Plant Growth-promoting Characteristics Research Articles

Pseudomonas spp., a zinc-solubilizing vermicompost bacteria with plant growth-promoting activity moderates zinc biofortification in tomato

ABSTRACT Zinc is an essential micronutrient necessary for optimal development of tomato (Solanum lycopersicum L.). Zinc-solubilizing microbes could be substitutes for zinc supplementation and transform inorganic zinc into accessible forms. The objective of the study was to culture and screen a variety of zinc-solubilizing bacteria (ZSB) from vermicompost for various plant growth-promoting (PGP) characteristics in tomato. Thirty-isolates from vermicompost were screened for Zn-solubilization and PGP activity. A quantitative assessment of Zn solubilization indicated maximum Zn solubilization was achieved with isolate VBZ4 (26.8 mg∙L−1) followed by isolate VBZ17 (22.2 mg∙L−1) on ZnO and 18.3 mg∙L−1 (isolate VBZ4), 15.6 mg∙mL−1 (isolate VBZ17) on ZnCO3 enriched media. The isolates were examined in association with tomato plants for growth, where isolate VBZ4 improved plant growth and maximum zinc content in tomato fruit (2.87 mg/100 g) followed by isolates VBZ4+ VBZ17 and isolate VBZ17 with 2.17 mg/100 g and 2.06 mg/100 g Zn content, respectively. Isolates VBZ4 and VBZ17 were identified as Pseudomonas sp. VBZ4 and P. stutzeri VBZ17. Application of these bacteria may help provide sufficient Zn bioavailability which could lead to improved plant growth in a sustainable manner.

Potential Plant Growth-Promoting Bacteria with Heavy Metal Resistance.

Plant growth-promoting (PGP) bacteria commonly have many strategies to cope with heavy metal toxicity. Heavy metal-resistant PGP bacteria can be used to improve the growth of plants in heavy metal contaminated soils. In this study, the soil samples were collected from the lead-zinc mineral deposits in Gümüşhane Province, Turkey. Nine bacterial isolates were obtained on the nutrient agar medium supplemented with 100mg/mL zinc and lead. All of the isolates were screened in terms of plant growth-promoting characteristics including production of indole-3-acetic acid and siderophore, nitrogen fixation and phosphate solubilisation. Nine bacteria were identified as Bacillus cereus, Bacillus atrophaeus, Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus tropicus, Bacillus subtilis, Bacillus halotolerans, Bacillus vallismortis, and Enterococcus mundtii by classical and 16S rDNA-PCR assays. In addition, these isolates were evaluated for their response to three heavy metals (lead, zinc, copper) dominant in the soil samples and minimal inhibitory concentration (MIC) of the heavy metals was determined with plate dilution method. Consequently, the bacterial isolates in this study possess plant growth-promoting traits and can ameliorate heavy metal contaminated soil. E. mundtii was reported to be found in heavy metal contaminated soil for the first time. This study is the first report about PGP characteristics (IAA production and phosphate solubilisation) of B. vallismortis.

Coal-Degrading Bacteria Display Characteristics Typical of Plant Growth Promoting Rhizobacteria

Coal mining produces large quantities of discard that is stockpiled in large dumps. This stockpiled material, termed coal discard, poses an environmental threat emphasising the need for appropriate bioremediation. Here, metagenomic analysis of the 16S rRNA from ten coal-degrading strains previously isolated from coal slurry from discard dumps and from the rhizosphere of diesel-contaminated sites was used to establish genetic relatedness to known plant growth-promoting (PGP) bacteria in the NCBI database. Measurement of indole and ammonium production and solubilisation of P and K were used to screen bacteria for PGP characteristics. BLAST analysis revealed ≥ 99% homology of six isolates with reference PGP strains of Bacillus, Escherichia, Citrobacter, Serratia, Exiguobacterium and Microbacterium, while two strains showed 94% and 91% homology with Proteus. The most competent PGP strains were Proteus strain ECCN 20b, Proteus strain ECCN 23b and Serratia strain ECCN 24b isolated from diesel-contaminated soil. In response to L-trp supplementation, the concentration of indolic compounds (measured as indole-3-acetic acid) increased. Production of ammonium and solubilisation of insoluble P by these strains was also apparent. Only Serratia strain ECCN 24b was capable of solubilising insoluble K. Production of indoles increased following exposure to increasing aliquots of coal discard, suggesting no negative effect of this material on indole production by these coal-degrading bacterial isolates and that these bacteria may indeed possess PGP characteristics.

Biocontrol and Plant-Growth-Promoting Traits of Talaromyces apiculatus and Clonostachys rosea Consortium against Ganoderma Basal Stem Rot Disease of Oil Palm.

Basal stem rot (BSR) disease caused by Ganoderma boninense basidiomycetous fungus is the most economically important disease in oil palms in South East Asia. Unfortunately, there is no single most effective control measure available. Tremendous efforts have been directed in incorporation of environmentally friendly biocontrol approaches in minimizing BSR disease. This study investigated the performance of two potential biocontrol agents (BCAs), AAT0115 and AAB0114 strains recovered from oil palm on suppression of BSR in planta, and also assessed their plant-growth-promoting (PGP) performance. ITS rRNA-sequence phylogeny discriminated the two ascomycetous Talaromyces apiculatus (Ta) AT0115 and Clonostachys rosea (Cr) AAB0114 biocontrol species with PGP characteristics. In vitro studies have demonstrated both Ta and Cr are capable of reducing linear mycelial growth of G. boninense. Inoculation of individual Cr and Ta—as well as Cr+Ta consortium—induced a significant increment in leaf area and bole girth of oil-palm seedlings five months post-inoculation (MPI) under nursery conditions. At five months post-inoculation, shoot and root biomass, and nutrient contents (nitrogen, phosphorus, potassium, calcium, magnesium and boron) were significantly higher in Ta-inoculated seedlings compared to control treated with non-Ta-inoculated maize. Chlorophyll and carotenoids contents in rapidly growing oil-palm seedlings challenged with Cr, Ta or a combination of both were not negatively affected. Cr, Ta and Cr+Ta consortium treated seedlings had 4.9–60% BSR disease reduction compared to the untreated control. Co-inoculation of Cr and Ta resulted in increased BSR control efficiencies by 18–26% (compared with Cr only) and 48–55% (compared with Ta only). Collectively, Cr and Ta, either individually or in consortium showed potential as BSR biocontrol agents while also possess PGP traits in oil palm.

Isolation and Characterization of Indigenous Plant Growth-Promoting Rhizobacteria (PGPR) from Cardamom Rhizosphere.

The present study was conducted to explore the native plant growth-promoting (PGP) bacteria from cardamom rhizosphere in few districts of Kerala and Tamilnadu under cardamom cultivation. The isolates obtained were screened for their PGP characteristics and their beneficial effect on cardamom was evaluated. Of the total 88 isolates, ten were screened as promising based on their performance in growth promoting attributes such as production of indole acetic acid, gibberellic acid, siderophore, hydrogen cyanide, heavy metal tolerance and antibiotic resistance. Diazotrophy of the screened isolates were tested by nitrogenase assay and evaluated using the diversity of nif genes. Genetic analysis was carried out to assess the phylogenetic relationship using 16S rRNA sequencing. The phylogenetic analysis exhibited clear clustering of isolates into three phyla namely Firmicutes, Actinobacteria and γ-proteobacteria. Majority of the isolates were grouped into Bacillus and Pseudomonas at genus level. Three different plant inoculation study at nursery and field level, viz., Bacillus subtilis TAUC1, Bacillus subtilis TAUC2 and Pseudomonas putida TAUC10. The combined inoculation of bioinoculants were superior over individual inoculation with respect to growth, soil and plant nutrient content, biochemical constituents, rhizosphere population, soil enzyme activities and yield. Hence the present study reveals the potential effect of PGPR for bioinoculant production for enhancing growth and development of cardamom under field conditions.

Endophytic Burkholderia sp. SSG as a potential biofertilizer promoting boxwood growth.

BackgroundBurkholderia sp. SSG is a bacterial endophyte isolated from boxwood leaves showing a resistant response to infection by the boxwood blight pathogen Calonectria pseudonaviculata. SSG acted as a protective and curative biocontrol agent for boxwood blight and as a bio-sanitizer of disease inoculum in the field. Many gene clusters involved in antibiotic production and plant growth promotion (PGP) were found in the genome, giving this endophyte great application potential as a treatment for plant protection. However, the PGP features have not been documented. This study investigated the plant growth promotion activity of SSG in boxwood.MethodsTo determine whether SSG is a plant growth promoting bacterium, four PGP traits, auxin and siderophore production, nitrogen fixation and phosphate solubilization, were examined in the laboratory with colorimetric or agar plate assays. The plant growth promoting activity of SSG was tested on three boxwood varieties characterized by slow, intermediate and fast growth rates, namely Justin Brouwers, Buddy and Winter Gem, respectively. These plants were drenched with an SSG cell suspension or water and washed plant weight was compared before and after treatment to determine growth changes after 10 months.ResultsThe SSG culture was sustainable on nitrogen free media, suggesting that SSG may fix atmospheric nitrogen. It was also a strong phosphate solubilizer and a potent siderophore and indole-3-acetic acid (IAA) producer. Significant growth promotion was observed on boxwood cultivars Justin Brouwers, Buddy and Winter Gem 10 months after plant roots were drenched with SSG cells. The growth rate of treated plants was 76.1, 58.3, and 37.3% higher than that of the control, respectively. The degree of growth promotion was significantly different among plant varieties, notably more pronounced with the slow and intermediate growers. This study demonstrates that the SSG bacterium has multiple PGP traits and is a prospective plant biofertilizer.

Actinobacteria Associated with Vineyard Soils of Algeria: Classification, Antifungal Potential Against Grapevine Trunk Pathogens and Plant Growth-Promoting Features

Grapevine trunk diseases(GTDs) are among the most destructive diseases of vineyards worldwide, including Algeria. In the fungal complex involved in GTD symptoms, referred as grapevine trunk-pathogens, Paeomoniella chlamydospora and Phaeoacremonium minimum have a determining infecting role as pioneer fungi. Due to the lack of efficiency of conventional disease management practices, a search for alternative strategies, such as biocontrol, is needed. Taking the approach of looking for biocontrol candidates in the environment surrounding the plant, the present study explored actinobacteria diversity within vineyard soils of six grape-producing regions in Algeria. Based on their 16S rRNA gene sequence, identification and phylogenic analysis were performed on the 40 isolates of actinobacteria obtained. Forty percent of strains were attached to Streptomyces, including two evidenced new species, and 32.5% were affiliated to Saccharothrix. The other less represented genera were Actinoplanes, Nocardia, Nocardiopsis, Lentzea, Nonomuraea, Promicromonospora, Saccharopolyspora and Streptosporangium. Screening based on antagonistic and plant growth promotion (PGP) abilities of the strains showed that 47.5% of the isolates exhibited appreciable antagonistic activities against both Pa. chlamydospora and Pm. minimum, with the two best strains being Streptomyces sp. Ms18 and Streptomyces sp. Sb11. Screening for plant growth promoting properties demonstrated that majority of the strains were able to produce indole acetic acid, siderophores, ammonia, ACC deaminase, cellulase and amylase, and fix N2. Through a PGP-traits-based cluster analysis, the most interesting strains were highlighted. Taking into account both antagonistic and PGP properties, Streptomyces sp Sb11 was selected as the most promising candidate for further evaluations of its efficiency in a GTDs context.

Antimony-oxidizing bacteria alleviate Sb stress in Arabidopsis by attenuating Sb toxicity and reducing Sb uptake

Antimony (Sb)-oxidizing bacteria play an important role in Sb biogeochemical cycle in soil, but the benefits of microbial oxidation for plants have not been well documented. The aim of this study was to explore the contribution of Sb(III)-oxidizing bacteria to alleviate the Sb toxicity in plants. The plant growth-promoting (PGP) characteristics of Sb(III)-oxidizing bacterium Bacillus sp. S3 and the effects of bacterial inoculation on Arabidopsis plants were evaluated under controlled and Sb stressed conditions. Indole acetic acid (IAA) production and 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase) activity were the only two PGP strategies that Bacillus sp. S3 possessed, despite the production level of IAA and the activity of ACC deaminase sharply decreased under Sb stress. Bacillus sp. S3 inoculation significantly increased the plant biomass and chlorophyll content, alleviated the peroxidation of membrane lipids, decreased the activities of the antioxidant enzymes, and reduced the transcription of Sb transporters and reactive oxygen species (ROS)-related enzymes in Arabidopsis. Noteworthily, inoculation of Bacillus sp. S3 not only significantly decreased the Sb accumulation but also reduced the percentage of Sb(III) of total Sb in Arabidopsis. This study indicates that the Sb(III)-oxidizing strain of Bacillus sp. S3 is a promising inoculant used for bacteria-assisted phytoremediation on Sb-contaminated sites.

Halotolerant plant growth–promoting bacteria: Prospects for alleviating salinity stress in plants

As one of the major non–biological stresses, soil salinity negatively affects agricultural productivity, microbial communities, and agricultural economics in impacted areas and is a significant agrarian problem worldwide that has expanded in the last few decades. The use of glycophytes (salt–sensitive plants) is the primary limitation to such an agricultural approach. However, halophytes, which are proficient at obtaining essential micro/macronutrients from exceedingly saline environments and thrive under conditions in which salinity–sensitive crops are either unproductive or inefficient, are prime candidates for utilization in these circumstances. In addition, the bacterial microbiome associated with the roots of halophytic plants is a useful resource for the isolation of salt–tolerant bacteria with multiple plant growth–promoting characteristics, such as the production of different phytohormones, dissolution of insoluble inorganic phosphates, siderophore production, molecular nitrogen fixation, the activity of 1–aminocyclopropane–1–carboxylic acid (ACC) deaminase enzyme, and pathogen suppression, which enhance salinity tolerance of these plants as well as glycophytes and thereby stimulate the growth of plants under salinity–induced stress. The most dominant among reported halotolerant bacterial genera in most of the halophytic plants are Halomonas, Bacillus, Streptomyces, Oceanobacillus, and Pseudomonas. Here, it is shown that a wide range of halotolerant bacteria with a variety of plant growth-promoting characteristics may provide an important resource for augmenting crop tolerance to salinity and thereby boosting saline soil–based agriculture.

Isolation, Identification and Characterization of Endophytic Bacterium Rhizobium oryzihabitans sp. nov., from Rice Root with Biotechnological Potential in Agriculture.

A flagellate, rod–shaped bacterium designated strain M15T was isolated from rice roots. Phylogenetic analysis based on the sequences of the 16S rRNA, housekeeping genes and genomes showed that the isolate belonged to the genus Rhizobium, with the highest 16S rRNA similarity to Rhizobium radiobacter LMG140T (99.64%) and Rhizobium pusense NRCPB10T (99.36%), respectively. The complete genome of the strain M15T has a 59.28% G+C content, and the highest average nucleotide identity (ANI) and DNA-DNA relatedness (DDH) values were obtained with R. radiobacter LMG140T (88.11%, 54.80%), R. pusense NRCPB10T (86.00%, 53.00%) and R. nepotum 39/7T (88.80%, 49.80%), respectively. Plant growth-promoting characteristics tests showed that the strain M15T produced siderophore, 1–aminocyclopropane–1–carboxylate (ACC) deaminase and indole-3-acetic acid (IAA) and also produced some secondary metabolites according to the analysis of the comparative genomes. Based on the data mentioned above, we proposed that the strain M15T represented a novel species of the genus Rhizobium, named Rhizobium oryzihabitans sp. nov. The type strain is M15T (=JCM 32903T = ACCC 60121T), and the strain M15T can be a novel biofertilizer Rhizobium to reduce the use of synthetic fertilizers for plant growth promotion.

Plant growth promotion by Pseudomonas putida KT2440 under saline stress: role of eptA.

New strategies to improve crop yield include the incorporation of plant growth-promoting bacteria in agricultural practices. The non-pathogenic bacterium Pseudomonas putida KT2440 is an excellent root colonizer of crops of agronomical importance and has been shown to activate the induced systemic resistance of plants in response to certain foliar pathogens. In this work, we have analyzed additional plant growth promotion features of this strain. We show it can tolerate high NaCl concentrations and determine how salinity influences traits such as the production of indole compounds, siderophore synthesis, and phosphate solubilization. Inoculation with P. putida KT2440 significantly improved seed germination and root and stem length of soybean and corn plants under saline conditions compared to uninoculated plants, whereas the effects were minor under non-saline conditions. Also, random transposon mutagenesis was used for preliminary identification of KT2440 genes involved in bacterial tolerance to saline stress. One of the obtained mutants was analyzed in detail. The disrupted gene encodes a predicted phosphoethanolamine-lipid A transferase (EptA), an enzyme described to be involved in the modification of lipid A during lipopolysaccharide (LPS) biosynthesis. This mutant showed changes in exopolysaccharide (EPS) production, low salinity tolerance, and reduced competitive fitness in the rhizosphere.

Isolation, plant growth-promoting traits, antagonistic effects on clinical and plant pathogenic organisms and identification of actinomycetes from olive rhizosphere

Soil actinomycetes are a highly common group of bacteria and frequently studied as having secondary metabolites in the potential of producing the most preferred antagonistic content. Considering the continuous variation in soil structure, there is a potential for encountering different organisms. Almost all of antibiotic contents are produced by these bacteria and their importance increase.In this study, eleven different actinomycetes strain were isolated from the rhizosphere of olive trees investigated for their plant growth-promoting (PGP) traits including ammonia production, indole-3-acetic acid production, phosphate solubilization, and siderophore production with antagonistic activities against a set of pathogenic bacteria, fungi, and yeasts. All actinomycetes were identified according to 16S rRNA regions were recognized in four different Streptomyces species but according to fatty acid analysis, there would be at least six different organisms. The potential for antagonistic and plant growth-promoting traits of olive tree rhizosphere actinomycetes were a promising tool for agricultural applications and clinical antibiotic resistance. Differentiation of organisms with the antagonism of pathogenic activities and PGP features could be a definitive method for future studies.

Complete Genome Sequence of Pseudomonas psychrotolerans CS51, a Plant Growth-Promoting Bacterium, Under Heavy Metal Stress Conditions.

In the current study, we aimed to elucidate the plant growth-promoting characteristics of Pseudomonas psychrotolerans CS51 under heavy metal stress conditions (Zn, Cu, and Cd) and determine the genetic makeup of the CS51 genome using the single-molecule real-time (SMRT) sequencing technology of Pacific Biosciences. The results revealed that inoculation with CS51 induced endogenous indole-3-acetic acid (IAA) and gibberellins (GAs), which significantly enhanced cucumber growth (root shoot length) and increased the heavy metal tolerance of cucumber plants. Moreover, genomic analysis revealed that the CS51 genome consisted of a circular chromosome of 5,364,174 base pairs with an average G+C content of 64.71%. There were around 4774 predicted protein-coding sequences (CDSs) in 4859 genes, 15 rRNA genes, and 67 tRNA genes. Around 3950 protein-coding genes with function prediction and 733 genes without function prediction were identified. Furthermore, functional analyses predicted that the CS51 genome could encode genes required for auxin biosynthesis, nitrate and nitrite ammonification, the phosphate-specific transport system, and the sulfate transport system, which are beneficial for plant growth promotion. The heavy metal resistance of CS51 was confirmed by the presence of genes responsible for cobalt-zinc-cadmium resistance, nickel transport, and copper homeostasis in the CS51 genome. The extrapolation of the curve showed that the core genome contained a minimum of 2122 genes (95% confidence interval = 2034.24 to 2080.215). Our findings indicated that the genome sequence of CS51 may be used as an eco-friendly bioresource to promote plant growth in heavy metal-contaminated areas.

Biocontrol potential index of pseudomonads, instead of their direct-growth promotion traits, is a predictor of seed inoculation effect on crop productivity under field conditions

Agricultural bioproducts became interesting alternatives for sustainable agricultural practices, because they aim to reduce the use of agrochemicals without losing crop yields. As Pseudomonas genus has been largely studied for the high number of plant probiotic species it contains, in this work we evaluated the field performance of 10 genetically diverse native Pseudomonas that have been isolated from productive plots of the Argentine Pampas. Previously, they have been characterized in vitro, and we have developed several indexes to organize the isolates’ collection based on their potential to perform biocontrol of fungal pathogens (BPI), to promote plant growth by direct mechanisms (DGPI), or by integrated direct plus indirect mechanisms (PGPI). At three geographical sites, we tested the effect of single- and co-inoculations with a commercial bio-input based on the fungus Trichoderma harzianum Th2, in wheat and maize crops during 3 consecutive seasons. Most of single inoculations improved wheat and maize grain yields. For wheat, improvement seemed to be related with a higher plant emergence by the positive correlation between yield and plant number; whereas for maize increased yields would be rather associated with a better plant structure by the positive correlation between yield and the vegetation index NDVI. The co-inoculation of Th2 with different P. chlororaphis isolates also increased the grain yield of both grain crops, despite P. chlororaphis strains displayed fungal inhibition in dual culture in vitro tests. We found a positive and significant correlation between BPI and the yield percentage improvement of both crops, but a negative correlation with DGPI. Thus, this work shows the usefulness of the in vitro characterization of biocontrol-related traits and the estimation of a biocontrol potential index as a proxy for crop yield performance, but not of direct plant growth-promoting features.

A preliminary study on L-asparaginase from mangrove detritus-derived fungi and its application in plant growth promotion

L-asparaginase enzyme has wide applications in medicine, food industry and developing biosensors. The present study was carried out to investigate the plant growth-promoting characteristics of L-asparaginase, an aspect that is poorly studied. Two filamentous fungi, Peroneutypa sp. GU-S and Lecanicillium sp. GU-G, derived from mangrove detritus in Goa, India, produced L-asparaginase enzyme in laboratory conditions which was active at room temperature, and 37 °C. A higher amount of enzyme was produced under aeration than without aeration. The optimum pH for asparaginase activity was 8. The enzyme isolated from Peroneutypa sp. GU-S was more stable at lower pH 4, and thus further processed. The enzyme was produced using economical sources, i.e., powdered soya and grass by solid-state fermentation. Germinating seeds of pea, Pisum sativum inoculated with crude enzyme extract produced a better quality of seedlings than the seedlings from un-inoculated seeds. The shoot and the root length were 1.2 and 2.2 times greater in the test than in control plants, within twenty days of incubation. This study demonstrates plant growth-promoting ability of the L-asparaginase, which can be further studied on other plants.

Plant growth-promoting characteristics of root fungal endophytes isolated from a traditional Cordillera rice landrace

Plant growth-promoting characteristics of root fungal endophytes isolated from a traditional Cordillera rice landrace

Insights of organic fertilizer micro flora of bovine manure and their useful potentials in sustainable agriculture.

Exploration of diverse environmental samples for plant growth-promoting microbes to fulfill the increasing demand for sustainable agriculture resulted in increased use of bacterial biofertilizer. We aimed for the isolation of plant growth-promoting as well as antibiotic sensitive bacteria from bovine manure samples. The basic theme of our study is to highlight potentials of bacteria in manure and the unchecked risk associated with the application of manure i.e. introducing antibiotic-resistant microbial flora, as fertilizer. Fifty-two, morphologically distinct isolates; from eight different manure samples, were subjected to plant growth-promoting parametric tests along with antibiotic resistance. Thirteen antibiotic sensitive bacterial strains with potentials of plant growth promotion further characterized by 16S rRNA ribotyping and the identified genera were Stenotrophomonas, Achromobacter, Pseudomonas, and Brevibacillus. Successful radish seeds germination under sterile in-vitro conditions showed the potential of selected bacterial isolates as plant growth-promoting bacteria. The results of this study confirmed plant growth-promoting characteristics of bovine manures’ bacterial strains along with an alarming antibiotic resistance load which comprises 75% of bacterial isolated population. Our study showed distinct results of un-explored manure bacterial isolates for plant growth promotion and flagged ways associated with unchecked manure application in agriculture soil through high load of antibiotic resistant bacteria.

Characterization of bacterial endophytes from the roots of native and cultivated Brazil nut trees (Bertholletia excelsa)

ABSTRACT Brazil nut is a very important nontimber forest product in the Amazon region. Propagation of this tree still represents a challenge due to slow and uneven seed germination. In this context, plant growth-promoting bacteria can facilitate the process of propagation. The aims of this study were to isolate and characterize endophytic bacteria from the roots of Brazil nut trees in native terra firme forest and cultivation areas in northern Brazil, and to identify mechanisms by which bacteria act in plant growth promotion. Overall, 90 bacterial isolates were obtained from the roots of Brazil nut trees in monoculture, agroforestry and native forest areas by using different semisolid media. The isolates were characterized by sequencing the 16S rRNA gene. Plant growth-promoting characteristics were evaluated by the presence of the nifH gene, aluminum phosphate solubilization and the production of indole compounds. The isolates were affiliated with 18 genera belonging to 5 different classes (α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Bacilli and Actinobacteria). The genus Bacillus was predominant in the forest and monoculture areas. Fourteen isolates presented the nifH gene. Most of the bacteria were able to solubilize aluminum phosphate and synthetize indole compounds. The results indicated high diversity of endophytic bacteria present among the roots of Brazil nut trees, mainly in the agroforestry area, which could be related to soil attributes. Among the 90 isolates, the 22 that presented the best results regarding plant growth promotion traits were good candidates for testing in seedling production of Brazil nut trees.

Isolation and Characterization of Phosphate Solubilizing Pseudomonas Species and Their Effect on Plant Growth Promotion

Plant growth-promoting rhizobacteria (PGPR) affect plant growth via various direct or indirect mechanisms. These microorganisms are the potential tools for sustainable agriculture. In this study, eight different Pseudomonas strains (PM1 - PM8) isolated from rhizospheric soil were characterized plant growth-promoting characteristics, including indole-3-acetic acid (IAA) and Gibberellin (GA3) production, phosphate solubilization, 1- aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and effects of direct inoculation on plant growth parameters (fresh weight, shoot length). All of these strains have their ability for solubilization of insoluble phosphate depending on pH decrease at the range around pH4 - 5 at 2 days after inoculation. PM1, PM4, PM5 and PM7 species was capable of IAA production and PM4, PM5, PM7 and PM8 species have high activity for production of gibberellin (GA3) hormone. For ACC deaminase activity, PM1, PM3 and PM8 show high activity. Furthermore, all these species have significantly promoted the growth of the lettuce seedling plants for fresh weight and shoot length enhancement, so that these Pseudomonas species could be used as potential bio-fertilizer agents. Production of plant hormone IAA (A) and GA3 (B) from isolated Pseudomonas species.

Bacterial antagonists and their cell-free cultures efficiently suppress canker disease in citrus lime

Proliferation of citrus canker disease caused by Xanthomonas citri subsp. citri (Xcc) has increasingly become a serious threat and has resulted in a significant loss in citrus production worldwide. This research aimed to identify efficient antagonistic bacteria for the biological control of canker disease in Citrus aurantifolia cultivar Pan (Pan-lime) and their antagonistic characteristics by experimental analysis. With the dual culture method, twenty isolates inhibited Xcc. Eight out of over fifty isolates showed clear inhibition zones and were further analyzed for plant growth-promoting characteristics. After the screening process, Bacillus velezensis isolate SWUA08 and Pseudomonas aeruginosa isolate SWUC02 were selected for further analysis of bacterial canker resistance in Pan-lime seedlings and trees. Experimental results show that both antagonists increased canker disease resistance. Furthermore, their cell-free cultures reduced canker disease severity index in Pan-lime tree. Our experimental results demonstrating that the antagonists offer an alternative perspective to evaluate a method of canker disease inhibition.