Rhizosphere Microbial Populations Research Articles

Rhizosphere microbial biomass is affected by soil type, organic and water inputs in a bell pepper system

Effects of environmental and management factors on the diversity and abundance of rhizosphere microbes in unmanaged ecosystems are well established. However, there is limited information about these interactions in vegetable cropping systems. In this two-year field study, we used organic amendments (humic substances, HS) and water supply (deficit irrigation) as soil management factors to characterize changes in bell pepper rhizosphere microbial population under two distinct soil types (clay and sandy). Path analysis revealed that soil type was the main factor constructing the microbial population. Clay soil indirectly increased bacterial biomass through the changes in root length, soil pH, P and K contents, while increased fungal biomass was linked with the enhanced above-ground plant yield. As organic inputs, HS had long-term positive influences on soil microbial activity through improvements in soil organic carbon content, which was also positively correlated with bacterial population. Water input became a less influential factor – deficit irrigation indirectly decreased fungal biomass but increased soil respiration through the reduction in pepper yield. These findings provide a better understanding of external factors controlling the abundance of rhizosphere microbiota under intensively managed cropping systems, and potential strategies to improve beneficial microbial diversity and soil health.

Biodiversitas Mikroba Rizosfer Tanaman Jeruk Keprok Borneo Prima (Citrus reticulata cv Borneo Prima)

Borneo Prima tangerine (Citrus reticulata cv Borneo Prima) is an indigenous plant from Tanjung Labu Village, Rantau Pulung District, East Kutai District, East Kalimantan Province. In the cultivation of these plants, there are pathogens that can cause a decrease in crop yields. This study aims to identify the diversity of rhizosphere microbial populations in Borneo Prima tangerine plants. The study was conducted at the Laboratory of Plant Pests and Diseases of the Faculty of Agriculture, Mulawarman University Samarinda in February-April 2018. This study was descriptive, using a survey method. The study consisted of two stages, namely (1) soil sampling on Borneo Prima tangerine citrus land in Makroman Village, Kutai Kartanegara Regency, East Kalimantan (2) isolation, characterization, identification, gram test, in the Laboratory of Pests and Plant Diseases. The data obtained were analyzed using quantitative descriptive analysis. The results of the study of the isolation of rhizosphere microbes in Borneo Prima tangerine citrus plants obtained 1 family of bacteria namely Azotobacteraceae and 4 fungal genera including Aspergilus, Mucor, Penicillium and Trichoderma. Microbes that belong to the group that benefit the soil ecosystem are Azotobacteraceae because they play a role in fixing (fixation) N2 or as biofertilizers. While the genus Mucor and Penicillium act as decomposers and Trichoderma acts as a controller of pathogens or biological agents and biological pesticides (biopestiside).

Effective Role of Beneficial Microbes in Achieving the Sustainable Agriculture and Eco-Friendly Environment Development Goals: A Review

Agriculture have a significant portion of the economies of world and therefore can contribute toward major continental priorities such as eradicating poverty, hunger, rapid industrialization, economic diversification, sustainable resource utilization, investments, and environmental management. Plant-associated microbiomes have tremendous potential to improve plant resilience and yields in farming systems. There is increasing evidence that biological technologies that use microbes or their metabolites can enhance nutrient uptake and yield, control pests and mitigate plant stress responses. Microbiological achievements of recent years have emerged as powerful tool to improve quality attributes of sustainable agriculture and environmental health. The chemical fertilizers used in the agriculture to increase yields but kill microflora, pests, and weeds, it have a big harmful impact on the ecosystem. Because of current public concerns about the side effects of agrochemicals, there is an increasing interest in improving the understanding of cooperative activities among plants and rhizosphere microbial populations. The review deals with microbes in biotechnology and their diversified applications in agriculture as bio-fertilizers, bio-pesticides, bio-herbicides, bio-insecticides, fungal based bio-insecticides and viral based bio-insecticides. Finally, a brief highlight has been given on the role of microbiology on development of sustainable agriculture and environment friendly approach to increase crop production and environmental health.

Rhizosphere Microbial Population and Plant Species Diversity as Influenced by Chromolaena odorata Invasion

Invasive plant species have been commonly implicated to cause loss in plant species diversity. Attention had however not been paid to the effects of these species loss on the soil microbiome. A study was conducted in 18 farmers’ fields within three states in southwestern Nigeria to examine the effect of Siam weed (Chromolaena odorata) invasion on native plant diversity as well as on the rhizosphere microbial population using randomized complete block design. Results indicated significant losses in plant species diversity and reduction in density per square meter compared with adjacent non infested fields. Results further showed C. odorata invasion exerted diverse influence on soil microbial population. Relationships were subsequently established among plant density, species diversity; and soil microbial population. Further studies were also recommended to accommodate more microbiological indices.

Effect of inoculation with nitrogen-fixing bacterium Pseudomonas stutzeri A1501 on maize plant growth and the microbiome indigenous to the rhizosphere

Plant growth promoting diazotrophs with the ability to associate with plant roots are in common use as inoculants to benefit crop yield and to mitigate chemical nitrogen fertilization. However, limited information is available in understanding to what extent the plant growth-promoting effect of the inoculum has on the plant’s nitrogen acquisition as well as on the impact of inoculation on the indigenous rhizosphere microbial population. Here we reported on experiments that assessed how endophytic Pseudomonas stutzeri A1501 inoculated on maize improved plant growth and plant nitrogen content using a 15N dilution technique under two water regime conditions. The effects of inoculation and different water regimes were also assessed for the maize rhizospheric and surface soil communities by MiSeq community sequencing combined with qPCR of functional genes and transcripts (nifH and amoA) related to nitrogen cycling. Results support maize inoculated with P. stutzeri A1501 grew better and accumulated more nitrogen with a lower δ15N signature after 60 days than did plants inoculated with nifH-mutant and sterilized A1501 cells (non N2-fixing controls). Inoculant contribution to the plant was estimated to range from 0.30 to 0.82g N/plant, depending on water conditions. Inoculation with P. stutzeri A1501 significantly altered the composition of the diazotrophic community that P. stutzeri became dominant in the rhizosphere, and also increased the population of indigenous diazotrophs and ammonia oxidizers and functional genes transcripts. Redundancy analysis revealed that soil compartment and A1501 inoculation treatments were the main factors affecting the distribution of the diazotrophic community.

Plant-microbe interactions endorse growth by uplifting microbial community structure of Bacopa monnieri rhizosphere under nematode stress

The modification of rhizosphere microbial diversity and ecological processes are of rising interest as shifting in microbial community structure impacts the mutual role of host–microbe interactions. Nevertheless, the connection between host-microbial community diversity, their function under biotic stress in addition to their impact on plant performances is poorly understood. The study was designed with the aim to analyze the tripartite interactions among Chitiniphilus sp., Streptomyces sp. and their combination with indigenous rhizospheric microbial population of Bacopa monnieri for enhancing the plant growth and bacoside A content under Meloidogyne incognita stress. Overall, plants treated with the microbial combination recorded enhanced growth as illustrated by significantly higher biomass (2.0 fold), nitrogen uptake (1.8 fold) and bacoside A content (1.3 fold) along with biocontrol efficacy (58.5%) under nematode infected field. The denaturing gradient gel electrophoresis (DGGE) fingerprints of 16S-rDNA revealed that microbial inoculations are major initiators of bacterial community structure in the plant rhizosphere. Additionally, the plants treated with microbial combination showed maximum diversity viz., Shannon’s (3.29), Margalef’s (4.21), and Simpson’s (0.96) indices. Likewise the metabolic profiling data also showed a significant variation among the diversity and evenness indices upon microbial application on the native microflora. We surmise that the application of beneficial microbes in combinational mode not only helped in improving the microbial community structure but also successfully enhanced plant and soil health under biotic stress.

Isolation of actinomycetes from maize rhizosphere from Kupang, East Nusa Tenggara Province, and evaluation of their antibacterial, antifungal, and extracellular enzyme activity

Actinomycetes are the one of the components of the rhizospheric microbial population and useful for producing secondary metabolites such as lytic enzymes, antibiotics, and antifungal. The aim of the study was to isolate the actinomycetes from maize rhizosphere collected from Kupang, East Nusa Tenggara. The screening was focused on the actinomycetes that showed the ability to produce antibacterial, antifungal, and extracellular enzymes such as amylase, cellulase, and protease. The actinomycetes were isolated using Humic-Acid Vitamin B (HV) agar media. The antagonistic assay was tested against Escherichia coli, Staphylococcus aureus, Sclerotium rolfsii and Fusarium oxysporum. Isolate JKP-8 was an isolate that showed the highest activity in inhibiting the growth of E. coli and S. aureus bacteria. Isolate JKP-5 showed the highest activity in inhibiting the growth of F.oxysporum. There were no actinomycetes isolates that showed an ability to inhibit the growth of S. rolfsii fungus based on dual culture assay. JKP-3 and JKP-4 isolates exhibited the highest ability to hydrolyze amylum, while JKP-5 and JKP-8 isolates exhibited the highest ability to hydrolyze CMC. The results of the amplification of 16S rRNA gene in selected potential isolates JKP 5 and JKP 8 indicated that both isolates belong to the genus Streptomyces.

Trichoderma-Based Biostimulants Modulate Rhizosphere Microbial Populations and Improve N Uptake Efficiency, Yield, and Nutritional Quality of Leafy Vegetables.

Microbial inoculants such as Trichoderma-based products are receiving great interest among researchers and agricultural producers for their potential to improve crop productivity, nutritional quality as well as resistance to plant pathogens/pests and numerous environmental stresses. Two greenhouse experiments were conducted to assess the effects of Trichoderma-based biostimulants under suboptimal, optimal and supraoptimal levels of nitrogen (N) fertilization in two leafy vegetables: Iceberg lettuce (Lactuca sativa L.) and rocket (Eruca sativa Mill.). The yield, nutritional characteristics, N uptake and mineral composition were analyzed for each vegetable crop after inoculation with Trichoderma strains T. virens (GV41) or T. harzianum (T22), and results were compared to non-inoculated plants. In addition, the effect of the Trichoderma-based biostimulants on microbes associated with the rhizosphere in terms of prokaryotic and eukaryotic composition and concentration using DGGE was also evaluated. Trichoderma-based biostimulants, in particular GV41, positively increased lettuce and rocket yield in the unfertilized plots. The highest marketable lettuce fresh yield was recorded with either of the biostimulant inoculations when plants were supplied with optimal levels of N. The inoculation of rocket with GV41, and to a lesser degree with T22, elicited an increase in total ascorbic acid under both optimal and high N conditions. T. virens GV41 increased N-use efficiency of lettuce, and favored the uptake of native N present in the soil of both lettuce and rocket. The positive effect of biostimulants on nutrient uptake and crop growth was species-dependent, being more marked with lettuce. The best biostimulation effects from the Trichoderma treatments were observed in both crops when grown under low N availability. The Trichoderma inoculation strongly influenced the composition of eukaryotic populations in the rhizosphere, in particularly exerting different effects with low N levels in comparison to the N fertilized plots. Overall, inoculations with Trichoderma may be considered as a viable strategy to manage the nutrient content of leafy horticulture crops cultivated in low fertility soils, and assist vegetable growers in reducing the use of synthetic fertilizers, developing sustainable management practices to optimize N use efficiency.

Populasi Bakteri Dan Jamur Pada Rizosfer Caisim (Brassica juncea L.) Yang Ditanam Di Tanah Dikontaminasi Insektisida Organoklorin Setelah Aplikasi Konsorsia Mikroba Dan Kompos

Organochlorine insecticide was banned for agriculture but nowadays its residue was still found in some agricultural soil. One of ways to lowering organochlorine residue in soil is by used of degrading-organochlorine microbial consortia accompanied with compost application. However, application of exogenous microbes might affect bacterial and fungal population in soil. The pot experiment has been set up to verify the influence of Pseudomonas mallei and Trichoderma sp. and compost on total bacteria and fungi on rhizosphere of Cai Sim (Brassica juncea L.) grown on Andisols which were contaminated with organochlorine insecticide of heptachlor, endosulfan, dieldrin and DDT. Experimental design was Factorial Randomized Block Design with three replicates. The first factor was microbial consortia of P.mallei and Trichoderma sp., and the second one was kind of compost. The result showed that effect of microbial consortia on total bacteria population was determined by kind of compost. Total bacterial population in rhizosphere of Cai Sim grown with cow manure compost and microbial consortia was more increased. However, microbial consortia as well as any kind of compost did not influence total fungal population in Cai Sim rhizosphere. In this experiment, total bacterial and fungal population in rhizosphere reached 109 cfu g-1 and 104 cfu g-1 respectively, indicating that major microbial population in rhizosphere was in the normal range.

Mutualism between Klebsiella SGM 81 and Dianthus caryophyllus in modulating root plasticity and rhizospheric bacterial density

AimsDianthus caryophyllus is a commercially important ornamental flower. Plant growth promoting rhizobacteria are increasingly applied as bio-fertilisers and bio-fortifiers. We studied the effect of a rhizospheric isolate Klebsiella SGM 81 strain to promote D. caryophyllus growth under sterile and non-sterile conditions, to colonise its root system endophytically and its impact on the cultivatable microbial community. We identified the auxin indole-3-acetic acid (IAA) production of Klebsiella SGM 81 as major bacterial trait most likely to enhance growth of D. caryophyllus.MethodsipdC dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to D. caryophyllus roots and correlated to root growth promotion and characteristic morphological changes. SGM 81 cells were localised on and within the plant root using 3D rendering confocal microscopy of gfp expressing SGM 81. Using Salkowski reagent IAA production was quantified and localised proximal to roots in situ. The effect of different bacterial titres on rhizosphere bacterial population was CFU enumerated on nutrient agar. The genome sequence of Klebsiella SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships.ResultsInoculation of D. caryophyllus roots with Klebsiella SGM 81 drastically promoted plant growth when grown in agar and soil, concomitant with a burst in root hair formation, suggesting an increase in root auxin activity. We sequenced the Klebsiella SGM 81 genome, identified the presence of a canonical ipdC gene in Klebsiella SGM 81, confirmed bacterial production and secretion of IAA in batch culture using LC-MS/MS and localised plant dependent IAA production by SGM 81 proximal to roots. We found Klebsiella SGM 81 to be a rhizoplane and endophytic coloniser of D. caryophyllus roots in a dose dependent manner. We found no adverse effects of SGM 81 on the overall rhizospheric microbial population unless supplied to soil in very high titres.ConclusionKlebsiella SGM 81 effectively improves root traits of D. caryophyllus in a dose dependent manner, likely through tryptophan dependent IAA production in the rhizoplane and potentially within the intercellular spaces of root tissue. Under optimal plant growth promoting conditions in non-sterile soil, the high total microbial titre in the rhizosphere supports a mutualistic relationship between Klebsiella SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.

Efecto de inoculantes bacterianos edáficos mixtos en el desarrollo temprano de cultivares mejorados de cacao (Theobroma cacao L.) en un sistema agroforestal tradicional del norte de Oaxaca, México

Cocoa plant (Theobroma cacao L.) is native from South America and it represents one of the most significant “bio-cultural” resources of Mesoamerica, since it is a region where it was domesticated and had a relevance as ritual drink and as currency in many pre-hispanic cultures until the arrival of the Spaniards who spread its use worldwide, and became it one of the most consumed commodity goods. Through this research, an alternative is proposed to address the problem of cultivars through the introduction of a wide variety of cocoa plants in traditional agroforestry systems, in synergy with the inoculation of nitrogen-fixing and insoluble phosphor solubilizing edaphic bacterial consortia. Four cultivars of improved grafted cocoa plants were introduced in a traditional agroforestry plot and three fertilization treatments were applied: application of biofertilizer, application of chemical fertilizer and control. Measurements of height, stem diameter, number of leaves and branches were recorded at 2 and 12 months after planting and rhizosphere microbial populations were characterized. Growth results showed good potential for all studied cultivars and it was observed that biofertilization foresees significant effects in some of the growth indicators of cocoa plant. Thereby, plant associations in an agroforestry system could be favorable to promote fruit development and resistance to pests and diseases.

An approach to mitigating soil CO2 emission by biochemically inhibiting cellulolytic microbial populations through mediation via the medicinal herb Isatis indigotica

Greenhouse gases (GHGs, particularly carbon dioxide (CO2)) emissions from soil under wheat production are a significant source of agricultural carbon emissions that have not been mitigated effectively. A field experiment and a static incubation study in a lab were conducted to stimulate wheat growth and investigate its potential to reduce CO2 emissions from soil through intercropping with a traditional Chinese medicinal herb called Isatis indigotica. This work was conducted by adding I. indigotica root exudates based on the quantitative real-time PCR (qPCR) analysis of the DNA copy number of the rhizosphere or bulk soil microbial populations. This addition was performed in relation to the CO2 formation by cellulolytic microorganisms (Penicillium oxalicum, fungi and Ruminococcus albus) to elucidate the microbial ecological basis for the molecular mechanism that decreases CO2 emissions from wheat fields using I. indigotica.The results showed that the panicle weight and full grains per panicle measured through intercropping with I. indigotica (NPKWR) increased by 39% and 28.6%, respectively, compared to that of the CK (NPKW). Intercropping with I. indigotica significantly decreased the CO2 emissions from soil under wheat cultivation. Compared with CK, the total CO2 emission flux during the wheat growth period in the I. indigotica (NPKWR) intercropping treatment decreased by 29.26%. The intensity of CO2 emissions per kg of harvested wheat grain declined from 7.53 kg CO2/kg grain in the NPKW (CK) treatment to 5.55 kg CO2/kg grain in the NPKWR treatment.The qPCR analysis showed that the DNA copy number of the microbial populations of cellulolytic microorganisms (P. oxalicum, fungi and R. albus) in the field rhizosphere around I. indigotica or in the bulk soil under laboratory incubation was significantly lower than that of CK. This finding indicated that root exudates from I. indigotica inhibited the activity and number of cellulolytic microbial populations, which led to decreased CO2 emissions, suggesting this plant's potential role in mitigating agricultural GHGs and in supporting agroecology.

Effect of plant species compositions on performance of lab-scale constructed wetland through investigating photosynthesis and microbial communities

This study focused on the effects of plant compositions on removal rates of pollutants in microcosms through investigating rhizosphere microbial populations, photosynthetic efficiency and growth characteristics. Mixed-culture groups improved the removal efficiency of TN and TP significantly but exhibited lower COD removal rates. Total plant biomasses were improved as the species richness increased, but the N/P content in the plants was mainly affected by the type of species. The mixed-culture groups showed lower photosynthesis rates and oxygen supply generated from roots under high irradiation. Microbial communities of the cultured groups in the rhizosphere exhibited significant differences. According to principal component analysis (PCA), the fungi were the typical microbes of SPA, SPAB, and SPABC, resulted in improvement in nutrient accumulation. These results demonstrated that a mixed culture strategy can represent the overyielding of biomass, promote the photo-protection mechanism, and will further increase the removal rates of pollutants in a constructed wetland.

Rhizobacteria and plant symbiosis in heavy metal uptake and its implications for soil bioremediation

Certain species of plants can benefit from synergistic effects with plant growth-promoting rhizobacteria (PGPR) that improve plant growth and metal accumulation, mitigating toxic effects on plants and increasing their tolerance to heavy metals. The application of PGPR as biofertilizers and atmospheric nitrogen fixators contributes considerably to the intensification of the phytoremediation process. In this paper, we have built a system consisting of rhizospheric Azotobacter microbial populations and Lepidium sativum plants, growing in solutions containing heavy metals in various concentrations. We examined the ability of the organisms to grow in symbiosis so as to stimulate the plant growth and enhance its tolerance to Cr(VI) and Cd(II), to ultimately provide a reliable phytoremediation system. The study was developed at the laboratory level and, at this stage, does not assess the inherent interactions under real conditions occurring in contaminated fields with autochthonous microflora and under different pedoclimatic conditions and environmental stresses. Azotobacter sp. bacteria could indeed stimulate the average germination efficiency of Lepidium sativum by almost 7%, average root length by 22%, average stem length by 34% and dry biomass by 53%. The growth of L. sativum has been affected to a greater extent in Cd(II) solutions due its higher toxicity compared to that of Cr(VI). The reduced tolerance index (TI, %) indicated that plant growth in symbiosis with PGPR was however affected by heavy metal toxicity, while the tolerance of the plant to heavy metals was enhanced in the bacteria-plant system.A methodology based on artificial neural networks (ANNs) and differential evolution (DE), specifically a neuro-evolutionary approach, was applied to model germination rates, dry biomass and root/stem length and proving the robustness of the experimental data. The errors associated with all four variables are small and the correlation coefficients higher than 0.98, which indicate that the selected models can efficiently predict the experimental data.

A Study on Methane Efflux and Rhizospheric Microbial Population Under Rice Based Ecosystem at Ambient and Elevated CO<SUB>2</SUB> Level

A Study on Methane Efflux and Rhizospheric Microbial Population Under Rice Based Ecosystem at Ambient and Elevated CO<SUB>2</SUB> Level

Effects of Nitrogen Application Rates on Rhizosphere Microbial Community Functional Diversity in Maize and Potato Intercropping

Field trials were carried out to investigate the effects of different nitrogen application rates N0(0 kg·hm-2), N1(125 kg·hm-2), N2(250 kg·hm-2)and N3(375 kg·hm-2)on the rhizosphere microbial population and metabolic function diversity of maize and potato under intercropping using plate culture method and BIOLOG technique. The results indicated that nitrogen(N1, N2 and N3) application in-creased the amounts of bacteria, actinomyces and total microbes, but decreased the quantities of fungi significantly in rhizosphere soil of maize and potato in intercropping, and the highest increment was with N2 treatment. In comparison with N0, nitrogen fertilizer application could increase significantly the diversities of soil microbial community, the utilization rate of carbon source, richness of soil microbial community. And the AWCD value, Shannon-Wiener index(H), Simpson index(D), Evenness index(E)and Richness index(S)in rhizosphere soil of maize under intercropping were the highest at N3 treatment, while that of potato were the highest at N2 treatment, but the effects of different N application rates on the ability of rhizospheric microbes in utilizing six types of carbon sources were different. Principal component analysis(PCA)and cluster analysis showed that there were differences in carbon substrate utilization patterns and metabolic characteristics of the soil microbes in maize and potato intercropping with different N application rates. It suggested that applying N could regulate the rhizosphere soil microbial communities and promote the functional diversity of crop intercropping.

Plant Growth Promoting Rhizobacteria (PGPR): Current and Future Prospects for Development of Sustainable Agriculture

Soil is dynamic living matrix and it is not only a critical resource in agricultural and food security but it is also towards maintenance of all life process. Pathogenic microorganisms affecting plant health are a major and chronic threat to sustainable agriculture and ecosystem stability worldwide. The chemical fertilizers used in the agriculture to increase yields, kill pathogens, pests, and weeds, have a big harmful impact on the ecosystem. Because of current public concerns about the side effects of agrochemicals, there is an increasing interest in improving the understanding of cooperative activities among plants and rhizosphere microbial populations. So, there is an urgent need of biological agents is accepted worldwide. The use of plant growth promoting Rhizobacteria (PGPR) is a better alternative to solve this problem. They play an important role to increase in soil fertility, plant growth promotion, and suppression of phytopathogens for development of ecofriendly sustainable agriculture. This review provides environment friendly approach to increase crop production and health, development of sustainable agriculture and commercialization by using of plant growth promoting rhizobacteria with global applicability.

TiO2 nanoparticle biosynthesis and its physiological effect on mung bean (Vigna radiata L.)

TiO2 nanoparticle (NPs) biosynthesis is a low cost, ecofriendly approach developed using the fungi Aspergillus flavus TFR 7. To determine whether TiO2 NPs is suitable for nutrient, we conducted a two part study; biosynthesis of TiO2 NP and evaluates their influence on mung bean. The characterized TiO2 NPs were foliar sprayed at 10mgL−1 concentration on the leaves of 14 days old mung bean plants. A significant improvement was observed in shoot length (17.02%), root length (49.6%), root area (43%), root nodule (67.5%), chlorophyll content (46.4%) and total soluble leaf protein (94%) as a result of TiO2 NPs application. In the rhizosphere microbial population increased by 21.4–48.1% and activity of acid phosphatase (67.3%), alkaline phosphatase (72%), phytase (64%) and dehydrogenase (108.7%) enzyme was observed over control in six weeks old plants owing to application of TiO2 NPs. A possible mechanism has also been hypothesized for TiO2 NPs biosynthesis.

Influence of soil type, cultivar and Verticillium dahliae on the structure of the root and rhizosphere soil fungal microbiome of strawberry.

Sustainable management of crop productivity and health necessitates improved understanding of the ways in which rhizosphere microbial populations interact with each other, with plant roots and their abiotic environment. In this study we examined the effects of different soils and cultivars, and the presence of a soil-borne fungal pathogen, Verticillium dahliae, on the fungal microbiome of the rhizosphere soil and roots of strawberry plants, using high-throughput pyrosequencing. Fungal communities of the roots of two cultivars, Honeoye and Florence, were statistically distinct from those in the rhizosphere soil of the same plants, with little overlap. Roots of plants growing in two contrasting field soils had high relative abundance of Leptodontidium sp. C2 BESC 319 g whereas rhizosphere soil was characterised by high relative abundance of Trichosporon dulcitum or Cryptococcus terreus, depending upon the soil type. Differences between different cultivars were not as clear. Inoculation with the pathogen V. dahliae had a significant influence on community structure, generally decreasing the number of rhizosphere soil- and root-inhabiting fungi. Leptodontidium sp. C2 BESC 319 g was the dominant fungus responding positively to inoculation with V. dahliae. The results suggest that 1) plant roots select microorganisms from the wider rhizosphere pool, 2) that both rhizosphere soil and root inhabiting fungal communities are influenced by V. dahliae and 3) that soil type has a stronger influence on both of these communities than cultivar.

Effect of PGPR Serratia marcescens BC-3 and AMF Glomus intraradices on phytoremediation of petroleum contaminated soil

Soil contamination caused by petroleum hydrocarbons has become a worldwide environmental problem. Microorganism combined with phytoremediation appears to be more effective for removal and/or degradation of petroleum hydrocarbons from impacted soils. The current study investigated the effect of inoculated with PGPR Serratia marcescens BC-3 alone or in combination with AMF Glomus intraradices on the phytoremediation of petroleum-contaminated soil. Pot experiments were conducted to analyze the effect on plant and soil for 90 days in greenhouse. The inoculation treatments showed higher plant biomass and antioxidant enzyme activities than the non inoculation control. Inoculation treatments also improved rhizosphere microbial populations in petroleum contaminated soil. The degradation rate of total petroleum hydrocarbons with PGPR and AMP co-inoculation treatment was up to 72.24 %. The results indicated that plant combined with microorganisms for remediation of petroleum hydrocarbons would be a feasible method.