This repressive effect may affect the performance of biocontrol bacteria that are sensitive to fusaric acid. A plant pathogen can also reduce the antibiotic production of a biocontrol agent, by altering its chemical environment. For example the plant pathogenic fungus Gaeumannomyces graminis var tritici acidifies the environment, thus disturbing the activity of the antagonistic bacterium P.
Finally, natural plasmid transfer between bacteria was also shown to provide a possible mechanism for plant pathogens to become resistant to biocontrol agents. This was the case for example for the soilborne bacterium A. The resistance resulted from the fact that this plasmid carries both the gene coding for the production of agrocin 84, the antibiotic responsible for the activity of the biocontrol agent, and the gene involved in the resistance to this antibiotic.
It was suggested that the establishment of large populations of Agrobacterium carrying plasmid pAgK84 could threaten the effectiveness of A. To minimize the risk of transfer of this plasmid by A. The judicious use of biocontrol agents and particularly of the new strain K should minimize the risk of pAgK84 transfer into pathogenic Agrobacterium strains and thus help to preserve the effectiveness of A.
Most biocontrol agents acting by hyperparasitism produce enzymes such as chitinases and glucanases. Specific mechanisms can help plant pathogens to protect themselves against these cell wall degrading enzymes.
For example, the synthesis of melanin polymers could help microorganisms to protect against microbial enzymes Bell and Wheeler, The formation of chlamydospore-like structures and vacuolated portions in mycelium allows the pigeonpea wilt pathogen Fusarium udum to maintain a slow growth and the production of conidia in presence of the hyperparasitic bacterium Bacillus subtilis AF1 Harish et al.
Another possible mechanism implies the repression of the synthesis of enzymes produced by the biocontrol agent. For instance, the mycotoxin DON, produced by Fusarium culmorum and Fusarium graminearum represses the expression of genes coding for chitinases in the biocontrol strain Trichoderma atroviride P1 Lutz et al. The induction of resistance in plants involves the synthesis and the activation of plant defense compounds as the result of activity of an elicitor.
This induction leads to rapid production of reactive oxygen species, modifications of cuticle thickness, cell wall appositions, accumulation of phenolic compounds and production of phytoalexins and pathogenesis-related proteins rendering the plants more resistance to pathogen attack Wiesel et al. To survive and become established in a resistance-induced plant, plant pathogens have to overcome these induced host defense chemicals. Plant pathogens may evolve a combination of strategies to colonize and survive in this environment.
Such strategies could include transporting toxic chemicals out of the cell or sequestrating them in cellular organelles, detoxifying host defense compounds by converting or modifying them and interfering with host signaling Morrissey and Osbourn, A way for plant pathogens to cope with host defense chemicals is to secrete them out of the cells as in the case of antimicrobial compounds produced by biocontrol agents see section above.
For example, ABC transporter activity has been implicated in the tolerance of Nectria haematococca to pisatin, a phytoalexine of Pisum sativum Denny et al. Similarly, a recent study on Grosmannia clavigera , a fungal pathogen of pine trees, showed that this fungus can survive and become established in pine tissues by the induced expression of an efflux ABC transporter GcABC-G1 Wang et al.
This allows the fungus to cope with intracellular levels of monoterpenes, which are among the most abundant antimicrobial pine defense chemicals. ABC transporters are potentially involved in the virulence and aggressiveness of fungal plant pathogens, by decreasing the toxic effect of phytoalexins Del Sorbo et al. Botrytis cinerea is for instance able to detoxify the alpha-tomatine, a phytoanticipin found in tomato plants Quidde et al. In this study, 12 out of 13 isolates of B.
The ability of B. A correlation between the ability of eight isolates of B. Some plant pathogens, like the fungus Microcyclus ulei , are tolerant to hydrocyanic acid, a volatile compound produced by plants in response to various damages Osbourn, This tolerance might be due to cyanide-resistant respiration.
Other fungi could also detoxify this compound by converting it to formamide, via cyanide-hydratases. Some plant pathogens are then able to degrade defense compounds and thus might be able to overcome the effect of biocontrol agents acting through plant defense induction.
The hypersensitive reaction HR involves the production of reactive oxygen species that leads to cell death and it is generally consider as a signal to induce the synthesis of antimicrobial compounds like phytoalexins. It usually prevents the fungal penetration into host tissue but it has been shown that HR facilitates the colonization of the plants by necrotroph fungal pathogens like B.
These plant pathogenic fungi might therefore exploit particular defense mechanisms of the plant to overcome the induced resistance effect of a biocontrol agent.
Moreover, many other plant pathogens can protect themselves against oxidative damage Duffy et al. Some plant pathogens can significantly slow down the growth of biocontrol agents by exploiting more rapidly the resources within their environment and then affecting their efficacy.
This was shown in a study conducted to evaluate the effect of several fungal root pathogens on the capacity of biocontrol strains P.
For instance, in presence of some Pythium species, the population of P. In this case, the infection by Pythium tends to reduce the root surface available for bacterial colonization which, as a consequence, tends to limit the population of potential antagonists.
In another study, the plant pathogenic oomycete P. This population size reduction limits the competition in the rhizosphere for nutrients leaking from wounds caused by P. Competition may also occur on the phyllosphere where the microbial community is also important in number and diversity and where microorganism—microorganism interactions can occur Vorholt, This microbial community may also affect the efficacy of biocontrol agents.
Knowledge about plant microbiome rhizosphere, phyllosphere, endosphere and the microbial interactions occurring on those niches should contribute to the improvement of biological control.
Despite the limited number of published studies dedicated to this topic, it is clear from this review that plant pathogens can display various including very low levels of sensitivity to biocontrol agents, regardless of the complexity of their mode of action.
Certain pathogens also have the potential to adapt in a few generation to the selection pressure exerted by biocontrol agents. Available information is sufficient to suggest that the assumption that durability of biological control is necessarily higher than that of chemical control may not always be justified.
However, it is not sufficient to draw conclusions about the existence of specific traits related to the plant pathogen or related to the biocontrol agent that could explain the loss of effectiveness of a biocontrol agent in practice. There is much need for further studies on issues related to this topic. Among them, the establishment of baseline sensitivity i.
Such monitoring is carried out routinely for fungicide resistance in fungal plant pathogens world-wide Brent and Hollomon, It is a first step to evaluate the distribution and the potential impact of resistance in the field. Moreover, detection of partially resistant isolates may indicate a risk of developing a more severe resistance that subsequently may initiate a possible loss of control in the field.
Monitoring can be done at specific sites, for example to ascertain the implication of resistance in cases when loss of biocontrol effectiveness is observed in the field. It can also be done at different dates to document the evolution of sensitivity following series of treatments with a given biocontrol agent and to monitor possible shifts in the natural populations of a plant pathogen, as suggested by Yang et al.
Finally, cross-resistance with other existing biocontrol agents or possibly fungicides may also be determined. In addition to the population approach described above, experimental evolution studies are also needed to evaluate the ability of plant pathogens to evolve under the selection pressure exerted by a biocontrol agent. This approach will result in identifying risk factors that can foster the selection of strains of plant pathogens resistant to biocontrol agents.
Various biocontrol agents and different plant pathogens must be tested in the future. This will result in identifying types of biocontrol agents with lower risk of efficacy loss, i. Even though all biocontrol agents should create selection pressure on target populations of plant pathogen, some modes of action may present a clear opportunity for pathogens to evolve resistance.
For example, a mechanism involving antibiosis would, by analogy with the fungicides, be considered a high risk to be overcome, whereas a multiple or a more complex mode of action would indicate relatively low risk. This knowledge is essential to ensure a durable efficacy of biocontrol agents on target plant pathogens. Even if the data are too sparse to suggest general statement on the use of biocontrol agents in practice, this review highlights the necessity for careful management of their use once they become commercially available in order to avoid repeating the mistakes made with chemical fungicides.
For instance, we should consider alternating or combining biocontrol agents with different mechanisms of action. In addition to possibly ensure the durability of biological control, the combination of several biocontrol agents have shown to improve the efficacy and reduce the variability of efficacy Flaherty et al.
The context of integrated pest management is probably an effective way to reduce the risk of resistance development but it necessitates to evaluate the compatibility of the biocontrol agents together with other protection methods. The combined use of biocontrol agents together with pesticides requires that their efficiency is not altered when applied in conjunction or in alternation.
Significant research efforts are also needed to anticipate the potential failure of biological control and integrate durability concerns in the screening procedure of new biocontrol agents.
According to the results mentioned in this review, caution should be applied when screening and selecting isolates of biocontrol agents, to ensure a wide representation of the targeted plant pathogen population. To test the efficacy of potential biocontrol agents or to screen for new biocontrol agents against plant diseases, most studies continue to use a single isolate or relatively few isolates. Innovative screening procedures based on the known mode of action have already been developed Schoonbeek et al.
We must go further by incorporating in the screening procedure, knowledge on the ability of plant pathogen to counteract these modes of action. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Ajouz, S. Comparison of the development in planta of a pyrrolnitrin-resistant mutant of Botrytis cinerea and its sensitive wild-type parent isolate. Plant Pathol. Variability of Botrytis cinerea sensitivity to pyrrolnitrin, an antibiotic produced by biological control agents. Biocontrol 56, — Adaptation to pyrrolnitrin in Botrytis cinerea and cost of resistance. Alabouvette, C.
Microbiological control of soil-borne phytopathogenic fungi with special emphasis on wilt-inducing Fusarium oxysporum. New Phytol. Ali, A. Biological control of fruit lesions caused by Xanthomonas campestris pathovars from Cuscuta pedicellata Ledeb. In vitro. Pure Appl. Google Scholar.
Asser-Kaiser, S. Rapid emergence of baculovirus resistance in codling moth due to dominant, sex-linked inheritance. Science , — Bacon, C. In planta reduction of maize seedling stalk lesions by the bacterial endophyte Bacillus mojavensis. Bardin, M. Diversity in susceptibility of Botrytis cinerea to biocontrol products inducing plant defence mechanisms. Relationship between the aggressiveness of Botrytis cinerea on tomato and the efficacy of biocontrol.
Diversity in the effect of an extract from Fallopia sachalinensis on isolates of cucurbit powdery mildews grown on melon. Compatibility between biopesticides used to control grey mould, powdery mildew and whitefly on tomato.
Control 46, — Bell, J. Biosynthesis and functions of fungal melanins. Berling, M. Cydia pomonella granulovirus genotypes overcome virus resistance in the codling moth and improve virus efficiency by selection against resistant hosts. Boukaew, S. Efficacy of Streptomyces spp. Brent, K. Brussels: CropLife International. Bryner, S. Hypovirus virulence and vegetative incompatibility in populations of the chestnut blight fungus.
Phytopathology , — Buck, J. Effect of pathogen aggressiveness and vinclozolin on efficacy of Rhodotorula glutinis PM4 against Botrytis cinerea on geranium leaf disks and seedlings. Plant Dis. Burse, A.
NorM, an Erwinia amylovora multidrug efflux pump involved in in vitro competition with other epiphytic bacteria. Cowen, L. Evolution of drug resistance in Candida albicans. Crowe, J. Induction of laccase activity in Rhizoctonia solani by antagonistic Pseudomonas fluorescens strains and a range of chemical treatments.
Daayf, F. Evidence of phytoalexins in cucumber leaves infected with powdery mildew following treatment with leaf extracts of Reynoutria sachalinensis. Plant Physiol. PubMed Abstract Google Scholar. Control of Fusarium wilt of radish by combining Pseudomonas putida strains that have different disease-suppressive mechanisms. Phytopathology 93, — Del Sorbo, G. Fungal transporters involved in efflux of natural toxic compounds and fungicides.
Fungal Genet. Denny, T. De Souza, J. Effect of 2,4-diacetylphloroglucinol on Pythium : cellular responses and variation in sensitivity among propagules and species. De Waard, M. Impact of fungal drug transporters on fungicide sensitivity, multidrug resistance and virulence.
Diaz, G. In vitro antagonism of Trichoderma and naturally occurring fungi from elms against Ophiostoma novo-ulmi. Duffy, B. Pathogen self-defense: mechanisms to counteract microbial antagonism. Eberle, K. Field resistance of codling moth against Cydia pomonella granulovirus CpGV is autosomal and incompletely dominant inherited.
Elad, Y. Biological control of foliar pathogens by means of Trichoderma harzianum and potential modes of action. Crop Prot. Dordrecht , eds Y. Elad B. Williamson, P. Tudzynski, and N. Delen Dordrecht: Kluwer Academic Press , — Faltin, F. Fedi, S. Evidence for signalling between the phytopathogenic fungus Pythium ultimum and Pseudomonas fluorescens F P.
Fillinger, S. Functional and structural comparison of pyrrolnitrin- and iprodione-induced modifications in the class III histidine-kinase Bos1 of Botrytis cinerea.
Flaherty, J. Control of bacterial spot on tomato in the greenhouse and field with h-mutant bacteriophages. HortScience 35, — Fleissner, A.
An ATP-binding cassette multidrug-resistance transporter is necessary for tolerance of Gibberella pulicaris to phytoalexins and virulence on potato tubers. Plant Microbe Interact. Fofana, B. Milsana-induced resistance in powdery mildew-infected cucumber plants correlates with the induction of chalcone synthase and chalcone isomerase.
Fritsch, E. Apfelwickler-Granulovirus: Erste Hinweise auf Unterschiede in der Empfindlichkeit lokaler Apfelwickler-Populationen Codling moth granulovirus: first indication of variations in the susceptibility of local codling moth populations. Gerlagh, M. Efficiency of isolates of Coniothyrium minitans as mycoparasites of Sclerotinia sclerotiorum , Sclerotium cepivorum and Botrytis cinerea on tomato stem pieces.
Govrin, E. The hypersensitive response facilitates plant infection by the necrotrophic pathogen Botrytis cinerea. An elicitor from Botrytis cinerea induces the hypersensitive response in Arabidopsis thaliana and other plants and promotes the gray mold disease. Bryan, M. Dysart and T. Caltigirone, L. Landmark examples in classical biological control. Entomol Day, W. Biological control of the alfalfa weevil in the Northeastern United States. Chap 25 In. Papavizas, G. Biological Control in Crop Protection.
Debach, P. Biological Control by Natural Enemies. Cambridge Univ. Press, Cambridge, UK. Doutt, R. The Rubus leafhopper and its egg parasitoid: an endemic biotic system useful in grape pest management. Forman, R. Landscape Ecology. New York: John Wiley and Sons. Headley, J. Hoy, M. Almonds: Integrated mite management for California almond orchards, pp.
In: W. Sabelis [eds. Elsevier, Amsterdam. Biological control of arthropods: genetic engineering and environmental risks.
Biological Control Hussey, N. Biological pest control: the glasshouse experience. Cornell Univ. Press, Ithaca. Kabiri, F. Frandon, J. Voegele, N. Hym Trichogrammatidae against the European corn borer, Ostrinia nubilalis Hbn.
Pyralidae ]. Kruess, A. Habitat fragmentation, species loss, and biological control. Science Li, Li-Ying. Worldwide use of Trichogramma for biological control on different crops: a survey, pp. In: E. Hassan, eds. Biological control with egg parasitoids. CAB International, Wallingford.
Landis, D. Marino, P. Effect of landscape structure on parasitoid diversity and parasitism in agroecosystems. Ecological Applications : in press. Odum, E. Trends expected in stressed ecosystems. BioScience 35 7 : Orr, D. Biological control tactics for European corn borer. Illinois Crop Prot. Champaign, IL.
Parrella, M. Biological pest control in ornamentals: status and perspectives. Pickett, S. White, eds. The ecology of natural disturbance and patch dynamics. San Diego: Academic Press. Reice, S. Nonequilibrium determinants of biological community structure. Scientist Robinson, G. Holt, M. Gaines, S. Hamburg, M. Johnson, H. Diverse and contrasting effects of habitat fragmentation. Ryszkowski, L. Karg, G. Margarit, M. Above-ground insect biomass in agricultural landscapes of Europe.
In Landscape ecology and agroecosystems , ed. Bunce, L. Other chemical controls limit physical growth or influence pest behavior in ways detrimental to their lives. Most chemical controls are fast acting and effective. They often offer control over many different insects at once and the various life stages of different pests.
Biological control methods use living organisms such as natural predators, parasites and pathogens to control pest populations on garden plants. They include beneficial bugs, such as lady beetles and parasitic wasps, which prey on harmful insects but leave your plants untouched.
Many beneficial insects are commercially available, and they can quickly reduce pests to manageable levels. Biological pesticides are based on naturally occurring organisms that prove toxic for certain insects. Bacillus thuringiensis Bt , for example, is a bacterium that kills caterpillars and other larvae after they feed on treated plant leaves. Planting certain plants to attract and keep beneficial insects helps control harmful insects as well. Chemical controls are often inexpensive and readily available.
Many have proven safe and effective for decades and remain in popular use due to their efficiency and quick results. Scientific advances have created many new chemical pesticides that mimic and, in some cases, improve on the effectiveness of natural substances. As gardeners seek out more natural and organic gardening solutions, biological controls have grown in use. Products have become more widely-available and are often comparable to chemical solutions in cost.
0コメント