Plant Growth Promoting Rhizobacteria Traits Research Articles

Isolation and evaluation of summer legumes Rhizobia as PGPR

Rhizobia are bacteria well known for biological nitrogen fixation through symbioses. These bacteria may also perform as plant growth promoting rhizobacteria (PGPR). In this study the role of rhizobia as PGPR was studied. Rhizobia was isolated from the root nodules of various summer legumes including Glycine max (Soybaen), Vigna radiata (Mung bean), Vigna unguiculata (Cowpea), Susbenia grandiflora (Sesbania) and Cymposistetra gonoloba (Guar) grown at New Developmental Farm (NDF), the University of Agriculture Peshawar, Pakistan during summer 2011. Rhizobia were isolated from root nodules by using yeast minitol agar media, pure culture of each isolate was prepared and examined for various PGPR traits. Data revealed that 9, 83, 47 and 21% of tested strains were found to produce cyanide (HCN), siderophores, indole-acetic acid (IAA) and solubilized phosphorus respectively. Among the tested rhizoial isolates, rhizobia isolated from Vigna radiata showed highest PGPR activity fallowed by Glycine max while relatively lower PGPR activity was observed for rhizobial isolates of Cymposistetra gonoloba (Guar). All the tested isolates were gram negative. Soybaen and cowpea isolates were found to be fast growing while mung bean, susbenia and guar were slow growing in nature. This study indicates that rhizobial isolates of Vigna radiata and Glycine max have the capability to be used as PGPR.

Relationship between in vitro characterization and comparative efficacy of plant growth-promoting rhizobacteria for improving cucumber salt tolerance.

Phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase activity and production of siderophores and indole acetic acid (IAA) are well-known traits of plant growth-promoting rhizobacteria (PGPR). Here we investigated the expression of these traits as affected by salinity for three PGPR strains (Pseudomonas fluorescens, Bacillus megaterium and Variovorax paradoxus) at two salinity levels [2 and 5% NaCl (w/v)]. Among the three strains, growth of B. megaterium was the least affected by high salinity. However, P. fluorescens was the best strain for maintaining ACC-deaminase activity, siderophore and IAA production under stressed conditions. V. paradoxus was the least tolerant to salts and had minimal growth and low PGPR trait expression under salt stress. Results of experiment examining the impact of bacterial inoculation on cucumber growth at three salinity levels [1 (normal), 7 and 10 dSm(-1)] revealed that P. fluorescens also had good rhizosphere competence and was the most effective for alleviating the negative impacts of salinity on cucumber growth. The results suggest that in addition to screening the PGPR regarding their effect on growth under salinity, PGPR trait expression is also an important aspect that may be useful for selecting the most promising PGPR bacterial strains for improving plant tolerance to salinity stress.

Improving nickel phytoextraction by co-cropping hyperaccumulator plants inoculated by plant growth promoting rhizobacteria

Phytomining is the conception of agro-metallurgical production chains based on cropping hyperaccumulator plants on contaminated or naturally rich (ultramafic) soils to produce high value metal compounds. This study aimed to evaluate the effect of enhancing multispecies hyperaccumulator covers with Plant Growth Promoting Rhizobacteria (PGPR) on Ni phytoextraction. Plant growth promoting rhizobacteria were isolated from the rhizosphere of two different plant associations (Bornmuellera tymphaea - Noccaea tymphaea (NB) and Bornmuellera tymphaea - Alyssum murale (AB)) collected from natural conditions. The screening of isolates from both plant associations for their PGPR traits revealed two PGPR strains (AB30 and NB24) affiliated to Variovorax paradoxus. Inoculation of mesocosms containing the same plant associations with these selected PGPR was performed after 5 months of culture. The biomass of the different plant parts and respective concentrations of nickel in the plants were recorded 1 month after inoculation. Root biomass of the inoculated plant associations was significantly higher than the respective non-inoculated ones. The total biomass of the inoculated plant association Bornmuellera tymphaea - Noccaea tymphaea was significantly higher than the total biomass of all others. Similarly, shoot biomass of the inoculated plant association B. tymphaea - N. tymphaea was significantly higher than that of all other covers. Results showed an increase in Ni uptake when plants were inoculated with PGPR strains, when compared with uninoculated plant associations. According to the plant cover, the inoculation increased Ni amounts in roots of 105.8 and 66.4 % respectively in ABi and NBi covers, and 39.9 and 79.6 % in the shoots. The combination of the hyperaccumulator plants N. tymphaea-B.tymphaea inoculated by one of the two PGPR strains (strain NB24), isolated from the rhizosphere of this mixed cover, seemed to be an interesting option for an efficient Ni phytoextraction to be tested in the field.

Characterization of Potential Plant Growth Promoting Rhizobacteria Isolated from Maize (Zea maysL.) in Central and Northern Benin (West Africa)

Our study aims to characterize Plant Growth Promoting Rhizobacteria (PGPR) isolated from maize roots in five agroecological zones of central and northern Benin. Sixty samples were collected at the rate of four samples per village and three villages per agroecological zone. Rhizobacteria strains were isolated from these samples and biochemically characterized. These strains were analyzed for some of their PGPR traits like ammonia production and hydrogen cyanide following conventional methods. Microbiological investigation of these samples has shown that maize rhizospheres in central and northern Benin contain a high diversity of microorganisms. A total of nine species of maize Plant Growth Promoting Rhizobacteria were identified. Those PGPR include fiveBacillusspecies (B. polymyxa, B. pantothenticus, B. anthracis, B. thuringiensis, andB. circulans), threePseudomonasspecies (P. cichorii, P. putida, andP. syringae), andSerratia marcescens. The microbial diversity does not depend on the soil types. The microbial density, generally high, varies according to both soil types and agroecological zones. AllSerratiastrains (100%) have produced ammonia, whereas 80% ofBacillusand 77.77% ofPseudomonasproduced this metabolite. The hydrogen cyanide was produced by all isolates (100%) independent of their genus. These results suggest the possibility to use these rhizobacteria as biological fertilizers to increase maize production.

Isolation, screening, and molecular characterization of plant growth promoting rhizobacteria isolates of Azotobacter and Trichoderma and their beneficial activities.

Objectives:The present study was conducted for isolation, screening, and identification of Azotobacter and Trichoderma from different soil samples.Methods:A total of 10 isolates of Azotobacter and Trichoderma were isolated from rhizospheric soils. The test isolates were biochemically characterized and screened in in-vitro conditions for their plant growth promoting properties. DNA polymorphism of isolates was studied using randomly amplified polymorphic DNA analysis.Results:A total of 41 bands were scored, out of which 35 bands were found to be 85.59% polymorphic in Azotobacter and in Trichoderma among total 37 bands scored of which 29 were found to be 78.37% polymorphic. The influence of isolated plant growth promoting rhizobacteria (PGPR) strains on plant growth was studied using different parameters such as height of the plant, number of leaves, and number of branches, and bio-control activity was studied.Conclusion:The present results concluded that the multiple beneficial activities of PGPR traits increase the plant growth and bio-control activity.

Population density and functional diversity of plant growth promoting rhizobacteria associated with avocado trees in saline soils

Rhizosphere bacteria that suppress stress ethylene production via 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity play an important role in alleviation of plant stress caused by salinity and drought. While there has been considerable research on development of soil inoculants that carry this trait, relatively little is known about the population dynamics and functional diversity of indigenous ACC-degraders in field soils. Here, we surveyed plant growth promoting rhizobacteria (PGPR) that are associated with avocado trees under different degrees of stress resulting from irrigation-induced soil salinity. Variations in PGPR populations were examined for 4 rootstocks at 3 locations with levels of salinity ranging from 0.91 to 3.90dSm−1. To characterize the culturable ACC degrading bacteria, soil water extracts from rhizosphere samples were streaked on to media containing ACC as sole nitrogen source. 105 colonies were isolated from which 20 were selected and identified by 16S rRNA gene sequence analysis. These strains were further characterized with respect to indole acetic acid (IAA) production, phosphate solubilization, and siderophore and cyanide production. Results of the survey revealed that all of the rootstocks supported indigenous ACC-degrading rhizobacteria at population densities that ranged from 1.5×104 to 8.5×106cellsg−1 rhizosphere soil, with the highest population densities occurring on the fine roots in the zone of elongation behind the root tips. The culturable ACC-degrading PGPR included species of Pseudomonas, Bacillus and Variovorax. All of the cultured isolates had different combinations of PGPR traits and varied substantially in their maximum activity levels as measured under laboratory conditions. PGPR population densities varied for the different rootstocks but were not significantly influenced by differences in soil salinity. The results suggest that indigenous PGPR are common in orchard soils, and that soil management practices that increase the population and activity of indigenous ACC degrading bacteria may serve as an alternative to soil inoculation for enhancing the stress tolerance of salt sensitive crops in saline soils.

Identification of multi-trait PGPR isolates and evaluating their potential as inoculants for wheat

Development of an effective plant growth promoting rhizobacteria (PGPR) inoculant necessitates the presence of a diverse set of traits that can help its colonization of the rhizosphere and survival under varying environmental conditions. In our investigation, a set of 100 bacterial isolates from the rhizosphere of wheat plants were screened initially on the basis of a seed germination assay; ten bacterial isolates (AW1–AW10) were selected. These isolates were then tested in vitro for specific PGPR traits, such as the production of IAA, siderophore, ammonia, HCN, P solubilization, ACC deaminase activity, acetylene reduction assay and antifungal activity. Of the ten isolates, AW5 was found to be promising for all PGP attributes. An experiment undertaken in the controlled conditions of the National Phytotron Facility revealed the potential of three isolates (AW1, AW5 and AW7) in enhancing the growth parameters of wheat plants. Characterization of these isolates using polyphasic approaches involving both phenotypic and genotypic attributes led to their identification as Bacillus sp. (AW1), Providencia sp. (AW5), and Brevundimonas diminuta (AW7), respectively. These strains could prove effective PGPR inoculants as they possess a number of traits useful for their establishment and proliferation in soil. The genus Providencia is reported for the first time for its PGP potential, using cultural as well as functional attributes to show its suitability as an inoculant for wheat crop.

Screening for Plant Growth–Promoting Rhizobacteria to Promote Early Soybean Growth

Although many studies have been conducted to identify the specific traits by which plant growth–promoting rhizobacteria (PGPR) promote plant growth, usually they were limited to studying just one or two of these traits. We selected 116 isolates from bulk soil and the rhizosphere of soybean [Glycine max (L.) Merr.] and examined them for a wide array of traits that might increase early soybean growth in nonsterile soil (PGPR traits). A subsample of 23 isolates, all but one of which tested positive for one or more of these PGPR traits, was further screened for traits associated with biocontrol, (brady)rhizobial inhibition, and rhizosphere competence. Six of eight isolates positive for 1‐aminocyclopropane‐1‐carboxylate (ACC, a precursor of ethylene) deaminase production, four of seven isolates positive for siderophore production, three of four isolates positive for β‐1,3‐glucanase production, and two of five isolates positive for P solubilization increased at least one aspect of early soybean growth. One isolate, which did not share any of the PGPR traits tested in vitro except antagonism to Sclerotium rolfsii and Sclerotinia sclerotiorum, also promoted soybean growth. One of the 23 isolates changed bradyrhizobial nodule occupancy. Although the presence of a PGPR trait in vitro does not guarantee that a particular isolate is a PGPR, the results suggest that rhizobacteria able to produce ACC deaminase and, to a lesser extent, β‐1,3‐glucanase or siderophores or those able to solubilize P in vitro may increase early soybean growth in nonsterile soil.