Rhizobacterial Strains Research Articles

Efficacy of Phytoremediation for Methylparaben Removal from Contaminated Water: A study by Alternanthera spp and Associated Rhizobacteria

In the present study, the potential of Alternanthera spp and its associated rhizobacteria to uptake and biodegrade methylparaben (MP) under hydroponic conditions was assessed. The experiments were conducted in vitro using glass reactors of 500-mL volume. The results indicated that the removal rates in hydroponic reactors were significantly higher (66.6±3%) than that of control reactors (<40%). MP reduction data fitted well a first-order kinetics model (R2>0.9). The presence of plants shortened the half-life (T1/2) of MP in aqueous solutions to 3.41 days compared to 34.8 days in control reactors. Bioconcentration factors (BCFs) of MP were higher for roots (1.9-5.2 L/kg) compared to stems (0-0.5 L/kg). High-tolerant rhizobacteria for MP were isolated from the roots of Alternanthera spp and characterized. It was shown that three isolates achieved noticeable efficiencies in removing MP in a separated biodegradation assay. Of the 3 isolated rhizobacteria, results revealed that Cronobacter sakazakii, diagnosed by gyrB gene, had the highest MP removal efficiency. These findings elucidated that both Alternanthera spp and a specific associated rhizobacterial strains have promising potentials in removing MP even though the latter possesses antimicrobial properties.

Suppression of tomato bacterial speck disease (Pseudomonas syringae pv. tomato (Okabe) Young, Dye, &amp; Wilkie) via induced systemic resistance by Pseudomonas and Bacillus strains

Bacterial speck Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye, &amp; Wilkie is a widespread disease in tomato plants. Four plant growth-promoting rhizobacterial (PGPR) strains 5(3), 68(2), 36(1), and 47(3) played a significant role (50% and higher) in reducing spot disease severity. Selected strains were identified as Pseudomonas koreensis 5(3), Bacillus mycoides 68(2), Bacillus mojavensis 36(1), and Bacillus simplex 47(3) using the MALDI Biotyper classification system. In planta assay using tomato seedlings were inoculated with the bacterial strains alone or in dual combination. Pseudomonas koreensis 5(3) (51.9%–74.29%) and Bacillus mycoides 68(2) (36.70%–65.56%) both provided a significant reduction in foliar severity caused by bacterial speck disease agent Pseudomonas syringae pv. tomato (Okabe) Young, Dye, &amp; Wilkie. Bacillus simplex 47(3) and Bacillus mojavensis 36(1) were successful only in combined treatments. Defense enzymes Proline, Peroxidase, and Catalase were induced by PGPR strains in comparison with those of control plants. Hydrogen peroxide (H2O2) and callose deposition were evident at reaction sites induced by PGPR strains. The accumulation of callose, H2O2, and high levels of defense enzymes via the treatment of PGPRs might play a significant role in a practical, safe, and effective way to control Pseudomonas syringae pv. tomato.

In vitro Screening of Different Rhizobacterial Strains against Egg Hatching of Rice Root-Knot Nematode, Meloidogyne graminicola

Meloidogyne graminicola is an economic yield loss causing major pest of rice globally. For managing this pest, biological control practices act as an alternate strategy, as it is the most effective and economic. Plant growth promoting rhizospheric bacteria (PGPR) are most significant because they benefit plants both directly and indirectly by enhancing plant growth and provides long lasting antagonistic effects against plant parasitic nematodes. Considering this an in vitro efficacy research experiment of nematoxicity of native rhizobacterial strains was conducted, against egg hatching of M. graminicola at S/2 and S/4 concentration levels of intact bacterial culture and cell free culture filtrates (CFCs). The hatching behavior of rice root-knot nematode eggs was observed on alternate days for ten days which resulted in inhibition of egg hatching by all bacterial cultures at both concentration levels. When compared to the untreated control, Bacillus spp. showed the most egg inhibition in the S/2 concentration of both culture filtrates i.e,86.8% and 84.8%. Similarly, in the S/4 level of concentration, most egg hating such as 83.7% and 79.8% was recorded in Bacillus spp. culture filtrates. The rate of hatching was inversely proportional to the concentration of strains at exposure time, decreasing as the concentration increased. The results of the experiment revealed the potential of rhizospheric bacteria which makes it more feasible and environmentally safe approach for the management of Meloidogyne graminicola.

In vitro Evaluation of Rhizobacterial Strains from Groundnut on Growth of Aflatoxigenic Aspergillus Flavus

In vitro Evaluation of Rhizobacterial Strains from Groundnut on Growth of Aflatoxigenic Aspergillus Flavus

Assessing the role of ACC deaminase-producing bacteria in alleviating salinity stress and enhancing zinc uptake in plants by altering the root architecture of French bean (Phaseolus vulgaris) plants.

The consortium inoculation with strains R1 and R4 modified the root system to boost seedling growth, increase the zinc content of French bean pods, and reduce salinity stress. The present study demonstrated the effect of two 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing plant growth-promoting rhizobacteria (Pantoea agglomerans R1 and Pseudomonas fragi R4) alone and consortia on the root system development, French bean growth, and zinc content as well as salinity stress tolerance. Both the strains were characterized for ACC utilization activity (426.23 and 380.54nmol α-ketobutyrate mg protein-1h-1), indole acetic acid (IAA) production, phosphate solubilization, ammonia, hydrogen cyanide (HCN), and siderophore production. The strains exhibited zinc solubilization in both plate and broth assays with zinc oxide and zinc carbonate as zinc sources as validated by atomic absorption spectroscopy (AAS). Single or combined inoculations with the selected strains significantly modulated the architectural and morphological traits of the root system of French bean plants. Furthermore, the application of R1and R4 consortia has enhanced zinc content in roots (60.83mgkg-1), shoots (15.41mgkg-1), and pods (30.04mgkg-1) of French bean plants grown in ZnCO3 amended soil. In another set of pot experiments, the consortium bacterization has significantly enhanced length as well as fresh and dry biomass of roots and shoots of the French bean plant under saline stress conditions. Additionally, inoculation with ACC-degrading rhizobacterial strains has increased chlorophyll and carotenoid contents, osmoprotectant content, and antioxidative enzyme (catalase and peroxidase) activity in comparison to their counterparts exposed to salt treatments only. Current findings suggested ACC deaminase-producing rhizobacterial strains hold the potential to improve root architecture which in turn promotes plant growth under salt-stressed conditions as well as enhances micronutrient concentration in host plants.

Effects of Different Rhizobacterial Strains on Plant Growth and Yield of Use with Chemical Fertilizer Reduction in Cauliflower (Brassica oleracea var. botrytis L.)

Effects of Different Rhizobacterial Strains on Plant Growth and Yield of Use with Chemical Fertilizer Reduction in Cauliflower (Brassica oleracea var. botrytis L.)

Novel halotolerant rhizobacterial strains mitigated the salt stress in-vitro and in-vivo and improved the growth of tomato plants

Increasing land salinization has become one of the most damaging threats to the global modern agriculture and has challenged food production and food security. Plant growth promoting rhizobacteria (PGPR) have emerged as efficient biological tools to improve plant growth in stressed environments. The present study was conducted to isolate, identify and characterize halotolerant PGPR from an unexplored saline area of Pakistan. The effect of the isolated strains was evaluated in-vitro and on the tomato varieties grown under 150 mM salt stress in the field. A total of 12 strains were isolated and further screened in-vitro to check their halotolerance. The isolates were screened using nutrient agar medium supplemented with different levels (5, 10, 15, 20 and 25%) of NaCl. After screening, two highly salt tolerant strains were selected and identified using 16S rRNA technique. Isolates B9 and B10 were successfully identified as Pseudarthrobacter oxydans (NR_026236.1) and Staphylococcus pasteuri (NR_024669.1). The isolates were tested qualitatively for their biochemical and plant growth promoting traits. These isolates promoted tomato growth under salinity stress when applied alone or in consortium. The isolates demonstrated catalase and protease activity, phosphorous solubilization (PSI: 2.45, 2.63) and produced indole acetic acid. The current findings established that the isolated strains were highly resistant and tolerant up to 25% NaCl stress as compared to the other reported strains. These halophiles possessed promising plant growth promoting traits hence, are assumed to have great potential to serve as bioinoculants for the alleviation of adverse effects of salinity on crops.

Biocontrol and plant growth promoting traits of two avocado rhizobacteria are orchestrated by the emission of diffusible and volatile compounds.

Avocado (Persea americana Mill.) is a tree crop of great social and economic importance. However, the crop productivity is hindered by fast-spreading diseases, which calls for the search of new biocontrol alternatives to mitigate the impact of avocado phytopathogens. Our objectives were to evaluate the antimicrobial activity of diffusible and volatile organic compounds (VOCs) produced by two avocado rhizobacteria (Bacillus A8a and HA) against phytopathogens Fusarium solani, Fusarium kuroshium, and Phytophthora cinnamomi, and assess their plant growth promoting effect in Arabidopsis thaliana. We found that, in vitro, VOCs emitted by both bacterial strains inhibited mycelial growth of the tested pathogens by at least 20%. Identification of bacterial VOCs by gas chromatography coupled to mass spectrometry (GC-MS) showed a predominance of ketones, alcohols and nitrogenous compounds, previously reported for their antimicrobial activity. Bacterial organic extracts obtained with ethyl acetate significantly reduced mycelial growth of F. solani, F. kuroshium, and P. cinnamomi, the highest inhibition being displayed by those from strain A8a (32, 77, and 100% inhibition, respectively). Tentative identifications carried out by liquid chromatography coupled to accurate mass spectrometry of diffusible metabolites in the bacterial extracts, evidenced the presence of some polyketides such as macrolactins and difficidin, hybrid peptides including bacillaene, and non-ribosomal peptides such as bacilysin, which have also been described in Bacillus spp. for antimicrobial activities. The plant growth regulator indole-3-acetic acid was also identified in the bacterial extracts. In vitro assays showed that VOCs from strain HA and diffusible compounds from strain A8a modified root development and increased fresh weight of A. thaliana. These compounds differentially activated several hormonal signaling pathways involved in development and defense responses in A. thaliana, such as auxin, jasmonic acid (JA) and salicylic acid (SA); genetic analyses suggested that developmental stimulation of the root system architecture by strain A8a was mediated by the auxin signaling pathway. Furthermore, both strains were able to enhance plant growth and decreased the symptoms of Fusarium wilt in A. thaliana when soil-inoculated. Collectively, our results evidence the potential of these two rhizobacterial strains and their metabolites as biocontrol agents of avocado pathogens and as biofertilizers.

Multifarious microbial biostimulants promote growth in Arachis hypogaea L.

Plant Growth Promoting Rhizobacteria (PGPR), a microbial biostimulant has been widely studied to stimulate plant growth through induction of natural biological processes. However, lack of successful validation under open field remains a barrier to mark their standard in agriculture. Therefore, the aim of the research was to highlight the potential of PGPR biostimulants via in vitro studies and subsequently to demonstrate the in planta evaluation in oilseed crop, Arachis hypogaea L. (Groundnut) under pot and field trials. The two rhizobacterial strain was identified as Pseudomonas fluorescens and Bacillus subtilis by 16s rRNA gene sequence analysis. Both the strains were functionally screened for plant growth promoting traits. Pot and field trials were conducted where seeds were inoculated with PGPR biostimulants and harvested at 30 and 90 days. Biostimulant treatments were applied as single and co-inoculation in groundnut and the growth factors, biochemical parameters, yield, and seed quality were analyzed. The study inferred that the consortium of PGPR biostimulants significantly (p &amp;lt; 0.05) showed highest growth, photosynthetic pigments, nodulation status, leghaemoglobin content, yield attributes, and also biofortification of seed nutrients in oilseed crop under both pot and field conditions than un-inoculated control. This study supports the idea of the application of PGPR as microbial biostimulants through successful open field trial to facilitate its implementation as a feasible and potential agricultural product to synthetic fertilizers thereby influencing sustainable and stable crop production.

Bio-control of Chocolate spot disease of Faba bean using potential rhizobacterial strains under field conditions in Northwestern Ethiopia

Bio-control of Chocolate spot disease of Faba bean using potential rhizobacterial strains under field conditions in Northwestern Ethiopia

Rhizobacteria control damping-off and promote growth of lima bean with and without co-inoculation with Rhizobium tropici CIAT899.

Rhizoctonia solani compromises the production of lima bean, an alternative and low-input food source in many tropical regions. Inoculation of bacterial strains has been used, but research on their biocontrol and growth promotion potential on lima bean is scarce. The objective of this study was to evaluate the effects of inoculation with rhizobacterial strains of the genera Bacillus, Brevibacillus, Paenibacillus, Burkholderia, Pseudomonas, and Rhizobium in combination or not with N2-fixing Rhizobium tropici on the control of damping-off disease and growth promotion in lima bean plants. Greenhouse experiments were conducted to evaluate the inoculation with bacterial strains with biocontrol potential in combination or not with R. tropici in substrate infected with R. solani CML 1846. Growth promotion of these strains was also assessed. Strains of Brevibacillus (UFLA 02-286), Pseudomonas (UFLA 02-281 and UFLA 04-885), Rhizobium (UFLA 04-195), and Burkholderia (UFLA 04-227) co-inoculated with the strain CIAT 899 (Rhizobium tropici) were the most effective in controlling R. solani, reducing the disease incidence in 47-60% on lima bean. The promising strains used in the biocontrol assays were also responsive in promoting growth of lima bean under disease and sterile conditions. A positive synergistic effect of co-inoculation of different genera contributed to plant growth, and these outcomes are important first steps to improve lima bean production.

Rhizobacteria Bacillus spp. enhance growth, influence root architecture, physiological attributes and canopy temperature of mustard under thermal stress

In arid and semi-arid regions, high temperature stress is one of the most common abiotic stresses affecting plant growth and development, as well as agricultural output. Growth and establishment of mustard, an important oilseed crop, is affected due to increased incidences of higher-than-normal temperatures during sowing of the crop. In the present study, we screened rhizobacterial isolates for their thermotolerance. Under high temperature stress, three thermotolerant rhizobacterial cultures were assessed for their plant growth promoting activities. There was beneficial effect of high temperature on their indole acetic acid and gibberellic acid production abilities. A pot experiment was conducted to evaluate the effect of the three rhizobacterial strains on mustard growth under high temperature stress. Inoculation with the rhizobacteria significantly improved plant biomass, root architecture and physiological attributes – relative water content, membrane stability index and chlorophyll content. There were lowering of hydrogen peroxide content and lipid peroxidation. Increased total leaf area and lowering of canopy temperature was observed in the inoculated plants, under high temperature. Significant positive correlation was observed between plant biometric traits and most of the physiological attributes, while negative correlation was observed with lipid peroxidation and hydrogen peroxide content. Under both no stress and high temperature stress, response to inoculation with Bacillus sp. strain MRD-17 was markedly more than the other rhizobacterial strains. Thus, these rhizobacteria were able to enhance thermotolerance of mustard during early stages of growth. As a result, thermotolerant rhizobacteria with plant growth-promoting activity can be utilized to alleviate high temperature stress in crops.

Influence of Thermotolerant Rhizobacteria Bacillus spp. on Biochemical Attributes and Antioxidant Status of Mustard Under High Temperature Stress

Due to global warming, increasing incidences of higher-than-normal temperatures have been observed, which adversely affect seed germination, crop growth, and productivity. Several reports are available on the effect of inoculation with rhizobacteria on plant growth and biochemical attributes; however, information on their influence on seed germination and plant stress levels is lacking. In the present study, under heat stress, we studied the effect of three thermotolerant rhizobacterial strains on mustard seed germination, seedling vigor, and plant growth. Effect of inoculation with the rhizobacterial strains on the plant stress levels, biochemical attributes and antioxidant activity was also determined. Under heat stress, inoculation with the rhizobacterial strains improved seed germination and seedling fresh weight and plumule length; while only Bacillus licheniformis SSA 61 inoculated plants showed better radicle length. There was a concomitant decrease in the plant ethylene levels in the inoculated treatments. Inoculated plants showed higher shoot fresh weight, however, Bacillus sp. MRD-17 inoculated plants only improved root growth. There was significant increase in most of the plant biochemical parameters and activities of antioxidant enzymes superoxide dismutase, catalase, and ascorbate peroxidase. Significant reduction in proline and total sugar content was noted in the inoculated treatments; while increase in the amino acid and phenolics content was observed. A further increase in the antioxidant enzyme activity was recorded in most of the inoculated treatments compared with no stress. Thus, our study indicated that thermotolerant rhizobacterial strains reduced plant stress levels; enhanced seed germination, seedling vigor, plant biomass, and thermotolerance of mustard.

Beneficial effects of selected rhizospheric and endophytic bacteria, inoculated individually or in combination, on non-native host plant development

Plant beneficial bacteria have been traditionally inoculated as unique strains, although combining bacteria with complementary traits could maximize their positive effect on plant growth and development. Our objective was to elaborate consortia from selected rhizospheric and endophytic bacteria with antifungal and plant growth promoting properties, and evaluate their beneficial effects on the growth of Physalis ixocarpa, an annual native Mexican species of horticultural importance. Bacterial strains were selected based on their antifungal activity against Fusarium spp. through in vitro antagonism assays. Characterization of the profile of volatile organic compounds (VOC) of newly-identified endophytic strains able to significantly inhibit Fusarium spp. evidenced the presence of sulfur compounds and ketones, reported for their antifungal activity. Seven bacterial strains were able to solubilize phosphate on NBRIP medium. Their capacity to promote the growth of A. thaliana in vitro was further tested. All stains stimulated the formation of lateral roots and root hairs, and enhanced A. thaliana biomass, most likely through auxin production. Twelve consortia were elaborated from rhizospheric and root endophytic bacteria, and the effects of consortia and individual strain inoculation on the growth and development of P. ixocarpa were evaluated in a greenhouse trial. Rhizobacterial strains A8a and 5911, and consortia formed by A8a + B3R7 and SO + B3R7 (all belonging to the Bacillus genus) showed the best results in terms of growth promotion and floral onset, with increases in plant height by up to 45% and flowering beginning 30 days before than in the Control. Our results confirm the potential of combining rhizospheric and endophytic bacteria with multiple beneficial traits for enhancing plant development and suggest that the most promising bacterial treatments could be applied to avocado trees, their natural host, to foster their productivity.

Biomining Sesuvium portulacastrum for halotolerant PGPR and endophytes for promotion of salt tolerance in Vigna mungo L.

Halophytic plants can tolerate a high level of salinity through several morphological and physiological adaptations along with the presence of salt tolerant rhizo-microbiome. These microbes release phytohormones which aid in alleviating salinity stress and improve nutrient availability. The isolation and identification of such halophilic PGPRs can be useful in developing bio-inoculants for improving the salt tolerance and productivity of non-halophytic plants under saline conditions. In this study, salt-tolerant bacteria with multiple plant growth promoting characteristics were isolated from the rhizosphere of a predominant halophyte, Sesuvium portulacastrum grown in the coastal and paper mill effluent irrigated soils. Among the isolates, nine halotolerant rhizobacterial strains that were able to grow profusely at a salinity level of 5% NaCl were screened. These isolates were found to have multiple plant growth promoting (PGP) traits, especially 1-aminocyclopropane-1-carboxylic acid deaminase activity (0.32-1.18 μM of α-ketobutyrate released mg-1 of protein h-1) and indole acetic acid (9.4-22.8 μg mL-1). The halotolerant PGPR inoculation had the potential to improve salt tolerance in Vigna mungo L. which was reflected in significantly (p < 0.05) higher germination percentage (89%) compared to un-inoculated seeds (65%) under 2% NaCl. Similarly, shoot length (8.9-14.6 cm) and vigor index (792-1785) were also higher in inoculated seeds. The strains compatible with each other were used for the preparation of two bioformulations and these microbial consortia were tested for their efficacy in salt stress alleviation of Vigna mungo L. under pot study. The inoculation improved the photosynthetic rate (12%), chlorophyll content (22%), shoot length (5.7%) and grain yield (33%) in Vigna mungo L. The enzymatic activity of catalase and superoxide dismutase were found to be lower (7.0 and 1.5%, respectively) in inoculated plants. These results revealed that halotolerant PGPR isolated from S. portulacastrum can be a cost-effective and ecologically sustainable method to improve crop productivity under high saline conditions.

Antagonistic Activity of Pseudomonas fluorescens Strain X1 Against Different Fusaria and it’s In Vivo Analysis Against Fusarium udum Infected Pigeon Pea

A plant growth-promoting rhizobacterial strain, Pseudomonas fluorescens X1 isolated from the garden soil was employed for antagonistic activity against different species of fusaria. Strain X1 inhibited four different fusaria (Fusarium moniliforme, Fusarium oxysporum, Fusarium semitectum and Fusarium udum) in dual culture plate assay, and in broth culture using cell-free culture filtrate. Scanning electron microscopic (SEM) analysis revealed deformation and shrinkage in mycelia of fusaria after treatment with strain X1. Confocal micrographs showed degeneration of nuclei inside the cells of fusaria for the same effect. Strain X1 exhibited maximum antifungal activity, when it was grown in nutrient broth yeast (NBY) medium amended with 1mM NH4MoO4 and 1% glucose. The antifungal extracts eluted from thin-layer chromatography (TLC) followed by high performance liquid chromatography (HPLC) showed two fractions active against different fusaria. Liquid chromatography-mass spectrometry (LCMS) analysis of the two fractions 1 and 2 corresponded to molecular ions at m/z 177.16 and m/z 177.09, respectively. Infra-red (IR) analysis showed five similar absorption bands in both the fractions analysed. In vivo analysis of strain X1 alone and along with fungicide inhibited the growth of F. udum and improved the biomass and growth of pigeon pea. These results indicated that strain X1 could be possibly used as a biocontrol agent to inhibit the growth of soil-borne diseases of different fusaria including F. udum that causes wilting in pigeon pea.

Bradyrhizobium japonicum IRAT FA3 promotes salt tolerance through jasmonic acid priming in Arabidopsis thaliana

BackgroundPlant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants’ responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress.ResultsThe plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress.ConclusionOur data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance.

Assessment of cumulative microbial respiration and their ameliorative role in sustaining maize growth under salt stress

Cumulative microbial respiration reflects microbial activities and their potential to support plant growth, where salt tolerant rhizobacteria can optimize their respiration, and ensure plant survival under salt stress. We evaluated cumulative microbial respiration of different salt tolerant rhizobacterial strains at different salinity levels, and checked their ability to sustain plant growth under natural saline conditions by using maize as test crop. Our results revealed that at the highest EC level (10 dS m−1), strain ‘SUA-14’ performed significantly better, and exhibited the greatest cumulative respiration (4.2 fold) followed by SHM-13 (3.8 fold), as compared to un-inoculated control. Moreover, results of the field trial indicated a similar trend, where significant improvements in shoot fresh weight (59%), root fresh weight (80%), shoot dry weight (56%), root dry weight (1.4 fold), leaf area (1.9 fold), straw yield (41%), cob diameter (33%), SPAD value (84%), yield (99%), relative water contents (91%), flavonoid (55%), 1000 grain weight (∼100%), soluble sugars (41%) and soluble proteins (45%) were observed due to inoculation of strain ‘SUA-14’ as compared to un-inoculated control. Similarly, substantial decline in leaf Na+ (34%), Na+/K+ ratio (69%), electrolyte leakage (8%), catalase (54%), peroxidase (73%), and H2O2 (50%) activities were observed after inoculation of ‘SUA-14’ with a concomitant increment in the leaf K+ contents (70%) under salinity stress than un-inoculated control. Hence, among all the tested rhizobacterial isolates, ‘SUA-14’ served as the most efficient strain in alleviating the detrimental impacts of salinity on maize growth and yield. The 16S rRNA sequencing identified it as Acinetobacter johnsonii.

Combined Effect of the Potassium Dose and Plant Biofertilization by Acinetobacter calcoaceticus on the Growth, Mineral Content, Nutritional Quality, Antioxidant Activity, and Metabolomic Features of Tomatillo Fruits (Physalis ixocarpa Brot.).

An Acinetobacter calcoaceticus UTMR2 strain was evaluated in tomatillo plants (Physalis ixocarpa Brot.) using a factorial design with different potassium doses (100, 75, 50 and 0% of the recommended dose). In addition to the agronomic parameters, an analysis of the physicochemical, antioxidant, and metabolomic properties of the fruit was performed. The application of the inoculant affected several parameters of the plant (chlorophyll, weight, and contents of several mineral elements) as well as of the fruit (yield, maturity index, FRAP antioxidant capacity, and contents of protein, fiber, and fat). A multivariate analysis was performed by means of a PCA and a heatmap, indicating that the inoculant induced a strong modulating activity in tomatillo plants for the evaluated parameters, with a remarkable effect at low K doses (0 and 50%). The inoculated treatment at 75% of the K dose resulted in similar plant and fruit characteristics to the fully fertilized control. On the other hand, the biofertilized treatment with no K addition resulted in the highest values in the plant and fruit parameters. In addition, from the metabolomics analysis of the fruits at 75% of the K dose, the up-regulation of 4,4″-bis(N-feruloyl)serotonin, salvianolic acid K, and chlorogenic acid was observed, which may have a role in anti-senescence and resistance mechanisms. In conclusion, the rhizobacterial strain had a positive effect on plant growth, nutritional quality, bioactive compounds, and antioxidant activity of tomatillo fruits at reduced doses of K fertilizer, which gives support for its consideration as an effective biofertilizer strain.

Biochemical and Molecular Evaluation of Rhizobium spp. and its Growth Promotion Studies with Lentil (Lens culinaris Medik. L.)

Growth promoting Rhizobium spp are frequently used as biofertilizers for agricultural cropping system. Furthermore, Isolation, screening and biochemical characterization of Rhizobium for a specific plant is necessary to examine ability of isolated bacteria to affect the growth and development of host plant in various ways. The current study was aimed to isolate plant specific rhizobacterial strains which are compatible with lentil (Lens culinaris Medik.L.) plant. 20 bacterial isolates have been isolated from root nodules of lentil from various agro ecological area and their biochemical characterization was performed by different plant growth promotion activities. The result showed that, among 20 isolates, four isolates have vigorous plant growth promoting activities. Four bacterial strains were able to solubilise phosphorous along with hormone production. Moreover, among four bacterial strains, two strongly produced HCN and siderophore in vitro. Subsequently, all selected bacterial isolates were inoculated in lentil seeds of variety HUL57 to study germination percentage and vigour index of the crop. Out of four isolates 26N isolate performed best growth promotion activities on lentil seedlings. Finally, on the basis of performance of bacteria on plant, four isolates were characterized using molecular approach of species identification such as 16S rRNA sequencing.