PLANT PATHOLOGY

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PLANT PATHOLOGY
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Plant disease

• Plants normal function is interrupted by a
  pathogen or the environment

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Plant disease

• Is this a disease?

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Biotic damage

• Caused by living pathogens or parasites

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Biotic damage

• Symptoms visible expressions of plant reaction
  to the pathogen

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Biotic damage

• Signs indications of disease from direct
  visibility of a pathogen
• Actually seeing the pathogen

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DISEASE TRIANGLE

• Disease needs all three to develop
• Only need to block one of them

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Pathogen

• Organisms capable of causing disease
• Fungus
• Bacteria
• Virus
• Other micro-organisms

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Pathogen

• Parasites obtain food from living organisms
  (host)

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Pathogen

• Obligate parasite require (obligated to) living
  plant cells as food to complete life cycle

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Pathogen

• Facultative parasite obtain nutrition from
  either living or dead plants

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Pathogen

• Saprophyte feeds on dead organic material on
  plant or in soil

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HOST

• Susceptible no ability to retard or resist
  disease
• Susceptible plant tissue
• Fertilization

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HOST

• Resistance some ability to retard or tolerate
  disease

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HOST

• Immunity complete resistance against disease

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ENVIRONMENT

• Moisture and temperature are the predominant
  factors

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ENVIRONMENT

• Moisture, water is critical
• Dry springs can reduce disease occurrence
• Often 24 to 48 hours continually wetness required
• Poor irrigation practice

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ENVIRONMENT

• Temperature, each pathogen has optimal range
• Predisposed condition of host
• Host is stressed, cant defend

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FUNGUS

• The vast majority of plant diseases are fungal

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FUNGUS

• What is a fungus?
• Microscopic organisms that lack chlorophyll,
  cannot produce own food
• Multicellular organism that is threadlike in
  composition

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FUNGUS

• Enormous genetic variability due to rapid
  reproduction

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FUNGUS

• Species of fungi are subdivided into strains that
  are very specific in
• Plant species or cultivars
• Virulence
• Temperature range
• Moisture requirements

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SPORE

• Fungal seed
• Very distinct shape and size used to
  differentiate pathogens
• Single celled or multi-celled

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SPORE

• Asexual, not requiring the union of sexual parts
  to be produced
• Conidia

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SPORE

• Sexual, requiring union of sexual parts to be
  produced
• Basidiospore, ascospore, oospore

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SPORE

• Where do you see spores when a plant is infected?
• Leaf surface
• Appears as mold (powdery mildew)

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SPORE

• Where do you see spores when a plant is infected?
• Fungal fruiting bodies
• Spore producing pockets
• Sporodochium, acervulus, pycnidium

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HYPHAE

• Hyphae is what germinates out of the spore
• Branches out into tubular filaments

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HYPHAE

• Mycelium refers to all the hyphae as a whole, as
  the fungal body
• Inside the plant, or outside the plant under high
  moisture

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PLANT INVASION

• Fungus enters plant through any of the following
• Wounds
• Mechanical, pruning or handling

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PLANT INVASION

• Wounds
• Insects, vectors or egg laying

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PLANT INVASION

• Wounds
• Naturally occurring
• Secondary roots rupture the main root when
  emerging
• Leaf scars

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PLANT INVASION

• Fungus enters plant through any of the following
• Natural openings
• Lenticels

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PLANT INVASION

• Fungus enters plant through any of the following
• Direct penetration
• Pushing through tissue
• Resistance can come in the form of thicker
  cuticle or hairy leaf

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FUNGAL LIFE CYCLE

• Peach brown rot is used as an example

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FUNGAL LIFE CYCLE

• Overwinter,
• Disease is dormant in infected fruit and stems

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FUNGAL LIFE CYCLE

• Dissemination
• Disease produces spores (conidia) that are spread
  by wind and rain

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FUNGAL LIFE CYCLE

• Inoculation
• Spores contact susceptible blooms

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FUNGAL LIFE CYCLE

• Penetration
• Spore germinates and enters tissue directly

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FUNGAL LIFE CYCLE

• Infection
• Establishes hyphae in tissue and feeds on cells

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FUNGAL LIFE CYCLE

• Incubation period
• Time between infection and appearance of symptoms

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FUNGAL LIFE CYCLE

• Invasion
• Spreads from bloom to other parts of the plant
  within tissue

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FUNGAL LIFE CYCLE

• Dissemination

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FUNGAL LIFE CYCLE

• Overwinter
• When temperature cools, fungus goes dormant

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Zombie Fungus

• http//www.huffingtonpost.com/2011/09/14/zombie-ca
  terpillars-virus_n_962256.html
• Brazilian rain forest
• Controls ants

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• Infection pegs grow from body
• Shoots at passing ants

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