Use Of Phosphate Solubilizing Bacteria Research Articles

Isolation, Selection and Characterization of Root-Associated Rock Phosphate Solubilizing Bacteria in Moroccan Wheat (Triticum aestivum L.)

Phosphorus (P) is the most important macronutrient next to nitrogen for the growth and development of plants. But often unavailable for plants because of its high reactivity with many soil constituents. Thus, the use of phosphate solubilizing bacteria (PSBs) as biofertilizers seems to be an effective way to resolve the soluble phosphorus availability in soil. The present study was conducted to isolate and characterize rock PSB associated with the rhizosphere of wheat (Triticum aestivum L.) from fourteen different wheat-growing sites of Meknes region in Morocco. A total of one hundred ninety-eight (198) rock PSBs were isolated employing NBRIP medium amended with rock phosphate (RP), out of which five strains (A17, A81, B26, B106, and B107) were selected for their strong ability to dissolve RP and were tested in vitro for plant growth-promoting (PGP) traits including production of indole acetic acid (IAA), siderophores, hydrogen cyanide (HCN), and antifungal activity, as well as their response to the effect of extrinsic and intrinsic stress. The 16S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to four genera, Pantoea, Pseudomonas, Serratia, and Enterobacter. The phosphate solubilization index (SI) of selected isolates ranged between 2.3 and 2.7, and the amount of solubilized phosphorus in the liquid medium varied from 59.1 to 90.2 µg mL−1. HPLC analysis revealed that all the selected isolates produced multiple organic acids (oxalic, citric, gluconic succinic, and fumaric acids) from glucose under aerobic conditions. Except for the A81 strain, all selected isolates were able to produce IAA ranging between 2.9 and 21.2 µg mL−1. The isolates A17, B26, and B107 showed the ability to produce siderophores ranging from 79.3 to 20.8% siderophore units. Only two strains (A17 and B26) were able to produce HCN. All selected isolates showed good resistance against different environmental stresses like 10–50 °C temperature, 0.5–2 g L−1 salt concentration and 4.5–9 pH range, and against different antibiotics. The antagonistic effect showed that among the five selected strains, only two strains (B26 and A17) were able to suppress the growth of tested fungi. This study clearly indicates that our selected rock PSBs can be used as biofertilizers for grain crops after studying their interaction with the host crop and field evaluation.

Isolation and characterization of insoluble inorganic phosphate solubilizer rice rhizosphere strain Enterobacter cloacae BAU3

The objective of the present study was to isolate and characterize most efficient phosphate solubilizing bacteria (PSB) from rice rhizosphere. The study was carried out during the Kharif season’2018 at Department of Soil Science and Agricultural Chemistry, Bihar Agricultural University, Sabour, Bhagalpur, Bihar. The availability of phosphorous to plants for uptake and utilization is limited in soil due to fixation in the form of Fe-P, Al-P and Ca-P. The use of phosphate solubilizing bacteria can prove to be helpful measure to supply phosphorous to the crops to increase the productivity. In the present investigation, a total of 10 isolates were obtained from rice rhizosphere soil samples. All ten isolated isolates were shown phosphorus solubilization. Out of ten isolates BAU3 was found to be most potent phosphate solubilizers showing clear halo zone around its colony. The isolate BAU3 showed 20.00 mm phosphate solubilizing halo zone around its colony. The solubilization index (SI) of the isolate BAU3 was also calculated at the end of the incubation period and observed phosphate solubilization index (SI) of 3.22. The isolate BAU3 showed maximum insoluble phosphate solubilization of 450.24 ?g ml-1 and isolates BAU3 was selected for subsequent studies. The bacterial isolates BAU3 was gram negative, non-spore forming rods shaped. On the basis of the 16SrDNA sequencing, isolate BAU3 was identified as Enterobacter cloacae strain BAU3 (Genebank Accession No. MK033472). The isolated strain of bacterial has potential to solubilize insoluble phosphorus and it can be utilized for preparation of microbial inoculants or biofertilizers.

Comparative phosphate solubilizing efficiency of psychrotolerant Pseudomonas jesenii MP1 and Acinetobacter sp. ST02 against chickpea for sustainable hill agriculture

Phosphorus (P) is an important plant nutrient for agricultural production. Adding phosphorus fertilizer to the soil not only increases the cost but also create environmental destruction. Therefore, the use of phosphate solubilizing bacteria (PSB) could be an eco-friendly approach for sustainable agricultural development. Large scale field trial study was conducted to explore inherent phosphate solubilizing potential of Himalayan psychrotrophic bacterial strains Pseudomonas jesenii MP1 and Acinetobacter sp. ST02 against native chickpea to achieve agricultural sustainability in traditional mountain agro-ecosystems. Both the strainsMP1 and STO2 were able to solubilise a maximum of 398.14 μg mL−1 and 329.9 μg mL−1 of P, respectively. Besides enhancing Chickpea seed germination of 92% (MP1) and 85% (STO2); both have shown a significant increment in plant agronomical as well as biochemical parameters with respect to their respective controls. The maximum grain yield of 26.23 kg and harvesting index 55.69 was observed for MP1 along with 40 Kg P2O5 ha−1 thereby, indicating the use of bio-inoculants with recommended dose of phosphate fertilizers to promote crop production. Further, contrary to chemical phosphatic fertilizers, they need to apply only once in the field and persist till the end of crop maturity. In the present scenario, they can be explored as natural “P” resource for high altitude agriculture; therefore, additional impetus in their bio-formulation will be a step forward towards sustainable hill agriculture systems and holistic growth.

Phosphorus Availability in Wheat, in Volcanic Soils Inoculated with Phosphate-Solubilizing Bacillus thuringiensis

The use of phosphate solubilizing bacteria (PSB) is an ecological strategy that allows for increasing the availability of phosphorus (P) in soil. The objective of this study was to evaluate P availability in wheat, in soils derived from volcanic ash (Andisol and Ultisol,) and inoculated with phosphate-solubilizing Bacillus thuringiensis, the experiment was conducted in pots under greenhouse conditions using a completely randomized design. Wheat plants were inoculated and re-inoculated at 20 and 46 days after sowing (DAS), respectively, with B. thuringiensis; and, soil and plant sampling was performed after 46, 66, and 87 days based on the Zadoks growth scale (Z). The inoculation resulted in an 11% increase in P of the rhizosphere at Z46 (Ultisol), P also increased 34% and 67% in aerial tissues at Z46 (Andisol and Ultisol), respectively, while an increase of 75% was observed in root tissues at Z87 (Ultisol). Similarly, the inoculation resulted in increases in acid phosphatase activity (Andisol), soil microbial biomass (Andisol and Ultisol), and root biomass in plants (Ultisol), without achieving increase of the aerial biomass of the plants. The phosphate solubilizing B. thuringiensis strain showed some positive, but also negative effects in soils and plants, depending on the soil.

Effects of phosphate-solubilizing bacteria, native microorganisms, and rock dust on Jatropha curcas L. growth.

Microorganisms with the ability to release nutrients to the soil from insoluble sources may be useful for plant cultivation. We evaluated the growth-promoting effect on Jatropha curcas L. of phosphate-solubilizing bacteria (PSB) and the native microbiota in soil with or without rock dust. J. curcas L. is important for biodiesel production. The experiments were performed in a greenhouse under a random-statistical design with 14 replicates. The soil received increasing dosages of rock dust. The presence of resident microorganisms and PSB inoculum was correlated with plant height, biomass production, and phosphorus content in plants for 120 days. Native soil microorganisms were detected and identified using denaturing gradient gel electrophoresis and DNA sequence analysis. Several bacterial populations belonged to the genus Bacillus. Populations associated with the phyla Chytridiomycota and Ascomycota were detected among the fungi. The best results for the variable plant height were correlated with the presence of resident microbiota and rock dust until the end of the experiment. The largest biomass production and the highest content of phosphorus occurred in the presence of soil-resident microbiota only up to 120 days. No significant effects were observed for biomass production with the use of PSB combined with rock dust. J. curcas L. under the influence of only resident microbiota showed the best plant growth results. Future research will focus on the specificity of resident microbiota activity in plant growth promotion and the isolation of these microorganisms to produce a new inoculum to be tested in various plants.

Mineralization of soluble P fertilizers and insoluble rock phosphate in response to phosphate-solubilizing bacteria and poultry manure and their effect on the growth and P utilization efficiency of chilli (<i>Capsicum annuum</i> L.)

Abstract. The ability of soil microorganisms and organic manure to convert insoluble phosphorus (P) to an accessible form offers a biological rescue system for improving P utilization efficiency in soil–plant systems. Our objective was to examine the P mineralization potential of two soluble P fertilizers (SPF), i.e., single superphosphate (SSP) and diammonium phosphate (DAP), and of insoluble rock phosphate (RP) with and without phosphate-solubilizing bacteria (PSB) and poultry manure (PM) and their subsequent effect on the growth, yield and P utilization efficiency (PUE) of chilli (Capsicum annuum L.). An incubation study was carried out on a loam (slightly alkaline) soil with 12 treatments: T0 – control; T1 – RP; T2 – SSP; T3 – DAP; T4 – PM; T5 – 1/2 RP+1/2 SSP; T6 – 1/2 RP+1/2 DAP; T7 – 1/2 RP+1/2 PM; T8 – RP+PSB; T9 – 1/2 RP+1/2 SSP+PSB; T10 – 1/2 RP+1/2 DAP+PSB; and T11 – 1/2 RP+1/2 PM+PSB. Phosphorus mineralization was measured by analyzing extractable P from the amended soil incubated under controlled conditions at 25 °C for periods of 0, 5, 15, 25, 35 and 60 days. A complementary greenhouse experiment was conducted in pots with chilli (Capsicum annuum L.) as a test crop. Growth, yield, P uptake and PUE of the chilli was determined during the study. Results indicated that P mineralization in soil amended with RP was 6.0–11.5 mg kg−1, while both soluble P fertilizers resulted in 68–73 mg P kg−1 at day 0, which decreased by 79–82 % at the end of incubation. The integrated use of PSB and PM with RP in T11 stimulated P mineralization by releasing a maximum of 25 mg P kg−1 that was maintained at high levels without any loss. Use of PSB decreased soil pH. In the greenhouse experiment, RP alone or RP+PSB did not have a significant impact on plant growth. However, the combined use of RP, PM and PSB in T11 resulted in similar growth, yield and P uptake of chilli as DAP. The PUE of applied P varied from 4 to 29 % and was higher in the treatments that included PSB. We conclude that the use of PSB and PM with insoluble RP or with soluble P fertilizers could be a promising approach to enhance P availability from both low-grade RP and SPF for crop production in intensive cropping systems.

Solubilization of inorganic phosphate by Pseudomonas strains isolated from rice rhizosphere

The use of phosphate solubilizing bacteria to mobilize large reserves of insoluble P in soils instead of phosphate fertilizers is an ecologically safe and economically reasonable alternative to assure a sustainable agriculture. In this work, the mineral phosphate solubilization activity was evaluated for 4 Pseudomonas strains isolated from rice rhizosphere. For qualitative tests, different media were used; NBRIP, YED and Pikovskaya (PVK) amended with 0.5% Ca3(PO4)2 and modified PVK medium containing CaHPO4, Ca5HO13P3, FePO4 and AlPO4 as P source. All bacteria were able to dissolve calcium phosphates, while none was surrounded by transparent halos when FePO4 and AlPO4 were the P source. Quantitative test was assessed in PVK substituting glucose by sucrose and galactose. The highest levels of soluble P were recorded in the presence of glucose, while it didn’t exceed 43.64 μg / ml and 19.19 µg / ml in the presence of galactose and sucrose, respectively. Therefore, glucose has been chosen as a carbon source to assay the effect of carbon concentration on P solubilization ability. The level of dissolved P was enhanced with increasing amount of glucose (1%, 2% and 3% (w/v)). In all cases, the P biosolubilisation was accompanied by a significant pH decrease of the liquid media. A significant inverse correlation was found between P concentrations and pH reduction. Thus, acidification of the media seems to be the main mechanism for calcium phosphates solubilization in this study, and these test strains could serve as efficient biofertilizer candidates for improving crop production in low P soils.

Effect of Organic and Inorganic Nutrients on Yield of Rajmash (Phaseolus Vulgaris L.) in Dry Temperate Zone of Himachal Pradesh

Spiti valley is endowed with mild summers and cool winters. The valley remains snow bound from mid November to March. Intense sun, high wind velocity, low humidity, scanty rainfall and high transpiration rate are the other features of climate of Spiti valley. Use of bio-fertilizers is gaining momentum by the farmers of Himachal Pradesh in organic farming. The use of phosphate solubilizing bacteria as inoculants simultaneously increases P uptake by the plant and crop yield. Strains from the genera Pseudomonas, Bacillus and Rhizobium are among the most powerful phosphate solubilizers. Rajmash (Phaseolus vulgaris L.) is a potential cash crop grown in dry temperate zone of Himachal Pradesh. Being a leguminous crop its phosphorus requirement is higher. Among the various components of production technology, fertilizers are the kingpin for improving the productivity of rajmash. The scarcity of organic material in the dry temperate zone indicates that the productivity depends on integrated nutrient management. Thus the present study with two inoculations (Rhizobium and Rhizobium+Phosphate solublising bacteria), four nitrogen levels (0,20,40,60 kg/ha) and two phosphorus levels (75% and 100% recommended) was undertaken. Rajmash yield increased by inoculation. Grain yield increased with increasing N levels. Substitution of 25% P did not increase the yield of rajmash significantly. Similarly straw yield of rajmash differ significantly by inoculation in both the years. Recommended level of P @ 60 kg/ha proved better than 75% of recommended P. After analyzing soil samples at harvest it was revealed that inoculation with Rhizobium+PSB gave more availability of N (222.8 kg/ha), P (26.6 kg/ha) and K (8.96 kg/ha) in comparison to Rhizobium alone.

Impact of Phosphate Solubilizing Bacteria and Phosphorus Application on Forage Yield and Quality of Berseem in West Bengal

Phosphorus availability is increased through the use of phosphate solubilizing bacteria for enhancing the forage yield and improving the quality of berseem fodder. A field experiment was conducted in the fodder farm of West Bengal University of Animal and Fishery Sciences, Belgachia during rabi, season 2013–14. The crop was sown with inoculated (I1) and un-inoculated (I0) seeds of berseem (Trifolium alexandrinum L.) of variety warden and was given phosphorus fertilizer at the levels 40 (P1), 60 (P2), 80 (P3) and 100 (P4) kg P2O5 ha−1 in the form of SSP in RCBD with three replications in plots of net size 6 m X 2 m. PSB inoculation significantly increases green forage and dry matter yield by increasing plant height, no. of branches, leaf-stem ratio, etc. All the quality traits except ash content and dry matter percentage were significantly affected by PSB inoculation. Higher green forage yield (320.4 qt ha−1), dry matter yield (39.2 qt ha−1), crude protein yield (7.89 qt ha−1), crude protein percentage (19.28%), ethyl extract (3.32%) and nitrogen free extract (41.75%) were recorded from the plots inoculated with PSB. Application of phosphorus fertilizers significantly influenced the green forage and dry matter yield of berseem, leafstem ratio, etc. though plant height and no. of branches were not-significant. All the quality parameters i.e. CP, CF, EE, NFE, except ash percentage were significantly influenced by phosphorus application. Best results were obtained with 80 kg P2O5 ha−1 in all the cases. Regarding interaction effect, higher yields of better quality green forage of berseem were obtained in I1P3 i.e. inoculation with PSB with phosphorus application of 80 kg P2O5ha−1.

Agronomic Effectiveness and Phosphorus Utilization Efficiency of Rock Phosphate Applied to Winter Wheat

Rock phosphate (RP) is an important natural source of P for plant nutrition, but the solubility and availability of P from RP is an issue in agricultural production systems. Integrated use of RP with various organic and inorganic byproducts has been reported to increase RP P use efficiency and stability of crop yields. A 2‐yr (2010–2011 and 2011–2012) field experiment was conducted to examine the agronomic effectiveness and P utilization efficiency (PUE) of RP supplemented with wood ash, compost, and poultry manure with and without phosphate‐solubilizing bacteria applied to rainfed wheat (Triticum aestivum L.) in the hilly region of Kashmir, Pakistan. The experiment was conducted in a completely randomized block design with factorial arrangement using three replications. Treatments included: control; RP; RP + wood ash (WA); RP + poultry manure (PM); RP + compost; control + phosphate‐solubilizing bacteria (PSB); RP + PSB; RP + WA + PSB; RP + PM + PSB; and RP + compost + PSB. Results indicated that RP alone did not show significant effects on growth and PUE of wheat; however, the use of RP with PM and compost improved straw yield (21 and 22%), grain yield (52 and 50%), plant P uptake (73 and 84%), and PUE (95 and 103%) over the RP alone. Also RP + PM and RP + compost, when inoculated with PSB, resulted in a further increase in yield of 9 and 8%, P uptake of 28 and 29%, and PUE of 35 and 42%, respectively. These results demonstrate that use of PSB and organic amendments with RP could be a promising management strategy and viable technology to utilize both low‐grade RP and organic materials efficiently for crop production and nutrient improvement in mountainous ecosystems.

Effect of Pseudomonas luteola on mobilization of phosphorus and growth of young apple trees (Ligol)—Pot experiment

The use of phosphate solubilizing bacteria as inoculants may increase the concentration of plant-available phosphorus in soil. Among soil microorganisms, bacteria from the genus Pseudomonas have received considerable attention as plant growth promoters. A phosphate solubilizing bacterium isolated from non-rhizosphere soil collected in Central Poland, was identified as Pseudomonas luteola BN0834 on the basis of biochemical methods and 16SrDNA sequence analysis. P. luteola strain BN08-34 was tested for: solubilization of inorganic and organic compounds of phosphorus (calcium phosphate, zinc phosphate, hydroxyapatite and calcium phytate); indole acetic acid (IAA), siderophore production and biosurfactant production; and the ability to grow on a medium without nitrogen added. Young apple trees, cultivar Ligol (rootstock M26), were grown in a pot-house for 14 weeks in pots filled with nonsterilized soil, classified as a sandy loam. The P. luteola BN0834 was introduced into the soil in a number equal to the number of native phosphate solubilizing microorganisms (PSM) (P. luteola) in soil or in a number ten times higher than the number of native PSM in soil (P. luteola×10). Shoot numbers; average and total shoot lengths; contents of P, K, Mg and Ca in plant material; contents of available P, K and total Mg in non-rhizosphere soil, changes in the number of cfu (colony forming units) of microorganisms (PSM, cophiotrophs, oligotrophs and fungi) in non-rhizosphere soil and in the rhizosphere of the apple trees were studied. When the higher number of P. luteola BN0834 was introduced into soil without a mineral fertilizer added near the surface of the roots, positive correlations were found between the number of PSM in the apple tree rhizosphere and the content of available P in non-rhizosphere soil and also between the number of PSM in the apple tree rhizosphere and the amount of P, K and Ca in plant leaves. The highest total shoot length was also obtained from P. luteola×10 application.

Pb remobilization by bacterially mediated dissolution of pyromorphite Pb5(PO4)3Cl in presence of phosphate-solubilizing Pseudomonas putida

Remediation of lead (Pb)-contaminated sites with phosphate amendments is one of the best studied and cost-effective methods for in situ immobilization. In this treatment, a very stable mineral, pyromorphite Pb5(PO4)3Cl, is formed. Several studies propose to improve this treatment method with the addition of phosphate-solubilizing bacteria (PSB). The effect of bacteria on solubilization of pyromorphite is unknown. In this study, the effect of the soil microorganisms on the stability of pyromorphite Pb5(PO4)3Cl has been investigated in a set of batch solution experiments. The mineral was reacted with Pseudomonas putida, a common soil microorganism. Dissolution of pyromorphite was enhanced by the presence of P. putida, resulting in an elevated Pb concentration in the solution. This occurred even when the bacteria were provided with an additional source of phosphate in the solution. Pyromorphite has been shown to be a potential source of nutrient phosphorus for common soil bacteria. Thus, the use of PSB in remediation treatments of Pb contaminated sites may have adverse long-term impacts on Pb immobilization. Conscious phosphate management is suggested for long-term sustainability of the in situ Pb immobilization by pyromorphite formation.

An integrated fertilization system of canola (Brassica napus L.) production under different crop rotations

Cropping systems in farmland areas of Iran are characterized by continuous cultivation of crops with consumption of chemical fertilizers leading to serious soil erosion and fertility decline. Information regarding the simultaneous evaluation of crop rotation and fertilization on the canola is lacking. Hence, field experiments were conducted during 2007–2010 using split–split plot design. Three crop rotations: chickpea, sunflower, wheat, and canola (R1); green manure, chickpea, green manure, wheat, green manure and canola (R2); canola, wheat, and canola (R3) were used as main plots. Sub plots were consisted of six methods of fertilization including (N1): farmyard manure (FYM); (N2): compost; (N3): chemical fertilizers; (N4): FYM+compost and (N5): FYM+compost+chemical fertilizers; and control (N6). Four levels of biofertilizers consisted of (B1): phosphate solubilizing bacteria (PSB); (B2): Trichoderma harzianum; (B3): PSB+T. harzianum; and (B4): without biofertilizers were arranged in the sub-sub plots. Results showed that green manure application in canola rotation (R2) increased grain yield and nutrient uptake. Combined application of FYM, compost and chemical fertilizers (N5) elevated the nitrogen uptake rate and grain oil yield. Simultaneous use of PSB and T. harzianum (B3) resulted in the increase of nitrogen and sulfur contents of grain. R2 rotation with regard to its biological and environmental efficiencies accompanied with FYM+compost and B3 (PSB+T. harzianum) is suggested as a low input system to obtain a more sustainable and productive farming in canola.

Phosphate solubilizers enhance NPK fertilizer use efficiency in rice and legume cultivation

It has been reported that phosphate solubilizing bacteria (PSB) are the most promising bacteria among the plant growth promoting rhizobacteria (PGPR); which may be used as biofertilizers for plant growth and nutrient use efficiency. Moreover, these soil micro-organisms play a significant role in regulating the dynamics of organic matter decomposition and the availability of plant nutrients such as nitrogen (N), phosphorus (P), potassium (K) and other nutrients. Through this study, the management of nutrient use efficiency by the application of PSB was targeted in order to make the applied nutrients more available to the plants in the rice (Oryza sativa) and yardlong bean (Vigna unguiculata) cultivation. Results have shown that the treatments with PSB alone or in the form of consortia of compatible strains with or without the external application of chemical NPK gave more germination index (G. I.) from 2.5 to 5 in rice and 2.7 to 4.8 in bean seeds. They also showed a higher growth in both shoot and root length and a higher biomass as compared to the control. This gives us an idea about the potentiality of these PSB strains and their application in rice and yardlong bean cultivation to get a better harvest index. Their use will also possibly reduce the nutrient runoff or leaching and increase in the use efficiency of the applied fertilizers. Thus, we can conclude that the NPK uptake and management can be improved by the use of PSB in rice and yardlong bean cultivation, and their application may be much more beneficial in the agricultural field.

Performance of phosphate solubilizing bacteria for improving growth and yield of sunflower (Helianthus annuus L.) in the presence of phosphorus fertilizer

The ability of phosphate solubilizing bacteria (PSB) to convert insoluble forms of phosphorus to an accessible form is an important trait in sustainable farming for increasing plant yields. The beneficial effects of PSB on crop productivity have been widely described, but the use of PSB as biofertilizer is scarcely documented in sunflower. The objective of this study was to evaluate the effect of application of PSB, Bacillus M-13, with and without varying amounts of phosphorus (P) fertilizer on growth and yield of sunflower under field conditions. The PSB application was able to mobilize P efficiently in the sunflower and improved seed quality and oil yield. It also enhanced the head diameter, 1000 seed weight, kernel ratio and oil content and led to seed and oil yield increases of 15.0 and 24.7% over no application, respectively. However, when PSB was used in conjunction with P fertilizers, a much greater effect was observed. It was found that the highest seed yield of sunflower possible with 100 kg P2O5 ha-1 fertilizer was achieved with about 50 kg P2O5 ha-1 when used in conjunction with PSB. But the important effect of PSB on oil yield was noted at 100 kg P2O5 ha-1, possibly indicating increased PSB activity in the rhizosphere following PSB application and consequently by enhanced P solubilization as evidenced by the higher levels of P content of seed.

Investigation of biological behavior of Iranian indigenous phosphate solubilizing bacteria and determinant of colonization ability of potato roots by these bacteria isolation

The ability of a few soil microorganisms to convert insoluble forms of phosphorus (P) to an accessible form is an important trait in plant growth-promoting bacteria for increasing plant yields. The use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants. In this study, isolation and characterization of 3 strains of phosphate solubilizing bacteria (PSB) from Central province of Iran were carried out. Identification of three isolates was carried out by 16S rDNA sequencing. Three strains namely Bacillus lentus strain PS5, Bacillus Licheniformis strain PS7 and Pseoudomonas putida strain PS13 were isolated from the rhizospere of Beta vulgaris and solanum tuberosom. All of the three strains were selected in vitro for their phosphate solubilizing abilities from alkaline soils. Among the three strains, PS5 and PS7 were the most efficient strains in terms of their capabilities to grow and solubilize phosphorus in the presence of 5% NaCl and 42°C. Root colonization analyses were performed to determine the distribution and metabolic activity of the strains in the potato rhizosper. The soil containing potato seedling was treated with all strains marked with lux genes for bioluminescence, as well as resistance to kanamycin and rifampin prior to planting in non-sterile natural soil. The introduced bacteria were quantified on roots by dilution plating on antibiotic media along with observation of bioluminescence. Results demonstrated the strains could survive in the potato root system under stress conditions. The significance of this study lies in the fact that the bacterial strains isolated from alkaline soils have ability to solubilize phosphate in high salt, pH and temperature conditions.

Phosphate solubilizing bacteria from subtropical soil and their tricalcium phosphate solubilizing abilities

The ability of a few soil microorganisms to convert insoluble forms of phosphorus to an accessible form is an important trait in plant growth-promoting bacteria for increasing plant yields. The use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants. In this study, isolation, screening and characterization of 36 strains of phosphate solubilizing bacteria (PSB) from Central Taiwan were carried out. Mineral phosphate solubilizing (MPS) activities of all isolates were tested on tricalcium phosphate medium by analyzing the soluble-P content after 72 h of incubation at 30 °C. Identification and phylogenetic analysis of 36 isolates were carried out by 16S rDNA sequencing. Ten isolates belonged to genus Bacillus, nine to genus Rhodococcus, seven to genus Arthrobacter, six to genus Serratia and one each to genera Chryseobacterium, Delftia, Gordonia and Phyllobacterium. In addition, four strains namely, Arthrobacter ureafaciens, Phyllobacterium myrsinacearum, Rhodococcus erythropolis and Delftia sp. are being reported for the first time as phosphate solubilizing bacteria (PSB) after confirming their capacity to solubilize considerable amount of tricalcium phosphate in the medium by secreting organic acids. P-solubilizing activity of these strains was associated with the release of organic acids and a drop in the pH of the medium. HPLC analysis detected eight different kinds of organic acids, namely: citric acid, gluconic acid, lactic acid, succinic acid, propionic acid and three unknown organic acids from the cultures of these isolates. An inverse relationship between pH and P solubilized was apparent from this study. Identification and characterization of soil PSB for the effective plant growth-promotion broadens the spectrum of phosphate solubilizers available for field application.

Effect of moisture conservation practices, phosphorus levels and bacterial inoculation on chickpea (Cicer arietinum) under rainfed condition

A field experiment was conducted during winter (rabr) seasons of 1997 98 and 1998 99 at the Indian Agricultural Research Institute, New Delhi, to study the effect of conserved soil moisture, levels of phosphorus and bacterial seed inoculation. In situ moisture conservation through field bunding farmyard manure (FYM) 10 tonneslha proved to conserve maximum moisture and improved the yield, nodulation and water use efficiency (WUE) in chickpea (Cicer arietinum L.). The next important practice was found to be field bunding green manure (GM) (dhaincha). However, both these practices did not exhibit marked differences on the yield during both the years as well as in pooled data. Application of phosphorus 60 kg P2051ha significantly increased yield attributes, yield, number of noduledplant, dry weight of nodules and consumptive use of water. The increase in above values was progressively related to P doses from 0 to 60 kg P2051ha. However, grain yield and WUE were maximum (20.02 ql ha and 8.38 kg/ha mm) up to 30 kg P2051ha in both the years. Use of phosphate solubilizing bacteria increased the yield attributes, like poddplants, seed weight1 plant and test weight and consumptive use of water and WUE of the chickpea in comparison to no inoculation.

Uptake and balance sheet of nitrogen and phosphorus in arietinum) as influenced by phosphorus, gram (Cicer biofertilizer and micronutrients under rainfed condition

A field experiment was conducted during 1995-96 and 1996-97 to study the effect of phosphorus, Rhizobium culture, phosphate-solubilizing bacteria (PSB) and micronutrients on uptake of nitrogen and phosphorus and their balance sheet in soil of chickpea (Cicer arietinum L.) crop in a rice (Oryza sativa L.) based cropping system under rainfed conditions. Uptake of N and P increased with the increasing levels of P and it was further increased with application of phosphate- solubilizing bacteria alone or in combination with rhizobium culture with each level of P. Use of phosphate-solubilizing bacteria and rhizobium culture along with inorganic phosphorus fertilizers increased the grain yield and uptake of N and P. This also solubilized the native and applied phosphorus and reduced phosphorus fixation.

Phosphate solubilizing bacteria and their role in plant growth promotion

The use of phosphate solubilizing bacteria as inoculants simultaneously increases P uptake by the plant and crop yield. Strains from the genera Pseudomonas, Bacillus and Rhizobium are among the most powerful phosphate solubilizers. The principal mechanism for mineral phosphate solubilization is the production of organic acids, and acid phosphatases play a major role in the mineralization of organic phosphorous in soil. Several phosphatase-encoding genes have been cloned and characterized and a few genes involved in mineral phosphate solubilization have been isolated. Therefore, genetic manipulation of phosphate-solubilizing bacteria to improve their ability to improve plant growth may include cloning genes involved in both mineral and organic phosphate solubilization, followed by their expression in selected rhizobacterial strains. Chromosomal insertion of these genes under appropriate promoters is an interesting approach.