Biological Control Of Pathogens Research Articles

Benefits of Crotalaria juncea L. as Green Manure in Fertility and Soil Microorganisms on the Peruvian Coast

The soils of the Barranca valley are among the best soils in Peru, but with so many years of application of agrochemicals and other agricultural practices, they are losing their productive capacity. Consequently, it was suggested to assess the impact of Crotalaria juncea L. as a green manure on soil fertility and the populations of bacteria and fungi present in the soil. Crotalaria was cultivated for 75 days and incorporated as green manure. After 90 days, the presence of bacteria and fungi was evaluated. Metabarcoding was employed, and the 16S rRNA and ITS2 amplicons were sequenced using the Illumina MiSeq platform. The sequences were processed using various bioinformatics tools. The results indicate that soils have a high diversity of bacteria and fungi. Likewise, in plots where the presence and action of natural biocontrol is suppressed (C0 and P0), pathogenic fungi increase their population in the fallow period (C1), while in P1, the addition of Crotalaria as a green manure promotes an increase in the population of bacteria and fungi, and at the same time it suppresses pathogenic fungi. The genera (bacterial and/or fungal) that increase due to the effect of Crotalaria are beneficial because they are involved as degraders of organic matter, promotion of plant growth and biological control of pathogens. Crotalaria is an alternative to improve soil fertility, increase the beneficial bacterial population, and reduce pathogenic fungi.

ENDOPHYTIC MICROORGANISMS AS BIOCONTROL AGENTS: AN ALTERNATIVE FOR SUSTAINABLE AGRICULTURAL PRODUCTION SYSTEM

Endophytic microorganisms emerge as a sustainable alternative, offering benefits to plants, such as increased resistance to stress and pathogens. This research aims to conduct a literature review on the potential of endophytic microorganisms in the biological control of pathogens in agricultural systems, as a sustainable alternative to traditional methods. Endophytes can act directly on insects or colonize plants, creating a natural defense against pests. They also show promise in the control of phytopathogens, helping to reduce the use of chemical fungicides and encouraging more sustainable agricultural practices, producing bioactive compounds with effective antifungal activity against pathogens. In addition, they show potential as natural herbicides, negatively affecting the germination and development of weeds. Although more research is needed on the potential of endophytes in agricultural systems, they show great promise for more sustainable management.

Assessment of the phenotypic and genotypic diversity of endophytic strains of Bacillus and closely related genera from Carpinus betulus in the Hyrcanian forests of Iran.

Identification and characterization of the endophytic microorganism, is gaining their underestimated significance in influencing health, performance, and other biological attributions of plants in general and forest tree species in particular. Because of the scarcity of information on the endophytic microbiome of the Hyrcanian forests species, including hornbeam (Carpinus betulus L.) trees, as a major constituent thereof, the present study aimed at the identification and partial characterization of the endophytic Bacillus species of Carpinus betulus as the first step in this context. Shoot samples were collected from the Hyrcanian forest locations of Mazandaran and Golestan provinces in Iran. Bacterial strains were isolated from the surface-disinfected shoot segments and subjected to phenotypic characterization. Following assessment of the genetic diversity of the isolates by BOX-PCR fingerprinting, the representative isolates of each of the 15 groups were used for further characterization. Analysis of the nucleotide sequences of the 16S rDNA and HSP60 gene of the isolates led to the identification of 10 species. The predominant species was B. cereus followed by B. subtilis. The other species encountered were B. thuringiensis, Priestia filamentosa, B. velezensis, B. mojavensis, B. amyloliquefaciens, B. safensis, P. aryabhattai, and Gottfriedia acidiceleris. Most isolates possessed characteristics which could contribute to the biocontrol potential of the isolates, including formation of biofilm, production of hydrogen cyanide, tolerant to relatively high concentration of sodium chloride, and antibacterial activity. Ten Bacillus species were identified as the prevailing endophytic species of C. betulus in the Hyrcanian forest of northern Iran, most turned up to possess biological activities involved in biocontrol capability of the isolates against some plant pathogens. These potentially capable bacteria could be implemented in the promotion of plant growth as well as in the biological control of pathogens. This is the first report on the characterization and elucidation of the diversity of the potentially beneficial endophytic species of Bacillus and the closely related genera living in the internal tissues of hornbeam trees.

EVALUATION OF THE IN VITRO ANTIFUNGAL POTENTIAL OF NATURAL EXTRACTS AND SYNTHETIC PESTICIDES ON THE GROWTH AND DEVELOPMENT OF THE PATHOGEN BOTRYTIS CINEREA

This study was carried out to evaluate the in vitro antifungal potential of natural extracts from marc, spontaneous flora plants, and synthetic pesticides. The biological control of pathogens is a modern alternative because does not represent a danger to humans and the environment. Thus, natural alternatives with a fungistatic or fungicidal effect on the pathogen Botrytis cinerea were identified. The results of the in vitro tests clearly indicated a significant inhibitory percentage on the growth rate of the Botrytis cinerea rot mycelium (62.38%), when was used the extract obtained from the Cabernet Sauvignon marc at a concentration of 15%, compared to the other two natural extracts used (Salvia officinalis and Chelidonium majus), where the diameter of the colonies recorded values close to the untreated control variant. Regarding the effect of the synthetic pesticides studied, the best results were recorded with fosetyl-aluminum where a 100% inhibition percentage on the Botrytis cinerea pathogen was recorded.

Testing Trichoderma species as biological agents for control of Dothistroma septosporum in Pinus radiata

Biological control of pathogens can be an important tool for long-term management of diseases. Species in the fungal genus Trichoderma have been used for a broad range of agricultural functions including biological control. Here we tested if isolates and mixes of Trichoderma spp. could be effective in reducing symptoms of dothistroma needle blight, caused by the foliar pathogen Dothistroma septosporum, on Pinus radiata. Pot trials with natural and artificial D. septosporum infection and field trials were undertaken. The majority of Trichoderma treatments were not significantly different from the control. However, in one experiment, the Trichoderma treatments significantly reduced disease symptoms in one seedlot but not in the other seedlot tested. Conversely, in the field trial, one Trichoderma treatment significantly increased symptoms in comparison to the control. PCR analysis indicated that Trichoderma can persist over time, 16 months after inoculation, in the soil P. radiata seedlings were grown in, however, further investigation is required. Overall, the results from our trials showed that the Trichoderma isolates and mixes tested were unable to control dothistroma needle blight in P. radiata and are not suitable as biological control agents.

Isolation and screening of Pseudomonas fluorescens isolates against Fusarium oxysporum f. sp. radicis-lycopersici and their effects on seedling growth of Paraserianthes falcataria

Abstract. Yusran Y. 2023. Isolation and screening of Pseudomonas fluorescens isolates against Fusarium oxysporum f.sp. radicis-lycopersici and their effects on seedling growth of Paraserianthes falcataria. Biodiversitas 24: 2294-2301. Pseudomonas fluorescens plays a major role in biological control of pathogens and plant growth promotion as well with various mechanisms. The aim of the present study was to determine the biochemical characteristics of several Pseudomonas spp. isolates and to screen them against root pathogenic fungus Fusarium oxysporum f.sp radicis-lycopersici (FORL) and to evaluate their effect on the growth enhancement of Paraserianthes falcataria (L.) I.C. Nielsen seedlings. About 28 Pseudomonas fluorescens isolates were isolated from the rhizosphere of several plants and identified based on their physiological and morphological characters as well as their biochemical reactions. All isolates were tested for their ability to suppress FORL growth in vitro. All isolates inhibited FORL growth with varying inhibition zones. Six P. fluorescens isolates showed highest inhibition zones, namely TMTP4, TMTP5, TMTP6, SCPA1, SCPB3 and Proradix. The results showed that eight Pseudomonas isolates, namely TMTP4, TMTP5, TMTP6, SCPA1, SCPB3, SMPB3, TMTA2 and Proradix had a significantly different effect compared to the control treatment in increasing the growth of Paraserianthes seedlings. Based on our findings, it was confirmed that some P. fluorescens isolates could be used as potential bio-inoculants for controlling plant diseases caused by FORL and as a biological fertilizer to increase plant growth.

A Scientometric and Bibliometric Analysis for Actinomycetes Research - Current Status and Future Trends

Actinomycetes are Gram-positive filamentous bacteria used as biocontrol agents against pathogens. Currently, little research on actinomycetes has been published in Indonesia. The study provides issues related to the most relevant keywords in actinomycetes, the most productive authors and countries on actinomycetes research, current research on actinomycetes, and future topics in actinomycetes research. This paper aims to understand the current status and trend of research on actinomycetes in biological control, especially their acts as biocontrol agents. We used VOSviewer and CiteSpace software to perform a scientometric and bibliometric analysis. Out of 452 Scopus publications published between 1971 and 2022. Research on actinomycetes has increased rapidly since 2000, leading to an exponential trend. The result shows that >50% of papers focus on Agricultural and Biological Sciences and indicate that actinomycetes are mainly applied as biocontrol agents. China is the most documented and powerful country, followed by the United States and Iran. In contrast, Indonesia ranks 19th in the world with nine published papers. Scientometric analysis shows Shahidi Bonjar nominated as the strongest citation burst author (4.01). Their topic is mainly on the biological control of pathogens by Actinomycetes, especially Streptomyces sp., while fungi are a dominant pathogen. These findings are related to bibliometric analysis, showing Streptomyces spp. and fungi are two primary keywords in the Scopus database, found on 183 and 139 documents. We found actinomycete research focuses on their ability to manage plant diseases naturally. In the future, we predict actinobacterial research is still essential to biological control, particularly those involving Streptomyces species. Also, several important topics are associated with their activities in controlling pests (nematode), postharvest disease, and growth promoter ability.

Application of Pseudomonas Strains for Biocontrol of Commercial Crops Susceptible to Plant Pathogens: A Review

Indiscriminate use of chemicals as fertilizers and pesticides gives rise to substantial harm to the environment and ecosystem along with animals and humans. More importantly, to replace such hazardous agrochemicals, many biological solutions are available in nature which is present in the form of microorganisms having the capacity to promote plant growth substantially. Pseudomonas play a major role in plants like inducing systemic resistance, colonizing plant roots or tissue interior, helping in modulating plant hormone levels, biological control of pathogens and more over regulating the growth-related genes in plants. The fluorescent pseudomonads belong to plant growth-promoting rhizobacteria (PGPR) and many strains of pseudomonas are well known to enhance plant growth promotion and decrease the severity of many diseases. Biocontrol strains of pseudomonas in plant bioassays synthesize one or more several antibiotic compounds. In vitro, these antibiotics have been proven as inhibitory compounds and have exhibited active responses for plant health management in field conditions. The current study mainly relies on the effective use of Pseudomonas spp. as a potential biocontrol agent for the biological control of many diseases in agriculture and horticultural crops.

A Detached Leaf Assay for Rapidly Screening Plant Pathogen-Biological Control Agents.

The detached leaf assay (DLA) is a nondestructive method for evaluating interactions between plants and disease-causing agents that allows quick characterization of potential pathogens' infectivity and plants' resistance to them. Here we show its utility for also assessing potential biological control agents (BCAs), by demonstrating its applicability for screening potential BCAs for the strawberry (Fragaria×ananassa) pathogen Phytophtora cactorum.

Stemphylium and Ulocladium between Benefit and Harmful

Background: Emerging of microbial resistance, spread of life-threatening diseases, and biological control of pathogens destroying economically important crops, are serious problems that encourage scientists to search for unusual sources for novel compounds with biological activities. Fungi are promising sources for such compounds due to their ability to produce variety of secondary metabolites that could be, if truly investigated, the solution for currently serious problems. Aim: The aim of this review is to highlight the diversity of compounds produced by endophytic Stemphylium and Ulocladium and represents their ability to produce biologically diverse metabolites. Materials and methods: This was a narrative review. A comprehensive literature search was done using PubMed, Google Scholar, Scopus, and EMBASE using the keywords, Stemphylium; Ulocladium; Secondary metabolites; biological activities. Results: Many studies reported that the endophytic Ulocladium especially, Ulocladium atrum Preuss, showed promising biocontrol activity against Botrytis cinerea on crops cultivated in the greenhouse and the field. The endophytic fungus Stemphylium especially, Stemphylium globuliferum was isolated from stem tissues of the Moroccan medicinal plant Mentha pulegium. Extracts of the fungus exhibited significant cytotoxicity when tested in vitro against L5178Y cells. Conclusion: Endophytic fungi are a noble and consistent source of unique natural mixtures with a high level of biodiversity and may also yield several compounds of pharmaceutical significance, which is currently attracting scientific surveys worldwide. Every study conducted on Stemphylium and Ulocladium resulted in discovery of new metabolites or pointing to a possible application, which made Stemphylium and Ulocladium species potential source of pharmaceuticals and attracted attention for further investigations of their biological control.

Exploring the Diversity and Biotechnological Potential of Cultured and Uncultured Coral-Associated Bacteria

Coral-associated microbes are crucial for the biology of their hosts, contributing to nutrient cycling, adaptation, mitigation of toxic compounds, and biological control of pathogens. Natural products from coral-associated micro-organisms (CAM) may possess unique traits. Despite this, the use of CAM for biotechnological purposes has not yet been adequately explored. Here, we investigated the production of commercially important enzymes by 37 strains of bacteria isolated from the coral species Mussismilia braziliensis, Millepora alcicornis, and Porites astreoides. In-vitro enzymatic assays showed that up to 56% of the isolates produced at least one of the seven enzymes screened (lipase, caseinase, keratinase, cellulase, chitinase, amylase, and gelatinase); one strain, identified as Bacillus amyloliquefaciens produced all these enzymes. Additionally, coral species-specific cultured and uncultured microbial communities were identified. The phylum Firmicutes predominated among the isolates, including the genera Exiguobacterium, Bacillus, and Halomonas, among others. Next-generation sequencing and bacteria culturing produced similar but also complementary data, with certain genera detected only by one or the other method. Our results demonstrate the importance of exploring different coral species as sources of specific micro-organisms of biotechnological and industrial interest, at the same time reinforcing the economic and ecological importance of coral reefs as reservoirs of such diversity.

The Efficacy of Functional Composts Manufactured Using Spent Coffee Ground, Rice Bran, Biochar, and Functional Microorganisms

Spent coffee grounds (SCGs), one of the world’s most discarded wastes, may be an excellent resource as an organic fertilizer because of its richness in nutrients. The objective of this study was to develop a quality functional compost using SCGs, rice bran, biochar, SCG extract, and functional microbes (plant growth promoting and plant pathogen-suppression bacteria), and then to test their functional efficacy for a potential commercial application. Essentially, two types of representative composts (Tr_1 and Tr_5 on the laboratory and pilot scale, respectively) were developed and passed all the official commercial quality standards. For pilot-scale composting, populations of Halotalea_uc, Corynebacterium nuruki, and Lactobacillus acidipiscis increased by augmentation of the composting microbes (MA-1) and the functional microbes (Bacillus cereus SB-3, Bacillus toyonensis SB-4, and Streptomyces sasae St-3). The higher total flavonoid content (11% increase compared to control) of pepper leaves in PT-1 and the higher TEAC in PT-1 (36.2%) and PT-2 (32.5%) proved the efficacy of the functional composts bioaugmented with the functional microbes. The seedling growth of radish seeds treated with Streptomyces sasae St-3 as a biocontrol agent significantly increased despite the presence of the pathogen Fusarium oxysporum f. sp. lactucae. The total phenol content and TEAC in pepper plant leaves were significantly higher in Tr_5 than in the control (Tr_4), whereas there were no differences in Tr_4 and Tr_5 infested with the fungal pathogens, indicating that SB-3, SB-4, and St-3 cultures amended within the compost (Tr_5) may facilitate the production of the antioxidants in the absence of the pathogens. However, a significant reduction in the antioxidants (total phenolic content and TEAC) was observed in the pepper plants whose roots were infected with the pathogens, indicating that the pathogens could neutralize functionalities of the functional microbes. It was concluded that the enhancement of functional microbes in the compost would aid in the biological control of pathogens in the soil environment. Further functional compost studies are necessary in terms of mechanisms of plant growth-promotion, mechanisms of pathogen suppression by the actinobacterial biocontrol agents, and interactions between the two mechanisms, as well as quality enhancement of the composts.

Coordination of Mesorhizobium sp. and endophytic bacteria as elicitor of biocontrol against Fusarium wilt in chickpea

Antagonistic Plant growth promoting rhizobacteria can contribute to disease management by induction of host defenses and biological control of pathogens. The present study was thus planned to develop a bio-inoculant with the ability to promote plant growth and reduce disease incidence due to Fusarium oxysporum sp. ciceris in chickpea. Isolates of Mesorhizobium sp. (6) and endophytic bacteria (5) were screened as potential antagonists exhibiting 50–93.7% growth inhibition of Fusarium wilt (in vitro). Selected Mesorhizobium sp. and endophytic bacteria were assessed for their compatibility to develop dual combinations with no mutual inhibition. Dual inoculants significantly enhanced in vitro plant growth promoting traits viz., Indole Acetic Acid, siderophores, phosphate solubilization and 1-aminocyclopropane-1-carboxylate-deaminase enzyme activity. Dual mesorhizobia and endophytic bio-inoculants (able to grow with recommended fungicide captan @ 3 g/kg seed) were further assessed in wilt-sick field conditions for growth, symbiosis, soil health, yield and bio-control parameters in two chickpea varieties (PBG-7 and PBG-1). Seed priming with dual inoculants significantly enhanced growth, symbiosis, soil quality parameters and antioxidant enzymes viz., catalase, peroxidase and total phenols over control. Dual bio-inoculant LGR2 + LCNE8 improved the grain yield by 6.5% over captan as the control. These results suggest that bio-inoculants of Mesorhizobium sp. and endophytic bacteria under a competitive environment can be explored as bio-fertilizers/bio-protectants for improving productivity and suppression of Fusarium wilt in chickpea.

Assessing the role of soil microbial communities of natural forest ecosystem

Abstract In forests, edaphic microbial communities are involved in litter decomposition and soil forming processes, with major contribution to humification, especially bacteria and fungi being responsible for the main ecosystem services fulfilled by the soil. Research has been carried out aiming to characterize the structure and diversity of microbial communities in the Rendzic Leptosols (WRB) under natural deciduous forest from Visterna, Babadag Plateau and to assess their contribution to ecosystem services provided by soil. The paper presents the results of quantitative estimations and taxonomic composition of soil and litter communities of heterotrophic bacteria and fungi, identification of cellulolytic species, as well as the microbial biomass and global physiological activities expressed as soil respiration potential. More than a half of bacterial species were common in litter and soil (SI=57.14%) and were represented by dominant species of fluorescent or non-fluorescent pseudomonads and Bacillus subtilis but no similarity was found between the two fungal communities. Fungal populations included cosmopolitan species, such as antagonists and strong cellulolytic representatives of genera Penicillium, Trichoderma, Mortierella, Chaetomium, Epicoccum, Aspergillus. Microbial density and microbial biomass presented the highest values in the litter (684 mg C x kg-1 d.s.) and in surface horizon Am1 of soil profile than in the bottom layers. The highest diversity was found in Am1 horizon (0-5 cm) H’=1.983 bits and ε=0.869 for cellulolytic community. Soil respiration reflected the intense physiological activity of microbiome, with high values associated to numerous effectives of bacteria and fungi especially in surface horizon. Microorganisms identified contribute to formation of soil by recycling of nutrients, cellulose decomposition, the synthesis of stable organic matter (humic acids), aggregation of soil particles, biological control of pathogens by antagonistic activity. They improve plant uptake of water and nutrients by forming symbioses (ectomycorrhizae), thus modelling the structure of vegetation.

Agrobacterium-Mediated Transformation of Diaporthe schini Endophytes Associated with Vitis labrusca L. and Its Antagonistic Activity Against Grapevine Phytopathogens.

Fungus-caused diseases are among the greatest losses in grapevine culture. Biological control of pathogens by endophytes may be used to decrease fungicide application rates and environmental impacts. Previously, Diaporthe sp. B46-64 and C27-07 were highlighted as antagonists of grapevine phytopathogens. Herein, molecular multigene (ITS-TUB-TEF1) identification and phylogenetic analysis allowed the identification of these endophytes as belonging to Diaporthe schini species. Agrobacterium tumefaciens-mediated transformation was employed for obtaining 14 stable and traceable gfp- or DsRed-expressing transformants, with high transformation efficiency: 96% for the pFAT-GFP plasmid and 98% for pCAM-DsRed plasmid. Transformants were resistant to hygromycin B with gene hph confirmed by polymerase chain reaction and proved to be mitotically stable, expressing the fluorescent phenotype, with morphological differences in the colonies when compared with wild strains. In vitro antagonism tests revealed an increased antagonistic activity of some transformant strains. The current genetic transformation of D. schini mediated by A. tumefaciens proved to be an efficient technique within the randomized insertion of reporter genes for the monitoring of the strain in the environment.

Antifungal activity against plant pathogens by compounds from Streptoverticillium morookaense

Biological control of pathogens by endophytes is a promising approach. The present study reports the significant impact of an antifungal compound that is isolated from Streptoverticillium morookaense as a potential biocontrol agent. This antifungal compound demonstrated a significant inhibitory activity against the three phytopathogenic fungi, Ustilaginoidea virens, Rhizoctonia solani and Bipolaris maydis and resulted in severe morphological distortions in their structure. Minimal inhibitory concentrations of the compound ranged from 50 to 150 μg/ml. In vitro evaluation of the compound showed strong control efficacy against U. virens, a causative agent of rice false smut fungus, on susceptible rice seedlings. In addition, it promoted plant growth with increased rate of seed germination and displayed no phytotoxicity. This compound also showed stability after its exposure to a temperature of 100 °C. The antifungal metabolite produced by this actinomycete may be developed as a safe and ideal bio-fungicide for the control of different fungal plant diseases.

Display of B. pumilus chitinase on the surface of B. subtilis spore as a potential biopesticide

BackgroundChitinases can inhibit the growth of many fungal diseases which are a great threat for global agricultural production. Biological control of pathogens like fungi, is believed to be one of the best ways to eliminate the adverse effects of plant pathogens. To this end, we expressed and displayed a chitinase from Bacillus pumilus (ChiS) on the surface of Bacillus subtilis spores, as a biocontrol agent. ResultChiS enzyme from B. pumilus was expressed on the spores of B. subtilis using CotG as a carrier protein. Immunofluorescence microscopy confirmed the expression of ChiS on the surface of the spores. Enzyme activity assay showed that the surface displayed ChiS was active and was also able to inhibit the growth of Rhizoctonia solani and Trichoderma harzianum fungi. Western blot analysis also indicated that CotG-ChiS is partially processed after display. Molecular dynamics simulation showed that the stability of the heterologous protein was decreased after fusion. ConclusionChiS was successfully displayed on the surface of Bacillus spores by fusion to the CotG, one of the main spore coat proteins. In-vitro experiments showed that the displayed enzyme was effective in growth inhibition of R. solani and T. harzianum fungi.

Effect of Yarrowia lipolytica on postharvest decay of grapes caused by Talaromyces rugulosus and the protein expression profile of T. rugulosus

Biological control of pathogens using biocontrol agents has been document to be an effective and safe method for managing postharvest diseases. A better understanding of the mode of action of postharvest biocontrol agents on fruit surfaces, is critical for the advancement of successful implementation of postharvest biocontrol products. We investigated the biocontrol efficacy of Yarrowia lipolytica against the postharvest decay of table grapes caused by Talaromyces rugulosus and the possible mechanisms involved. Y. lipolytica significantly decreased the decay incidence of the treated grape berries compared to the untreated control. The response of T. rugulosus to different components of Y. lipolytica indicated that only the yeast cells exhibited inhibitory effect on fungal mycelium, while extracellular metabolites did not show any significant effect on T. rugulosus. The in vitro experiment showed that Y. lipolytica significantly inhibited spores germination and lesion diameter caused by T. rugulosus. We observed that the grape wounds were rapidly colonized by the antagonistic yeast at 25°C and 4°C. Thirty-five differential proteins were identified in T. rugulosus out of which 31 were down-regulated. Majority of the down-regulated proteins were related to basic metabolism, which suggested that the basic metabolism of T. rugulosus was suppressed.

A new bacterial strain, Pseudomonas koreensis IB-4, as a promising agent for plant pathogen biological control

A bacterial strain IB-4, antagonistic to plant pathogenic fungi of the genera Fusarium, Bipolaris, and Alternaria, was isolated from arable soils of the Mechetlinskii district, Bashkortostan. Physiological, biochemical, and culture morphological properties of strain IB-4 supported its classification within the genus Pseudomonas. In spite of some discrepancies in the results of phenotypic and chemotaxonomic research, analysis of the 16S rRNA gene sequence, DNA–DNA hybridization, GC-content, and MALDI mass spectral data provide considerable evidence supporting its identification as a Pseudomonas koreensis strain. P. koreensis strain IB-4 was shown to possess the valuable features characteristic of PGPR microorganisms: antifungal and nitrogenase activities and ability to synthesize indole-3-acetic acid (IAA) and cytokinin-like compounds. Field test, in which potato plants were treated with the culture liquid of P. koreensis strain IB-4 revealed a positive effect on potato yield and resistance to plant pathogens.

Functional identification of phenazine biosynthesis genes in plant pathogenic bacteria Pseudomonas syringae pv. tomato and Xanthomonas oryzae pv. oryzae

Phenazines are secondary metabolites with broad spectrum antibiotic activity and thus show high potential in biological control of pathogens. In this study, we identified phenazine biosynthesis (phz) genes in two genome-completed plant pathogenic bacteria Pseudomonas syringae pv. tomato (Pst) DC3000 and Xanthomonas oryzae pv. oryzae (Xoo) PXO99A. Unlike the phz genes in typical phenazine-producing pseudomonads, phz homologs in Pst DC3000 and Xoo PXO99A consisted of phzC/D/E/F/G and phzC/E1/E2/F/G, respectively, and the both were not organized into an operon. Detection experiments demonstrated that phenazine-1-carboxylic acid (PCA) of Pst DC3000 accumulated to 13.4 μg L−1, while that of Xoo PXO99A was almost undetectable. Moreover, Pst DC3000 was resistant to 1 mg mL−1 PCA, while Xoo PXO99A was sensitive to 50 μg mL−1 PCA. Furthermore, mutation of phzF blocked the PCA production and significantly reduced the pathogenicity of Pst DC3000 in tomato, while the complementary strains restored these phenotypes. These results revealed that Pst DC3000 produces low level of and is resistant to phenazines and thus is unable to be biologically controlled by phenazines. Additionally, phz-mediated PCA production is required for full pathogenicity of Pst DC3000. To our knowledge, this is the first report of PCA production and its function in pathogenicity of a plant pathogenic P. syringae strain.