Co-inoculation Of Plant Growth Promoting Rhizobacteria Research Articles

Enhancing olive tree (Olea europaea) rhizosphere dynamics: Co-inoculation effects of arbuscular mycorrhizal fungi and plant growth- promoting rhizobacteria in field experiments

We investigated the outcome of the interaction between the arbuscular mycorrhizal fungus (AMF) Rhizophagus (R) irregularis DAOM 197198 and the Plant-Growth-Promoting Rhizobacteria (PGPR) (mix of Bacillus megaterium, Burkholdria cedrus and Streptomyces beta-vulgaris) by conducting an olive field experiment. Our data provide evidence that the co-inoculation of R. irregularis and PGPR has important effects on the rhizosphere microbial community. The largest proportional increase was found for the PLFA biomarkers indicative of Gram-negative bacteria (16:1ω9, 18:1ω7 and 18:1ω9), fungi (18:2ω6) and actinobacteria (10Me16:0 and 10Me18:0). Microbial inoculants application of all tested treatments caused a significant decrease in the level of trehalose in the olive rhizosphere. The most pronounced decrease was observed in the plant inoculated with R. intraradices only, suggesting that the presence of AMF may have relaxed the bacterial stress. Co-inoculation of PGPR and AMF significantly improved the nutritional status of olive roots. Specifically, the interaction of PGPR and R. intraradices led to an increase in N (26 %), P (60 %), Fe (25 %), Mn (18 %), Zn (26 %), B (22 %) and Cu (14 %) compared with the control. We also found that the co-inoculation of AMF with PGPR causes a shift in the accumulation of secondary metabolites in olive roots. In particular, the most important effect induced by AMF was an improvement of oleuropein concentration, while co-inoculation of R. irregularis and PGPR positively modulated verbascoside concentration. The novelty of the present work lies in the use of microbial inoculants in the field of olive trees. This approach provided direct information regarding the advantages of using AMF and PGPR inoculants, allowing the reduction of chemical inputs and positively influencing the olive tree performance.

Scanning electron microscopy indicates Pseudomonad strains facilitate AMF mycorrhization in litchi (Litchi chinensis Sonn.) air-layers and improving survivability, growth and leaf nutrient status.

The efficacy of two plant growth promoting rhizobacteria (PGPR) viz. Pseudomonas jessenni strain R62 and Pseudomonas synxantha strain R81 was examined for mycorrhization of arbuscular mycorrhizal (AM) fungi (Glomus intraradices), survivability, growth and leaf nutrient status in litchi air-layer system. Therefore, the litchi air-layers were inoculated with PGPR i.e., Pseudomonad strains and AM fungi alone and with combination during the preparation of air-layers on the mother tree and planting of air-layers in root trainers just after detachment of the fresh air-layers from the mother tree. The scanning electron microscopy of the litchi roots indicated that Pseudomonad strains enhanced the process of mycorrhization of AM fungi and accounted near about 11.5 (tree inoculation) to 14.5 (root trainer inoculation) per cent increase in colonization over the sole inoculation of AM fungi in respective air-layers. No sign of mortality in any air-layered plants was noted in PGPR+AM fungi and sole AM fungi inoculated air-layers up to 18 months of growing. Significantly the highest shoot and root dry weight, and root length were recorded in the air-layers inoculated with both PGPR and AM fungi. This co-inoculation of PGPR with AM fungi was also responsible for the significant enrichment of the primary (N, P and K) and micro (Zn, Cu and Fe) nutrient concentration of the leaves in the litchi air-layers. However, the inoculation of air-layers with these microorganisms failed to produce any significant effects on leaf secondary (Ca, Mg and S) nutrient content. Further, the inoculation treatments had an adverse impact on leaf Mn content. The fresh air-layers inoculated after detachment from the mother tree were performed better for most of the studied parameters than the tree inoculated air-layers.

Reduction in nitrogen fertilization in Triticum sp. inoculated and co-inoculated

Using techniques of inoculation and co-inoculation of plant growth-promoting rhizobacteria (PGPR) could be an alternative with great potential for the wheat agricultural market, aiming towards a higher fertilizer efficiency and a subsequent reduction in environmental impacts. The objective of this study was to evaluate the efficiency of rhizobia symbiont inoculants isolated from legumes, individually and combined with Azospirillum brasilense, in promoting the growth of the wheat crop. The experiments were performed with the cultivars BRS Parrudo and TBIO Sossego, both inoculated and co-inoculated with the rhizobia UFRGS Vp16 and UFRGS Lc348, and A. brasilense, and under nitrogen dosage levels recommended for wheat plants. Inoculation of rhizobia, isolated or combined with A. brasilense, promotes increases in the production of wheat grains with half of the nitrogen dose recommended in the two evaluated cultivars, standing as an economically viable and ecologically sustainable alternative for the agricultural market.

Co-inoculation of selected nodule endophytic rhizobacterial strains with Rhizobium tropici promotes plant growth and controls damping off in common bean

Production of common bean (Phaseolus vulgaris) is limited by the occurrence of damping off (rhizoctoniosis), which is caused by the fungus Rhizoctonia solani. However, the co-inoculation of plant growth-promoting rhizobacteria (PGPR) involved in biological control along with diatomic nitrogen (N2)-fixing rhizobia can enhance N nutrition and increase production. In this context, finding microorganisms with synergistic effects that perform these two roles is of fundamental importance to ensure adequate yield levels. The aim of this study was to evaluate the effects of co-inoculation of nodule endophytic strains of the genera Bacillus, Paenibacillus, Burkholderia, and Pseudomonas with Rhizobium tropici CIAT 899, an N2-fixing rhizobial strain, on the biocontrol of damping off and growth promotion in common bean plants. Greenhouse experiments were conducted under axenic conditions using the common bean cultivar Pérola. The first experiment evaluated the potential of the 14 rhizobacterial strains, which were inoculated alone or in combination with CIAT 899, for the control of R. solani. The second experiment evaluated the ability of these 14 rhizobacterial strains to promote plant growth with three manners of N supply: co-inoculation with CIAT 899 at low mineral N supply (5.25 mg N mL−1), low mineral N supply (5.25 mg N mL−1), and high mineral N supply (52.5 mg N mL−1). The use of rhizobacteria combined with rhizobia contributed in a synergistic manner to the promotion of growth and the control of damping off in the common bean. Co-inoculation of the strains UFLA 02-281/03-18 (Pseudomonas sp.), UFLA 02-286 (Bacillus sp.), and UFLA 04-227 (Burkholderia fungorum) together with CIAT 899 effectively controlled damping off. For the common bean, mineral N supply can be replaced by the co-inoculation of CIAT 899 with plant growth-promoting strains UFLA 02-281/02-286/02-290/02-293. Nodule endophytes UFLA 02-281/02-286 are promising for co-inoculation with CIAT 899 in the common bean, promoting synergy with rhizobial inoculation and protection against disease.

Rhizobacteria inoculation benefits nutrient availability for phytostabilization in copper contaminated soil: Drivers from bacterial community structures in rhizosphere

Plant growth-promoting rhizobacteria (PGPR) and rhizobia are potentially advantageous in improving plant growth in heavy metal contaminated soils. However, only limited information is available in literature on the manner through which the co-inoculation of PGPR and rhizobia can potentially supply nutrients to benefit plant growth in heavy metal contaminated soil. Accordingly, this study investigated the effects of Paenibacillus mucilaginosus (PGPR) and Sinorhizobium meliloti (rhizobia) co-inoculation on soil nutrients, enzyme activities, and microbial biomass in copper (Cu) contaminated soil planted with alfalfa (Medicago sativa). Moreover, we assessed soil bacterial community structure using high-throughput Illumina sequencing of 16S rRNA genes. Results showed that PGPR and/or rhizobia inoculation improved alfalfa growth. In particular, we found that this co-inoculation approach decreased Cu accumulation (48.6%) in shoots compared to the control (uninoculated). Both partial least squares path modeling (PLS-PM) and the relative importance of regressors in the linear models identified that enzyme activities, microbial biomass, and microbial community structure in Cu contaminated soil were major controlling variables of soil nutrient availability. The co-inoculation treatment significantly increased soil carbon (C) and nitrogen (N) concentrations by increasing urease (55.6%), saccharase (29.5%), and β-glucosidase (31.4%) activities compared to the control. Furthermore, the rhizosphere microbial community structure in the co-inoculation treatment was mainly regulated by soil N concentrations (i.e., both total N and available N) while altering alpha diversity (α-diversity). The relative abundances of Firmicutes (including biomarkers of the Bacillus genus) and Acidobacteria were enriched in the co-inoculated treatment, which can potentially improve soil nutrient availability and subsequently benefit plant growth. These findings indicated that the co-inoculation of PGPR and rhizobia plays an important role in promoting plant growth in Cu contaminated soil. This is because this approach can increase soil nutrient availability by enhancing soil enzyme activities and regulating rhizosphere microbial community structure.

Functionally dissimilar soil organisms improve growth and Pb/Zn uptake by Stachys inflata grown in a calcareous soil highly polluted with mining activities

Micro- and macro-organisms are key components of sustainable soil-plant systems; and are involved in plant growth stimulation and accumulation of heavy metals in the plant, with great contribution to phytoremediation of heavy metal-contaminated soils. However, the combined effect of arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR) and earthworms on plant growth and metal uptake is not yet clear. The main objective of this study was to examine the combined influences of these soil organisms on the growth and metal uptake by a native plant species (Stachys inflata), and subsequently on potential phytoremediation in a soil highly polluted with Pb/Zn mining activities. Metal tolerant AMF, PGPR and earthworms were used either alone or in combination in a factorial pot experiment under greenhouse conditions for 4 months. Inoculation of AMF, PGPR and earthworm led to an increase of soil Pb/Zn availability with the greatest Zn availability (about 2 times) with triple inoculation of all the organisms and the highest Pb availability (about 3 times) with co-inoculation of PGPR and earthworms. Triple inoculation of soil organisms increased the total plant biomass 3 times, total Pb uptake 6 times and total Zn uptake 5 times as compared with the uninoculated plants. The growth-stimulating effect of combined soil organisms was much greater than that of individual or dually-inoculated organisms. These results showed that it is possible to use the combination of metal-tolerant soil organisms as a potential bioaugmentation tool to accelerate metal phytoremediation rate in calcareous soils polluted by Pb/Zn mining activity under arid conditions. This could occur as a consequence of the synergistic effects of AMF, PGPR and earthworms on metal availability in the soil, S. inflata growth, metal tolerance and uptake. However, it would practically require more than hundreds of cropping cycles (360 for Pb and 250 for Zn) to achieve metal maximum permissible limits under the conditions of this pot experiment.

Alleviation of heavy metals toxicity by the application of plant growth promoting rhizobacteria and effects on wheat grown in saline sodic field

ABSTRACTThe aim of the study was to determine tolerance of plant growth promoting rhizobacteria (PGPR) in different concentrations of Cu, Cr, Co, Cd, Ni, Mn, and Pb and to evaluate the PGPR-modulated bioavailability of different heavy metals in the rhizosphere soil and wheat tissues, grown in saline sodic soil. Bacillus cereus and Pseudomonas moraviensis were isolated from Cenchrus ciliaris L. growing in the Khewra salt range. Seven-day-old cultures of PGPR were applied on wheat as single inoculum, co-inoculation and carrier-based biofertilizer (using maize straw and sugarcane husk as carrier). At 100 ppm of Cr and Cu, the survival rates of rhizobacteria were decreased by 40%. Single inoculation of PGPR decreased 50% of Co, Ni, Cr and Mn concentrations in the rhizosphere soil. Co-inoculation of PGPR and biofertilizer treatment further augmented the decreases by 15% in Co, Ni, Cr and Mn over single inoculation except Pb and Co where decreases were 40% and 77%, respectively. The maximum decrease in biological concentration factor (BCF) was observed for Cd, Co, Cr, and Mn. P. moraviensis inoculation decreases the biological accumulation coefficient (BAC) as well as translocation factor (TF) for Cd, Cr, Cu Mn, and Ni. The PGPR inoculation minimized the deleterious effects of heavy metals, and the addition of carriers further assisted the PGPR.

Co-inoculation Effect of Rhizobia and Plant Growth Promoting Rhizobacteria on Common Bean Growth in a Low Phosphorus Soil.

Nitrogen (N) fixation through legume-Rhizobium symbiosis is important for enhancing agricultural productivity and is therefore of great economic interest. Growing evidence indicates that other soil beneficial bacteria can positively affect symbiotic performance of rhizobia. Nodule endophytic plant growth promoting rhizobacteria (PGPR) were isolated from common bean nodules from Nakuru County in Kenya and characterized 16S rDNA partial gene sequencing. The effect of co-inoculation of rhizobium and PGPR, on nodulation and growth of common bean (Phaseolus vulgaris L.) was also investigated using a low phosphorous soil under greenhouse conditions. Gram-positive nodule endophytic PGPR belonging to the genus Bacillus were successfully isolated and characterized. Two PGPR strains (Paenibacillus polymyxa and Bacillus megaterium), two rhizobia strains (IITA-PAU 987 and IITA-PAU 983) and one reference rhizobia strain (CIAT 899) were used in the co-inoculation study. Two common bean varieties were inoculated with Rhizobium strains singly or in a combination with PGPR to evaluate the effect on nodulation and growth parameters. Co-inoculation of IITA-PAU 987 + B. megaterium recorded the highest nodule weight (405.2 mg) compared to IITA-PAU 987 alone (324.8 mg), while CIAT 899 + B. megaterium (401.2 mg) compared to CIAT 899 alone (337.2 mg). CIAT 899 + B. megaterium recorded a significantly higher shoot dry weight (7.23 g) compared to CIAT 899 alone (5.80 g). However, there was no significant difference between CIAT 899 + P. polymyxa and CIAT 899 alone. Combination of IITA-PAU 987 and B. megaterium led to significantly higher shoot dry weight (6.84 g) compared to IITA-PAU 987 alone (5.32 g) but no significant difference was observed when co-inoculated with P. polymyxa. IITA-PAU 983 in combination with P. polymyxa led to significantly higher shoot dry weight (7.15 g) compared to IITA-PAU 983 alone (5.14 g). Plants inoculated with IITA-PAU 987 and B. megaterium received 24.0 % of their nitrogen demand from atmosphere, which showed a 31.1% increase compared to rhizobium alone. Contrast analysis confirmed the difference between the co-inoculation of rhizobia strains and PGPR compared to single rhizobia inoculation on the root dry weight. These results show that co-inoculation of PGPR and Rhizobia has a synergistic effect on bean growth. Use of PGPR may improve effectiveness of Rhizobium biofertilizers for common bean production. Testing of PGPR under field conditions will further elucidate their effectiveness on grain yields of common bean.

Role of carrier-based biofertilizer in reclamation of saline soil and wheat growth

Two plant growth promoting rhizobacteria (PGPR), Pseudomonas moraviensis and Bacillus cereus, were used as bioinoculants on wheat, applied alone and in combination. Ground maize straw and sugarcane husk were used as carriers. Experiment was conducted for two consecutive years (2010 and 2011) under axenic conditions in the greenhouse of Quaid-e-Azam University, Islamabad. Sodium chloride (NaCl) (150 mM) was applied with irrigated water after 7 and 14 days of seed germination. Measurements made 40 days after sowing (DAS) revealed that P. moraviensis and B. cereus have better survival efficiency (as evidenced by higher colony forming units (CFUs)) in the carriers. The substantial increase in CFU of both PGPR was also observed in the soil at 57 DAS. Coinoculation of PGPR with both the carrier materials significantly decreased electrical conductivity (EC) and Na+ content of soil over control. The N, P, K+, Ca+, and Mg+ contents were 30–40% higher in soil, and 30–45% higher in leaves. Coinoculation of PGPR with carriers significantly increased chlorophyll, protein, sugar, phytohormone contents, and antioxidant activities of leaves. The application of biofertilizers improved the yield of wheat by 15–25% over control. It is inferred that the carriers assisted PGPR for long-time survival, and the formulation was applicable in promoting crop production under salt stress.

Effect of co-inoculation of plant growth-promoting rhizobacteria on the growth of amaranth plants

This study shows the effect of co-inoculation of three bacterial isolates, viz. Bacillus firmus KUCr1, Cellulosimicrobium cellulans KUCr3 and Pseudomonas aeruginosa KUCd1, on selected growth parameters of amaranth plants. KUCr1 and KUCr3 are reported to be P-solubilizers and indole acetic acid (IAA) producers, and KUCd1 is a siderophore producer. Co-inoculation of the three isolates gave the best results for overall growth of amaranth plants followed by co-inoculation with KUCr1 and KUCd1, then KUCr1 alone. Among the test isolates, KUCr1 and KUCd1 were found to be better rhizosphere colonizers when co-inoculated. KUCr1 and KUCr3 when co-inoculated produced more IAA in liquid medium. Co-inoculation gave insignificant variation in P-solubilization, but siderophore production by KUCd1 was greatly enhanced when inoculated with other isolates in culture conditions. The augmentation of plant growth, whenusing a consortium culture, might be due to better IAA production andsiderophore production by the test isolates. This report suggests that co-inoculation of microbes promotes plant growth better than individual isolates.

Co-inoculation dose and root zone temperature for plant growth promoting rhizobacteria on soybean [ Glycine max (L.) Merr] grown in soil-less media

Inoculation dose affects the efficacy of bacterial inoculants applied in agriculture. Effects of the co-inoculation dose of two plant growth promoting rhizobacteria (PGPR) strains, Serratia proteamaculans 1-102 and S. liquefaciens 2-68, with Bradyrhizobium japonicum on soybean [ Glycine max (L.) Merr.] growth, nodulation and nitrogen fixation were investigated under controlled root zone temperatures (RZTs; 25, 20 and 15 °C) in soil-less media. The results showed that the effective dose range for both PGPR strains is 10 7–10 9 and their optimal co-inoculation dose was 1×10 8 cells per seedling. This was not affected by RZT. The co-inoculation of PGPR at their optimal dose increased nodule number, plant dry weight and fixed nitrogen. Nitrogen fixation efficiency was also improved by the co-inoculations. Use of nodulation dynamic linear models made the quantitative description of the nodulation process possible. The calculated dynamic parameters revealed that PGPR co-inoculation shortened the nodule initiation time and increased the nodulation rate.