Downloaded 1,681 times
Uploaded byPlant Disease Control Hub
Biological control of plant pathogens
The document discusses biological control methods for plant pathogens, emphasizing the use of microbial antagonists like bacteria and fungi to suppress diseases. It outlines the mechanisms of biocontrol, including antibiosis, competition, parasitism, and induced systemic resistance, as well as the advantages and limitations of such methods. Additionally, it mentions application techniques and examples of commercial biocontrol agents available in the market.
More Related Content
Similar to Biological control of plant pathogens
Biological control of plant pathogens
- 1. RUFUS AKINRINLOLA Graduate Student PlantPathology Department. University of Nebraska-Lincoln BIOLOGICAL CONTROL OF PLANT PATHOGENS BIOS/PLPT 369
- 2. Topics 1. Biological control 2.Importance of biological control 3. Mode of actions of biocontrol 4. Biocontrol application methods 5. Requirements for successful biocontrol agents 6. Limitations of biological control 7. Some commercial biological control agents 8. Summary BIOLOGICAL CONTROL OF PLANT PATHOGENS
- 3. The term biologicalcontrol :- as defined by Plant Pathologist; the use of microbial antagonists (including bacteria or fungi) to suppress plant disease pathogens BIOLOGICAL CONTROL Inhibition of test organisms by biocontrol organism Sources: google image
- 4. Alternative methodof disease control Can be used in where other methods are not applicable. Biocontrol agents are nontoxic to man and the environment. Act on selective target organism. Biocontrol agents are self-sustaining-easy adaptation Diversify mode of actions Reduced possibility of inducing resistance in pathogens Cost effective Long term effects Importance of biological control Emmert, E. A., & Handelsman, J. (1999). Biocontrol of plant disease: a (Gram‐) positive perspective. FEMS Microbiology letters, 171(1), 1-9.
- 5. Mode of actionsof biocontrol 1. Direct mechanism: Direct lysis or killing of pathogen by biocontrol agent Antibiosis Parasitism Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. 2. Indirect mechanism: Exclusion of plant pathogen as a result of the presence, activity or products of biocontrol agent. Competition Induced systemic resistance
- 6. Mode of actionsof biocontrol 1. Direct mechanism: Direct lysis or killing of pathogen by biocontrol agent Antibiosis Parasitism Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. 2. Indirect mechanism: Exclusion of plant pathogen as a result of the presence, activity or products of biocontrol agent. Competition Induced systemic resistance
- 7. Mode of actionsof biocontrol 1. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms. Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
- 8. Mode of actionsof biocontrol 1. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms. Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Inhibition of pathogens by biocontrol bacteria. Photo credit: Rufus Akinrinlola
- 9. Mode of actionsof biocontrol 1. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms. Volatile antibiotics • Hydrogen cyanide, • Aldehydes • Alcohols • Ketones • Sulfides Nonvolatile antibiotics: • Polyketides (diacetylphloroglucinol; DAPG and mupirocin). • Heterocyclic nitrogenous compounds. Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
- 10. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. 2. Parasitism Direct utilization of pathogens as source nutrients. Mycoparasitism refers to association in which a parasitic fungus (hyperparasite) live as a parasite to another fungus (hypoparasiste). Also known as Hyperparasitism, when hyperparasites (biocontrol fungi) utilize hypoparasites (pathogenic fungi) as source of nutrients. Hyperparasites produce parasitizing hyphae to acquire host nutrients. May also requires cell wall degrading enzymes. Source: The Microbial World.
- 11. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. A B Source: The Microbial World. Example of Mycoparasitism: Pythium oligandrum Vs Fusarium culmorum A. Single hypha of Pythium oligandrum stopped the advancement of Fusarium culmorum hyphae across an agar plate. B. At higher magnification F. culmorum hyphae are seen disrupted - the contents are highly vacuolated and coagulated.
- 12. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Steps involved in Mycoparasitism 1. Chemotropic growth: the biocontrol fungi grow toward the target fungi chemical stimuli. 2. Recognition stage: interaction between biocontrol receptors and that of the host fungus 3. Attachment and cell wall degradation (chitinases and glucanases). 4. Penetration (appressoria-like structures).
- 13. Mode of actionsof biocontrol Ahanger et al., 2014; Dubey and Dwivedi, 1986. Steps involved in Mycoparasitism 1. Chemotropic growth: the biocontrol fungi grow toward the target fungi chemical stimuli. 2. Recognition stage: interaction between biocontrol receptors and that of the host fungus 3. Attachment and cell wall degradation (chitinases and glucanases). 4. Penetration (appressoria-like structures). Coiling Penetration Barrier formation by host hypha Branching and sporulation Chlamydospores formation Lysis of host hypha Hyperparasite (bicontrol) Host fungus (pathogen) hypha Source: biocylopedia.com
- 14. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Source: Koutb and Ali, 2010 3. Competition Exclusion of pathogens by biological control agents via competition for space or nutrients. Production of substances (such as siderophore) for nutrient (such as iron) acquisition. Deprive pathogens of nutrients. It’s an indirect mechanism
- 15. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Source: Koutb and Ali, 2010 3. Competition Exclusion of pathogens by biological control agents via competition for space or nutrients. Production of substances (such as siderophore) for nutrient (such as iron) acquisition. Deprive pathogens of nutrients. It’s an indirect mechanism Competition for space and nutrients between Pythium irregulare pathogen (white restricted growth) and the Epicoccum purpurascens (reddish wide growth) on PDA medium after
- 16. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. 4. Induced systemic resistance (ISR): Also known as systemic acquired resistance (SAR), resistance in plants to varieties of pathogens induced by the presence or products of biocontrol agent.
- 17. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. ISR biocontrol agent may be; Necrogenic pathogen (applied on leaf). Non-pathogenic bacteria (PGPR) (applied to root or seed). Metabolites of pathogenic or saprophytic bacteria.
- 18. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Microbial metabolites able to induce ISR Polyacrylic acid Ethylene Salicylic acid Acetyl salicylic acid Amino acid derivatives Harpin ( Erwinia amylovora) • Stress can induce defense mechanisms against pathogens
- 19. Mode of actionsof biocontrol Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58. Physical thickening of cell walls by; Lignification. Deposition of callose. Accumulation of antimicrobial low-molecular-weight substances (e.g., phytoalexins). Synthesis of various proteins (e.g., chitinases, glucanases, peroxidases, and other pathogenesis related (PR) proteins). Induced systemic resistance- defense responses
- 20. Mode of actionsof biocontrol Ahanger et al., 2014; Lee et al., 2015 Induced systemic resistance- defense responses C. Induced systemic resistance by biocontrol agent Bacillus amyloliquefaciens HK34 B. Plant treated with 0.1mM benzothiadiazole (positive control) A. Plant treated with distill water
- 21. Biocontrol application methods There are five application methods
- 22. Biocontrol application methods 1.Seed treatment
- 23. Biocontrol application methods 2.Seedling dip method
- 24. Biocontrol application methods 3.Soil drench
- 25. Biocontrol application methods 4.Foliar spray
- 26. Biocontrol application methods 5.Irrigation drips
- 27. Biocontrol application methods 1.Seed treatment 2. Dipping 3. Drench 4. Foliar prays 5. Drips Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
- 28. Requirements for successfulbiocontrol agents 1. Able to compete and persist 2. Able to colonize and proliferate 3. Must be non-pathogenic to host and environments 4. Must have excellent shelf life 5. Must be inexpensive 6. Must be able to produce in large quantities 7. Able to maintain viability 8. Delivery and application methods must support product establishment. http://flax.nzdl.org/greenstone3/flax?c=BAWELS&a=d&rt=r&d=D2712&dt=simple&p.a=b&p.s=ClassifierBrowse&cls=
- 29. Limitations of biologicalcontrol 1. Expensive/difficult to develop 2. Handling requires training 3. High Selectivity/Host Specificity 4. Variability in effectiveness 5. More susceptible to environmental conditions 6. Short shelf-life of formulations 7. Slow action 8. Storage Problem http://flax.nzdl.org/greenstone3/flax?c=BAWELS&a=d&rt=r&d=D2712&dt=simple&p.a=b&p.s=ClassifierBrowse&cls=
- 30. Commercial biological control Active microbe: Bacillus subtilis strain GB03 Mode of actions: Antibiosis Company : Gustafson, Inc, Plano, TX, USA Junaid, J. M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal Sciences, 1(2), 39-57.
- 31.
- 32. Some commercial biologicalcontrol agents Control of blue mold and gray mold on cherries, apples, citrus. Mode of action: Competition Applicational methods: • Dip or Drench • Spray Control of seed rot, root and stem rot and wilt caused by Fusarium, Alternaria and Phomopsis on ornamentals aand vegetables Mode of actions: Competition; Hyperparasitism; Antibiosis Junaid, J. M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal Sciences, 1(2), 39-57.
- 33. Summary Biological controlinvolves the use of microbial antagonists such as bacteria or fungi to suppress plant disease pathogens. Biocontrol have several importance and advantages over other control methods Their mode of actions include antibiosis, competition, parasitism and induced systemic resistance. There are however some limitations to the general use of biological control agents such variability in effectiveness, low spectrum action, short shelf life of products etc. Some of the commercial available biocontrol agents include Biosave, Kodiak, Mycostop etc. A biological control agent can be applied as seed treatment, root dip, soil or furrow drench, foliar sprays or through drip irrigation.
- 34.
- 35. • Junaid, J.M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal Sciences, 1(2), 39-57. • Jetiyanon, K., Fowler, W. D., & Kloepper, J. W. (2003). Broad-spectrum protection against several pathogens by PGPR mixtures under field conditions in Thailand. Plant Disease, 87(11), 1390-1394. • Lee, B. D., Dutta, S., Ryu, H., Yoo, S. J., Suh, D. S., & Park, K. (2015). Induction of systemic resistance in Panax ginseng against Phytophthora cactorum by native Bacillus amyloliquefaciens HK34. Journal of ginseng research, 39(3), 213-220. • Koutb, M., & Ali, E. H. (2010). Potential of Epicoccum purpurascens Strain 5615 AUMC as a biocontrol agent of Pythium irregulare root rot in three leguminous plants. Mycobiology, 38(4), 286-294. • Kilic-Ekici, O., & Yuen, G. Y. (2003). Induced resistance as a mechanism of biological control by Lysobacter enzymogenes strain C3. Phytopathology, 93(9), 1103-1110. Sources
Editor's Notes
- #3 As an introduction, I suggest that define what is biological control and explain why biological control is important. As the topic, I suggest you explain the advantages and limitations of biological control.
- #5 Huffaker, C. B. (Ed.). (2012). Theory and practice of biological control. Elsevier. Advantages of biological control Biological control has many advantages as a pest control method, particularly when compared with insecticides. One of the most important benefits is that biological control is an environmental friendly method and does not introduce pollutants into the environment. As Kok (1999) points out, biological control should be implemented whenever possible because it does not pollute the environment. We mentioned earlier several problems which are caused by insecticides and are related with environment pollution. The great advantage of this method is its selectivity. By this way, there is a restricted danger of damage to non target plant species. Weeden and Shelton (2005) underline that biological control does not create new problems, like conventional pesticides. According to van Emden (2004:149) "this does not mean that side effects can be totally excluded, although they have been very rare in the history of biological control". Selectivity is the most important factor regarding the balance of agricultural ecosystems because a great damage to non target species can lead to the restriction of natural enemies' populations. This can cause increased pest populations as mentioned earlier. How successfully a Biological control agent (BCA) can be deployed in an agricultural ecosystem, so as not to damage non target pests, depends on appropriate host specificity tests which determine the potential host range (Kok, 1999). The ability to self-perpetuate is an extremely interesting advantage of biological control method. According to Kok (1999), BCAs will increase in number and spread. Because BCAs are self-propagating and dispersing, pest control is self-perpetuating too. This is quite important regarding the economic feasibility of biological control (Reichelderfer, 1981). Another advantage of biological control method, which is a proof of environmental safety of BCAs, is that the pest is unable (or very slow) to develop resistance (Weeden and Shelton, 2005). It is probably possible a target pest to develop mechanisms of defence against attack by a natural enemy. For example, we could imagine that an effective control of a pest by a natural enemy could cause strong selection on the pest so as to develop mechanisms of escape or tolerance to attacks by the control agent, breaking down biocontrol system (Holt and Hochberg, 2005). Some examples of defence mechanisms that could develop by pests are escape behaviour and repellent chemicals. However, as Van Emden (2004) mentions, "we know of no cases where previously successful biological control has failed because of selection for resistance". Biological control can be cost effective. Its effectiveness is based on self-perpetuation and self-propagation as we mentioned earlier. Therefore, if we establish a control agent in a specific area, it will reduce the target pest in an acceptable threshold for quite long time (Kok, 1999). A small number of biocontrol agents can grow to very high densities and provide continuous control of a pest over a large area. When the cost of deployment of BCAs is considered in contrast to pesticide applications, biological control is generally less expensive than chemical control (Agriculture, Food and Rural Development of Canada, 2000). The financial benefit of biological control is greatest in cases when there is no other option. For example, biological control is very effective in inaccessible areas. Another interesting point regarding the cost efficiency of this method is that the yield benefit of biological control is probably less than yield achieved by agrochemicals, but the primary cost of BCA is generally lower than chemical pesticides (Reichelderfer
- #6 4. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms.Antibiotics produced by bacteria include volatile antibiotics (hydrogen cyanide, aldehydes, alcohols, ketones, and sul?des) and nonvolatile antibiotics: polyketides (diacetylphloroglucinol; DAPG and mupirocin), heterocyclic nitrogenous compounds
- #7 4. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms.Antibiotics produced by bacteria include volatile antibiotics (hydrogen cyanide, aldehydes, alcohols, ketones, and sul?des) and nonvolatile antibiotics: polyketides (diacetylphloroglucinol; DAPG and mupirocin), heterocyclic nitrogenous compounds
- #8 4. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms.Antibiotics produced by bacteria include volatile antibiotics (hydrogen cyanide, aldehydes, alcohols, ketones, and sul?des) and nonvolatile antibiotics: polyketides (diacetylphloroglucinol; DAPG and mupirocin), heterocyclic nitrogenous compounds
- #9 4. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms.Antibiotics produced by bacteria include volatile antibiotics (hydrogen cyanide, aldehydes, alcohols, ketones, and sul?des) and nonvolatile antibiotics: polyketides (diacetylphloroglucinol; DAPG and mupirocin), heterocyclic nitrogenous compounds
- #10 4. Antibiotic mediated suppression Antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms.Antibiotics produced by bacteria include volatile antibiotics (hydrogen cyanide, aldehydes, alcohols, ketones, and sul?des) and nonvolatile antibiotics: polyketides (diacetylphloroglucinol; DAPG and mupirocin), heterocyclic nitrogenous compounds 5. Competition This process is considered to be an indirect interaction whereby pathogens are excluded by Biocontrol agents and their mechanism in plant disease management 51 depletion of a food base or by physical occupation of site (Loritoet al., 1994). Biocontrol by nutrient competition can occur when the biocontrol agent decreases the availability of a particular substance thereby limiting the growth of the pathogen. Particularly, the biocontrol agents have a more efficient uptake or utilizing system for the substance than do the pathogens (Handelsman and Parke, 1989). For example, iron competition in alkaline soils may be a limiting factor for microbial growth in such soils (Leongand Expert 1989). Some bacteria, especially fluorescent pseudomonads produce siderophores that have very high affinities for iron and can sequester this limited resource from other microflora thereby preventing their growth (Loper and Buyer
- #11 6. Parasitism This process involves the direct utilization of one organism as food by another (Handelsman and Parke 1989). Fungi that are parasitic on other fungi are usually referred to as mycoparasites (Ba ker and Cook 1974.). Many mycoparasites occur on a wide range of fungi and some of them have been proposed to play an important role in disease control (Adams, 1990). For example, Darlucafilum( nowSphaerellopsisfilum) was described by Saccardo as a parasite of some rust fungi, especially Pucciniaand Uromyces(Sundheim and Tronsmo 1988). Trichodermalignorum(T. viride) parasitizing hyphae of Rhizoctoniasolaniand suggestion of RayeesA.Ahanger, Hilal A. Bhatand Nisar A. Dar 52 inoculating soil with Trichodermaspores to control damping-off of citrus seedling was reported by Weindling and Fawcett in 1936. This and other Trichodermaspecies were observed to parasitize Rhizoctoniabataticolaand Armillariamellea(Baker and Cook. 1974). Generally, mycoparasitism can be described as a four-step process (Chet, 1987): The first stage is chemotropic growth. The biocontrol fungi grow tropistically toward the target fungi that produce chemical stimuli. For example, a volatile or water- soluble substance produced by the host fungus serves as a chemo attractant for parasites. The next step is recognition. Lectins of hosts (pathogens) and carbohydrate receptors on the surface of the biocontrol fungus may be involved in this specific interaction (Inbar and Chet 1994). The third step is attachment and cell wall degradation. Mycoparasites can usually either coil around host hyphae or grow alongside it and produce cell wall degrading enzymes to attack the target fungus (Chet, 1987). These enzymes such as chitinases and b-1,3-glucanase may be involved in degradation of host cell walls and may be components of complex mixtures of synergistic proteins that act together against pathogenic fungi (Di Pietro, et al, 1992). The final step is penetration. The biocontrol agent produces appressoria-like structures to penetrate the target fungus cell wall (Chet, 1987). In hyperparasitism, the pathogen is directly attacked by a specific BCA that kills it or its propagules.
- #12 6. Parasitism This process involves the direct utilization of one organism as food by another (Handelsman and Parke 1989). Fungi that are parasitic on other fungi are usually referred to as mycoparasites (Ba ker and Cook 1974.). Many mycoparasites occur on a wide range of fungi and some of them have been proposed to play an important role in disease control (Adams, 1990). For example, Darlucafilum( nowSphaerellopsisfilum) was described by Saccardo as a parasite of some rust fungi, especially Pucciniaand Uromyces(Sundheim and Tronsmo 1988). Trichodermalignorum(T. viride) parasitizing hyphae of Rhizoctoniasolaniand suggestion of RayeesA.Ahanger, Hilal A. Bhatand Nisar A. Dar 52 inoculating soil with Trichodermaspores to control damping-off of citrus seedling was reported by Weindling and Fawcett in 1936. This and other Trichodermaspecies were observed to parasitize Rhizoctoniabataticolaand Armillariamellea(Baker and Cook. 1974). Generally, mycoparasitism can be described as a four-step process (Chet, 1987): The first stage is chemotropic growth. The biocontrol fungi grow tropistically toward the target fungi that produce chemical stimuli. For example, a volatile or water- soluble substance produced by the host fungus serves as a chemo attractant for parasites. The next step is recognition. Lectins of hosts (pathogens) and carbohydrate receptors on the surface of the biocontrol fungus may be involved in this specific interaction (Inbar and Chet 1994). The third step is attachment and cell wall degradation. Mycoparasites can usually either coil around host hyphae or grow alongside it and produce cell wall degrading enzymes to attack the target fungus (Chet, 1987). These enzymes such as chitinases and b-1,3-glucanase may be involved in degradation of host cell walls and may be components of complex mixtures of synergistic proteins that act together against pathogenic fungi (Di Pietro, et al, 1992). The final step is penetration. The biocontrol agent produces appressoria-like structures to penetrate the target fungus cell wall (Chet, 1987). In hyperparasitism, the pathogen is directly attacked by a specific BCA that kills it or its propagules.
- #15 5. Competition This process is considered to be an indirect interaction whereby pathogens are excluded by Biocontrol agents and their mechanism in plant disease management 51 depletion of a food base or by physical occupation of site (Loritoet al., 1994). Biocontrol by nutrient competition can occur when the biocontrol agent decreases the availability of a particular substance thereby limiting the growth of the pathogen. Particularly, the biocontrol agents have a more efficient uptake or utilizing system for the substance than do the pathogens (Handelsman and Parke, 1989). For example, iron competition in alkaline soils may be a limiting factor for microbial growth in such soils (Leongand Expert 1989). Some bacteria, especially fluorescent pseudomonads produce siderophores that have very high affinities for iron and can sequester this limited resource from other microflora thereby preventing their growth (Loper and Buyer
- #16 5. Competition This process is considered to be an indirect interaction whereby pathogens are excluded by Biocontrol agents and their mechanism in plant disease management 51 depletion of a food base or by physical occupation of site (Loritoet al., 1994). Biocontrol by nutrient competition can occur when the biocontrol agent decreases the availability of a particular substance thereby limiting the growth of the pathogen. Particularly, the biocontrol agents have a more efficient uptake or utilizing system for the substance than do the pathogens (Handelsman and Parke, 1989). For example, iron competition in alkaline soils may be a limiting factor for microbial growth in such soils (Leongand Expert 1989). Some bacteria, especially fluorescent pseudomonads produce siderophores that have very high affinities for iron and can sequester this limited resource from other microflora thereby preventing their growth (Loper and Buyer
- #17 These defense responses physical thickening of cell walls by lignification, deposition of callose, accumulation of antimicrobial low-molecular-weight substances (e.g., phytoalexins), and synthesis of various proteins (e.g., chitinases, glucanases, peroxidases, and other pathogenesisrelated (PR) proteins) (Hammerschmidt, et al, 1984). This defense system is also triggered when plants are colonized by plant growth- promoting rhizobacteria (Sticher, et al., 1997) and a few binucleate Rhizoctonia(BNR) AG-K (Poromarto, et al., 1988). Recently, many strains of PGPR have been shown to be effective in controlling plant diseases by inducing plant systemic resistance (Liu, et al., 1995). Plants colonized by these strains are more resistant to foliar diseases, even though the PGPR is present only on roots (Wei, 1996). The chemical compounds that induce resistance of plants to pathogens may include polyacrylic acid, ethylene, salicylic acid and acetyl salicylic acid, various amino acid derivatives, the herbicide phosphinotricin, and harpin produced by Erwiniaamylovora(Sequeira, 1983). It is known that stress can induce defense mechanisms against pathogens (Maurhofer, et al., 1994). However, the hypothesis should be proved by genetic analysis such as heterologous expression, which shows that inducing ability may be transferred to other potent strains as an additional complementary mode of action, and gene mutation, which knocks out the ability and leads to less disease control. Induced resistance is an important mechanism of biological control by a number of strains of plant growth-promoting rhizobacteria (PGPR) applied to roots or seed (17,20,27,28). It also can be induced by foliar application of plant-pathogenic bacteria (24), their metabolites (25,30), and metabolites produced by saprophytic bacterial strains (23).
- #18 These defense responses physical thickening of cell walls by lignification, deposition of callose, accumulation of antimicrobial low-molecular-weight substances (e.g., phytoalexins), and synthesis of various proteins (e.g., chitinases, glucanases, peroxidases, and other pathogenesisrelated (PR) proteins) (Hammerschmidt, et al, 1984). This defense system is also triggered when plants are colonized by plant growth- promoting rhizobacteria (Sticher, et al., 1997) and a few binucleate Rhizoctonia(BNR) AG-K (Poromarto, et al., 1988). Recently, many strains of PGPR have been shown to be effective in controlling plant diseases by inducing plant systemic resistance (Liu, et al., 1995). Plants colonized by these strains are more resistant to foliar diseases, even though the PGPR is present only on roots (Wei, 1996). The chemical compounds that induce resistance of plants to pathogens may include polyacrylic acid, ethylene, salicylic acid and acetyl salicylic acid, various amino acid derivatives, the herbicide phosphinotricin, and harpin produced by Erwiniaamylovora(Sequeira, 1983). It is known that stress can induce defense mechanisms against pathogens (Maurhofer, et al., 1994). However, the hypothesis should be proved by genetic analysis such as heterologous expression, which shows that inducing ability may be transferred to other potent strains as an additional complementary mode of action, and gene mutation, which knocks out the ability and leads to less disease control. Induced resistance is an important mechanism of biological control by a number of strains of plant growth-promoting rhizobacteria (PGPR) applied to roots or seed (17,20,27,28). It also can be induced by foliar application of plant-pathogenic bacteria (24), their metabolites (25,30), and metabolites produced by saprophytic bacterial strains (23).
- #19 These defense responses physical thickening of cell walls by lignification, deposition of callose, accumulation of antimicrobial low-molecular-weight substances (e.g., phytoalexins), and synthesis of various proteins (e.g., chitinases, glucanases, peroxidases, and other pathogenesisrelated (PR) proteins) (Hammerschmidt, et al, 1984). This defense system is also triggered when plants are colonized by plant growth- promoting rhizobacteria (Sticher, et al., 1997) and a few binucleate Rhizoctonia(BNR) AG-K (Poromarto, et al., 1988). Recently, many strains of PGPR have been shown to be effective in controlling plant diseases by inducing plant systemic resistance (Liu, et al., 1995). Plants colonized by these strains are more resistant to foliar diseases, even though the PGPR is present only on roots (Wei, 1996). The chemical compounds that induce resistance of plants to pathogens may include polyacrylic acid, ethylene, salicylic acid and acetyl salicylic acid, various amino acid derivatives, the herbicide phosphinotricin, and harpin produced by Erwiniaamylovora(Sequeira, 1983). It is known that stress can induce defense mechanisms against pathogens (Maurhofer, et al., 1994). However, the hypothesis should be proved by genetic analysis such as heterologous expression, which shows that inducing ability may be transferred to other potent strains as an additional complementary mode of action, and gene mutation, which knocks out the ability and leads to less disease control. Induced resistance is an important mechanism of biological control by a number of strains of plant growth-promoting rhizobacteria (PGPR) applied to roots or seed (17,20,27,28). It also can be induced by foliar application of plant-pathogenic bacteria (24), their metabolites (25,30), and metabolites produced by saprophytic bacterial strains (23).
- #20 Callose is a plant polysaccharide. It is composed of glucose residues linked together through β-1,3-linkages, and is termed a β-glucan. It is thought to be manufactured at the cell wall by callose synthases and is degraded by β-1,3-glucanases.
- #21 Fig. 2. Effect of HK34 on the induction of systemic resistance against Phytophthora cactorum in leaves obtained from plants treated once under greenhouse conditions. Leaves are from plants treated with (A) sterile distilled water (negative control), (B) 0.1mM benzothiadiazole (positive control), and (C) HK34.
- #22 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #23 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #24 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #25 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #26 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #27 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #28 METHODS OF APPLICATION Before application, BioSave T' 1 should be resuspended in water for at least 10 minutes for the frozen pellet formulation, and for 30 minutes for the dry formulation to allow for cell rehydration. The recommended rate is 250 g of frozen pellets or dry formulation per 150 liters, which results in a suspension containing 1.6 x 10 CFU/ml (a minimum guarantied by the manufacturer). BioSaveTM has been applied as a drench to bins with apples and pears, as a drip application with rotating brushes to apples, pears and citrus fruit on packing lines, or as a dip to apples and pears on packing lines. Application to potatoes has been mainly through a lowvolume spray during piling up of potatoes in storages, and to sweet potatoes as a dip. Since BioSavelM is exempt from residue tolerance, it can be applied to the commodities at any time prior, during and after storage, even immediately before packing.
- #29 Limitations or Disadvantages of Microbial Control 1) High Selectivity/Host Specificity: Since the microbial agent is effective against only single pest species there is a very limited market potential. 2) Requirement of Additional Control Measures: An additional control measures are needed for non-target insect pest species. It present and not kept below ETL by natural control factor. 3) The Correct Time of Application: In this respect, the incubation period of disease, which is a critical factor and difficult to judge because of age specificity and stage specificity. The pathogens attack on certain stage (larval) and do not produce effect on eggs or adults. Susceptibility of larvae also decreases with increase in age. 4) Delayed Effect/Mortality: The pathogens require some time to produce response in their target host owing to its long disease incubation period. 5) The pathogens like viruses, bacteria must be ingested as early as possible to produce effects, while the fungi required entry through body integument for which good coverage of spray deposits is important. 6) Storage Problem: It is necessary to maintain the pathogen in viable condition. Even average temperature and sunlight degrade the microbial preparations. Exposure to sunlight causes UV radiation and losses its virulent immediately. The pathogens have very short self life. 7) Difficulty of Culturing in Large Quantities: Rearing host insect on artificial diet is more cumbersome and laborious works which requires constant supervision. The whole organisms techniques for in vivo prorogation of virus are fairly labourious and expensive. 8) Short Residual Effectiveness: This is the major limitation absent the effectiveness of pathogen under field conditions as sunlight causes UV radiation. 9) Not legally protected and data needed for registration is highly expensive.
- #30 Limitations or Disadvantages of Microbial Control 1) High Selectivity/Host Specificity: Since the microbial agent is effective against only single pest species there is a very limited market potential. 2) Requirement of Additional Control Measures: An additional control measures are needed for non-target insect pest species. It present and not kept below ETL by natural control factor. 3) The Correct Time of Application: In this respect, the incubation period of disease, which is a critical factor and difficult to judge because of age specificity and stage specificity. The pathogens attack on certain stage (larval) and do not produce effect on eggs or adults. Susceptibility of larvae also decreases with increase in age. 4) Delayed Effect/Mortality: The pathogens require some time to produce response in their target host owing to its long disease incubation period. 5) The pathogens like viruses, bacteria must be ingested as early as possible to produce effects, while the fungi required entry through body integument for which good coverage of spray deposits is important. 6) Storage Problem: It is necessary to maintain the pathogen in viable condition. Even average temperature and sunlight degrade the microbial preparations. Exposure to sunlight causes UV radiation and losses its virulent immediately. The pathogens have very short self life. 7) Difficulty of Culturing in Large Quantities: Rearing host insect on artificial diet is more cumbersome and laborious works which requires constant supervision. The whole organisms techniques for in vivo prorogation of virus are fairly labourious and expensive. 8) Short Residual Effectiveness: This is the major limitation absent the effectiveness of pathogen under field conditions as sunlight causes UV radiation. 9) Not legally protected and data needed for registration is highly expensive.
- #34 As an introduction, I suggest that define what is biological control and explain why biological control is important. As the topic, I suggest you explain the advantages and limitations of biological control.
- #35 As an introduction, I suggest that define what is biological control and explain why biological control is important. As the topic, I suggest you explain the advantages and limitations of biological control.