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Title: The Plant Disease Triangle - How
Plants Defend Themselves, Part I
Speaker: Dean Glawe
online.wsu.edu
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Plant Pathology 501
The Plant Disease Triangle-How Plants
Defend Themselves, Part I
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Topics Covered in this Lecture
• The plant disease triangle
• Review of basic plant structures and
their functions
• Overview of plant health
• Basic kinds of resistance to plant
pathogens
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The Plant Disease Triangle
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Plant diversity—a blessing and a difficulty for
plant pathologists
• Medical doctors focus on one species (Homo sapiens)
• Vetrinarians focus on a few species (almost all
vertebrates)
• Plant pathologists deal with diseases of hundreds of
extremely diverse plants
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Plant diversity—a blessing and a difficulty for
plant pathologists
• Because a disease is a divergence from the normal, or
health condition, understanding a plant disease starts
with understanding the healthy plant
• This would be a good time to review your basic
botany
• Following are a few ideas to help your review
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Basic organization of plants
• Plant cells are the basic
“building blocks”
• Cell walls add rigidity,
protection
• Nuclei and organelles
involved in regulation
and function
• Cells form tissues that
play different roles
From:
http://micro.magnet.fsu.edu/ce
lls/plants/plantmodel.html
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Basic organization of plants
• Stems comprised mostly of
parenchyma, xylem, and
phloem
• Phloem cells transfer
nutrients (such as sugars)
through the plant
• Xylem cells enlarge, die,
function like hollow,
microscopic “soda straws” to
transport water and solutes
up from the roots
From Wikipedia
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Basic organization of plants
• Leaves consist of several
tissues
• Epidermal cells covered with
waxy cuticle
• Stomata consist of guard
cells and central opening
• Typically sites of
photosynthetic activity, send
sugars into plant
• Leaves often persist for a
single season
From Wikipedia
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Basic organization of plants
• Leaves also contain xylem
and phloem
• Epidermal cells may form
trichomes (sometimes called
leaf hairs)
From Wikipedia
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Basic organization of plants
• Roots are extremely diverse,
play different roles (often
simultaneously)
– Absorb water and nutrients
– Anchor plant
– Storage of nutrients
• In many plants form an
association with a parasitic
fungus to form a mycorrhyza
• Not to be confused with root-
like structures
– Rhizomes, tubers, etc
From Wikipedia
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Basic organization of plants
• Basic unit is the cell
– Plants contain many kinds of cells
– Parenchyma, xylem, phloem, etc
• Cells are organized into tissues
• Tissues are organized into organs
– Stems
– Leaves
– Roots
– Flowers
– fruits
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Plant health
• Different parts of plants (ranging from
sub-cellular components to organs)
function properly to enable it to
reproduce successfully
• From a human perspective, the plant
provides us with what we want from it
– Fruit
– Seed
– Fiber (wood, cotton, etc)
– Beauty
– Other?
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Resistance to plant pathogens
• Phenology—timing of plant life cycle events
• Late season strawberries seem less affected by Botrytis rot in the
Pacific Northwest
• Spore release by the powdery mildew fungus that attacks
grapevines is “synchronized” with the host so that spores can attack
vulnerable new shoots in the spring
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Resistance to plant pathogens • Anatomical barriers and defenses
– Cell walls
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Resistance to plant pathogens • Anatomical barriers
and defenses
– Bark,
cork layers
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Resistance to plant pathogens
• Anatomical barriers and
defenses
– Abscission layers
From: Schumann and D’Arcy
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Resistance to plant pathogens
• Anatomical barriers
and defenses
– Tyloses
From: Schumann and D’Arcy
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Resistance to plant pathogens
• Physiological factors – Absence of recognition factors in plant
– Absence of host receptors for toxins
– Lack of essential substances for pathogen
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• Physiological factors – Host receptors that recognize
pathogen (inducing response)
– Cell wall development and
strengthening
– Hypersensitive response
– Antimicrobial substances
• Phenolics
• phytoalexins
Resistance to plant pathogens
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Resistance to plant pathogens--summary
• Most plants are resistant to most pathogens
– Non-host resistance
• Resistance to plant pathogens occurs at all
organizational levels of plants (sub-cellular to whole
plant)
• Many of our strategies for managing plant diseases
are based on taking advantage of these features of
plants