Bot350/550 Practical Study Guide Isolation of Fungal Pathogens




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BOT350/550 Practical Study Guide
Isolation of Fungal Pathogens:

  • Pathogens with which life strategy (e.g. facultative parasite) are incapable of growing on culture media? Why?

  • What is the purpose of surface sterilizing infected plant tissue before culturing it?

  • Why isolate pathogens from the interface between healthy and diseased tissue rather than from the diseased tissue itself?

  • What is selective media? What is differential media? (Remember that media can be both selective and differential)

  • Why are antibiotics commonly added to isolation media for fungi?

  • What special technique is often used to isolate soilborne Oomycetes? Why?


Koch’s Postulates:

  • What is the purpose of Koch’s Postulates?

  • What are the four steps of Koch’s Postulates? Note: “Determine the pathogen,” is not an acceptable answer for postulate one.


Oomycetes (Water Molds):

  • Know two features that distinguish Oomycetes from true fungi.

  • Know: oospore, oogonium/antheridium, zoospore, and sporangium.

  • Which of the above structures are asexual? Which are sexual or the direct product of sexual reproduction?

  • Which of the above is a resting or overwintering structure?

  • Know how to recognize sporangia and oospores under the compound microscope.

  • Why does wet, poorly drained soil often contribute to the establishment and spread of Oomycete diseases?

  • Diseases: white rust, downy mildew, late blight of potato, damping off.


Ascomycetes (Sac Fungi):

  • Do Ascomycetes have septate or aseptate hyphae?

  • Are they predominately haploid, diploid, or dikaryotic?

  • Know: ascospores, ascus, ascocarps (cleistothecium/ascoma, perithecium, apothecium), sclerotium, stroma, conidia, conidiophores (separate, synnema, sporodochium), asexual fruiting bodies (acervulus, pycnidium).

  • Which of the above are sexual structures? Which are asexual structures? (Remember that regular or teleomorphic ascomycetes have both sexual and asexual structures while asexual or anamorphic ascomycetes have only asexual structures)

  • Which are overwintering structures?

  • What is an anamorph? What is a teleomorph?

  • How many ascospores does an ascus contain?

  • Powdery Mildews have which of the three ascocarps?

  • What three traits are used to key out powdery mildews?

  • Be able to recognize asci, cleistothecia, perithecia, stroma, conidia/conidiophores, and asexual fruiting bodies under the compound microscope.

  • Diseases: eastern filbert blight, white mold, tar spot of maple, apple scab, ergot, powdery mildew, grey mold, early blight, Verticillium wilt.


Basidiomycetes (Club Fungi):

  • Are Basidiomycetes predominately haploid, diploid or dikaryotic?

  • Are they septate or aseptate?

  • Know: basidiospores, basidia (naked or in basidiocarps), basiodocarps, teleospores, telium, spermatia, receptive hyphae, spermagonium, uredospores, uredium, aeciospores, aecium.

  • Which of the above structures belong to ascocarp basidiomycetes? Which belong to rusts? Which belong to smuts?

  • Which of the above spores is the direct product of sexual reproduction? Which of the above are overwintering structures?

  • For some rusts the only functional spore is the uredospores….how does a rust of this type overwinter?

  • Be able to identify basidia with basidiospores, uredospores in uredia and teliospores in telia under the comound microscope.

  • Define: macrocyclic, microcyclic, heteroecious, autoecious.

  • Are smuts monocyclic or polycyclic?

  • Diseases: rusts, smuts, wood rots/decays.


Bacteria:

  • What are five methods used to diagnose bacterial diseases and identify bacteria?

  • Define peritrichous and polar flagella.

  • Know the basis of the gram stain test and the colors of gram positive and negative bacteria.

  • Know the basis of the hypersensitivity response when testing for pathogenic bacteria, including the importance of the type III secretion system.

  • What characteristic of bacteria does the oxidation/fermentation test investigate?

  • Diseases: soft rot and ring rot of potato, fire blight, crown gall.



Viruses:

  • What are five methods used to diagnose viral diseases and identify viruses?

  • Know the basics of how an ELISA test works.

  • What is the difference between a local lesion host and a systemic host when conducting a viral pathogenicity bioassay? How do the two differ in resistance?

  • Diseases/symptoms: chlorotic mosaics (Tobacco Mosaic Virus), leaf curls, vein clearing, stunt syndromes.


Botrytis Predisposition:

  • Know why Botrytis is considered an example of a weak pathogen (i.e. know its life strategy).

  • Why would the addition of rose petals or potato dextrose broth aid in the establishment of Botrytis?


Race Identification of Wheat Strip Rust:

  • Define race and differential cultivar.

  • Do necrosis and chlorosis in wheat cultivars indicate susceptibility or resistance to a particular rust race?

  • How do r-genes fit in?


Biocontrol of Crown Gall:


Nematodes:

  • There are ten characteristics commonly used to identify nematodes…..know five.

  • What is the importance of the stylet in plant parasitic nematodes?

  • What is the difference between endoparasitic, ectoparasitic, sedentary, and migratory nematodes?

  • What are two methods used to extract nematodes from roots or soil?

  • Be prepared to key out or identify nematodes.


Electron Microscopy:

  • The electron microscope is especially useful for viewing which major pathogen group?

  • What differences are there between transmission electron microscopy (TEM) and scanning electron microscopy (SEM)?

  • What are positive and negative staining in TEM?


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