69 (Rhizobium sp.) and JURB48 (Pseudomonas sp.) showed significant (p<0.05) increment over control (Fig. 1). Accordingly, co-inoculants and JURMB69 increased seed germination over control by 21.4 and 19% and radicle by 25.3 and 8.8%, respectively. On the other hand, the plumule length increased by co-inoculants (50%) and JURB48 (37.5%) over non-inoculated (Table 1).
||Germinated seeds of Faba bean; JURB48+JURMB69 (co-inoculants),
JURB48 and JURMB69 (single inoculants) and control
|| Effect of phosphate solubilizing bacteria on germination
of Faba bean seeds
|Values in the parentheses are transformed data, Means with
the same letter in the columns are not significantly different, LSD: Least
significant difference, *Significance p<0.05, JURB48, isolates from rhizosphere
of Faba bean, and JURMB69, isolates from Faba bean root nodule. For all
isolates the leading letter JU: Jimma University
Effect of PSB inoculation on seed germination and seedling growth of Faba bean fresh biomass: The results of Faba bean inoculation with Pseudomonas sp. and Rhizobium sp. isolates in the presence and absence of phosphate sources on growth parameters are presented in Table 2. All of the inoculated treatments significantly (p<0.05) increased plant height compared to the control (Fig. 2). Among the treatments, OG (Orga)+JURB48 (Pseudomonas sp.) gave the maximum plant height (46.22 cm) followed by BRP (Bikilal Rockphosphate)+OG+JURMB69 (Rhizobium sp.) (44.89 cm). In case of shoot weight, the plant supplemented with OG+JURB48+JURMB69 gave the maximum weight of shoot (23.38 g plant-1) compared to the other treatments (Table 2).
Most of the plants inoculated with PSB produced the higher number of leaves
compared to non-inoculated. The maximum number of leaves were observed on the
plant inoculated with BRP+OG+JURB48+JURMB69 (43.6) followed by JURMB69 (43.33)
without any phosphate sources (Table 2). Significant (p<0.05)
differences in both root length and fresh weight of Faba bean were observed
due to inoculation with PSB. The plant inoculated with BRP+JURB48 and JURB48+JURMB69
showed the highest root length (36.61 cm) and weight (15.19 g plant-1),
||Effect of PSB inoculants on growth of Faba bean
|Means with the same letter in the columns are not significantly
different, LSD: Least significant difference, ***:Significant at p<0.001,
BRP: Bikilal rock phosphate, OG: Orga, JURB48: Pseudomonas isolated from
Faba bean rhizosphere, JURMB69: Rhizobium isolated from nodule of Faba bean,
W: White nodule, P: Pink nodule, for all isolates the leading letter JU:
||Growth of Inoculated Faba bean (a) Inoculated and (b) Control
||Effect of PSB inoculation on Faba bean flowering, (a) Inoculated
and (b) Control
All the inoculated treatments gave the highest number of nodule compared to
control (Table 2). Similarly, most of the treatments gave
higher nodule fresh weight than the control. The plants inoculated with OG+JURMB69
showed the largest number of nodule (13.89/plant) and weight (2.32 g plant-1)
compared to the other treatments and control.
The inoculants also enhanced early flowering and more number of flowers per plant in all inoculated treatments than control (Fig. 3). Particularly OG+JURB48+JURMB69 (12.78/plant) increased number of flowers four fold over the uninoculated plant.
|| Effect of PSB inoculants on dry matter content and nutrient
uptake of Faba bean
|Mean with the same letter are not significantly different
in the columns, LSD: Least significant difference, ***Significant at p<0.001,
BRP: Bikilal rock phosphate, OG: Orga, JURB48: Pseudomonas isolated
from Faba bean rhizosphere, JURMB69: Rhizobium isolated from nodule
of Faba bean. For all isolates the leading letter JU: Jimma university
Dry matter biomass: The results on shoot, root, nodule, total dry weight, P content and up take of plants are presented in Table 3. Most of the inoculated treatments recorded significantly (p<0.05) higher shoot dry weight over uninoculated control. BRP+OG+JURB48 recorded the maximum shoot dry weight (4.29 g plant-1). On the other hand, majority of the inoculated treatments enhanced root dry weight significantly over the uninoculated control. The highest root dry weight was recorded for plants inoculated with JURB48+JURMB69 (5.2 g plant-1). Almost all inoculated treatments gave significantly (p<0.05) higher dry mass of root nodules compared to the control. However, BRP+JURB48 and BRP+OG+JURMB69 are at par with the control. The treatments inoculated with OG+JURMB69 recorded the maximum nodule dry weight (0.006 g plant-1) compared to the control.
All the inoculated treatments gave significantly higher total dry matter than
uninoculated control, except BRP+JURMB69 which is at par with control. Among
the inoculated treatments, JURB48+JURMB69 showed the maximum total dry matter
content (9.02 g plant-1) (Table 3). Most of the
inoculated treatments gave significantly (p<0.05) the greatest P content
in Faba bean compared to the control. Among the inoculated treatments, the highest
percentage of P content was recorded in the presence of JURB48 (Table
3). Similar to P content, most of the inoculated treatments showed the greatest
P up take in Faba bean. The maximum P uptake was recorded in plants inoculated
with JURB48 (4.79 mg plant-1) followed by JURB48+JURMB69 (4.72 g
plant-1) (Table 3).
In the present study, the co-inoculants (JURB48+JURMB69) increased the percent
of seed germination, which is comparable with the result of Gholami
et al. (2009) who reported the increment of maize seeds germination
by (18.5%) over control due to plant growth promoting rhizobacteria inoculants.
The increment of seed germination with inoculants could be due to the isolates
ability to synthesis seed germination hormone. Gholami et
al. (2009) demonstrated the enhancement of seed germination by inoculants
because of the synthesis of seed germination hormone like gibberellins which
triggered the activity of specific enzymes that promoted early germination,
such as α-amylase that increase the availability of starch assimilation.
Furthermore, the co-inoculants increased vigor index, radicle and plumule length
compared to control. This result is in accordance with the report of Sharma
et al. (2007) in which the PSB co-inoculants (P. fluorescens and
B. megaterium) increased percent of radicle and plumule length ranging
from 13.8-59.7 and 19-56.4%, respectively. Aipova et
al. (2010) also reported the co-inoculation of PSB enhanced the radicle
and root length of wheat as compared to individuals. This could be because of
higher amount of growth promoting substances and biocontrol substances released
by inoculants. Egamberdiyeva (2007) and Sharma
et al. (2007) attributed the enhancement of seed parameters to auxins
(IAA) and growth promoting substance produced by PSB inoculants. In general,
in addition to phosphate solubilizing, both genera of bacteria isolated from
legume plants have ability to improve seed germination.
In pot experiment, the selected inoculants improved significantly the growth
of Faba bean compared to uninoculated plant either individually or co-inoculation.
Among the treatments, OG+JURB48 (Pseudomonas sp.), BRP+OG+JURMB69 (Rhizobium
sp.) and BRP+OG+JURB48+JURMB69 were superior in enhancing shoot height over
the other treatments. This could be due to high P-solubilizing and mineralizing
ability from P-sources, production of growth promoting substances such as IAA
and production of biocontrol compounds like HCN (Aditya
et al., 2009; Akhtar and Siddiqui, 2009).
The fresh weight and leaves numbers of Faba bean were enhanced with co-inoculants
(JURB48+JURMB69) supplemented with OG and BRP. The highest in fresh shoot weight
and leaves number could be due to the synergistic effect of co-inoculants for
releasing of growth substances as well as mineralization and solubilization
of P-sources (Kumari et al., 2009).
The highest root length of Faba bean was attained by JURB48 (Pseudomonas
sp.) along with Rock phosphate which recorded 36.6 cm long, this result support
our in vitro evaluation of isolates in which high amount of IAA was produced
by JURB48 (Pseudomonas sp.). Hence, the enhancement in root length might
be due to higher amount of IAA produced by JURB48 (Pseudomonas sp.),
mobilization of phosphate from inorganic pool and production of bioactive compound
that suppress the Faba bean pathogen (Vassilev et al.,
The co-inoculants (JURB48+JURMB69) significantly increased the root weight
of Faba bean than the rest of treatments and this could be due to positive relationship
of the inoculated bacteria for improving root weight by accumulation of balanced
nutrients in the roots and production of growth regulators hormone like IAA
and biocontrol compounds that improved root development, which enhanced water
and nutrient uptake and ultimately helped better root development. Our results
confirmed the previous findings of Afzal and Bano (2008)
who reported large amount of wheat root mass due to co-inoculation of PSB. But,
by far less than the result of Qureshi et al. (2011),
who recorded 50.54 cm root length and 77.1 g plant-1 root mass of
Mung bean (Vigna radiata L.) from the co-inoculation of phosphate solubilizing
R. phaseoli and B. megaterium.
The plants inoculated with OG+JURMB69 gave high number of nodules (13.9/plant)
and nodule weight (2.32 g plant-1). This could be due to the symbiotic
effect of Rhizobium on Faba bean along with organic phosphate. In addition,
the nodules showed pink color. The number of nodules recorded in the present
finding was less than the report of Workalemahu (2009),
who recorded 96/plants. This showed that the isolates were weak in nodule formation.
All of the inoculated plants produced highest number of flowers and flowering
at the 38 days after sowing compared to control. Specially, OG+JURB48+JURMB69
treated plants gave significant number flowers (12.78/plant) and this was four
times higher than the uninoculated plant. This finding is congruent with the
investigation of Kumari et al. (2009), who recorded
up to 21 flowers/plants from Lens culinaris inoculated by PSB inoculants.
The co-inoculants (OG+JURB48+JURMB69) enhancing the uptake of nutrient from
organic phosphate amendment, production of phytohormones and higher biocontrol
agent from two sides. Similarly, the earliness of bud initiation in PSB-inoculated
plants could be due to easy uptake of nutrients and simultaneous transport of
growth promoting substances such as cytokinins to the auxiliary buds resulting
in breakage of apical dominance, ultimately this has resulted in a better sink
for faster mobilization of photosynthates and early transformation of plant
parts from vegetative to reproductive phase as earlier demonstrated by Jayamma
The overall results on dry matter showed that, most of the treatments receiving
inoculants gave highest dry biomass of plant compared to control. This could
be due to accumulation of nutrient in the plant tissue either from organic and
inorganic source of phosphate or soils due to the activities of PSB, which could
have contributed to improve the dry weight of shoot. Most of the inoculated
treatment significantly increased dry weight of root over uninoculated control.
The highest root dry weight was recorded in plant inoculated with JURB48+JURMB69
(5.2 g plant-1). This could be due to co-inoculants promote the growth
of root through nitrogen fixation, phosphate solubilization and production of
growth promoting substances which are known to change the root morphology and
increase the biomass of Faba bean root. These observations are less than the
earlier findings of Qureshi et al. (2011) who
reported that co-inoculation of PSB such as Bacillus and Rhizobium sp.
significantly increased (231.3 g pot-1) the root biomass of Mung
bean (Vigna radiata L.).
The total dry weight of the Faba bean inoculated with PSB was significantly
increased over control. For instance the plant inoculated with co-inoculant
(JURB48+JURMB69) recorded the maximum dry weight (9.02 g plant-1)
of Faba bean compared to the other treatments. This result is in line with the
report of El-Komy (2005), who reported increase in the
total dry weight of wheat due to the co-inoculation of Azospirillum lipoferum
and Bacillus megaterium. These isolates possessed high P-solubilizing
ability, nitrogen fixing capacity as well as production of growth hormone and
production of biocontrol, which might have contributed to the enhanced plant
vigor. Increase in plant height, number of leaves and root growth in inoculated
treatments might have led to the increased total dry matter production of Faba
bean plants as earlier suggested by Afzal et al.
The two isolates (JURB48 and JURMB69) either in combination or separately enhanced
both P content and uptake of Faba bean plants significantly over uninoculated
treatments. The increase in P uptake due to PSB inoculation could be because
of the ability to solubilize insoluble inorganic and mineralize organic phosphate
sources as a result higher amount of P accumulated in plant tissue. The significant
increase in the percentage of P content (0.07) and uptake (4.79 mg plant-1)
were observed due to inoculation with isolates of JURB48 (Pseudomonas
sp.). It was clearly evident that inoculants which solubilized higher amount
of phosphorus enhanced content and uptake of P over the rest of the treatments.
Improved in P content due to inoculation with fluorescent pseudomonas was reported
by Zargar et al. (2005) in other crop plants.
This investigation has clearly indicated that PSB enhanced the P up take in
Faba bean plants through multitrophic beneficial traits. However, El-Komy
(2005) reported that the inoculation of PSB increased the P content of wheat
plant upto 53%. In general, the growth parameters of Faba bean were enhanced
either single or co-inoculate when amended with Orga. This enhancement could
be due to mineralization of Orga than solubilization of inorganic phosphate.
This could be substantiated by the findings of Ekin (2010)
who reported that the growth and yield of Sunflower was enhanced due to phosphate
fertilizers amended with PSB.
In the current study, the co-inoculants (JURB48 and JURMB69) enhanced seed germination, radicle and plumule length significantly compared to the other treatments. From the two inoculants, JURMB69 (Rhizobium sp.) is more effective than JURB48 in enhancing seed germination parameters. Most of the plant biomass such as fresh weight of shoot, root and total dry weight, flowering and leave number were significantly increased as a result of co-inoculants (JURB48 and JURMB69) either with or without of phosphate sources. In contrast to in vitro situation, JURB48 (Pseudomonas sp.) highly increased most biomass and nutrient content of Faba bean compared to JURMB69 (Rhizobium sp.) inoculant. Both single and co-inoculants are more effective with Orga to enhance the growth of Faba bean rather than rockphosphate. Moreover, if the effectiveness of our PSB isolates will be tested on other crops and vegetables, it would be better to reduce dependance on commercial fertilizers.
We would like to thank Jimma University for financial support and arranging all the logistics required for the execution of this study. We gratefully credit the farmer owners of the Faba bean farms for their permission and guidance.
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