Multiple Plant Growth Promoting Research Articles

Plant growth promoting traits shown by bacteria Brevibacterium frigrotolerans SMA23 Isolated from Aloe vera rhizosphere

Brevibacterium frigrotolerans SMA23 is a gram positive rod shaped bacteria isolated from Aloe vera rhizosphere. 16S rRNA sequencing confirmed the identity of the bacterium as Brevibacterium frigrotolerans. It was capable of growing at temperatures ranging from 10°C to 35°C, but maximum growth was observed at 30°C. It is endowed with multiple plant growth promotion attributes such as phosphate solubilization, IAA production and siderophore production, which are expressed differentially at sub-optimal temperatures. At 10°C it was found to exhibit all the plant growth promotion attributes. This bacterial isolate was able to positively influence and promote the growth and nutrient uptake parameters of wheat (HD 2967) under glasshouse conditions.

Plant Growth-Promoting Traits in Rhizobacteria of Heavy Metal-Resistant Plants and Their Effects on Brassica nigra Seed Germination

Phytoremediation is an emerging technology that uses plants and their associated microbes to clean up pollutants from the soil, water, and air. In order to select the plant growth-promoting rhizobacteria (PGPR) for phytoremediation of heavy metal contamination, 60 bacterial strains were isolated from the rhizosphere of two endemic plants, Prosopis laevigata and Spharealcea angustifolia, in a heavy metal-contaminated zone in Mexico. These rhizobacterial strains were characterized for the growth at different pH and salinity, extracellular enzyme production, solubilization of phosphate, heavy metal resistance, and plant growth-promoting (PGP) traits, including production of siderophores and indol-3-acetic acid (IAA). Overall, the obtained rhizobacteria presented multiple PGP traits. These rhizobacteria were also resistant to high levels of heavy metals (including As as a metalloid) (up to 480 mmol L−1 As(V), 24 mmol L−1 Pb(II), 21 mmol L−1 Cu(II), and 4.5 mmol L−1 Zn(II)). Seven rhizobacterial strains with the best PGP traits were identified as members of Alcaligenes, Bacillus, Curtobacterium, and Microbacterium, and were selected for further bioassay. The inoculation of Brassica nigra seeds with Microbacterium sp. CE3R2, Microbacterium sp. NE1R5, Curtobacterium sp. NM1R1, and Microbacterium sp. NM3E9 facilitated the root development; they significantly improved the B. nigra seed germination and root growth in the presence of heavy metals such as 2.2 mmol L−1 Zn(II). The rhizobacterial strains isolated in the present study had the potential to be used as efficient bioinoculants in phytorremediation of soils contaminated with multiple heavy metals.

Multi-metal resistance and plant growth promotion potential of a wastewater bacterium Pseudomonas aeruginosa and its synergistic benefits.

Water and soil pollution by toxic heavy metals (HMs) is increasing globally because of increase in population, industrialization and urbanization. It is a burning problem for the public, scientists, academicians and politicians how to tackle the toxic contaminants which jeopardize the environment. One possible solution for pollution abatement is a bioremediation-effective and innovative technology that uses biological systems for treatment of contaminants. Many bacteria synthesize indole-3-acetic acid (IAA) which is a product of L-tryptophan metabolism and belongs to the auxin class of plant growth-promoting hormone. The present study aimed at assessing the resistance pattern of wastewater bacteria against multiple HMs and plant growth promotion activity associated with IAA. A Gram-negative bacterial strain Pseudomonas aeruginosa KUJM was isolated from Kalyani Sewage Treatment Plant. This strain showed the potential to tolerate multiple contaminations such as As(III) (50mM), As(V) (800mM), Cd (8mM), Co (18mM), Cu (7mM), Cr (2.5mM), Ni (3mM) and Zn (14mM). The capability of IAA production at different tryptophan concentration (1, 2, 5 and 10mgmL-1) was determined, and seed germination-enhancing potential was also estimated on lentil (Lens culinaris). Such type of HM-resistant, IAA-producing and seed germination-enhancing P. aeruginosa KUJM offer great promise as inoculants to promote plant growth in the presence of toxic HMs, as well as plant inoculant systems useful for phytoremediation of polluted soils. Hence, P. aeruginosa KUJM finds significant applications in HM-contaminated poor agricultural field as well as in bioremediation of HM-contaminated wastewater system.

Plant growth-promoting effect and genomic analysis of the beneficial endophyte Streptomyces sp. KLBMP 5084 isolated from halophyte Limonium sinense

Soil salinity is a worldwide environmental problem that can hinder plant development and therefore negatively impact crop production. Inoculation of halophytic plants with plant growth-promoting (PGP) actinobacteria has been suggested as one strategy to improve salt tolerance. Here we performed a glasshouse experiment to test the effect of a PGP halotolerant endophytic actinomycete strain, KLBMP 5084 on the performance of the halophyte Limonium sinense under conditions of salt stress. Strain KLBMP 5084 was identified and screened for multiple PGP traits. The complete genome of strain KLBMP 5084 was sequenced and analyzed. L. sinense control seedlings (no inoculation) and seedlings inoculated with KLBMP 5084 were given different NaCl (0, 100 and 250 mM) salt-stress treatments. Growth parameters and physiological responses of L. sinense were determined after harvest. Compared with the control, plants inoculated with strain KLBMP 5084 had greater in fresh weight, root length, leaf length and total chlorophyll and proline contents under both normal and high salinity conditions. Compared with control, inoculated plants had significantly lower leaf malondialdehyde (MDA) content and significantly more antioxidant enzymes. Moreover, inoculated plants had significantly lower accumulation of Na+ in both leaves and roots under high salt-stress conditions. Genomic analysis of strain KLBMP 5084 revealed many PGP related genes, including some genes putatively involved in salt tolerance and harsh environment adaptation. Strain KLBMP 5084 seems to confer salt tolerance to host plant L. sinense through more than one mechanism, suggesting KLBMP 5084 could be a strong PGP agent to improve plant yields and tolerance to salinity stress.

Selection and evaluation of phosphate-solubilizing bacteria from grapevine rhizospheres for use as biofertilizers

Phosphate-solubilizing bacteria (PSB) have the ability to solubilize insoluble phosphorus (P) and release soluble P. Extensive research has been performed with respect to PSB isolation from the rhizospheres of various plants, but little is known about the prevalence of PSB in the grapevine rhizosphere. In this study, we aimed to isolate and identify PSB from the grapevine rhizosphere in five vineyards of Northwest China, to characterize their plant-growth-promoting (PGP) traits, evaluate the effect of stress on their phosphate-solubilizing activity (PSA), and test their ability to stimulate the growth of Vitis vinifera L. cv. Cabernet Sauvignon. From the vineyard soils, 66 PSB isolates were screened, and 10 strains with high PSA were identified by 16S rRNA sequencing. Sequence analysis revealed that these 10 strains belonged to 4 genera and 5 species: Bacillus aryabhattai, B. megaterium, Klebsiella variicola, Stenotrophomonas rhizophila, and Enterobacter aerogenes. The selected PSB strains JY17 (B. aryabhattai) and JY22 (B. aryabhattai) were positive for multiple PGP traits, including nitrogen fixation and production of indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinase, and protease. JY17 and JY22 showed strong PSA under stress conditions of high pH, high salt, and high temperature. Therefore, these two isolates can be used as biofertilizers in saline-alkaline soils. The inoculation with PSB significantly facilitated the growth of V. vinifera cv. Cabernet Sauvignon under greenhouse conditions. Use of these PSB as biofertilizers will increase the available P content in soils, minimize P-fertilizer application, reduce environmental pollution, and promote sustainable agriculture.

Phytohormone production endowed with antagonistic potential and plant growth promoting abilities of culturable endophytic bacteria isolated from Clerodendrum colebrookianum Walp.

In this study, culturable endophytic bacterial isolates obtained from an ethnomedicinal plant Clerodendrum colebrookianum Walp., were assessed for their diversity, in vitro screening for their plant growth promoting (PGP) activities and to use them as inoculant for in vivo PGP activities with biocontrol potential. Totally, 73 isolates were recovered from different tissues of C. colebrookianum were identified by 16S rRNA gene sequencing and phylogenetically analyzed by using BOX-PCR fingerprinting. Out of 73 isolates, 52 exhibited varying extents of antagonistic potential were selected for screening for various PGP traits. Concerning the PGP activities, the percentage of isolates positive for P-solubilisation, indolic compounds production, siderophore and ammonia production were 84.6, 92.3, 78.8 and 98.0 respectively. All isolates were positive for the production of hydrocyanic acid (HCN) and 86.5%, 84.6% and 90.3% of isolates showed significant cellulase, amylase and protease production respectively. Further, the top 10 bacterial isolates based on a bonitur scale with multiple PGP activities were screened for root surface colonization and biofilm formation ability. Out of selected 10 isolates, 9 showed significant potential for root surface colonization on tomato roots. Isolate BPSAC6 identified as Bacillus sp. was most efficient in biofilm formation as assessed with respect to the intensity of crystal violet, which further showed their potential to withstand various biotic and abiotic stresses. Furthermore, Bacillus sp. strain BPSAC6 showed a significant increase in shoot and root height as well as fresh weight after 45 and 60 d of inoculation with tomato seedlings. Additionally, biosynthetic potential of antagonistic isolate was detection by using PKSI, PKSII and NRPS biosynthetic genes. Two isolates Pseudomonas psychrotolerans and Labrys wisconsinensis were reported first time as an endophyte. At last, first time an endophytic bacterial strain Bacillus sp. BPSAC6 was reported to produce altogether three phytohormones (IAA, Kinetin and 6-Benzyladenine). This study is the first report that bacteria isolated from C. colebrookianum has biocontrol as well as PGP abilities endowed with phytohormones production and can be used for the preparation of bioinoculant for plant growth promotion.

Screening of Multi-Trait Rhizobacteria for Improving the Growth, Enzyme Activities, and Nutrient Uptake of Tea (Camellia sinensis)

ABSTRACTThe use of plant growth-promoting rhizobacteria (PGPR) as agricultural inputs for increasing crop production needs the selection of efficient bacteria with plant growth-promoting (PGP) attributes. Therefore, the purpose of this study was to evaluate the effects of 20 multi-traits bacteria on tea growth, nutrient uptake, chlorophyll contents, and enzyme activities under field conditions for over 3 years. These isolates were screened in vitro for their PGP traits such as the production of indole acetic acid (IAA), nitrogenase activity, phosphorus (P) solubilization, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Screening of rhizobacteria that show multiple PGP traits suggests that they stimulated overall plant growth, including shoot development and leaf yield, improving macro- and micro-nutrient uptake, chlorophyll contents, and activities of enzymes of tea plant. Use of strains with multiple PGP traits could be a more effective approach and have great potential for the environmentally-friendly tea production.

Detection of biosynthetic gene and phytohormone production by endophytic actinobacteria associated with Solanum lycopersicum and their plant-growth-promoting effect

In the present study, fifteen endophytic actinobacterial isolates recovered from Solanum lycopersicum were studied for their antagonistic potential and plant-growth-promoting (PGP) traits. Among them, eight isolates showed significant antagonistic and PGP traits, identified by amplification of the 16S rRNA gene. Isolate number DBT204, identified as Streptomyces sp., showed multiple PGP traits tested in planta and improved a range of growth parameters in seedlings of chili (Capsicum annuum L.) and tomato (S. lycopersicum L.). Further, genes of indole acetic acid (iaaM) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase (acdS) were successively amplified from five strains. Six antibiotics (trimethoprim, fluconazole, chloramphenicol, nalidixic acid, rifampicin and streptomycin) and two phytohormones [indole acetic acid (IAA) and kinetin (KI)] were detected and quantified in Streptomyces sp. strain DBT204 using UPLC-ESI-MS/MS. The study indicates the potential of these PGP strains for production of phytohormones and shows the presence of biosynthetic genes responsible for production of secondary metabolites. It is the first report showing production of phytohormones (IAA and KI) by endophytic actinobacteria having PGP and biosynthetic potential. We propose Streptomyces sp. strain DBT204 for inoculums production and development of biofertilizers for enhancing growth of chili and tomato seedlings.

Evaluation of Gram-positive rhizosphere and endophytic bacteria for biological control of fungal rice (Oryzia sativa L.) pathogens

Gram-positive bacteria isolated from the rhizosphere and inside the roots of rice were characterized for plant growth promoting (PGP) traits and antifungal activity against some rice plant pathogenic fungi of rice. The results showed the endophytic and rhizosphere isolates had different PGP traits and antifungal activity. Only one rhizosphere isolate and one endophytic isolate showed highly inhibitory effects against the mycelial growth of all fungal rice pathogens tested in this study. The best bacterial isolates, based on multiple PGP traits and inhibitory effects against the mycelial growth of all fungal rice pathogens, were identified. Based on biochemical tests and by comparison of 16S rDNA sequences, the endophytic isolate REN3 and the rhizosphere isolate REN4 were closely related to Bacillus cereus and Bacillus mojavensis respectively. The broad-spectrum antifungal strains, the REN3 and REN4 isolates analyzed here, exert multiple PGP and antagonistic activity and represent an excellent option to be used as either potent bio-promoting or bio-control agents in rice under in vitro conditions. This application may help to minimize dependence on pesticides, which have adverse effects on the environment, finally leading to have sustainable environments. In conclusion, the results of antifungal activity showed rice harbors bacteria with a good potential in biocontrol of rice fungal pathogens.

Multifunctional Pseudomonasputida strain FBKV2 from arid rhizosphere soil and its growth promotional effects on maize under drought stress

In the present study, rhizobacteria were isolated from the rhizosphere of maize, okra, eggplant, tomato, green gram, peanut and red gram grown in arid and semi-arid regions in India and were screened for drought tolerance in Trypticase soy broth (TSB) supplemented with different concentrations of polyethylene glycol 6000 (PEG 6000). Out of 23 isolates, three could tolerate minimal negative water potential of −1.03MPa and were evaluated for plant growth promoting (PGP) traits under control and drought stress (−1.03MPa) conditions. Pseudomonas spp. strain FBKV2 isolated from eggplant (Solanum melongeana L.) rhizosphere, showed multiple PGP traits under both control and drought stress conditions. The strain was identified as Pseudomonas putida by 16S rRNA sequence analysis and the sequence was submitted to GenBank under the accession number KT311002.1. The strain was evaluated for growth promotion of maize (Zea mays L.) under drought stress. Seedlings inoculated with P. putida strain FBKV2 showed better growth in terms of shoot, root length, and dry biomass. Furthermore, inoculation improved cellular metabolites and stomatal conductance in maize seedlings. Scanning electron microscopy confirmed the colonization of P. putida strain FBKV2 on the root surface of maize seedlings. The present study demonstrates that the isolation of indigenous drought tolerant P. putida strain FBKV2 from stressed ecosystems can be a very useful approach for the development of bio-inoculants for drought stress management in crops.

Strategic assessment of multiple plant growth promotion traits for shortlisting of fluorescent Pseudomonas spp. and seed priming against ragi blast disease

Biocontrol and induction of resistance through rhizosphere microflora against plant pathogens is a major area of interest. Fluorescent Pseudomonas (FPs), the highly noted diverse rhizospheric bacteria which are widely used for disease management in various plant–pathogen systems. Management of ragi blast disease by Magnaporthe grisea is a major challenge because of its wide host specificity. The present study is intended towards isolation of FPs for priming ragi seeds which could induce resistance against blast disease. They were characterized for PGP traits (production of indole acetic acid and siderophore, phosphate solubilisation, biofilm formation and cyanogenesis) and their antagonistic behaviour against M. grisea. Selection of the potential isolates was based on quantitative PGP traits through a nonparametric analysis. Principal Co-ordinate Analysis based on PGP traits classified 136 isolates into two clusters. Twelve best isolates were used for further studies on induction of resistance by seed priming under greenhouse conditions, followed by challenge inoculation with M. grisea. The isolate JUP121 showed best disease protection when compared to the control plants. Out of twelve treatments, four showed significant disease resistance under greenhouse conditions, which were further validated by biochemical determinants. A time course study on the accumulation of pathogenesis related (PR) proteins (β-1,3-glucanase and chitinase) was carried out which showed significant results on priming.

Plant growth promoting activities of rhizobacteria isolated from Podophyllum hexandrum growing in North-West regions of the Himalaya

A collection of 50 rhizospheric and 43 endorhizospheric bacteria was obtained from Podophyllum hexandrum grown in high hills of Churdhar, Himachal Pradesh, India and subjected to replica plating for one step screening of plant growth promoting (PGP) traits. After replica plating, 41 bacterial isolates simultaneously growing on Pikovskaya’s, Chrome-azurol-S, and Jensen’s medium were characterized for additional PGP traits. Of the total, 80.48 % isolates produced indole-3-acetic acid, 12.20 % produced HCN, 53.65 % exhibited chitinase and 41.46 % exhibited protease activity. In vitro inhibition of fungal pathogens viz., Alternaria solani, Fusarium oxysporum, Dematophora necatrix, Sclerotium rolfsii and Phytophthora spp. ranged from 44 % to 88 %. Twenty most efficient PGPR under in vitro conditions were evaluated for growth promotion of tomato in growth chamber. Significantly highest root length (43.00 mm), shoot length (73.00 mm), plant dry weight (12.90 mg plant−1) and vigour index (10,567.60) were recorded for isolate 2a1. The efficacy of isolate 2a1 was further evaluated under net house and resulted in remarkable increase in root length (58.02 %), shoot length (66.89 %), root dry weight (98.67 %), shoot dry weight (88.58 %), available nitrogen (31.89 %), phosphorus (22.15 %) and potassium (4.51 %) content in soil over untreated control. Remarkable increase was also recorded in nitrogen (11.85 %), phosphorus (23.08 %) and potassium (36.84 %) content of shoot biomass over control. Strain 2a1 was identified as Bacillus subtilis after biochemical and phylogenetic analysis. These results demonstrated that strain 2a1 from Podophyllum hexandrum exhibited multiple PGP attributes for development as a biofertilizer to enhance soil fertility and promote plant growth.

Rhizosphere and endorhiza of oilseed rape (Brassica napus L.) plant harbor bacteria with multifaceted beneficial effects

In this study, bacteria were isolated from the rhizosphere and inside the roots of oilseed rape (Brassica napus L.) plant grown in the field in Iran. A total of 150 isolates were obtained from the rhizosphere (90 isolates) and endorhiza (60 isolates) of B. napus plants grown in rotation with rice. All of the isolates were characterized for production of plant growth promoting (PGP) traits and antifungal activity against some rice plant pathogen fungi. The results showed the endophytic and rhizosphere isolates had different PGP traits in terms of both the number and the production amount of these traits. Only one rhizosphere isolate and two endophytic isolates showed highly inhibitory effects against the mycelial growth of all fungal rice pathogens tested in this study. In addition, thirty-seven isolates inhibited only the mycelial growth of some the fungal rice pathogens. A higher percentage of the endophytic isolates were positive for production of IAA, siderophore, and ACC deaminase as compared to rhizosphere isolates respectively. The best bacterial isolates (one endophytic isolate and one rhizosphere isolate), based on multiple PGP traits and inhibitory effects against the mycelial growth of all fungal rice pathogens, were identified. Based on biochemical tests and by comparison of 16S rDNA sequences, the endophytic isolate CEN3 and the rhizosphere isolate CEN5 were closely related to Bacillus subtilis and Bacillus cereus respectively. These bacteria exhibited a broad-spectrum antifungal activity towards all rice phytopathogenic fungi. We also studied the PGP effect of these isolates as single and co-inoculation on rice seedlings. All treatments resulted in significant increases (p<0.05) in root length, root fresh weight, and shoot dry weight, as compared to control. When these isolates were applied as co-inoculation on rice seedlings, the highest increase in rice plant growth indices and population size of these isolates after 20days was observed as compared to treatments receiving these isolates alone. In conclusion, the B. subtilis CEN3 and B. cereus CEN5 strains analyzed here exert multiple PGP and antagonistic mechanisms, show positive root colonization capability, and represent an excellent option to be used as either potent bio-promoting or bio-control agents in crops such as rice.

Endophytic culturable bacteria colonizing Lavandula dentata L. plants: Isolation, characterization and evaluation of their plant growth-promoting activities

Aromatic plants such as lavender are stirring the attention of many researchers due to their content in bioactive secondary metabolites that can be used in traditional medicine. However, information regarding naturally occurring lavender associated bacterial endophytes (BE) is limited. To the best of our knowledge, this is the first study which aims to assess the phylogenetic diversity of the culturable endophytic bacteria of Lavandula dentata cultivated under organic management and to evaluate their potential as plant growth promoting (PGP) agents. BE were grouped by random amplified polymorphic DNA and identified by 16S ribosomal RNA gene sequencing. Endophytes were further characterized for the ability to produce several PGP substances, like ammonia, siderophores, indol-3-acetic acid, and hydrogen cyanide and for the ability to solubilize phosphate. Plant cell-wall degrading enzymes were also determined. Densities of BE were higher in roots (log6.39CFUg−1 fresh weight) than in shoots (log5.56CFUg−1 fresh weight). Phylogenetic analysis showed that BE were affiliated to two major groups: γ-Proteobacteria (50%) and Firmicutes (31.6%) and a small part belonged to α- (7.9%) and β-Proteobacteria (10.5%), being Pseudomonas and Bacillus the most highly represented genera. Higher bacterial diversity was found in the lavender roots, with endophytes belonging to 6 different genera (Pseudomonas, Variovorax, Rhizobium, Caulobacter, Bacillus and Paenibacillus), than in shoots where only 3 genera (Bacillus, Pseudomonas and Xanthomonas) were found. Overall, BE showed ability to produce extracellular enzymes and multiple PGP traits, suggesting their potential use as efficient bioinoculants in sustainable cultivation of medicinal and aromatic plants.

Oasis desert farming selects environment-specific date palm root endophytic communities and cultivable bacteria that promote resistance to drought.

Oases are desert-farming agro-ecosystems, where date palm (Phoenix dactylifera L.) plays a keystone role in offsetting the effects of drought and maintaining a suitable microclimate for agriculture. At present, abundance, diversity and plant growth promotion (PGP) of date palm root-associated bacteria remain unknown. Considering the environmental pressure determined by the water scarcity in the desert environments, we hypothesized that bacteria associated with date palm roots improve plant resistance to drought. Here, the ecology of date palm root endophytes from oases in the Tunisian Sahara was studied with emphasis on their capacity to promote growth under drought. Endophytic communities segregated along a north-south gradient in correlation with geo-climatic parameters. Screening of 120 endophytes indicated that date palm roots select for bacteria with multiple PGP traits. Bacteria rapidly cross-colonized the root tissues of different species of plants, including the original Tunisian date palm cultivar, Saudi Arabian cultivars and Arabidopsis. Selected endophytes significantly increased the biomass of date palms exposed to repeated drought stress periods during a 9-month greenhouse experiment. Overall, results indicate that date palm roots shape endophytic communities that are capable to promote plant growth under drought conditions, thereby contributing an essential ecological service to the entire oasis ecosystem.

Exploring plant growth promoting potential of non rhizobial root nodules endophytes of Vigna radiata

Plant growth promoting (PGP) rhizobacteria exert beneficial effects and may establish as endophytes in their hosts. Here, plant growth promoting traits of 26 non rhizobial and one fungal endophyte previously isolated from Vigna radiata root-nodules were assessed for IAA and siderophore production, phosphate solubilization and hydrolytic enzymes production. Most bacterial endophytes improved seedling vigor index while fungal endophyte (Macrophomina phaseolina) lacked all PGP traits. Endophytes Ml, M10 and M15 were most influential in improving Seedling Vigor Index. Three endophytes having multiple PGP traits with maximum siderophore production: 46.77 μg mL−1 (Bacillus anthracis; Ml), IAA production: 10.81 μg mL−1 (Paenibacillus taichungensis; M10) and phosphate solubilization: 134.483 μg mL−1 (Paenibacillus xylanilyticus; M15) significantly increased root length (RL), shoot length (SL), number of lateral roots (NLR) and plant dry weight (DW) when inoculated/co inoculated with E. adhaerens (native rhizobia) to V. radiata in a small field trial. M10 inoculation produced longest RL while Ml when coinoculated with E. adhaerens produced highest SL and NLR. Ml inoculation or coinoculation was most effective in improving dry weight of mature plants. Most of the endophytes coinoculated with E. adhaerens improved growth parameters. We report that non rhizobial endophytes with PGP traits in combination with native rhizobia can be prospective candidates for use as biofertilizer.

Estimation of Plant Growth Promoting Potential of Two Nickel Accumulating Morphotypes Isolated from River Hooghly on Indian Yellow Mustard (Brassica hirta)

Plant growth promoting bacteria (PGPB) are known to influence plant growth by various direct or indirect mechanisms. Present study was conducted with an aim to estimate the PGPB potential of two nickel tolerant bacterial isolates from river Hooghly. Isolates (I-3) (Gram negative coccobacilli) and (II-1) (Gram positive rods) were observed, among a total of 22 other isolates, to tolerate and accumulate significant amounts of nickel and also have multiple Plant Growth Promoting (PGP) activities like IAA production and phosphate solubilization. Present study also shows that seeds of yellow mustard (Brassica hirta) inoculated with both the test isolates individually, significantly enhanced root and shoot growth and also protected the plant from the various phytotoxic effects of nickel.DOI: http://dx.doi.org/10.3126/ijasbt.v2i4.11107 Int J Appl Sci Biotechnol, Vol. 2(4): 413-419

Characterization of the antifungal and plant growth-promoting effects of diffusible and volatile organic compounds produced by Pseudomonas fluorescens strains

We analyzed the antifungal and plant growth-promoting (PGP) effects of diffusible and volatile organic compounds (VOCs) produced by new rhizospheric isolates. The bacterial strains were identified as Pseudomonas fluorescens UM16, UM240, UM256, and UM270, based on their complete 16S ribosomal gene sequencing. These pseudomonads showed a high degree of antagonism against the phytopathogen Botrytis cinerea during confrontation assays. In addition, all strains significantly increased Medicago truncatula biomass and chlorophyll content. Interestingly, these activities were exerted by the emission of either diffusible organic compounds or VOCs. During biocontrol experiments, the four P. fluorescens strains were able to protect M. truncatula plants from B. cinerea infection by reducing stem disease symptoms and root browning. The potential presence of phenazines, cyanogens, and ACC (1-aminocyclopropane-1-carboxylate) deaminase, as well as the production of biofilm, siderophores, proteases, and indole-3-acetic acid were identified in most of the strains. The VOCs emitted by all four Pseudomonas strains were similar, and sulfur-containing compounds were among the most abundant, including dimethyl disulfide. Interestingly, the strain UM270 was the only one that produced dimethylhexadecylamine, a compound with antifungal and PGP activities. In conclusion, the Pseudomonas strains analyzed here exert multiple antagonistic and PGP mechanisms, and represent an excellent option to be used as either biocontrol or biopromoting agents in crops.

Isolation and selection of fluorescent pseudomonads based on multiple plant growth promotion traits and siderotyping

Fluorescent pseudomonads, acclaimed plant associated bacterial group, are well-known plant growth promoting-biocontrol agents in rhizosphere arena. In this study, 144 fluorescent pseudomonad isolates from rhizosphere soil samples were screened with King's medium B supplemented with 8-hydroxyquinoline (8-HQ) chelator and comprehensively profiled for plant growth promotion viz., production of indole acetic acid (IAA), siderophore, ammonia, hydrogen cyanide, motility, phosphate solubilization, root growth promotion, and biofilm forming ability, along with two known control strains of pseudomonads. Iron and IAA regulated secondary metabolite siderophore production were investigated quantitatively. All isolates were positive for ammonia production and motility; 46% isolates were positive for hydrogen cyanide, 44% shown positivity for phosphate solubilization, and 40% isolates for siderophore production. Siderotyping showed production of hydroxamate type of siderophores which are known to be more efficient biocontrol agents. All isolates stimulated root growth to varying extent and had potentiality to form biofilms, a critical constituent for survival on different environments. Forty-two isolates of pseudomonads showed antagonistic behavior against the deleterious fungal pathogen Fusarium oxysporum (MTCC1755). Based on the above observations and statistical analysis, 11 isolates were shortlisted for further scrutiny. The study of biogeographic correlation and secondary metabolite profiling in association with plant growth promotion focalizes significant assessment on the behavior and antagonistic action, which probably brings out a competent biocontrol agent in a sustainable eco-friendly dimension.

Exploration of novel rhizospheric yeast isolate as fertilizing soil inoculant for improvement of maize cultivation.

Chemical input in agriculture is a common practice but makes a serious impact to the environment. In this context, soil isolates having multiple plant growth-promoting (PGP) attributes have been studied. The isolates were tested for their PO4 and Zn solubilization, indole-3-acetic acid (IAA) production and N2 fixation ability. The selected isolate SSm-39 was characterized to molecular level. The isolate SSm-39 was applied to maize cultivation in various combinations with chemical fertilizers. Also, the chemical and microbial status of soil, its effect on maize growth and yield were investigated. Isolate SSm-39 found most suitable for its PGP attributes and identified as Candida tropicalis. The inoculant (100%) with reduced dose of chemical fertilizer (T5) application notably increased the growth and yield performance of maize. It has improved grain quality by 85% as indicated by carbohydrate and protein content, in comparison to uninoculated control (T3). Soil nutrient status was found to increase twofold with T5 treatment compared with T3 treatment. Enhanced soil nutrient quality supported microbial growth and diversity, thus accelerating soil enzymatic activities. The results validate the multiple PGP traits of C. tropicalis SSm-39, advocating reduction of chemical fertilizer for maize cultivation.