Biocontrol Of Soilborne Plant Pathogens Research Articles

Pseudomonas Species in Soil as a Natural Resource for Plant Growth Promotion and Biocontrol Characteristics - An Overview

Plant growth-promoting Pseudomonads regulate plant growth by several direct and indirect mechanisms; direct mechanisms include producing phytohormones, increasing nutrient availability and indirect mechanisms include suppressing soil-borne plant pathogens by the production of siderophores, antibiotics, inducing systemic resistance and competing with pathogens. Pseudomonas spp. in soil has been reported from diverse ecological niches and has been well-documented as a model organism for regulating plant growth promotion. These bacteria are endowed with tremendous genetic and metabolic diversity and serve multiple ecological functions in the soil ecosystem. This versatile genus is one of the most commercially exploited bacteria in agriculture. The potential of the different species of Pseudomonas has not been realized sufficiently and requires emphasis on sustainable agriculture for the benefit of humankind. Research in the past decade has revealed that several species of Pseudomonas other than the common species such as P. fluorescens, P. putida, P. aeruginosa, have both plant growth promotion and biocontrol characteristics and have not been commercially exploited. According to the recent List of Prokaryotic names with Standing in Nomenclature (LPSN) there are 507 species of Pseudomonas and the present literature review brings out that 7.29% of them posses plant growth promotion (PGP) and biocontrol traits and thus can be utilized as biofertilizers in the field of agriculture. The role of different Pseudomonas spp. in the supply of plant nutrients and biocontrol of soilborne plant pathogens are covered in this review.

Co-occurrence and Diversity of Soil Trichoderma and Fusarium species from Different Land Use Intensities in Machakos County, Kenya

Soil fungi are important components of the soil biota and their diversity is a good indicator of soil health. Soil fungi respond differently to land use practices and to their relative populations. The cooccurrence and diversity of Trichoderma and Fusarium species against various land use types (LUTs) was investigated. The genus Trichoderma contains many important species with potential for biocontrol of soil-borne plant pathogens as well as high saprophytic capacity while the genus Fusarium has many species that are highly pathogenic to plants and with potential for mycotoxin production. This research adopted a cross-sectional study design. Soil samples were collected from 3 land-use types (LUTs) in Kabaa irrigation scheme in Machakos County, Kenya, that is, intensive land-uses under irrigation and rain-fed agriculture and undisturbed lands. From the top soil layer, 100 soil samples were collected. The samples were processed and 369 Trichoderma Original Research Article Maina et al.; ACRI, 4(1): 1-13, 2016; Article no. ACRI.24894 2 and 1,546 Fusarium isolates recovered. Fusarium had a higher abundance than Trichoderma in the highly disturbed lands. In the undisturbed lands, Trichoderma had a higher abundance than Fusarium. There was a clear negative correlation between Trichoderma and Fusarium occurrence and diversity. The study further revealed that disturbance had a positive effect on Fusarium but a negative one on Trichoderma.

Trichoderma species for biocontrol of soil-borne plant pathogens of pasture species

Soil-borne plant pathogens such as Rhizoctonia solani (Kuhn), Pythium ultimum (Trow) and Sclerotinia trifoliorum (Eriks) can reduce grass and forage legume establishment. The potential for biocontrol of these pathogens by Trichoderma fungi was evaluated. Following dual culture assays, nine Trichoderma isolates (five of Trichoderma atroviride and one each of Trichoderma hamatum, Trichoderma koningiopsis, Trichoderma viride and Trichoderma virens) were chosen for assessment in pot experiments. In the presence of R. solani, perennial ryegrass (Lolium perenne L.) emergence was increased by 60–150% by two isolates of T. atroviride and by 35–212% by the isolate of T. virens, with the increase depending on growing medium and amount of pathogen inoculum. Red clover (Trifolium pratense L.) emergence in the presence of S. trifoliorum was significantly increased by two T. atroviride isolates and the T. hamatum isolate. In the presence of P. ultimum, white clover (Trifolium repens L.) emergence was increased by 25–42% by one isolate of T. atroviride and the T. hamatum isolate. However, for all three pasture species, some Trichoderma isolates reduced seedling emergence. Seedling growth (shoot and root fresh weight/plant) of the three pasture species was significantly increased by one or more T. atroviride isolates. On the basis of these results for both disease reduction and growth promotion, four T. atroviride isolates were selected for field assessment as biocontrol agents of soil-borne pathogens of pasture species.

In-Vitro Efficacy of Trichoderma viride Against Sclerotium rolfsii and Macrophomina phaseolina

The fungal pathogen causes serious widespread losses to agricultural crops worldwide. Therefore, economy of countries may worsen especially of developing countries. In addition, harmful chemical pesticides which are being used today for increasing crop production creates very serious health hazardous problems to human beings and ecosystem as a whole. The antagonistic potential of Trichoderma species which has been long known to control various soil-borne fungal pathogens in biological way may be utilized. The faster growth rates with which it competes with fungal pathogen mainly brings upon their antagonistic characteristics. An investigation was carried out in laboratory condition towards biological efficacy of T. viride on potato dextrose agar (PDA) medium for the bio-control of soil-borne plant pathogens Sclerotium rolfsii and Macrophomina phaseolina in in-vitro condition. The dual culture technique was followed in which T. viride showed significant antifungal activities towards both the pathogens. T. viride significantly inhibited the mycelial radial growth of S. rolfsii by 75% and M. phaseolina by 71.42%. The results showed variable mycelial growth rate for all fungal isolates which was determined after 6 days of incubation in which T. viride showed minimum of 4.00 days to completely cover the petri-plates and S. rolfsii showed 4.33 days whereas M. phaseolina showed 6.33 days. Thus, T. viride showed encouraging results regarding their biopesticidal and biofungicidal potential against plant pathogens which may be endorsed to substitute harmful chemical supplements that exists in modern day agricultural practices.

RNA Interference of Endochitinases in the Sugarcane Endophyte Trichoderma virens 223 Reduces Its Fitness as a Biocontrol Agent of Pineapple Disease

The sugarcane root endophyte Trichoderma virens 223 holds enormous potential as a sustainable alternative to chemical pesticides in the control of sugarcane diseases. Its efficacy as a biocontrol agent is thought to be associated with its production of chitinase enzymes, including N-acetyl-ß-D-glucosaminidases, chitobiosidases and endochitinases. We used targeted gene deletion and RNA-dependent gene silencing strategies to disrupt N-acetyl-ß-D-glucosaminidase and endochitinase activities of the fungus, and to determine their roles in the biocontrol of soil-borne plant pathogens. The loss of N-acetyl-ß-D-glucosaminidase activities was dispensable for biocontrol of the plurivorous damping-off pathogens Rhizoctonia solani and Sclerotinia sclerotiorum, and of the sugarcane pathogen Ceratocystis paradoxa, the causal agent of pineapple disease. Similarly, suppression of endochitinase activities had no effect on R. solani and S. sclerotiorum disease control, but had a pronounced effect on the ability of T. virens 223 to control pineapple disease. Our work demonstrates a critical requirement for T. virens 223 endochitinase activity in the biocontrol of C. paradoxa sugarcane disease, but not for general antagonism of other soil pathogens. This may reflect its lifestyle as a sugarcane root endophyte.

Production of Bacillomycin- and Macrolactin-Type Antibiotics by Bacillus amyloliquefaciens NJN-6 for Suppressing Soilborne Plant Pathogens

Bacillus amyloliquefaciens strains have been used as biocontrol agents for the suppression of several soilborne plant pathogens. A clearer understanding of the antagonistic mechanisms of action of these bacteria will facilitate their use in the control of plant diseases. Antagonistic substances were isolated from the fermentation broth of B. amyloliquefaciens strain NJN-6 cultures. These compounds were preconcentrated using an XAD-16 column and were purified using reversed-phase high-performance liquid chromatography (RP-HPLC). Fractions were collected from the column and were analyzed, and two homologues of bacillomycin D [molecular weights of 1030 Da (C14) and 1044 Da (C15)] and three homologues of members of the macrolactin family, macrolactin A, 7-O-malonyl macrolactin A, and 7-O-succinyl macrolactin A (molecular weights of 402, 487, and 502 Da, respectively) were identified using HPLC/electrospray ionization mass spectrometry (ESI-MS) analysis. An antagonistic assay showed that bacillomycin D and macrolactin exhibited significant antagonistic effects against Fusarium oxysporum and Ralstonia solanacearum , respectively. A reliable method for the isolation and purification of bacillomycin D and macrolactin from bacterial broth cultures was developed. These data will help elucidate the mechanisms that B. amyloliquefaciens NJN-6 uses for the biocontrol of soilborne plant pathogens.

Arbuscular mycorrhizal fungal spores host bacteria that affect nutrient biodynamics and biocontrol of soil-borne plant pathogens.

SummaryThe aim of this research was to isolate and characterize bacteria from spores of arbuscular mycorrhizal fungi (AMF). We designated these bacteria ‘probable endobacteria’ (PE). Three bacterial strains were isolated from approximately 500 spores of Gigaspora margarita (Becker and Hall) using a hypodermic needle (diameter, 200 μm). The bacteria were identified by morphological methods and on the basis of ribosomal gene sequences as Bacillus sp. (KTCIGM01), Bacillus thuringiensis (KTCIGM02), and Paenibacillus rhizospherae (KTCIGM03). We evaluated the effect of these probable endobacteria on antagonistic activity to the soil-borne plant pathogens (SBPPs) Fusarium oxysporum f. sp. lactucae MAFF 744088, Rosellinia necatrix, Rhizoctonia solani MAFF 237426, and Pythium ultimum NBRC 100123. We also tested whether these probable endobacteria affected phosphorus solubilization, ethylene production, nitrogenase activity (NA), and stimulation of AMF hyphal growth. In addition, fresh samples of spores and hyphae were photographed using an in situ scanning electron microscope (SEM) (Quanta 250FEG; FEI Co., Japan). Bacterial aggregates (BAs), structures similar to biofilms, could be detected on the surface of hyphae and spores. We demonstrate that using extraction with an ultrathin needle, it is possible to isolate AMF-associated bacterial species that are likely derived from inside the fungal spores.

The role of pathogen suppression on the growth promotion of wheat byPenicillium radicum

The fungus Penicillium radicum can be used as an inoculant to promote the growth of wheat crops. Phosphate solubilisation by microorganisms has been suggested to be a major mechanism of plant growth promotion (PGP), but field trials and glasshouse trials with P. radicum have shown that other mechanisms are involved. This work tested the potential for biocontrol of soilborne plant pathogens as an alternative mechanism of P by P. radicum. In vitro, P. radicum significantly (P<0.05) inhibited the growth of Gaeumannomyces graminis var. tritici (Ggt), Rhizoctonia solani, Pythium irregulare and Phytophthora cinnamomi but not the beneficial fungus Trichoderma koningii. Sterilised culture extracts of P. radicum contained inhibitory activity, suggesting production of antibiotic compounds. Subsequently, the effect of P. radicum on take-all disease of wheat was investigated in a series of glasshouse trials. In the first two experiments, P. radicum did not exhibit biological control activity against take-all disease, but rather increased disease severity (P=0.02). Furthermore, PGP by P. radicum (21% increase in shoot dry weight; P=0.001) was removed when inoculum of Ggt was added to soil. An experiment was conducted to investigate the interactions between the fungicide fluquinconazole (Jockey), the biocontrol agent T. koningii 7a and P. radicum on wheat growth in the presence of Ggt. All treatments significantly reduced take-all disease severity on wheat roots (P<0.05), with the most effective treatment being P. radicum+Jockey (11% disease reduction). Similarly, dual inoculation with P. radicum+Jockey resulted in significantly higher shoot dry weights (31%; P<0.05). The detrimental effect of take-all disease on PGP by P. radicum may explain some of the variability associated with the use of P. radicum in field situations. The integration of P. radicum with a chemical treatment for take-all control has shown excellent potential and could be used to increase the reliability and efficacy of P. radicum in situations of potential disease.

TmkA, a mitogen-activated protein kinase of Trichoderma virens, is involved in biocontrol properties and repression of conidiation in the dark.

Trichoderma virens is a mycoparasitic fungus used in biocontrol of soilborne plant pathogens. It inhibits or kills plant-pathogenic fungi through production of antifungal antibiotics and parasitism of hyphae and sclerotia. Conidiation, or the production of asexual spores, an inducible process triggered by light or nutrient stress, is an important trait in survival and also development of formulation products. In many fungi, signaling pathways, including mitogen-activated protein kinase (MAPK) cascades, have been implicated in parasitism of host plants as well as in the production of asexual spores. Here, we have studied the role of a MAPK gene, that for TmkA, in conidiation and antagonistic properties of a biocontrol strain of T. virens. Through single- and double-crossover recombination, we obtained three tmkA loss-of-function mutants. The TmkA transcript was not detectable in these mutants. The mutants conidiated in the dark, although photoinduction was normal and the light sensitivities of the wild type and the mutant were the same. The mutants had, overall, normal colony morphology, but their radial growth rate was reduced by about 16%, with no decrease in biomass production. Against Rhizoctonia solani hyphae, the knockout mutants exhibited mycoparasitic coiling and lysis of host hyphae similar to that of the wild type. The mutants, however, were less effective in colonizing the sclerotia of R. solani. On Sclerotium rolfsii, the MAPK loss-of-function mutants had reduced antagonistic properties in confrontation assays and failed to parasitize the sclerotia. TmkA-dependent and -independent pathways are thus involved in antagonism against different hosts. Finally, in contrast to the case for other filamentous fungi studied so far, signaling through a MAPK represses, rather than induces, asexual sporulation.

Biodiversity of &lt;i&gt;Trichoderma&lt;/i&gt; species in agricultural soils and their potential use as seed coat amendments for the biocontrol of soilborne plant pathogens

Biodiversity of &lt;i&gt;Trichoderma&lt;/i&gt; species in agricultural soils and their potential use as seed coat amendments for the biocontrol of soilborne plant pathogens

Biocontrol of Soilborne Plant Pathogens.

Biocontrol involves harnessing disease-suppressive microor? ganisms to improve plant health. Disease suppression by biocontrol agents is the sustained manifestation of interactions among the plant, the pathogen, the biocontrol agent, the microbial community on and around the plant, and the physi? cal environment. Even in model laboratory systems, the study of biocontrol involves interactions among a minimum of three organisms. Therefore, despite its potential in agricultural ap? plications, biocontrol is one of the most poorly understood areas of plant-microbe interactions. The complexity of these systems has influenced the accep? tance of biocontrol as a means of controlling plant diseases in two ways. First, practical results with biocontrol have been variable. Thus, despite some stunning successes with biocon? trol agents in agriculture, there remains a general skepticism born of past failures (Cook and Baker, 1983; Weiler, 1988). Second, progress in understanding an entire system has been slow. Recently, however, substantial progress has been made in a number of biocontrol systems through the application of genetic and mathematical approaches that accommodate the complexity. Biocontrol of soilborne diseases is particularly complex be? cause these diseases occur in the dynamic environment at the interface of root and soil known as the rhizosphere, which is defined as the region surrounding a root that is affected by it. The rhizosphere is typified by rapid change, intense microbial activity, and high populations of bacteria compared with nonrhizosphere soil. Plants release metabolically active cells from their roots and deposit as much as 20% of the carbon allocated to roots in the rhizosphere, suggesting a highly evolved relationship between the plant and rhizosphere microorgan? isms. The rhizosphere is subject to dramatic changes on a short temporal scale?rain events and daytime drought can result in fluctuations in salt concentration, pH, osmotic poten? tial, water potential, and soil particle structure. Over longer temporal scales, the rhizosphere can change due to root growth, interactions with other soil biota, and weathering processes. It is the dynamic nature of the rhizosphere that makes it an interesting setting for the interactions that lead to disease and biocontrol of disease (Rovira, 1965,1969,1991; Hawes, 1991; Waisel et al., 1991).

Biocontrol of soil‐borne plant pathogens: Concepts and their application

AbstractA few soil‐borne plant pathogens have been controlled successfully by commercial formulations of biocontrol agents, but many attempts to develop biocontrol inoculants, although promising under experimental conditions, have met with difficulties in practice. The reasons for this are discussed in this review, which outlines some of the major findings on the behaviour of microbial inoculants in soil. It is emphasized that biocontrol also occurs naturally in current agricultural practice and can be exploited purposely, but it is vulnerable to disruption by agrochemicals or mismanagement. The future of biocontrol of soilborne plant pathogens probably lies in integrated (biorational) control systems that combine the use of commercial inoculants, where appropriate, with management practices that maintain and enhance the natural biocontrol systems.

Suppressive compost for biocontrol of soilborne plant pathogens

Compost produced from agricultural wastes can be used as the organic component of container media. We have studied the properties of composted grape marc (CGM) and composted separated cattle manure (CSM). Media amended with these composts were found to be suppressive to soilborne plant pathogens such asRhizoctonia solani andPythium aphanidermatum. Suppression is the result of microbial activity developing during the composting process. It is suggested that suppressive compost can be used in horticulture as a means of biological control.

Method To Enhance Growth and Sporulation of Pelletized Biocontrol Fungi

The biocontrol fungi Trichoderma harzianum, used to control soilborne plant pathogens, and Beauveria bassiana, used to control insect pests, were formulated as mycelial biomass in alginate pellets with wheat bran added. After drying for 0, 4, or 16 h, pellets were placed in water or in aqueous solutions of polyethylene glycol (PEG) 8000 for 4 to 24 h and then allowed to continue drying. PEG-treated pellets containing T. harzianum showed significantly greater proliferation of hyphae in soil than untreated pellets or pellets treated with water. Production of conidia of T. harzianum from PEG-treated pellets was lower than production from untreated pellets after 4 days, although rates were equivalent after 7 days. In contrast, production of conidia of B. bassiana was significantly more rapid from PEG-treated pellets than from untreated pellets. Biocontrol of soilborne plant pathogens or insect pests may be enhanced by rapid hyphal growth of T. harzianum in soil or rapid sporulation of B. bassiana on foliage, respectively. Therefore, PEG treatment may improve the efficacy of these biocontrol agents.

Mechanisms of biocontrol of soil-borne plant pathogens by Rhizobacteria

Mechanisms of biocontrol of soil-borne plant pathogens by Rhizobacteria

Biocontrol of soil-borne plant pathogens with introduced inocula

Despite more than 60 years of research on biocontrol of plant pathogens, introduced inocula of only two control agents are used widely and successfully against soil-borne or root-infecting pathogens in current commercial practice. Several others are undergoing exploratory commercial development or are used on a limited or local commercial scale. This review adopts a critical approach to the strategies for control of soil-borne pathogens with applied antagonists, and identifies some areas in which rapid developments could occur. In most instances it will be necessary to combine the use of microbial inocula with management practices designed to minimize disease losses. Also, in most instances, biocontrol strategies should be targeted against small pathogen populations, to prevent or delay the build up of disease, rather than to control existing high levels of pathogens. Natural, rapid senescence of cereal root cortices, which is influenced by both genetic and environmental factors, offers prospects for developing the use of weak parasites for control of take-all disease, caused by Gaeumannomyces graminis var. tritici . Recent studies on biocontrol of take-all by the fungus Microdochium bolleyi are presented, and special emphasis is given to the strategies most likely to be of value for take-all control.