Title: The Plant Disease Triangle - How

Plants Defend Themselves, Part I

Speaker: Dean Glawe

online.wsu.edu

Plant Pathology 501

The Plant Disease Triangle-How Plants

Defend Themselves, Part I

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

The Plant Disease Triangle

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

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

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

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

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

Basic organization of plants

• Leaves also contain xylem

and phloem

• Epidermal cells may form

trichomes (sometimes called

leaf hairs)

From Wikipedia

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

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

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?

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

Resistance to plant pathogens • Anatomical barriers and defenses

– Cell walls

Resistance to plant pathogens • Anatomical barriers

and defenses

– Bark,

cork layers

Resistance to plant pathogens

• Anatomical barriers and

defenses

– Abscission layers

From: Schumann and D’Arcy

Resistance to plant pathogens

• Anatomical barriers

and defenses

– Tyloses

From: Schumann and D’Arcy

Resistance to plant pathogens

• Physiological factors – Absence of recognition factors in plant

– Absence of host receptors for toxins

– Lack of essential substances for pathogen

• Physiological factors – Host receptors that recognize

pathogen (inducing response)

– Cell wall development and

strengthening

– Hypersensitive response

– Antimicrobial substances

• Phenolics

• phytoalexins

Resistance to plant pathogens

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