pl sc 380 final p. 2

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  1. barley yellow dwarf virus
    • most important viral disease of cereals
    • transmitted by aphids
    • reduces seed size and number
    • symptoms: diffuse yellowing near tips of leaves, later bright yellow discoloration of leaves, stunting of plants
  2. control of barley yellow dwarf virus
    • avoid aphids (seed early)
    • tolerant cereal cultivars
    • spraying against aphids - sometimes successful
  3. infection
    process by which a pathogen establishes contact with susceptible cells or tissues of the host and procures nutrients from them
  4. types of inoculum
    • viruses/viroids
    • phytoplasmas
    • bacteria
    • fungi
    • nematodes
    • flowering plants
  5. types of host penetration
    • direct penetration
    • penetration through wounds
    • penetration through natural openings
  6. static resistance
    mechanisms that are continuous or on the host
  7. dynamic resistance
    • mechanisms that are initiated by the host in the presence of the pathogen
    • 1. mechanical barriers
    • 2. hypersensitivity reaction
    • diffusible toxic substances
  8. hypersensitivity reaction
    • expression of plant resistance involving rapid death of host cells at or near site and time of infection
    • results in restriction or death of pathogen
  9. hydrophobins
    low molecular mass secreted proteins of fungi, are characterized by moderate to high levels of hydrophobicity (repelled by water)
  10. elicitor
    a molecule produced by the host (or pathogen) that induces a response by the pathogen (or host)
  11. Mechanisms of hypersensitivity
    • 1. browning reaction
    • 2. generation of reactive oxygen species
    • 3. elicitation of phytoalexins
  12. browning reaction
    • increase in level of phenolic compounds through activation of shikimic acid pathway
    • activation of polyphenol oxidase
  13. reactive oxygen species
    • NADPH + O2 reduces O2 to O2- (superoxide)
    • superoxide generates O2 (singlet oxygen), H2O2 (hydrogen peroxide), OH- (hydroxyl radical)
  14. phytoalexin
    a substance produced in higher plants in response to a number of chemical, physical, and biological stimuli that inhibits the growth of certain microorganisms
  15. factors that determine effectiveness of elicitation of photoalexins
    • 1. presence or absense of phytodetoxification mechanisms in the pathogen?
    • 2. timing and speed of production
    • 3. type and concentration of phytoalexin
    • 4. type of pathogen
  16. types of resistance to pathogens
    • non-host plant resistance
    • escape from infection
    • tolerance to disease
    • true resistance
  17. monogenic resistance
    • 'vertical' resistance
    • plant reaction is a qualitative trait, controlled by 1 gene
    • usually broken in a few years by pathogen race change
  18. polygenic resistance
    • 'horizontal' resistance
    • controlled by many genes, cannot be broken by a race change in the pathogen
    • not as complete as vertical resistance
  19. resistance genes
    • R-genes
    • absence allows susceptibility
  20. avirulence genes
    in pathogens, absence allows virulence
  21. gene-for-gene concept
    for every gene conferring virulence to the pathogen, there is a corresponding gene in the host that confers resistance to the pathogen (and vice-versa)
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Card Set
pl sc 380 final p. 2
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lectures 19-23
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