Fastidious Prokaryotic Plant Pathogens

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wsucoug12
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311344
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Fastidious Prokaryotic Plant Pathogens
Updated:
2015-11-11 20:42:21
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Fastidious Prokaryotic Plant Pathogens
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Fastidious Prokaryotic Plant Pathogens
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  1. What is a fastidious organism?
    An organism that either has a very difficult time grown on artificial media or cannot at all be grown outside of a host
  2. Examples of Fastidious Prokaryotic Plant Pathogens
    Xylella, Phytoplasma, & Spiroplasma
  3. Describe Fastidious Prokaryotic Plant Pathogens
    • Functionally obligate parasites
    • Similar disease cycles
    •  vascular pathogens
    • “yellows” diseases
    • insect vectors, vegetative
    • propagation
  4. Characteristics of Xylella fastidiosa
    • Bacilliform with rippled cell wall
    • 1-4 µm x 0.2-0.5 µm
    • Reproduction by fission
    • Non-spore-forming
    • Non-motile
    • Distributed in xylem or phloem
    • Disseminated by insects & vegetative
    • propagation
    • e.g. Pierce’s disease of grapes,
    • Almond leaf scorch, Alfalfa dwarf
    • Citrus variegated
    • chlorosis (CVC)
    • Rickettsia-Like-Organisms = RLO
  5. Characteristics of Phytoplasma sp.
    • No cell wall
    • Pleomorphic,
    • ~ 0.2 µm (200 nm) diameter
    • Reproduce by fission & budding
    • Non-spore-forming
    • Non-motile
    • Kingdom Prokaryotae
    • Taxonomy of Bacteria
    • Mollicutes – no cell wall
    • Family Mycoplasmataceae
    • Phytoplasma
    • mycoplasma-like-organisms
  6. Characteristics of Phytoplasma sp. continued
    • Located in the phloem
    • Disseminated by insects & vegetative
    • propagation
    • e.g. Pear decline, Aster yellows, X-disease
    • of peach
    • Purple Top of Potato (serious outbreaks
    • in WA last couple of years)
  7. Describe Phytoplasma Transmission
    • Phytoplasmas are transmitted in a persistent propagative manner by several
    • phloem-feeder hemipterans: planthoppers (Cixiidae), leafhoppers (Cicadellidae)
    • and psyllids (Psyllidae). Transmission consists of three steps, acquisition, latency,
    • and inoculation.
  8. Transmission specificity is determined by
    • Feeding behaviour (phloem feeding)
    • Insect host range
    • Membrane proteins from both phytoplasmas and insects
  9. What are the Barriers to insect body colonization
    • Salivary gland barrier
    • Midgut barrier
  10. Characteristics of Spiroplasma citri
    • No cell wall
    • Helical, sometimes branched
    • 0.1 µm x 2-4 µm
    • Reproduce by fission
    • Non-spore-forming
    • Motile, but no flagella
    • Located in the phloem
    • Disseminated by insects & vegetative
    • propagation
    • e.g. Citrus stubborn, Corn stunt
  11. What are the impacts of these types of Disease
    • Plants die prematurely
    • • Evidence of very significant yield loss
    • • Evidence of reduction in tuber
    • processing quality (fries and chips
    • commercially unacceptable)
    • • Causes millions of dollars in losses to
    • potato producers and processors
  12. Disease/Causal Agents?
    • Caused by Phytoplasmas (Group I)
    • • Mycoplasma-like organisms (MLO)
    • • Small prokaryotes related to bacteria
    • and belonging to the class Mollicutes
    • • Lack cell wall and non-culturable
    • • Phloem-limited and insect-transmitted
    • in persistent manner
    • • Usually transmitted by leafhoppers,
    • planthoppers, and psyllids

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