Fungal Biological Control Research Articles

Competition between a biological control fungus, Ophiostoma piliferum, and symbionts of the southern pine beetle

A colorless isolate of O. piliferum was paired in a series of competitive interactions with three fungal symbionts of Dendroctonus frontalis, the southern pine beetle. Two of these fungi, Ceratocystiopsis ranaculosus and Entomocorticium sp. A, are considered to be mutualists of the southern pine beetle. The third fungal symbiont, O. minus, is considered to be an antagonist. I found strong evidence of differential competition between O. piliferum and all three symbionts. In primary and secondary resource capture contests on an artificial medium O. piliferum outcompeted all three fungi. In inoculations of natural substrate, O. piliferum outcompeted the two mutualists but did not outcompete O. minus. The ability of O. piliferum to outcompete beetle mutualists on both artificial and natural substrates indicates promise for this fungus as a biological control agent of the southern pine beetle. However, it may not be able to always prevent colonization by O. minus and the resultant discoloration of colonized wood.

The Safe Use of Fungi for Biological Control of Weeds

The Safe Use of Fungi for Biological Control of Weeds

Interactions of mycophagous collembola and biological control fungi in the suppression of Rhizoctonia solani

A rhizosphere-inhabiting collembolan, Proisotoma minuta (Insecta: Isotomidae), and three known biocontrol fungi were studied in sterilized and non-sterilized soil for suppression of Rhizoctonia solani on cotton in a greenhouse environment. R. solani in dried oat culture was incorporated into soil at four inoculum densities ranging from 10 to 150mg kg −1. Trichoderma harzianum on wheat bran and Gliocladium virens as dried oatmeal culture were incorporated at 200 and 50 mg kg −1 soil, respectively, and Laetisaria arvalis dried, micromilled mycelium was applied as a seed dressing. Each fungus was applied either alone or with a population of P. minuta at 1000 kg − soil. Most effective biological control occurred in sterilized soil when the fungal biocontrol agents were integrated with the insect population; all combinations provided more effective disease suppression than the fungal agents used alone. In non-sterilized soil, having a natural competitive microflora, only P. minuta used alone and the L. arvalis + P. minuta treatment provided consistently significant disease reduction compared to R. solaniinfested soil without added agents. Moderate disease control in non-sterilized soil was obtained with T. harzianum or G. virens when combined with the insect population. Plant-growth dry weight measurements did not consistently reflect the disease control benefit. The specific mechanisms promoting increased biocontrol capacity of insect + fungus combinations, though not clearly defined here, must lie within a complex of factors including preference of R. solani as a food source for P. minuta, aversion of the insect to the two sporulating Hyphomycetes used for biocontrol, and direct parasitism of R. solani by the fungal agents.

Production and characterization of monoclonal antibodies to the sapstaining fungus Ophiostoma piceae

A sensitive immunological tool has been developed to detect the sapstaining fungus Ophiostoma piceae 3871, which plagues the wood industry. Monoclonal antibodies (1F3(1), 4G3(14), 4G2(4), and 2B6(24)) produced against cell wall protein extracts of this fungus were specific. Specificity was estimated by enzyme linked immunosorbent assay, western blotting, and light and electron microscopy using the immunogold technique. Electron microscopy revealed gold particles localized on the outer surface of the cell wall. When screened against 24 biological control fungi the antibodies showed pratically no cross-reactivity (< 4%). When tested against 19 other staining fungi, the antibodies recognized three strains of Ophiostoma piceae, 1F3(1) recognized Phialophora botulispora, and the antibodies showed less than 5% reactivity with the other fungi. Chemical and enzymatic modification of the antigen revealed that the epitopes recognized by the monoclonal antibodies were glycospecific. Although the antibodies were produced against the cell wall protein extracts of the fungus grown in liquid culture, they also recognized the fungus growing in wood and therefore can be employed to investigate wood colonization by this fungus.Key words: Ophiostoma piceae, monoclonal antibodies, glycoprotein.

Development and benefits of rhizosphere competent fungi for biological control of plant pathogens

(1992). Development and benefits of rhizosphere competent fungi for biological control of plant pathogens. Journal of Plant Nutrition: Vol. 15, Root Distribution, and Chemistry and Biology of the Root-Soil Interface, pp. 835-843.

Genetic Manipulation of Broad Host-Range Fungi for Biological Control of Weeds

Few plant pathogens are both lethal and specific enough to be effective weed control agents. In short, highly specific organisms seldom kill. Two genetic approaches to overcome this problem are to delimit the host range of lethal pathogens or to enhance the efficacy of host-specific ones. Narrowing the virulence or survival of a deadly pathogen seems more plausible than imparting new characters to a nonlethal organism. Our approach has been to genetically restrict the host range or to decrease the survival and/or spread ofSclerotinia sclerotiorum(Lib.) de Bary, a highly virulent and aggressive pathogen of several weeds. Working with this fungus, three classes of induced mutants which meet criteria for delimitation were obtained: auxotrophic mutants that only attack plants when applied concomitantly with an exogenous source of the required nutrient; mutants unable to form sclerotia, structures required for long-term survival and precursors to fruiting bodies; and mutants with reduced virulence and/or host ranges. These studies demonstrate the validity of genetically improving bioherbicides and greatly expanding the number of fungi that may be useful as bioherbicides.

Immunological discrimination between a sap-staining fungus and a biological control fungus

An enzyme-linked immunosorbent assay (ELISA) was used to detect a sap-staining fungus, Ophiostoma piceae, and a biological-control agent, Gliocladium roseum, grown in liquid culture and in wood. A polyclonal serum prepared against whole cell fragments from broken mycelia of O. piceae detected O. piceae in liquid culture at 0.25 μg dry weight/mL; however, there was moderate cross-reactivity with G. roseum. Antiserum adsorbed on G. roseum had almost no reactivity with G. roseum but still reacted strongly with O. piceae. The specificity of these sera was verified, and the antigenic sites were localized, by immunogold labeling and electron microscopy. These studies confirmed that the adsorbed serum could differentiate between G. roseum and O. piceae and showed that the cell wall was the most reactive cellular component. These results are discussed in relation to the development of immunological probes for the detection of sap-staining and biological control fungi. Key words: polyclonal serum, enzyme-linked immunosorbent assay, immunogold labeling, sap-staining and biological control fungi, electron microscopy.

Evaluation of Endemic Foliar Fungi for Potential Biological Control of Johnsongrass (Sorghum halepense): Screening and Host Range Tests

(...) After preliminary evaluation of virulence, dew requirements and sporulation capacity, Exserohilum turcicum, Colletotrichum graminicola and Gloeocercospora sorghi were selected for second-stage tests. (...) Isolates of each fungus differed in their virulence and host specificity.(...) Moderate to high levels of leaf damage were observed in most compatible reactions.(...) Overall results suggest that the three tested fungi are too virulent to be used as mycoherbicides in corn and sorghum but may be safe in dicotyledonous crops

Interactions between root pathogens and soil microarthropods

Major biotic components of the rhizosphere include the microflora and the micro/mesofauna which, through their complex interactions, create an environment that may be either conductive or suppressive to plant growth, health and function. Many species of the Protozoa, free-living nematodes, and microarthropods (Acarina and Collembola) are microphagous or specifically mycophagous and capable of modifying the natural rhizosphere microflora. Recently, the potential of these animals as plant-pathogen deterrents has been recognized. Rhizosphere-inhabiting collembolans, Proisotoma minuta Tullberg and Onychiurus encarpatus Denis, grazed preferentially upon the cotton-seedling pathogen Rhizoctonia solani Kuhn in the presence of three well-known biological control fungi, Laetisaria arvalis Bierdsall, Trichoderma harzianum Rifai and Gliocladium virens Miller et al. Subsequent tests showed that the insects in populations of 1000–2000 kg −1 soil, suppressed R. solani significantly and cotton-seedling disease and, when integrated with each of the biocontrol fungi, disease control was further enhanced. Biocontrol value of the Collembola is being assessed in the light of certain potentially adverse effects on plants.

Variation Between Strains of the Nematophagous Fungus, Verticillium Chlamydosporium Goddard. I. Factors Affecting Growth in Vitro

The growth and sporulation of six strains of Verticillium chlamydosporium isolated from Heterodera avenae eggs, were tested in vitro. Strains differed in their average growth rate, optimum temperature for growth, and production of chlamydospores. The optimal temperature for growth was 18°C for strains I, III, IV and V and appreciable growth occurred at 10°C but was slight at 5°C; strains II and VI grew best at 20 and 25°C. All strains grew well over a pH range 4-8 and there was little effect on hyphal growth at water potentials above -15 bars and only at - 80 bars did growth cease. Large numbers (up to 84 x 106/ml) of conidia, but not chlamydospores were produced in shaken liquid culture. Strains varied significantly in their pathogenicity to H. avenae eggs in tests on water agar; strain II was the most virulent at 12°C but grew fastest at 25°C. This strain readily produced chlamydospores on CMA and produced most propagules in liquid culture and may have potential as a biological control agent. The variation within V. chlamydosporium indicates that careful strain selection is essential in the development of this fungus for biological control.

Inhibitory Interactions Between Ceratocystis Ulmi and Several Species of Entomogenous Fungi

Inhibition by 14 isolates of nine species of entomogenous fungi against two strains of the Dutch elm fungus, Ceratocystis ulmi (aggressive and non-aggressive), was evaluated under laboratory conditions. Eleven of the 14 inhibited one or both strains of C. ulmi. Different levels of antagonism were observed at different light levels and temperatures. Beauveria bassiana, Metarhizium anisopliae, and Nomuraea rileyi were antagonistic to both strains of C. ulmi under the four tested combinations of light and temperature. Metarhizium anisopliae produced the highest qualitative level of inhibition. The growth rate of the cultures differed Conventional control measures for the Dutch elm disease (DED) have em- phasized control of the insect vectors, Scolytus scolytus Fabr. and Scolytus mul- tistriatus Marsham, mainly due to the inaccessibility of the pathogen, Ceratocystis ulmi (Buis.) Moreau in the xylem vessels of the elm (Holmes, 1980). Several workers (Doane, 1959; Barson, 1976,1977; Doberski, 1981) have reported patho- genicity in tests for control of the DED insect vectors by the entomogenous fungi, Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metsch.) Sorokin, Pae- cilomyces farinosus (Dicks ex Fr.) Vuill., and Verticillium lecanii (Zimm.) Viegas. The possible use of these entomogenous fungi in biological control of DED requires investigation of antagonistic interactions between vector and control agent, and also between C. ulmi and each entomogenous fungus. Gibbs and Smith (1978) and Webber (1981) identified several fungal antagonists of C. ulmi. The bacterium, Pseudomonas syringae van Hall, has also demonstrated in vivo an? tagonism in studies by Myers and Strobel (1983), and earlier Holmes (1954) showed Bacillus polymyxa to be an effective inhibitor. The objectives of the present study were to assess the interactions between potential vector control agents (such as entomogenous fungi), and two strains of C. ulmi. Fungal antag? onists of C. ulmi would be efficiently brought into action if they were transported

Viability tests for the biological control fungus Peniophora gigantea (Fr.) Mass.

A sequential sampling scheme is in operation to test the viability and wood decaying ability of commercially produced sachets of Peniophora giganitea suspension in the treatment of pine stumps against Heterobasidion annosum.

Metarrhizium anisopliae(metschnikoff) sorokin strains in New Zealand and their possible use for controlling pasture-inhabiting insects

Abstract The green muscardine fungus, Metarrhizium anisopliae (Metsch.) Sorokin, is recorded for the first time on Costelytra zealandica White, Heteronychus sanctae-helenae Blanch., and Pericoptus truncatus Fabr. The three distinctive culture types isolated from these hosts and from Oxycanus sp. are described, and their selective pathogenicity is discussed and compared with cultures of M. anisopliae and Metarrhizium brunneum obtained from the Commonwealth Mycological Institute, Kew, and the Agricultural Research Service Collection, Peoria, Illinois. It is considered that this culture of M. brunneum comes within the species limits of M. anisopliae. Literature on M. anisopliae, its host range, and the use of the fungus for biological control, is reviewed. From a consideration of the strains of M. anisopliae in this country and an evaluation of overseas work, it is believed that this fungus is unlikely to be of much use for biological control of injurious pasture-inhabiting grubs in New Zealand.