Exer 2

• Isolation


  the separation of the suspected pathogen from the host tissues and growing it into a pure culture on a nutrient medium
• PDA for fungi

  potato dextrose agar
• PDPA for bacteria

  potato dextrose peptone agar
• obligate parasites


  cannot be grown in a nutrient medium and must be maintained in a living host
• Koch's Postulates


  set of rules used to identify the pathogen of a new or unknown disease.
• Koch's Postulates

  Heinrich Hermann Robert Koch and Friedrich Loeffer
• Koch's Postulates

  1 - Association

  2 - Isolation

  3 - Inoculation

  4 - Re-isolation
• Association


  Suspected pathogen must be consistently associated with the diseased plant
• Isolation


  the pathogen must be isolated and grown in pure culture and its characteristics described
• inoculation

  the pathogen from pure culture is inoculated into a healthy plant of the same species or variety and it must produce the same symptoms and signs
• Re-isolation


  the pathogen is re-isolated from the inoculated plant and its characteristics must be the same as the organism initially isolated
• Types of Culture Media

  Based on Consistency:

  • Solid Media
  • Liquid Media

  Based on Chemical Composition:

  • chemically-defined (synthetic) medium
  • non-synthetic/complex media
• solid media

  • useful in studying characteristics of bacterial colonies
  • mixed bacterial cultures can be separated/distinguished (pure culture)
  • commonly uses agar as a solidifying agent (bacteriologically inert, remains solid at 37 degree C and transparent)
• Liquid Media

  • useful to obtain profuse growth of bacterial cultures (commonly aerated)
  • mixed organisms cannot be separated
• Chemically-defined (synthetic) medium

  • the exact chemical composition is known.
• Non-synthetic/complex media


  are usually composed of pure biochemicals off the shelf and complex materials of biological origin such as blood or milk or yeast extract or beef extract (exact chemical composition of which is obviously undetermined)
• wireloop


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• dissecting/teasing needle


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• forcep


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• Alcohol lamp


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• scalpel


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• petri plates


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• test tube


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• reagent bottle


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• pressure cooker


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• laminar flow


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• compound microscope


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• stereo/dissecting microscope


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