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Under cold and wet weather conditions, one of the most important diseases that affect potato crops is the rhizoctoniasis caused by the fungus Rhizoctonia solani Kühn. Aiming to assess the effect of Plant Growth Promoting Rhizobacteria (PGPRs) in R. solani and to promote plant growth in potatoes, two strains of Bacillus subtilis (Bac17M8: T1 and Bac17M9: T2), native to the Peruvian plateau and B. amyloliquefaciens from Bolivia (T3), were used. Furthermore, soil infested with R. solani, without rizobacteria (T4) and without rizobacteria nor R. solani (T5) under greenhouse conditions was evaluated. The seedlings of Ccompis and Andina varieties inoculated with the three strains of PGPR showed lower mortality (average 18.90% and 12.13% in Ccompis and Andina, respectively) compared to non-inoculated (28.02% and 19.89% in Ccompis and Andina, respectively). Likewise, in both varieties, the tubers harvested from inoculated plots with rhizobacteria also presented lower incidence values (average 15.19% and 6.99% in Ccompis and Andina, respectively) and severity (5.75 to 9.06% and 5.73 to 7.31% in Ccompis and Andina, respectively), compared to tubers harvested from the non-inoculated plot that showed an incidence of 25.24% and 12.78% in Ccompis and Andina, respectively, and a severity greater than 30% in both varieties. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a toxic, biologically non-essential and highly mobile metal that has become an increasingly important environmental hazard to both wildlife and humans. In contrast to conventional remediation technologies, phytoremediation based on legume-rhizobia symbiosis has emerged as an inexpensive decontamination alternative which also revitalize contaminated soils due to the role of legumes in nitrogen cycling. In recent years, there is a growing interest in understanding symbiotic legume-rhizobia relationship and its interactions with Cd. The aim of the present review is to provide a comprehensive picture of the main effects of Cd in N2-fixing leguminous plants and the benefits of exploiting this symbiosis together with plant growth promoting rhizobacteria to boost an efficient reclamation of Cd-contaminated soils. [ABSTRACT FROM AUTHOR]

The genus Eucalyptus comprises economically important species, such as Eucalyptus grandis and Eucalyptus globulus , used especially as a raw material in many industrial sectors. Species of Eucalyptus are very susceptible to pathogens, mainly fungi, which leads to mortality of plant cuttings in rooting phase. One alternative to promote plant health and development is the potential use of microorganisms that act as agents for biological control, such as plant growth-promoting rhizobacteria (PGPR). Rhizobacteria Streptomyces spp have been considered as PGPR. This study aimed at selecting strains of Streptomyces with ability to promote plant growth and modulate secondary metabolism of E. grandis and E. globulus in vitro plants. The experiments assessed the development of plants (root number and length), changes in key enzymes in plant defense (polyphenol oxidase and peroxidase) and induction of secondary compounds (total phenolic and quercetinic flavonoid fraction). The isolate Streptomyces PM9 showed highest production of indol-3-acetic acid and the best potential for root induction. Treatment of Eucalyptus roots with Streptomyces PM9 caused alterations in enzymes activities during the period of co-cultivation (1–15 days), as well as in the levels of phenolic compounds and flavonoids. Shoots also showed alteration in the secondary metabolism, suggesting induced systemic response. The ability of Streptomyces sp. PM9 on promoting root growth, through production of IAA, and possible role on modulation of secondary metabolism of Eucalyptus plants characterizes this isolate as PGPR and indicates its potential use as a biological control in forestry. [ABSTRACT FROM AUTHOR]

El objetivo de la presente investigación fue caracterizar y determinar el efecto de cepas nativas de Azotobacter spp. en el desarrollo vegetativo de Lycopersicon esculentum Mill. “tomate”, como una alternativa al uso indiscriminado de fertilizantes químicos. Se tomaron muestras de raíces y suelo rizosférico de hortalizas con las que se realizaron diluciones (10-4) en caldo Ashby-Sacarosa y se incubaron a 30 ºC hasta observar un color amarillo, turbidez y película superficial. El género Azotobacter se identificó en agar mineral sin nitrógeno y Ashby-Benzoato, obteniéndose 96 cepas con una producción de 7.10 a 57.99 mgL-1 de ácido indolacético, 0.13 a 1.64 mgL-1 de nitrógeno fijado como amonio y hasta 1.61 % de eficiencia en la solubilización de roca fosfórica de Bayóvar. Se obtuvo una suspensión celular (108) de cada una de las cuatro cepas con los mayores valores y se inocularon independientemente y en consorcio, así como una combinación con 50 % de urea-100 % de roca fosfórica, en la rizósfera de tomate cv. Río Grande, en un diseño experimental completamente aleatorio. Todas las cepas nativas incrementaron la altura, volumen radicular, materia seca total, parte aérea y radicular frente al testigo absoluto.

Highlights: [•] Rhizosphere of wilted tomato plant could be a better reservoir of biocontrol agents. [•] Novel biocontrol agents were observed in wilted tomato rhizosphere. [•] Isolates collected from wilted tomato rhizosphere showed strong colonization ability. [ABSTRACT FROM AUTHOR]

High performance liquid chromatographic (HPLC) analysis of culture filtrates of plant growth promoting rhizobacteria (PGPR) and medium of inhibitory zone of interaction of Sclerotium rolfsii with PGPR, viz. Pseudomonas aeruginosa, Pseudomonas fluorescens 4, Pseudomonas fluorescens 4 (new) and Pseudomonas sp. varied from sample to sample. In all the culture filtrates of PGPRs, P. aeruginosa had nine phenolic acids in which ferulic acid (14.52 μg/ml) was maximum followed by other phenolic acids. However, the culture filtrates of P. fluorescens 4 had six phenolic acids with maximum ferulic acid (20.54 μg/ml) followed by indole acetic acid (IAA), caffeic, salicylic, o-coumeric acid and cinnamic acids. However, P. fluorescens 4 culture filtrate had seven phenolic acids in which salicylic acid was maximum (18.03 μg) followed by IAA, caffeic, vanillic, ferulic, o-coumeric and cinnamic acids. Pseudomonas sp. also showed eight phenolic acids where caffeic acid (2.75 μg) was maximum followed by trace amounts of ferulic, salicylic, IAA, vanillic, cinnamic, o-coumeric and tannic acids. The analysis of antibiosis zone of PGPRs showed fairly rich phenolic acids. A total of nine phenolic acids were detected in which caffeic acid was maximum (29.14 μg/g) followed by gallic (17.64 μg/g) and vanillic (3.52 μg/g) acids but others were in traces. In P. aeruginosa, antibiosis zone had seven phenolic acids where IAA was maximum (3.48 μg/g) followed by o-coumeric acid (2.08 μg/g), others were in traces. The medium of antibiosis zone of P. fluorescens 4 and P. fluorescens 4 new had eight phenolic acids in which IAA was maximum with other phenolic acids in traces. [ABSTRACT FROM PUBLISHER]

Root-colonizing non-pathogenic bacteria can increase plant resistance to biotic and abiotic stress factors. Bacterial inoculates have been applied as biofertilizers and can increase the effectiveness of phytoremediation. Inoculating plants with non-pathogenic bacteria can provide ‘bioprotection’ against biotic stresses, and some root-colonizing bacteria increase tolerance against abiotic stresses such as drought, salinity and metal toxicity. Systematic identification of bacterial strains providing cross-protection against multiple stressors would be highly valuable for agricultural production in changing environmental conditions. For bacterial cross-protection to be an effective tool, a better understanding of the underlying morphological, physiological and molecular mechanisms of bacterially mediated stress tolerance, and the phenomenon of cross-protection is critical. Beneficial bacteria-mediated plant gene expression studies under non-stress conditions or during pathogenic rhizobacteria–plant interactions are plentiful, but only few molecular studies on beneficial interactions under abiotic stress situations have been reported. Thus, here we attempt an overview of current knowledge on physiological impacts and modes of action of bacterial mitigation of abiotic stress symptoms in plants. Where available, molecular data will be provided to support physiological or morphological observations. We indicate further research avenues to enable better use of cross-protection capacities of root-colonizing non-pathogenic bacteria in agricultural production systems affected by a changing climate. [ABSTRACT FROM AUTHOR]

Abstract: Biofertilizer has been identified as an alternative to chemical fertilizer to increase soil fertility and crop production in sustainable farming. The objective of this greenhouse study was to evaluate the effects of four biofertilizers containing an arbuscular mycorrhizal fungus (Glomus mosseae or Glomus intraradices) with or without N-fixer (Azotobacter chroococcum), P solubilizer (Bacillus megaterium) and K solubilizer (Bacillus mucilaginous) on soil properties and the growth of Zea mays. The application treatments included control (no fertilizer), chemical fertilizer, organic fertilizer and two types of biofertilizer. The application of biofertilizer containing mycorrhizal fungus and three species of bacteria significantly increased the growth of Z. mays. The use of biofertilizer (G. mosseae and three bacterial species) resulted in the highest biomass and seedling height. This greenhouse study also indicated that half the amount of biofertilizer application had similar effects when compared with organic fertilizer or chemical fertilizer treatments. Microbial inoculum not only increased the nutritional assimilation of plant (total N, P and K), but also improved soil properties, such as organic matter content and total N in soil. The arbuscular mycorrhizal fungi (AMF) had a higher root infection rate in the presence of bacterial inoculation. By contrast, the AMF seemed to have an inhibiting effect on the P-solubilizing bacteria. The nutrient deficiency in soil resulted in a larger population of N-fixing bacteria and higher colonization of AMF. [Copyright &y& Elsevier]

The effect of two plant growth-promoting rhizobacteria (PGPRs) on the germination and growth of pepper seedlings was investigated in a culture chamber. The two strains showed metabolic capacities related to their potential PGPR action. Two different patterns of inoculation were carried out. In the first, strains were inoculated when seeds were sown, and in the second when seedlings showed fully developed cotyledons. In both cases the following parameters were measured: aerial and root surface, aerial and root length and aerial and root weight. In the first pattern of inoculation no aerial parameters were modified, probably because the bacteria did not colonize the root. In the second pattern of inoculation, all parameters were significantly modified by Chryseobacterium balustinum, except root surface, which indicated that this bacterium was able to colonize the root. Serratia fonticola did not modify any parameter. In both inoculation patterns root length was reduced by both bacteria probably due to a hormonal effect. C. balustinum enhanced aerial surface, aerial length and also the dry aerial and root weight. This resulted in stronger and more robust plants with a higher adaptative capacity and a greater resistance against pathogens. [ABSTRACT FROM AUTHOR]

The effects of three Plant Growth-Promoting Rhizobacteria (PGPRs) on tomato and pepper seedlings grown in two types of peat (brown and black, each sterilized or unsterilized) were studied. After sterilization, the seeds were unable to germinate in the brown peat. All three bacteria had the capacity to modify the growth, but tomato seedlings responded better than pepper seedlings, possibly indicating better root colonization in the former. All bacteria increased total stem length of tomato seedlings in nonsterilized brown peat, nonsterilized black peat and sterilized black peat. Plant shoot surface was also increased in nonstenlized brown peat and in sterilized black peat. The results show that plants, especially tomato, grown in nonsterilized black peat are smaller than in nonsterilized brown peat. The results obtained in sterilized peat show that there are no differences between sterilized and nonsterilized peat. Therefore, factors other than competition with other microorganisms must be more important in the performance of the bacterial inoculants. Root growth was only modified in nonsterilized black peat with two bacteria, in pepper it increased, and in tomato, decreased. These different effects could be due to a hormonal effect of the auxins, which influence root growth. [ABSTRACT FROM AUTHOR]

Biodegradable chelant (S,S)–N,N′ -ethylenediaminedisuccinic acid (EDDS) has the more advantages of enhanced metal mobility, rapid degradation, environmental friendliness, and ammonium release. However, the risk of metal and/or nitrate residues and leaching within EDDS biodegradation remains as the bottleneck for the widespread application of EDDS-induced phytoremediation. This study aims to explore if the inoculation of plant growth-promoting rhizobacteria (PGPRs) can eliminate the risk associated with the short-term application of EDDS by investigating Cu phytoextraction and soil nitrate content. Results showed that EDDS application significantly increased the copper (Cu) concentration in shoots, soil total Cu, NH 4 +-N and NO 3 −-N content, but decreased plant biomass. The inoculation of PGPRs in the soil showed a strong ability to increase plant biomass, Cu phytoextraction and soil NH 4 +-N content, and decrease soil Cu and NO 3 −-N content. Moreover, bacterial dominant taxa were found to be the largest contributors to soil NH 4 +-N and NO 3 −-N variation, and the abundance of denitrifying bacteria (Bacteroidetes and Stenotrophomonas) decreased in the treatment with PGPRs. The risk of residual Cu and nitrate leaching was reduced by the inoculation of PGPRs without significantly changing the stability of the bacterial community. These new findings indicate that the exogenous application of beneficial rhizobacteria can provide an effective strategy to reduce the risk in metal-contaminated soils of chelant-assisted phytoextraction. [Display omitted] • Short-term addition of EDDS increased Cu uptake but inhibited plant growth. • The leaching risk of Cu and/or nitrate was exposed in the EDDS biodegradation. • Soil Cu and NO 3 −-N concentrations were reduced in the presence of PGPRs. • Bacterial dominant taxa were the main contributors to NO 3 −-N variation. • Chelant-PGPRs system minimized environmental risks with enhanced phytoextraction. [ABSTRACT FROM AUTHOR]

The European Green Deal strategy currently implemented in the EU aims to, among others, reduce the negative impact of fertilization on the environment. One of the solutions influencing the nutritional status of plants and the improvement of soil quality is the use of plant symbiosis with microorganisms. Thus, in this study we investigated the effect of arbuscular mycorrhizal fungi (AMFs) and plant-growth-promoting rhizobacteria (PGPR) colonization on the nutritional status of apple leaves and fruit, depending on the nitrogen treatment. In a fully factorial experiment, trees were grown for nine years with or without AMFs and PGPR. We compared several ammonium nitrate treatments as well as growth without fertilization as a control. The interactions between inoculation and doses of nitrogen fertilization were observed. AMF + PGPR significantly increased the concentration of nitrogen (N), phosphorus (P), and potassium (K) in leaves up to 5%, 23%, and 19%, respectively, depending on the N dosage. Conversely, in uninoculated trees, the nitrogen treatment had a negative impact on the leaf P mineral status. On the other hand, under microbial inoculation conditions, the dose of 100 kg N∙ha−1 diminished the leaf phosphorus content in comparison to other N doses, by a maximum of 9.6%. AMF + PGPR, depending on the N treatment, either did not influence or it decreased the Mg and Ca concentrations in the leaves by maximums of 8% and 15%, respectively. Microbial inoculation had no effect on the acquisition of Ca and Mg by fruits, except for the coupled negative influence of the 100 kg N∙ha−1 treatment. Symbiosis positively conditioned the K in fruits under a specific N regime—100 kg N∙ha−1 divided into two applications during the season and 50 kg N∙ha−1 applied to the herbicide strip, increasing the concentration by approximately 4% and 8%, respectively. This study greatly contributes to our understanding of the benefits of AMF and PGPR on perennials and encourages the future exploration of their effects on apple yield and fruit quality. [ABSTRACT FROM AUTHOR]

Inducing the plant immune system to fight off pathogens is an eco-friendly strategy and needs to be a major component in disease management. Tomato (Solanum lycopersicum) is regarded as a suitable model plant for studying disease resistance and the underlying mechanisms. A remarkable body of knowledge has been generated in recent years spanning the tripartite interactions between tomato, pathogens, and resistance inducers (e.g. biologic, natural or synthetic products, etc.), suggesting what signaling pathways/molecules are potential targets to be manipulated for improving disease resistance. This review explores diverse types of stimulators in tomatoes, the most responsive genes involved in defense, and future research directions. Among the stimulators, biological stimulators significantly reduce soil-borne pathogens. Transcription of ERF transcription factor gene was significantly suppressed in the innate immune responses induced by PGPRs. It seems regulating the expression of this gene family (de novo resistance) could play critical roles in inducing systemic resistance against diseases of Solanaceae. • Major bio inducers act against soilborne pathogens. • Understanding of mechanisms will improve use efficacy. • Responsive genes could be target of GMO. [ABSTRACT FROM AUTHOR]

• PGPR Consortium to suppress phytopathogens and promote plant growth was developed. • The PGPR consortiums G1 and G2 were plant growth promoters and pathogen suppressors. • From Pot culture, G2 was more effective against phytopathogens and beneficial to plants. • Results indicates Successful pathogen suppression and promotion of plant growth. In this study, we have attempted to develop a plant growth promoting rhizobacteria (PGPR) consortia against early-stage diseases in Arachis hypogaea (Groundnut crop) plantation of Andhra Pradesh, India. The dominant PGPRs were selected by considering the various plant growth and protection qualities, followed by characterisation and grouping based on compatibility to form a consortium of PGPRs [ Group-1 includes EX-1 (Acinetobacter baumannii stain HAMBI 1846); EX-3 (Pseudomonas aeruginosa strain A1K319); EX-5 (Bacillus subterraneus strain CF1.9); KNL-1 (Bacillus subtilis strain JMP-B); CTR-4 (Enterobacter cloacae strain VITKJ1); ANT-4 (Bacillus subtilis strain SBMP4) and Group-2 includes EX-4 (Pseudomonas otitidis strain SLC8); KDP-4 (Pseudomonas aeruginosa strain Kasamber 11); NLR-4 (Bacillus species ADMK68); ANT-6 (Bacillus subtilis subsp. inaquosorum strain KCTC 13429)]. In addition to resistance to early stage pathogens, in both in vitro and pot experiments the PGPR consortium showed significantly higher germination rate and root induction (Aspergillus niger ; A. flavus ; Fusarium oxysporum) when compared to control and fertilizer treated groups. In addition, Group 2 was more successful in stimulating and protecting plant growth among the two groups of PGPRs developed. The PGPR consortia developed showed multiple plant growth characteristics, including phosphate solubilization, production of HCN and Indole acetic acid along with broad antagonism against the tested phytopathogens. [ABSTRACT FROM AUTHOR]

Abiotic stresses are the major constraints in agricultural crop production across the globe. The use of some plant–microbe interactions are established as an environment friendly way of enhancing crop productivity, and improving plant development and tolerance to abiotic stresses by direct or indirect mechanisms. Silicon (Si) can also stimulate plant growth and mitigate environmental stresses, and it is not detrimental to plants and is devoid of environmental contamination even if applied in excess quantity. In the present review, we elaborate the interactive application of Si and plant growth promoting rhizobacteria (PGPRs) as an ecologically sound practice to increase the plant growth rate in unfavorable situations, in the presence of abiotic stresses. Experiments investigating the combined use of Si and PGPRs on plants to cope with abiotic stresses can be helpful in the future for agricultural sustainability. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR), which include isolates from genera Paraburkholderia, Burkholderia and Serratia, have received attention due to their numerous plant growth-promoting mechanisms such as their ability to solubilize insoluble phosphates and nitrogen-fixation. However, there is a dearth of information on the potential plant growth-promoting effects of these three groups of bacteria on non-legumes such as maize. This study determined the influences of the aforementioned strains on soil properties, maize growth, nutrient uptake and nutrient use efficiency. A pot trial using maize as a test crop was done using a randomized complete block design with 7 treatments each replicated 7 times. The treatments used in this study were: Control (no fertilizer), chemical fertilizer (CF), organic-chemical fertilizers combination without inoculum (OCF) and with inocula consisting of single strains [cellulolytic bacteria (TC), organic fertilizer and chemical fertilizer with N-fixing bacteria (TN), organic fertilizer and chemical fertilizer with P-solubilizing bacteria (TP)) and three-strain inocula (TCNP), respectively. The variables measured included plant growth and nutrient content, soil nutrient content and functional rhizospheric bacterial populations. Paraburkholderia nodosa NB1 and Burkholderia cepacia PB3 showed comparable effects on maize biomass and also improved N and P use efficiencies when compared to full chemical fertilization. Nitrogen-fixing rhizobacteria had a positive effect on above-ground biomass of maize. Paraburkholderia nodosa NB1 improved soil total C and organic matter contents, besides being the only bacterial treatment that improved K use efficiency compared to OCF. The results suggest that P. nodosa NB1 and B. cepacia PB3 have potential usage in bio-fertilizers. In contrast, treatments with Serratia nematodiphila C46d and consortium strains showed poorer maize nutrient uptake and use efficiency than the other single strain treatments. Bacterial treatments generally showed comparable or higher overall N and P use efficiencies than full chemical fertilization. These findings suggest that at least half the amounts of N and P fertilizers could be reduced through the use of combined fertilization together with beneficial bacteria. [ABSTRACT FROM AUTHOR]

Farmers rely heavily on the use of strobilurin fungicides to manage sheath blight (ShB) caused by Rhizoctonia solani AG1-IA, the most important disease in rice in the southern United States. Greenhouse and field studies were conducted to evaluate the potential use of plant growth-promoting rhizobacteria (PGPRs) in combination with a reduced rate of azoxystrobin application as a strategy to improve the current fungicide-reliant management. Of the nine antagonistic PGPR strains screened in the greenhouse, Bacillus subtilis strain MBI600 provided the most significant and consistent suppression of ShB. Efficacy of strain MBI600 was further evaluated at the concentrations of 0, 10 3 , 10 6 , 10 9 , and 10 11 CFU/ml alone or in combinations with 0, 17, 33, 50, 67, 83, and 100% of the recommended application rate (0.16 kg a.i./ha) of azoxystrobin. Strain MBI600 applied at 10 6 ,10 9 , and 10 11 CFU/ml alone was effective in reducing ShB severity. Combinations of this strain at these rates with ≥33% of the recommended application rate of azoxystrobin further reduced ShB severity. A dose-response model defining the relationships between strain MBI600, azoxystrobin, and ShB severity was established. Estimates of the effective concentrations (EC 50 and EC 90 ) of strain MBI600 when applied in combination with 50% of the recommended application rate of azoxystrobin were 10 4 and 10 9 CFU/ml, respectively. A field trial was conducted over 4 years to verify the efficacy of their combinations. Strain MBI600 alone, when applied at 10 9 CFU/ml at the boot stage, reduced ShB severity but did not significantly increase grain yields each year. Combination of strain MBI600 with azoxystrobin at half of the recommended application rate improved efficacy of strain MBI600, reducing ShB severity to a level comparable to that of azoxystrobin applied at the full rate in all 4 years. The combined treatment also increased grain yield by 14 to 19%, comparable to the fungicide applied at the full rate in 3 of 4 years. Combined use of PGPR strain MBI600 with a reduced rate of azoxystrobin application can be a viable management option for control of ShB while allowing producers to use less fungicide on rice.

Salinity is a major environmental stress that limits crop production worldwide. It is well-understood that environmental adaptations, physiological and biochemical traits adjust salinity tolerance in plants, but imparting the knowledge gained towards crop improvement remain arduous. Utilizing the potentially of beneficial microorganisms present in the rhizosphere is an alternative strategy to improve crop production under optimal or stress conditions. The current study aims at examining the ability of plant growth-promoting rhizobacteria (PGPR) in improving coriander growth under salt stress condition. Coriander seeds were inoculated via dual culture of Azospirillum brasiliense and Azotobacter chroococcum , and therefore subjected to four levels of salt stress (0, 40, 80 and 120 mM NaCl) with three replications in a research greenhouse. Seventy-five days after sowing, when leaves fully developed, leaf samples were collected and the traits were measured. The results indicated that the dual inoculation improved chlorophyll a and b content, in comparison to the un-inoculated plants. The dual inoculation increased grain yield, stem fresh and dry weights by 11.6, 11.3 and 17.2%, respectively; it also enhanced total plant fresh and dry weights by 6.1 and 10.2%, respectively, as compared to control. As a result, the dual inoculation significantly improved catalase (CAT), but decreased ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) enzymes activities, as compared to control plants. Salt stress significantly increased (CAT) activity in the leaves, whereas it resulted in significant reduction in (APX) and (GPX) activity, especially in inoculated plants. Furthermore, dual inoculation decreased Na and subsequently increased K concentration in coriander leaves comparing with untreated plants. Overall, these results indicate that the PGPRs has improved coriander growth under control as well as salt stress conditions. Thus, PGPR can could significantly contribute to solve the coriander plant production problems caused by high salinity., (© 2020 Published by Elsevier Ltd.)

Numerous microbes reside in the rhizosphere having plant growth promoting activity, and enhancing the property by increasing plant yield. Plant growth promoting rhizobacteria (PGPR) has gradually increased in agriculture and offers an attractive way to replace chemical fertilizers, pesticides and supplements. Soil was collected from the rhizosphere of an agricultural farm and the psychrotrophic bacterial strains STA 3 (KY888133) and RM 2 (KY888134) were successfully isolated, and screened on the basis of phosphate solubilization. Further characterization was carried out by morphological, biochemical, and 16S rDNA characterization methods. The unique nature of psychrotrophic Pentoea ananatis and a suitable combination with Pseudomonas fluorescens regarding plant growth promotion activity has not been studied before to our knowledge. An assessment of various parameters of plant growth promoting activity, such as IAA, phosphate solubilization, bio-control activity, HCN and siderophore production, has been carried out. Both strains were found to be positive in various parameters except HCN and Biocontrol activity, which were positive only for the strain RM 2 . Also, shelf life and their efficacy was determined before and after formulation. A great consistency was observed in all the cultures, even after 70 days of storage under bio-formulation at room temperature, while in the case of the co-culture CPP-2, the cfu ml -1 was greater, followed by RM 2 and STA 3 . Moreover, the growth indices of the pea plant were found to be better in the co-culture CPP-2 compared with individual strains, followed by RM 2 and STA 3 . Thus, the study suggests that the co-culture CPP-2 has a great potential for plant growth promotion as compared with individual strains followed by RM 2 and STA 3 .

Twenty one dinitrogen (N2 )-fixing bacteria were isolated from the rhizosphere of Lolium perenne grown for more than 10 years without N-fertilization. The nearly complete sequence of the 16S rRNA gene of each strain and pairwise alignments among globally aligned sequences of the 16S rRNA genes clustered them into nine different groups. Out of the 21 strains, 11 were members of genus Bacillus, 3 belonged to each one of genera Paenibacillus and Pseudoxanthomonas, and the remaining 2 strains to each one of genera Burkholderia and Staphylococcus, respectively. A representative strain from each group contained the nifH gene and fixed atmospheric N2 as determined by the acetylene-dependent ethylene production assay (acetylene reduction activity, ARA). The nine selected strains were also examined to behave as plant growth promoting bacteria (PGPRs) including their ability to act as a biocontrol agent. The nine representative strains produced indol acetic acid (IAA) and solubilized calcium triphosphate, five of them, strains C2, C3, C12, C15, and C16, had ACC deaminase activity, and strains C2, C3, C4, C12, C16, and C17 produced siderophores. Strains C13, C16, and C17 had the capability to control growth of the pathogen Fusarium oxysporum mycelial growth in vitro. PCA analysis of determined PGPR properties showed that ARA, ACC deaminase activity, and siderophore production were the most valuable as they had the maximal contribution to the total variance., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)