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What is a Disease?

What is a Disease?. An organism that lives on or in another organism and obtains food from the second organism is a parasite . Pythium on bentgrass. Rhizobium japonicum. Fits definition of parasitic bacterium in soybeans Soybeans benefit from infection (symbiosis).

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What is a Disease?

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  1. What is a Disease?

  2. An organism that lives on or in another organism and obtains food from the second organism is a parasite. Pythium on bentgrass

  3. Rhizobium japonicum • Fits definition of parasitic bacterium in soybeans • Soybeans benefit from infection (symbiosis)

  4. What is Pathogenicity and Disease? • Pathogenicity- is the ability of a pathogen to interfere with one or more of the essential plant cell functions. • Disease– the process in which a pathogen interferes with one or more essential plant cell functions

  5. Pathogens may interfere with plant cell functions using: • Toxins • Growth regulators • Enzymes • By absorbing water and nutrients from host cells

  6. Pathogens can also cause disease by : • Blocking xylem or phloem vessels • By inserting parts of their DNA or RNA into the host cell and “commandeering” the cell’s replication machinery.

  7. Plant Stresses may cause “Abiotic Diseases” Usually caused by “to much” or “to little” of something Stress factors include temperature, moisture, pH, mineral nutrients, etc. Pollutants, pesticides, and salt may also be causes.

  8. Examples of stresses not considered causes of “Abiotic Diseases” • Pruning • Animal feeding • Lawn mowing • Lightening

  9. Fungi Prokaryotes Viruses Viroids Nematodes Protozoa Algae Parasitic Seed Plants Infectious Plant Disease Causes

  10. Infectious disease agents are called pathogens. Pathogens can be classified as : Biotrophs, Facultative Parasites Facultative Saprophytes

  11. Biotrophs – do not kill plant cells. They penetrate the cell wall and establish a continuous relationship or move from cell to cell. Cedar Hawthorne Rust

  12. Powdery mildews Downy mildews Rusts White Rusts Some species of Xylella Mollicutes Viruses Viroids Phytoparasitic nematodes Phytoparasitic Protozoa Dwarf mistletoe A biotroph can reproduce and grow in nature on living hosts

  13. Other Types of Pathogens Facultative Parasite: usually grows and completes life cycle on dead material, but can do so on living tissue. Facultative Saprophyte:usually grows and completes life cycle on living tissue, but can do so on dead material.

  14. Nonbiotrophs – may secrete toxins or enzymes that disrupt cells (kill them) before feeding on the cells or the cell’s contents. Necrotrophs – live on dead tissue.

  15. Disease Triangle Host Disease Pathogen Environment Disease is not an discrete event. It isdynamic.

  16. Disease Cycle Disease Cycle – a series of events that occur during a pathogenic relationship of a pathogen and host that leads to disease A pathogen’s life cycle may follow events similar to the disease cycle, but they are not the same thing.

  17. Disease Cycle • Inculation • Penetration • Infection • Invasion • Reproduction • Dissemination

  18. Primary Disease Cycle Monocyclic Disease Dissemination Primary Inoculum Primary Infection Over wintering

  19. Secondary Disease Cycle Polycyclic Disease PrimaryInfection Secondary Infection Reproduciton and Dissemination Overwintering

  20. Signs and Symptoms Signs are the physical presence of the pathogen. Symptoms are the plant’s response to disease.

  21. How do you determine the cause of an unknown disease? Koch’s Postulates

  22. Koch’s Postulates] • Identify symptoms and signs associated with all diseased plants • Pathogen must be isolated in culture or transferred to susceptible host • Inoculate plant with pathogen from culture and get same symptoms and signs as in #1. • Isolate same pathogen that was isolated in #2.

  23. Koch’s Postulates • Identify symptoms and signs associated with all diseased plants • Pathogen must be isolated in culture or transferred to susceptible host • Inoculate plant with pathogen from culture and get same symptoms and signs as in #1. • Isolate same pathogen that was isolated in #2.

  24. Koch’s Postulates • Identify symptoms and signs associated with all diseased plants • Pathogen must be isolated in culture or transferred to susceptible host • Inoculate plant with pathogen from culture and get same symptoms and signs as in #1. • Isolate same pathogen that was isolated in #2.

  25. Koch’s Postulates • Identify symptoms and signs associated with all diseased plants • Pathogen must be isolated in culture or transferred to susceptible host • Inoculate plant with pathogen from culture and get same symptoms and signs as in #1. • Isolate same pathogen that was isolated in #2.

  26. Reading Assignment:Chapter 2 and 3

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