Plant Growth-promoting Microorganisms Research Articles

Microbial Community Dynamics and Response to Plant Growth-Promoting Microorganisms in the Rhizosphere of Four Common Food Crops Cultivated in Hydroponics.

Plant growth promoting microorganisms (PGPMs) of the plant root zone microbiome have received limited attention in hydroponic cultivation systems. In the framework of a project aimed at the development of a biological life support system for manned missions in space, we investigated the effects of PGPMs on four common food crops (durum and bread wheat, potato and soybean) cultivated in recirculating hydroponic systems for a whole life cycle. Each crop was inoculated with a commercial PGPM mixture and the composition of the microbial communities associated with their root rhizosphere, rhizoplane/endosphere and with the recirculating nutrient solution was characterised through 16S- and ITS-targeted Illumina MiSeq sequencing. PGPM addition was shown to induce changes in the composition of these communities, though these changes varied both between crops and over time. Microbial communities of PGPM-treated plants were shown to be more stable over time. Though additional development is required, this study highlights the potential benefits that PGPMs may confer to plants grown in hydroponic systems, particularly when cultivated in extreme environments such as space.

Biochemical and Molecular Mechanisms of Plant-Microbe-Metal Interactions: Relevance for Phytoremediation.

Plants and microbes coexist or compete for survival and their cohesive interactions play a vital role in adapting to metalliferous environments, and can thus be explored to improve microbe-assisted phytoremediation. Plant root exudates are useful nutrient and energy sources for soil microorganisms, with whom they establish intricate communication systems. Some beneficial bacteria and fungi, acting as plant growth promoting microorganisms (PGPMs), may alleviate metal phytotoxicity and stimulate plant growth indirectly via the induction of defense mechanisms against phytopathogens, and/or directly through the solubilization of mineral nutrients (nitrogen, phosphate, potassium, iron, etc.), production of plant growth promoting substances (e.g., phytohormones), and secretion of specific enzymes (e.g., 1-aminocyclopropane-1-carboxylate deaminase). PGPM can also change metal bioavailability in soil through various mechanisms such as acidification, precipitation, chelation, complexation, and redox reactions. This review presents the recent advances and applications made hitherto in understanding the biochemical and molecular mechanisms of plant–microbe interactions and their role in the major processes involved in phytoremediation, such as heavy metal detoxification, mobilization, immobilization, transformation, transport, and distribution.

Plant Growth-Promoting Microorganisms for Environmental Sustainability

Agrochemicals used to meet the needs of a rapidly growing human population can deteriorate the quality of ecosystems and are not affordable to farmers in low-resource environments. Here, we propose the use of plant growth-promoting microorganisms (PGPMs) as a tool for sustainable food production without compromising ecosystems services.

Improving fertilizer-depot exploitation and maize growth by inoculation with plant growth-promoting bacteria: from lab to field

Among other responses, plants tend to increase root growth to scavenge nutrients from more soil when soil nutrient concentrations are low. Placement of fertilizers near seeds or roots facilitates nutrient acquisition by target crop plants. Nevertheless, nutrient uptake from soil-placed fertilizer-depots depends on increased uptake rates and efficient spatial exploitation of the depot by roots. The aim of our study was to optimize exploitation of subsurface fertilizer-depots by inoculating the depot zone with promising plant growth-promoting microorganisms (PGPMs) as bio-effectors. If included in depots, root-attracting NH4 + or HPO4 2−/H2PO4 − ions may also enhance rooting within the depot, which in turn improves survival and root colonization by inoculated PGPMs; a consequence of high levels of microbial nutrients exuded in densely rooted soil. We tested maize (Zea mays L.) in two greenhouse (pot and rhizobox) and two field experiments (2014 and 2015). A core treatment was NH4 +-fertilizer placed as a subsurface depot (Depot). In the field, there was also NH4 +-fertilizer broadcasted and incorporated in soil (Broad). Depot and Broad were each with PGPM as bio-effector (BE) or without (NoBE). Bio-effectors included: Pseudomonas sp. DSMZ 13134 (BE1) and Bacillus amyloliquefaciens FZB42 (BE2, only in field trials). In pots, Depot with BE1 led to 59 % higher shoot dry matter, 50 % higher shoot N content, and 64 % higher shoot P content than without PGPM. In rhizoboxes, higher root length density (RLD), lower rhizosphere pH, and higher BE1-colonization rate were measured in the fertilizer depot compared to the corresponding zone for controls with homogenous NO3 − supply. Depot led to higher shoot N and P concentrations (+26.6 % N; +20.6 % P) and contents (+11.1 % N; +17.6 % P) than control. BE1 led to higher shoot N concentration (+13.5 %) than NoBE. In the field, fertilizer-depot soil had higher RLD than corresponding non-depot soil. BE1 led to doubled fertilizer-depot RLD in comparison to without (2014). In 2014, Depot led to 7.4 % higher grain yield than Broad (not statistically significant), whereas BE broadcast had no effect. In 2015, Depot led to 5.8 % higher fresh shoot biomass than Broad, below-seed placement of BE1 led to higher fresh (+7.1 %) and dry (+8.0 %) shoot biomass than NoBE. Results show promising growth-effects of Pseudomonas sp. DSMZ 13134 on field-grown maize.

Micronutrient enrichment mediated by plant-microbe interactions and rice cultivation practices

ABSTRACTA field experiment was conducted to evaluate the effect of different plant growth promoting microorganisms (PGPM) on micronutrient enrichment of rice crops grown under conventional (flooded) and SRI (System of Rice Intensification) practices. Significant differences were recorded among treatments and cultivation practices in terms of soil microbial activity reflected in enhanced nutrient uptake, enzyme activity, and yield. The Anabaena-based biofilm inoculants were particularly superior under both methods of cultivation, leading to 13–46% enhancement of iron and 15-41% enhancement of zinc in rice grains over uninoculated controls. SRI was found to be superior in terms of enhancing the concentration of zinc, copper, iron, and manganese (Zn, Cu, Fe and Mn), particularly in grains, and significant in increasing the activity of defense- and pathogenesis- related enzymes and yield parameters. This study illustrates the utility of cyanobacteria-based inoculants for both methods of rice cultivation and their significant interactions with the plant, leading to micronutrient enrichment of rice grains. Such formulations can complement the current biofortification strategies and help in combating the problems of malnutrition globally.

A need for disclosure of the identity of microorganisms, constituents, and application methods when reporting tests with microbe-based or pesticide-based products

Plant growth-promoting microorganisms, biological control agents, pesticides, and a variety of stimulants to enhance plant performance are commonly tested and commercially applied worldwide on increasing scales each year (Bashan et al. 2014; Calvo et al. 2014; Lugtenberg and Kamilova 2009). In recent years, inoculation of plants with microorganisms to enhance productivity has become widespread, with more sophisticated and complex formulations and application methods. These formulations use a variety of application techniques, such as using natural and synthetic polymers or add more than one microorganism to the inoculants. These microbial consortia in inoculants may have over ten different microorganisms. Inoculants may have synthetic vitamins, plant hormones, and humic and fulvic acids. Other inoculants add different plant or algae or seaweed extracts, protein hydrolytes and amino acids as stimulants, as well as bulking materials, such as clays, minerals (vermiculite and perlite), talcum, or undisclosed soil fractions. Numerous adhesives, surfactants, stabilizing and dispersing materials, and preservatives to enhance survival and dispersal of the microorganisms are commonly added. The identity of these components in microbial formulations is often not disclosed in the product label. Specific details of application are usually explained by the manufacturer on the container label, but rarely in a formal publication. As product formulations change, performance of bacterial strains in the product may change. Hence, it might not be possible to objectively compare the effects of an inoculated microorganism in laboratory experiments with the effects of the same microbe in a commercial formulation. This results from some components in the formulations having synergistic bioactivities that are greater than a single strain of microorganism. As an example, the plant growth-promoting bacterium Azospirillum brasilense strain AZ39 is one of the most common Azospirillum strains used in Latin America. Yet, its performance significantly varies, depending on the specific formulation and the method of inoculation. Similar phenomenon occurs with rhizobia. Pesticides are commonly used in agriculture and are classified, according to the pest organism, in insecticides, fungicides, herbicides (weeds killers), nematocides, and rodenticides. The first three pesticides are those most used. Pesticides differ greatly for their chemical structures, and this result in a great variety of toxicological properties, most of them contain aromatic rings and some are chlorinated, just to mention a few chemical characteristics. Field rates depend on several factors including soil type (Bremner and Mulvaney 1976; Cervelli et al. 1976). Usually, pesticides are applied in formulations containing several other constituents often not disclosed in the product label, as mentioned above for the microbial inocula. These additives may include solvents, by-products of the target compounds, salts, chemical vehicles of the target compound, etc. Obviously toxicological studies of the target pesticide should also consider the effect of all other constituents; these effects may be synergic or antagonist with those by the target pesticide (Cervelli et al. 1976). * Yoav Bashan ybb0001@auburn.edu

Effect of Piriformospora indica and Azotobacter chroococcum on mitigation of zinc deficiency stress in wheat (Triticum aestivum L.)

Zinc deficiency is a global nutritional problem in agricultural soils in large number of countries, causing decreased crop yields and grain nutritional quality. This study was conducted to investigate the effect of individual and co-inoculation of two plant-growth-promoting microorganisms (PGPMs); Azotobacter chroococcum and Piriformospora indica; on some physiological traits such as uptake of mineral nutrients, antioxidant enzyme activities, photosynthetic pigments, lipid peroxidation in leaves of wheat plants under Zn deficiency conditions. Bacterial treatment either alone or in combination with P. indica, significantly increased shoot and root biomass compared to non-inoculated controls under Zn deficiency conditions. Highest levels of Zn and P and also chlorophyll (a & b) and carotenoid concentrations were recorded in P. indica- inoculated plants both under Zn-sufficient and - deficient conditions. Individual and co-inoculation of A. chroococcum with P. indica caused a significant decrease in Fe and P concentrations in shoot compared with the control treatment. MDA (Malondialdehyde) content of inoculated plants with all microbial treatments was lower than in leaves of corresponding non-inoculated plants under Zn-deficiency conditions. Ascorbate peroxidase and peroxidase activity of inoculated plants with A. chroococcum and A. chroococcum + P. indica were higher than the other treatments under Zn-deficient conditions. Also, activity of peroxidase enzyme was induced in endophyte-inoculated plants, while ascorbate peroxidase activity was declined in such conditions. Generally, the studied microbial treatments, particularly A. chroococcum, can be proposed as a useful tool for alleviating Zn deficiency stress in sensitive plants to zinc deficiency.

PGPM-induced defense-related enzymes in aerobic rice against rice leaf blast caused by Pyricularia oryzae

Rice blast caused by Pyricularia oryzae is the most devastative disease especially under aerobic cultivation systems. The bio-efficacy of plant growth-promoting microorganisms: Pseudomonas aeruginosa (UPMP1), Corynebacterium agropyri (UPMP7), Enterobacter gergoviae (UPMP9) and Bacillus amyloliquefaciens (UPMS3), Trichoderma harzianum (UPMT1) and Trichoderma virens (UPMT2) in induction of defense-related enzymes against Pyricularia oryzae was evaluated in rice cultivated under aerobic conditions. Under dual culture plate testing, all PGPMs indicated antagonism against P. oryzae with percentage inhibition radial growth (PIRG) which ranged from 51.69–81.97 %. The bio-efficacy of the respective PGPM in induction of defense-related enzymes in rice seedlings was evaluated based on individual inoculation before challenged inoculation with P. oryzae under greenhouse conditions. Inoculation of all PGPMs significantly reduced rice leaf blast severity at day eight after P. oryzae inoculation. The reduction in rice leaf blast disease severity was associated to the increase of peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities in rice seedlings when pre-inoculated with PGPMs. The highest leaf blast disease reduction (59.17 %) occurred with rice seedlings pre-inoculated with C. agropyri (UPMP9), followed by P. aeruginosa (UPMP1) (40.65 %), T. harzianum (UPMT1) (42.23 %), T. virens (UPMT2) (20.85 %), E. gergoviae (UPMP9) (17.84 %) and B. amyloliquefaciens (UPMS3). The high efficiency of PGPM in leaf blast disease suppression was associated with significant increase in total microbial activity (FDA hydrolysis) in rhizosphera soil (4.80–7.86 μg/g/0.5 h) compared to the control (2.25 μg/g/0.5 h). Thus, the application of PGPM is a potential alternative approach in rice leaf blast disease management of aerobic rice.

Development of Microbial-Fortified Rice Straw Compost to Improve Plant Growth, Productivity, Soil Health, and Rice Blast Disease Management of Aerobic Rice

In aerobic rice cultivation systems, compost mulching and incorporation are important to rehabilitate the soil. Microbial-fortified compost is increasingly accepted as a safe approach in agro-waste management to recycling of crop residuals in agriculture soil and also to promote growth and suppress disease. This study aims to examine the stability and viability of the selected plant growth-promoting microorganisms (PGPM) in rice straw compost (RSC) over incubation period and its bio-efficacy in promoting rice (Oryza sativa) plant growth, productivity, soil health, and controlling of Pyricularia oryzae in aerobic cultivation conditions. Six selected PGPM: Pseudomonas aeruginosa (UPMP1), Corynebacterium agropyri (UPMP7), Enterobacter gergoviae (UPMP9), Bacillus amyloliquefaciens (UPMS3), Trichoderma harzianum (UPMT1), and Trichoderma virens (UPMT2) were used as a consortium of microbial inoculants to develop the microbial-fortified rice straw compost (MRSC). The MRSC was incorporated into mineral soil used for aerobic rice cultivation and its bio-efficacy was evaluated at harvest. The viability of Trichoderma spp. found stabilized at 6.78–6.00 log cfu/g and declined for all the bacterial isolates. At harvest, soil amended with MRSC significantly increased in plant height, leaf area index, 1000 grain weight, and productivity. The MRSC amended plots had significant low in rice blast disease severity with area under disease progress curve (AUDCP) of 748.22 unit/square, as compared to control (1782.67 unit/square). The physicochemical and microbiological properties of soil amended with MRSC were improved at harvest. The application of MRSC has potential to improve plant growth, productivity, rice blast disease management, and soil health of rice under aerobic cultivation systems.

Metabolomics Suggests That Soil Inoculation with Arbuscular Mycorrhizal Fungi Decreased Free Amino Acid Content in Roots of Durum Wheat Grown under N-Limited, P-Rich Field Conditions

Arbuscular mycorrhizal fungi (AMF) have a major impact on plant nutrition, defence against pathogens, a plant’s reaction to stressful environments, soil fertility, and a plant’s relationship with other microorganisms. Such effects imply a broad reprogramming of the plant’s metabolic activity. However, little information is available regarding the role of AMF and their relation to other soil plant growth—promoting microorganisms in the plant metabolome, especially under realistic field conditions. In the present experiment, we evaluated the effects of inoculation with AMF, either alone or in combination with plant growth–promoting rhizobacteria (PGPR), on the metabolome and changes in metabolic pathways in the roots of durum wheat (Triticum durum Desf.) grown under N-limited agronomic conditions in a P-rich environment. These two treatments were compared to infection by the natural AMF population (NAT). Soil inoculation with AMF almost doubled wheat root colonization by AMF and decreased the root concentrations of most compounds in all metabolic pathways, especially amino acids (AA) and saturated fatty acids, whereas inoculation with AMF+PGPR increased the concentrations of such compounds compared to inoculation with AMF alone. Enrichment metabolomics analyses showed that AA metabolic pathways were mostly changed by the treatments, with reduced amination activity in roots most likely due to a shift from the biosynthesis of common AA to γ-amino butyric acid. The root metabolome differed between AMF and NAT but not AMF+PGPR and AMF or NAT. Because the PGPR used were potent mineralisers, and AMF can retain most nitrogen (N) taken as organic compounds for their own growth, it is likely that this result was due to an increased concentration of mineral N in soil inoculated with AMF+PGPR compared to AMF alone.

The Role of Biofertilization in Improving Apple Productivity―A Review

Biofertilization of crops with plant growth promoting microorganisms is currently considered as a healthy alternative to chemical fertilization. Biofertilizers are microbial preparations containing living cells of different microorganisms which have the ability to mobilize plant nutrients in soil from unusable to usable form. They are environmentally friendly, play a significant role in the crop production, help to build up the lost microflora and improve the soil health. Also, they increase crop yield by 20% - 30%, stimulate plant growth, are cost effective and provide optimal conditions for soil biological activity. They suppress pathogenic soil organisms, restore natural soil fertility and provide protection against drought and some soil borne diseases. Moreover, they degrade toxic organic chemicals, improve seed germination and aid in balancing soil pH in reducing soil erosion.

Morphoanatomical and Biochemical Changes in the Roots of Rice Plants Induced by Plant Growth-Promoting Microorganisms

The goal of the present study was to characterize anatomical and biochemical changes in rice plant roots in response to seed treatment with rhizobacteria (Burkholderia pyrrocinia(R-46) +Pseudomonas fluorescens(R-55)) andTrichoderma asperellum(Ta: mixture of strains T-06, T-09, T-12, and T-52). The experimental design was completely randomized, with six treatments (R-46, R-55, R-46 + R-55, Ta+ R-46 + R-55, Ta, and control) and ten replicates. Treatments Ta and R-46 + R-55 increased the root length and diameter as well as the cortex expansion and induced a 2% expansion of the aerenchymal space. Treatments Ta and R-46 increased the vascular cylinder diameter. The number of protoxylem poles and metaxylem vessel elements was increased by R-46 and R-55. The total phenol content increased with treatments Ta, R-46 + R-55, R-46, and R-55, and all the treatments increased the flavonoid content. The lignin content increased with the Ta and R-55 treatments. All the root architecture modifications resulting from the interaction between seedlings and bioagents (rhizobacteria andTrichodermaspp.) observed in the present study favored the root plasticity of rice seedlings.

Cucumber performance is improved by inoculation with plant growth-promoting microorganisms

We investigated the effects of inoculation of Rhodobacter sphaeroides, Lactobacillus plantarum, and Saccharomyces cerevisiae on cucumber plant growth promotion and on the contents of plant hormones, amino acids, and mineral nutrients. We showed that treatment with all three bio-inoculants significantly increased the shoot length, root length, shoot fresh weight, shoot dry weight, and chlorophyll content, via secretion of indole acetic acid and/or organic acids. Inoculation with R. sphaeroides had more favorable effect on plant growth than did inoculation with L. plantarum or S. cerevisiae, by significantly enhancing the gibberellin and reducing the abscisic acid contents. The results of amino acid analysis revealed that inoculation with R. sphaeroides, L. plantarum, and S. cerevisiae generally increased the contents of 17 amino acids, namely, aspartic acid, threonine, serine, glutamic acid, glycine, alanine, cysteine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline. With the exception of cysteine, all these amino acids were present in higher concentrations in plants inoculated with R. sphaeroides than in control plants or in plants inoculated with L. plantarum and S. cerevisiae. Furthermore, inoculation with R. sphaeroides significantly increased the calcium, potassium, magnesium, and phosphate contents. Our results suggest that the use of R. sphaeroides, L. plantarum, and S. cerevisiae in agricultural fields can improve plant growth. Moreover, inoculation of cucumber plants with R. sphaeroides regulates plant functional metabolites, thereby promoting plant growth.

New insights into 1-aminocyclopropane-1-carboxylate (ACC) deaminase phylogeny, evolution and ecological significance.

The main objective of this work is the study of the phylogeny, evolution and ecological importance of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, the activity of which represents one of the most important and studied mechanisms used by plant growth–promoting microorganisms. The ACC deaminase gene and its regulatory elements presence in completely sequenced organisms was verified by multiple searches in diverse databases, and based on the data obtained a comprehensive analysis was conducted. Strain habitat, origin and ACC deaminase activity were taken into account when analyzing the results. In order to unveil ACC deaminase origin, evolution and relationships with other closely related pyridoxal phosphate (PLP) dependent enzymes a phylogenetic analysis was also performed. The data obtained show that ACC deaminase is mostly prevalent in some Bacteria, Fungi and members of Stramenopiles. Contrary to previous reports, we show that ACC deaminase genes are predominantly vertically inherited in various bacterial and fungal classes. Still, results suggest a considerable degree of horizontal gene transfer events, including interkingdom transfer events. A model for ACC deaminase origin and evolution is also proposed. This study also confirms the previous reports suggesting that the Lrp-like regulatory protein AcdR is a common mechanism regulating ACC deaminase expression in Proteobacteria, however, we also show that other regulatory mechanisms may be present in some Proteobacteria and other bacterial phyla. In this study we provide a more complete view of the role for ACC deaminase than was previously available. The results show that ACC deaminase may not only be related to plant growth promotion abilities, but may also play multiple roles in microorganism's developmental processes. Hence, exploring the origin and functioning of this enzyme may be the key in a variety of important agricultural and biotechnological applications.

Effects of plant-growth-promoting microorganisms and fertilizers on growth of cabbage and tomato and Spodoptera litura performance

Fertilizer and plant-growth-promoting microorganisms (PGPMs) both benefit crop growth; however, little is known about the interaction effects when they are combined. This study assessed the effect of PGPMs and fertilizer on plant growth, foliar chemistry, and subsequent insect feeding. Cabbage and tomato plants were inoculated with PGPMs (fungi and bacteria) and various levels of fertilization. Plant growth parameters (fresh weight, dry weight, and leaf area) and foliar chemistry (water content, protein content, and polyphenol oxidase activity) were then analyzed. In addition, foliage was also fed to the third instar larvae of Spodoptera litura to evaluate foliage quality. The results indicated that plant performance differed significantly among treatments, and the combined fungi Meyerozyma guilliermondii and fertilizer treatment promoted the greatest plant growth. In summary, PGPMs and fertilization can have their own effect; their interaction effect, however, need to be clarified.

Combined use of Alkane-Degrading and Plant Growth-Promoting Bacteria Enhanced Phytoremediation of Diesel Contaminated soil

Inoculation of plants with pollutant-degrading and plant growth-promoting microorganisms is a simple strategy to enhance phytoremediation activity. The objective of this study was to determine the effect of inoculation of different bacterial strains, possessing alkane-degradation and 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase activity, on plant growth and phytoremediation activity. Carpet grass (Axonopus affinis) was planted in soil spiked with diesel (1% w/w) for 90 days and inoculated with different bacterial strains, Pseudomonas sp. ITRH25, Pantoea sp. BTRH79 and Burkholderia sp. PsJN, individually and in combination. Generally, bacterial application increased total numbers of culturable hydrocarbon-degrading bacteria in the rhizosphere of carpet grass, plant biomass production, hydrocarbon degradation and reduced genotoxicity. Bacterial strains possessing different beneficial traits affect plant growth and phytoremediation activity in different ways. Maximum bacterial population, plant biomass production and hydrocarbon degradation were achieved when carpet grass was inoculated with a consortium of three strains. Enhanced plant biomass production and hydrocarbon degradation were associated with increased numbers of culturable hydrocarbon-degrading bacteria in the rhizosphere of carpet grass. The present study revealed that the combined use of different bacterial strains, exhibiting different beneficial traits, is a highly effective strategy to improve plant growth and phytoremediation activity.

Inoculation with Pseudomonas putida PCI2, a phosphate solubilizing rhizobacterium, stimulates the growth of tomato plants

The use of phosphate solubilizing plant growth-promoting microorganisms as inoculants assists in the hydrolysis of insoluble forms of phosphorus leading to increased plant growth. Pseudomonas putida PCI2 was evaluated for phosphatase activity and solubilization of AlPO4 and FePO4. The effect of different incubation temperatures, concentrations of NaCl and different pH on growth of PCI2 and P solubilization was studied. PCI2 proved to be positive for phosphatase activity, solubilized AlPO4 and hydrolyzed Ca3(PO4)2 even in medium with 5 % NaCl. In addition, PCI2 produced 45 % units of siderophores. The production of IAA by PCI2 was stimulated in vitro by the addition of different concentrations of L-tryptophan to the culture medium. Assays with tomato seedlings showed that the length of the root was reduced as the concentration of IAA increased. On the other hand, inoculation with PCI2 caused a clear growth-promoting effect on shoot growth in the presence of L-tryptophan. P. putida PCI2 is adapted to different environmental conditions and has potential to be developed and used as an inoculant for increasing the growth of tomato plants.

Up to 52 % N fertilizer replaced by biofertilizer in lowland rice via farmer participatory research

Rice production needs to rise substantially without increasing inputs such as chemical fertilizers to feed the world’s growing population in a sustainable manner. In this regard, plant growth-promoting microorganisms, formulated as inoculant biofertilizers, show strong potential by improving nutrient use efficiency. However, the practical use of biofertilizers by farmers remains limited because of inconsistent results under field conditions. We hypothesized that biofertilizer performance depends on the amount and type of chemical fertilizer applied in concert with the biofertilizer and that such knowledge can improve inoculation efficacy. Farmer participatory field experiments were conducted at 20 different farms from two localities in the Vietnamese Mekong Delta over four growing seasons. On each farm, one half of a split-plot was treated with chemical fertilizer at conventional rates. The remaining area was given only 50–80 % of the usual chemical fertilizer rates but supplemented with the commercial biofertilizer BioGro containing four plant growth-promoting microorganisms. Our results demonstrate that the biofertilizer can replace between 23 and 52 % of nitrogen (N) fertilizer without loss of yield but cannot substitute for phosphorus (P) fertilizer. In addition, we found that up to 45 % of the variability in biofertilizer performance is related to the amount and timing of N, P, and K fertilizers applied to the crop. Importantly, the yield response to both biofertilizer and N fertilizer is strongly affected by the seasonal growing conditions. Overall, our findings show for the first time that farmer participatory experiments can be used to increase the efficacy of biofertilizers through manipulating chemical fertilizer inputs. This new information will accelerate the uptake of biofertilizer technology if managed correctly.

1-Aminocyclopropane-1-Carboxylate Deaminase from Pseudomonas fluorescens Promoting the Growth of Chinese Cabbage and Its Polyclonal Antibody

Bacterial 1-aminocyclopropane-1-carboxlyate (ACC) deaminase (AcdS) is an enzyme that cleaves ACC, a precursor of the plant hormone ethylene, into α-ketobutyrate and ammonia. The acdS gene was cloned from Pseudomonas fluorescens, which was capable of improving the seedling of Chinese cabbage under salinity condition. The recombinant AcdS (rAcdS) exhibited optimal activity at pH 8.5 and 30°C. Strong activity was sustained at up to 100 mM NaCl. The polyclonal anti-P. fluorescens AcdS antibody was produced in a rabbit that had been immunized with the purified rAcdS. This antibody successfully recognized the homologous antigens derived from the total proteins of isolated plant growth-promoting microorganisms. A statistically significant correlation was observed between the intensity of hybridization signal and AcdS activity measured by a biochemical method, suggesting its application as a useful indicator for active deaminases.

Investigating the Role of PGPM in Assisting Plant Growth Under Stress Caused by Organophosphate Pesticide- Phorate

Farmers across the world face the challenge of compromised agriculture productivity due to abiotic stress. Residual pesticides accumulating in the soil rhizospere are often found to cause a chemical imbalance in the soil microclimate resulting in chemical toxicity and osmotic stress. Plant growth promoting microorganisms (PGPM) are popularly studied for their ability to enhance plant growth by providing stress tolerance to plants. The present study is to investigate the role of PGPM in reducing toxicity caused due to accumulation of organophosphate pesticide (OPP) - Phorate. Isolation, evaluation and selection of best phorate tolerant PGPM strains was done by various rounds of purification and biochemical characterization assays. Isolates of PGPM from the rhizospere of Pearl Millet-PB, Maize PM, Pigeon Pea-PA, Sugarcane-PS and Sorghum-PJ were studied for their ability to tolerate a wide range of OPP (150 ppm to 1050 ppm). Subsequently, in vitro plant bioassay was performed to select the isolate that can provide best growth promotion property to host plant when challenged with pesticide phorate. The parameters studied to evaluate growth promotion abilities were percentage germination, seed vigor and total biomass. We were successful in isolating, evaluating and selecting best PGPM strains for providing tolerance to host plant under phorate induced stress. Out of the four isolates tested, isolates PM and PB showed better tolerance to phorate and recorded higher LD50 and MIC values as compared to other isolates. When compared with control, OPP stress subjected PM and PB showed best tolerance to OPP with LD50 981 ppm/unit OD and 1249 ppm/unit respectively and MIC values as 1050 ppm. However from the plant bioassay it was evident that between PM and PB, PM was a better bioinoculant as it contributed to plant growth with respect to all studied parameters (viz. percentage germination and seed vigor) where as PB stood as second best at providing growth support to host plants when challenged with phorate. Culture isolate PM emerged as the choicest isolate that can be further explored as a potential bioinoculant under pesticide stressed conditions. Isolate PB, with comparable pesticide tolerance (very near MIC & LD50 values) as PM, was clearly outcompeted by PM when it came to supporting plant growth (evident from in vitro plant bioasaay). A Culture having high pesticide tolerance under in vitro conditions, may or may not possess the ability to support plant growth when used as a bioinoculant at high pesticide concentrations. The study clearly emphasizes the importance of host response studies for making selection of rhizobacteria for the purpose of remediating pesticides. PB with comparable pesticide tolerance with PM under in vitro conditions was clearly outcompeted by PM when it came to supporting plant growth (as evident from results of plant bioasaay). The study offers proof that, inoculation with carefully selected pesticide tolerant PGPM can have a positive impact on plant growth even under high concentration of organophosphate pesticides. © 2015 iGlobal Research and Publishing Foundation. All rights reserved. NOTE: Full length manuscript of Gupta et al. Investigating the Role of PGPM in Assisting Plant Growth