Use Of Biocontrol Agents Research Articles

Tick control: Thoughts on a research agenda

Tick control is critical to the control of tick borne disease, while the direct impact of ticks on livestock productivity is also well known. For livestock, tick control today rests overwhelmingly on the twin approaches of genetics and chemical acaricides, although the disadvantages and limitations of both are recognized. The achievement of the full potential of vaccination, the application of biocontrol agents and the coordinated management of the existing technologies all pose challenging research problems. Progress in many areas has been steady over the last decade, while the acquisition of molecular information has now reached a revolutionary stage. This is likely to have immediate impact on the identification of potential antigens for improved vaccines and novel targets for acaricide action. In many circumstances, the rate limiting step in making scientific progress will remain unchanged, namely the resource constraint on evaluating these appropriately in large animals. For other approaches, such as the use of biocontrol agents, the limitation is likely to be less in the identification of suitable agents than in their delivery in an efficient and cost effective way. Our scientific understanding of the molecular basis for the tick vector–tick borne disease interaction is in its infancy but the area is both challenging and, in the long term, likely to be of great practical importance. What is arguably the most difficult problem of all remains: the translation of laboratory research into the extremely diverse parasite control requirements of farming systems in a way that is practically useful.

Effect of substrates on growth and shelf life of Trichoderma harzianum and its use in biocontrol of diseases

A study on the effect of different agrowastes on the population density and shelf life of Trichoderma harzianum indicated that all the substrates showed effective propagation of T. harzianum; however, the population count after 30 days was maximum in used tea leaves (8 × 10 8 cfu/g) and shelf life was found to be maximum (2.9 × 10 5 cfu/g after 210 days) in wheat bran–sawdust. The application of these formulations on chickpea and groundnut plants significantly reduced the percent mortality due to chickpea wilt complex and groundnut collar rot disease, respectively.

Isolation, Identification and Screening of Potential Antagonistic Microorganism for the Biocontrol of Phytophthora meadii McRae Causing Fruit Rot of Arecanut (Areca catechu L.)

Fruit rot of arecanut caused by Phytophthora meadii McRae is a major constraint in arecanut production causing substantial loss in yield. Use of biocontrol agents is effective, ecofriendly and nonhazardous possibility for fruit rot management. The present investigation focuses on the screening of potential biocontrol agents against the fruit rot pathogen . Phytophthora meadii on arecanut. Among the 14 isolates screened on dual culture method and bioassav experiments, Trichoderma viride (04), Bacillus cereus , B. polymyxa and B. licheniformis were emerged as potential biocontrol agents.

Biological Control of Tropical Weeds: Research Opportunities in Plant–Herbivore Interactions1

INVASIVE EXOTIC SPECIES ARE A MAJOR ECOLOGICAL PROBLEM in many of the world's ecosystems (Sala et al. 2000). With some notable exceptions, however, most tropical moist forests appear to be resistant to the impacts of invasive exotic plants (Rejmainek 1996, Denslow & DeWalt in press). Sala et al. (2000), for example, identified land use change, but not biotic exchange, as the major threat to tropical ecosystems. However, the impacts of invasive exotic plants are a leading threat to native ecosystems on oceanic islands, where naturalized exotic plants have doubled the sizes of floras (Sax et al. 2002). On tropical islands, exotic species invade intact forests, alter successional trajectories, impede restoration of endangered plant communities, and contribute to the degradation of fragmented ecosystems (Denslow & DeWalt in press). These impacts are of special concern because tropical islands are repositories of great biodiversity and are characterized by high levels of endemism and large numbers of threatened and endangered species. Furthermore, continental tropical forests that are fragmented or otherwise disturbed also are vulnerable to the impacts of exotic invaders (e.g., Humphries et al. 1992), and control of invasive exotic plants is a major cost for many land managers. Unfortunately, the options available for management of established invasive species are few and costly and carry risk of unintended consequences. A tool with great promise is the introduction of exotic hostspecific arthropods or pathogens to reduce the abundance, rate of spread, and/or habitat distribution of the target plant in its invasive range. Classical biological control is based on the premise that the population explosions of some exotic species in their introduced ranges are due in part to their escape from their native herbivoresthe ecological release hypothesis (Keane & Crawley 2002, DeWalt etal. 2004, Levine etal. 2004). Historically, the primary objective of weed biocontrol has been the direct reduction in density, cover, and range of target weeds that suppress desirable forage species, are toxic or unpalatable to livestock or that impede waterways. Most of this experience has developed in nonforest ecosystems (Coombs et al. 2004) and at temperate as opposed to tropical latitudes; among weed genera targeted by biocontrol worldwide (except Australia which has both tropical and nontropical ecosystems), 51 percent have been exclusively nontropical and only 25 percent exclusively tropical (Julien & Griffiths 1998). In some cases, this approach has met with dramatic success, e.g., St. John's wort: Hypericumperforatum L. (Harris et al. 1969), leafy spurge: Euphorbia esula L. (Harris 1993), various cactus species: Opuntia spp. (e.g., Moran & Zimmermann 1991), water hyacinth: Eichornia crassipes (Martius) Solms-Laubach (Center et al. 1999b), and giant salvinia: Salvinia molesta D. S. Mitchell (Room et al. 1981). The use of introduced arthopods and pathogens to control exotic wildland weeds is more recent but is showing promise in the control of paperbark: Melaleuca quinquenervia (Cav.) Blake in the Florida Everglades (Center et al. 2000), purple loosestrife: Lythrum salicaria L. in the northern (U.S.) wetlands (Blossey 2002), saltcedar: Tamarix spp. along western (U.S.) stream courses (DeLoach & Carruthers 2004), and several Acacia species in South Africa (Impson et al. 2000). Concern has been expressed over the use of biocontrol agents because of their potential to cause'both direct and indirect nontarget impacts (Simberloff & Stiling 1996; Louda et al. 1997, 2003; McEvoy & Coombs 2000). Nontarget impacts of introduced biocontrol agents for weeds can take the form of direct feeding by the agent on nontarget plant species (Pemberton 2000) or indirect interactions such as competition with native herbivores (Louda et al. 1997) and alteration of the community trophic structure (Henneman & Memmott 2001). Recent reviews provide evidence that the risk of direct nontarget impacts is greatest in closely related species and that the agents released following modern, widely accepted host-range testing protocols and review processes rarely affect nontarget species (Pemberton 2000). However, only a small proportion of agents released are effective at reducing the target species, and our understanding of indirect interactions of introduced biocontrol agents is rudimentary (McEvoy & Coombs 2000). As our appreciation grows of the harm caused by invasive plants in native ecosystems, the use of biological control agents in wildlands becomes increasingly attractive. Extensive use of chemical and mechanical control methods in native ecosystems also can have substantial secondary effects, including impacts on nontarget species and ecosystem processes. In addition to their high host specificity, biocontrol agents can be effective over large areas of poorly accessible terrain. In many tropical countries, where available resources-both financial and human-for the long-term control of invasive species in natural areas are small, cost-effectiveness makes biological control an attractive conservation tool. 1 Received 3 March 2005; revision accepted 17 June 2005. 2 Corresponding author; e-mail: jdenslow@fs.fed.us

Abundance and Spread of the Invasive Red Algae, Kappaphycus spp., in Kane’ohe Bay, Hawai’i and an Experimental Assessment of Management Options

Several species of Kappaphycus were intentionally introduced into Kane’ohe Bay, Hawai’i in the 1970s. Subsequent research has demonstrated that these algae have spread rapidly throughout the bay and can be found in a variety of reef habitats overgrowing and killing corals. This study was conducted to (a) quantify Kappaphycus spp. abundance both spatially and temporally, and (b) investigate control options including manual removal and the use of biocontrol agents. Kappaphycus spp. distribution has increased in the bay over the period between surveys conducted in 1999 and 2002, with variation among reefs. The biomass of Kappaphycus spp. removed, and the amount of time required to manually remove them from the reef varied with habitat type, but in all cases amounted to at least 10 kg/m 2 requiring almost 2 person-hours to clear 1 m 2 . Re-growth of the algae following their removal was rapid at most sites, likely due to the experimentally demonstrated ability of the algae to re-grow from minute attachment points and the low palatability of the algae to native herbivorous fishes. The native sea urchin, Tripneustes gratilla, reduced the biomass of Kappaphycus spp. in small experimental enclosures and may be a useful biocontrol agent. Because Kappaphycus spp. are still spreading in Kane’ohe Bay and can overgrow over 50% cover on some reefs, we recommend that rapid management action be taken to prevent further damage and spread to other Hawaiian coral reefs.

PHENOTYPIC TRAITS OF WOUND COMPETENCE OF POSTHARVEST BIOCONTROL YEASTS AND POTENTIAL OF THESE MICROORGANISMS FOR PREVENTION/ DETOXIFICATION OF MYCOTOXIN ACCUMULATION

Knowledge of the mechanisms of action of biocontrol agents (BCAs) is crucial to identify underlying pivotal traits, whose enhancement could boost antagonist activity and encourage the use of BCAs as alternative/integration of fungicides. We had previously shown that resistance of postharvest BCAs to oxidative stress is a possible key mechanism for their wound competence to successfully outcompete wound pathogens in stored apples. In this work we describe recent studies aimed at elucidating the phenotypic traits underlying wound competence of postharvest biocontrol yeasts. Further, we show that some BCAs display a potential activity in addressing other major issues of food safety: contamination of apple-based food products with Patulin and of wine with Ochratoxin A, mycotoxins produced by the fungal pathogens of apples and grape Penicillium expansum and Aspergillus carbonarius, respectively.

Fungos endofíticos isolados de ápices caulinares de pupunheira cultivada in vivo e in vitro

A perda de plantas micropropagadas ocorre, principalmente, pela presença de microrganismos, responsáveis pela morte das plantas no início da cultura ou em seu estabelecimento no campo. O trabalho teve como objetivo a identificação, por taxonomia clássica, e por meio de técnicas moleculares, de fungos presentes nos ápices caulinares de pupunheiras sadias, cultivadas no campo, e a comparação com os fungos isolados, em plantas micropropagadas há dois anos. Os isolados da microbiota fúngica endofítica, das plantas cultivadas in vitro, foram: Fusarium oxysporum, Neotyphodium sp. e Epicoccum nigrum; e das plantas in vivo, foram: Fusarium sp., F. proliferatum, F. oxysporum, Colletotrichum sp., Alternaria gaisen, Neotyphodium sp. e Epicoccum nigrum. As sete espécies de fungos foram reintroduzidas in vitro na planta hospedeira, demonstrando diferentes comportamentos. Neotyphodium sp. e E. nigrum estabeleceram uma interação endofítica com a planta, e as demais comportaram-se como patógenos, diminuindo o desenvolvimento das plântulas em relação às plantas sem inoculação. As espécies endofíticas apresentam potencial para o uso no controle biológico de patógenos de pupunha.

After biocontrol: Assessing indirect effects of insect releases

Development of biological control agents for weeds has been motivated by the need to reduce the abundance and distribution of a pest plant where chemical and mechanical control were not cost effective. Primary objectives have been direct reduction in abundance of the target and, secondarily, the increase of desirable species. Recently, wildland weeds have become a focus of biological control projects. Here, desired outcomes include both reduction of the target and indirect effects of increased diversity and abundance of native species and restoration of ecosystem services. However, goals and benefits of biocontrol programs are not always well-articulated and direct and indirect impacts are not easily predicted. We evaluated the extent to which several successful biological control projects for weeds of rangelands and waterways measured indirect impacts on invaded ecosystems. We also examined biocontrol of a wildland pest tree for which the principal objective is restoration of ecosystem services. We found few quantitative assessments of the impacts of pest plant reduction on community composition or ecosystem processes. All examples documented variation in the impacts of agent(s) across the invasive range of the target plant as well as variation in impacts on the invaded ecosystem. However, without appropriate quantitative information, we cannot evaluate site characteristics that may influence vegetation responses. Most successful weed management programs integrated the use of biocontrol agents with other weed management strategies, especially modifications of disturbance and competing vegetation. Discussion and evaluation of responses of nontarget species would improve our understanding of the context-specificity of outcomes.

Biological Control of Fusarium Wilt of Tomato – A Review

Fusarium wilt of tomato (Lycopersicum esculentum) caused by Fusarium oxysporum f.sp. lycopersici leads to high losses of tomatoes in many countries. Increasing restraints on the use of pesticides encourages adoption of use of alternative strategies of controlling the disease. Alternative strategies include use of biocontrol agents. Bacterial biocontrol agents with promising biocontrol activities against F. 0xysporum f. sp. lycopersici include Pseudomonas flourescens, P. putida, P. chlororaphis, P. alcaligenes, Bacillus subtilis, Streptomyces pulcher, S. canascens, S. citreoflourescens, S. corchorusii and S. mutabilis. Fungal biocontrol agents that are efficacious against F. oxysporum f.sp. lycopersici include Penicillium oxalicum, P. purpurogenum, Trichoderma harzianum, T. piluliferum, Pythium oligandrum, non-pathogenic Fusarium oxysporum Fo47 and Trametes versicolor. Biological control agents including bacteria and fungi have shown some promise for the control of Fusarium wilt of tomato. This paper discusses the mode of action of non-pathogenic strains of F. oxysporum, other fungi and bacteria including fluorescent pseudomonads in the management of Fusarium wilt of tomato. The relative importance of systemic induced resistance in the suppression of Fusarium wilt is discussed. Key Words: biocontrol, induced resistance, rhizosphere, tomato wilt. J. Trop. Microbiol Vol.1 2002: 74-78

United States Department of Agriculture-Agricultural Research Service research programs in biological control of plant diseases.

A number of USDA-ARS programs directed at overcoming impediments to the use of biocontrol agents on a commercial scale are described. These include improvements in screening techniques, taxonomic studies to identify beneficial strains more precisely, and studies on various aspects of the large-scale production of biocontrol agents. Another broad area of studies covers the ecological aspects of biocontrol agents-their interaction with the pathogen, with the plant and with other aspects of the environmental complex. Examples of these studies are given and their relevance to the further development and expansion of biocontrol agents is discussed.

Plant chitinase as a possible biocontrol agent for use instead of chemical fungicides.

We investigated whether a plant chitinase can be used as a biocontrol agent instead of chemical fungicides by spraying chitinase E (family 19; class IV) from a yam (Dioscorea opposita Thunb) alone or together with beta-1,3-glucanase directly onto the surface of a powdery mildew infecting strawberry berries and leaves. Results were observed by eye and with a scanning electron microscope. The powdery mildew infecting the strawberries was degraded, mainly by the chitinase, and the disease did not appear again for more than 2 weeks. These results indicated that this kind of plant chitinase might be safe and biodegradable biocontrol agent for use instead of conventional fungicides.

Mechanisms Employed by Trichoderma Species in the Biological Control of Plant Diseases: The History and Evolution of Current Concepts.

Fungal species belonging to the genus Trichoderma are worldwide in occurrence and easily isolated from soil, decaying wood, and other forms of plant organic matter. They are, for the most part, classified as imperfect fungi, in that they have no known sexual stage. Rapid growth rate in culture and the production of numerous spores (conidia) that are varying shades of green characterize fungi in this genus. The reverse side of colonies is often uncolored, buff, yellow, amber, or yellow-green, and many species produce prodigious quantities of thick-walled spores (chlamydospores) in submerged mycelium (8). The potential of Trichoderma species as biocontrol agents of plant diseases was first recognized in the early 1930s (31), and in subsequent years, control of many diseases has been added to the list (1,3,5,7,9,11,19, 23,29,34,37,40). This has culminated in the commercial production of several Trichoderma species for the protection and growth enhancement of a number of crops in the United States (24), and in the production of Trichoderma species and mixtures of species in India, Israel, New Zealand, and Sweden (D. R. Fravel, personal communication). One of the most interesting aspects of the science of biological control is the study of the mechanisms employed by biocontrol agents to effect disease control. Past research indicates that the mechanisms are many and varied, even within the genus Trichoderma. In order to make the most effective use of biocontrol agents for the control of plant diseases, we must understand how the agents work and what their limitations are. We can then develop effective means of culturing, storing, applying, and utilizing biocontrol agents so that we harness their best effort for disease control. The selected research papers cited in this article were chosen because they illustrate what has been learned about mechanisms involved in biocontrol with Trichoderma species.

Infection of Chrysanthemoides monilifera ssp. monilifera by the rust fungus Endophyllum osteospermi is associated with a reduction in�vegetative growth and reproduction

The perennial shrub Chrysanthemoides monilifera ssp. monilifera (Asteraceae: Calendulae), indigenous to South Africa, has become a serious weed of native vegetation in cool-temperate, winter-rainfall areas in southeastern Australia. The microcyclic, autoecious, rust fungus Endophyllum osteospermi induces the production of witches’ brooms on C. monilifera ssp. monilifera. Field observations indicate that the presence of witches’ brooms may reduce the growth and reproduction of the remaining symptomless parts of the host bushes and, therefore, this rust fungus is currently being considered as a biocontrol agent for use against C. monilifera ssp. monilifera in Australia. The vegetative growth and reproductive output of symptomless branches on bushes with different levels of E. osteospermi infections were measured at three South African sites with naturally infected populations of C. monilifera ssp. monilifera. The growth of symptomless branches on infected bushes was 26–81% less than that of symptomless branches on uninfected bushes. The number of buds, flowering capitulae, fruiting capitulae and drupes on individual symptomless branches of infected bushes was 35–75%, 45–90%, 15–99%, and 15–90% less, respectively, than those on uninfected bushes. The presence of witches’ brooms was consistently associated with reduced growth and reproductive output of bushes. Very little flowering and drupe production occurred on witches’ brooms themselves.

Biocontrol of Pests on Plant Crops in Denmark: Present Status and Future Potential

In this review, the status of biocontrol in plant crops in Denmark is analysed and factors governing the present use and future potential are described. In glasshouse vegetables, biocontrol is the dominant method to control pests while it is much less used in glasshouse ornamentals. On outdoor crops, the use of biocontrol is negligible. The main factors determining future prospects include: research, political initiatives, the scale of organic farming, the interest of companies marketing and advising on biocontrol, and public opinion. Good communication between scientists, advisers, growers, government authorities and the public has occurred for many years in Denmark, and has been essential for the successful implementation of biocontrol in glasshouses. Future development of microbial control (to which some organic growers and some members of the public show concerns) will require both research and a debate among the partners, particularly about environmental safety.

Cytological effects of cellulases in the parasitism of Phytophthora parasitica by Pythium oligandrum.

The ubiquitous oomycete Pythium oligandrum is a potential biocontrol agent for use against a wide range of pathogenic fungi and an inducer of plant disease resistance. The ability of P. oligandrum to compete with root pathogens for saprophytic colonization of substrates may be critical for pathogen increase in soil, but other mechanisms, including antibiosis and enzyme production, also may play a role in the antagonistic process. We used transmission electron microscopy and gold cytochemistry to analyze the intercellular interaction between P. oligandrum and Phytophthora parasitica. Growth of P. oligandrum towards Phytophthora cells correlated with changes in the host, including retraction of the plasma membrane and cytoplasmic disorganization. These changes were associated with the deposition onto the inner host cell surface of a cellulose-enriched material. P. oligandrum hyphae could penetrate the thickened host cell wall and the cellulose-enriched material, suggesting that large amounts of cellulolytic enzymes were produced. Labeling of cellulose with gold-complexed exoglucanase showed that the integrity of the cellulose was greatly affected both along the channel of fungal penetration and also at a distance from it. We measured cellulolytic activity of P. oligandrum in substrate-free liquid medium. The enzymes present were almost as effective as those from Trichoderma viride in degrading both carboxymethyl cellulose and Phytophthora wall-bound cellulose. P. oligandrum and its cellulolytic enzymes may be useful for biological control of oomycete pathogens, including Phytophthora and Pythium spp., which are frequently encountered in field and greenhouse production.

USE OF BIOCONTROL AGENTS AGAINST SOIL-BORNE PATHOGENS: RESULTS AND LIMITATIONS

USE OF BIOCONTROL AGENTS AGAINST SOIL-BORNE PATHOGENS: RESULTS AND LIMITATIONS

Biological control of vertebrate pests

Author(s): Pech, R. P. | Abstract: Biological control of vertebrate pest species has evolved from classical and forget strategies to current programs of integrated management, which in the future may include the use of genetically modified organisms. Key stages in the use of biocontrol are illustrated with the history of managing rabbits (Oryctolagus cuniculus) in Australia. Two pathogens have been successfully released, myxoma virus in the 1950s and rabbit haemorrhagic disease (RHD) virus in 1995, and both have been highly effective in suppressing rabbit populations. The rapid attenuation of myxoma virus, as well as bioclimatic constraints on its distribution, and the development of resistance in wild rabbits prompted the later release of insect vectors and highly virulent strains of the virus. The evolution of the current rabbit-myxomatosis-RHD-predator system is still being monitored, and research is in progress to add immunocontraceptive strains of myxoma virus to the suite of rabbit control techniques. Increased attention to measuring the outcomes of pest management resulted in a nationwide program to document the economic and environmental consequences of RHD. This program was conducted much more systematically than for introduction of myxoma virus or its vectors, and similar monitoring is likely to be mandatory for future biocontrol agents.

Method To immobilize the aphid-pathogenic fungus erynia neoaphidis in an alginate matrix for biocontrol

Erynia neoaphidis is an important fungal pathogen of aphid pests worldwide. There have been few reported attempts to formulate this natural agent for use in biocontrol. In the current study, factors involved in the immobilization of E. neoaphidis hyphae in an alginate matrix were investigated. Hyphae of two isolates cultured in liquid medium were 220 to 620 &mgr;m in length and 7 to 19 &mgr;m in diameter with a 74 to 83% cytoplasmic content. The optimal concentration of low-viscosity sodium alginate for production of conidia from entrapped hyphae was 1.5% (wt/vol), and 0.1 and 0.25 M calcium chloride were equally suitable for use as the gelling solution. Alginate beads were rinsed with 10% sucrose after gelling. However, beads should not be left for longer than 40 min in 0.1 M calcium chloride or 10% sucrose to prevent a 10% loss in conidial production. A 40% (vol/vol) concentration of fungal biomass produced significantly more conidia than either 20% or the standard concentration of 10%. This effect persisted even after beads were dried overnight in a laminar flow hood and stored at 4 degreesC for 4 days. Conidia from freshly produced alginate beads caused 27 to 32% infection in Pea aphids as determined by standardized laboratory bioassays. This finding was not significantly different from infections in aphids inoculated with fresh mycelial mats or plugs from Petri dish cultures. In conclusion, algination appears to be a promising technique for utilizing E. neoaphidis in the biocontrol of aphid pests.

Aggressiveness of French isolates of Ralstonia solanacearum and their potential use in biocontrol1

Differences in the pathogenicity of French isolates of Ralstonia solanacearum were found using standardized root inoculations of tomato, aubergine and tobacco. Aggressiveness was assessed by comparing percentage wilted plants over 12 days, following root inoculation of tomato and aubergine, expressed as the mean of four independent replicates for each. The isolates could be separated into four aggressiveness groups on these hosts. None of them provoked any symptoms after root inoculation of tobacco, but they did induce a typical hypersensitive response, or disease symptoms, when infiltrated into tobacco leaves of tolerant or susceptible cultivars, respectively. Samples taken from stems of symptomless tobacco demonstrated high percentages of latent infections. The development of wilting symptoms was strictly correlated with large numbers of the bacterial parasite in xylem vessels and was thus related to the invasiveness of the bacterial strain. Root inoculation with an Hrp‐ mutant strain of R. solanacearum induced protection against subsequent inoculation by a pathogenic strain. The more invasive the Hrp‐ mutant strain, the more protection it gave. Thus aggressiveness should be assessed with a view to epidemiological studies and control measures, since it is an important characteristic of R. solanacearum isolates.

Clinical and physiologic analysis of the efficacy of scoliotic disease treatment at the specialized rehabilitation center

The work is based on the analysis of treatment results of 52 scoliotic patients, aged 7-14 years. All patients were treated at the rehabilitation center for children with locomotor disorders. 14 patients had the 1st degree of scoliosis, 21 - lst-2nd degree, 13 - 2nd degree and 4 children - 2nd-3rd degree. Prior to and after treatment all patient were subjected to complex examination including the evaluation of their condition by clinical numbered scale, electromyography, apparatus evaluation of tonus, contact thermometry. In various groups of patients the main therapeutic course was supplemented with the seances of biocontrol with feedback, acupuncture, magnetic pulse stimulation, expanded physiotherapeutic course in various combinations. Authors conclude that clinical numbered scale supplemented with several indices may be used in clinical practice. Entering on the curative complex the methods which contribute to the improvement of circulation and metabolism processes with following use of biocontrol with feedback by EMG will allow to raise the efficacy of scoliotic disease treatment.