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1. Introduction to
Plant
Pathology
2. History
Plant Pathology
The Study & Control of
Microbes & Environmental
Factors that Cause Diseases
3. Diagnosis of
Plant Diseases
Microbes
• Biotic, Pathogens, Parasites
– Parasite
• Lives on or in some other Organism
• Gets Food from the Host
– Pathogen
• A Specific Organism that Causes Disease
• Usually Is a Parasite
Abiotic Factors
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Moisture
Light
Pollution including Pesticides
Nutrition
Soil pH
Temperature
Pollution
Oxygen
Improper Cultural Practices
Categories
• Fungi
• Bacteria
– Spiroplasmas, Phytoplasmas
• Viruses & Viroids
• Nematodes
• Parasitic Higher Plants
Costs
• 14.1% of Crops
• $220 Billion
• Mycotoxins
(Ergotism)
• Aflatoxins
• Pesticides,
Pollution
• Limit Plants in a
Region
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Disease
• “Series of Invisible & Visible Responses
– of Plant Cells & Tissues
• to a Pathogenic Organism or Environmental
Factor
• that Result in Adverse Changes in the Form,
Function or Integrity of the Plant
• & may Lead to Partial Impairment or Death
• Any Malfunctioning of
Host Cells or Tissues
• Caused by another
Living Organism or by
an Environmental
Factor
Tomato Spotted Wilt Virus
– of Plant Parts or of the Entire Plant.”
http://ipm.ncsu.edu/current_ipm/99PestNews/99News6/fruitveg.html
Healthy
• Carry out
Physiological
Functions to Best of
their Genetic
Potential
Sick or „Diseased‟
• Microbes or Abiotic
Factors Interfere
with Essential
Functions
Progression of Disease
• Localized  Widespread  Visible
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How Pathogens Cause Disease
• Cell Metabolism
• Vascular System
• Absorb Food
How Environment Causes Disease
• Levels above or below Tolerance
Types of Plant Diseases
• How many Diseases Are out
There?
• How many Diseases can a
Single Plant Species Get?
• How many Plant Species
can a given Pathogen
Species Infect?
Categories of Diseases
Classifying Diseases
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Symptoms
Affected Plant Organ
Plants Affected
Type of Pathogen
Most Useful Category?
Plant Doctors
• Type of Pathogen
Indicates
– Cause of Disease
– Probable Development
& Spread
– Possible Control
Measures
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• Help Bioengineers
Plant Pathologists
– Develop Disease-Resistant Plant Varieties
• Diagnose
• Determine
• Decide
• Develop
• Conduct Research
• Private Practitioners
– Preserve Food from Spoilage
– Develop New Strains of Organisms for
Biological Control
– Develop Composting Processes for Solid Waste
Disposal
Plant Diseases under
Homeland Security
Microscope
History of
Plant
Pathology
• Added Significance since 9/11
• „Agroterrorism‟
• National Plant Disease
Diagnostic Network
• „First Detector Network‟
History of Plant Pathology
Very Early History
• Diseases Were Curses from God
• Festivals & Sacrifices to Thank,
Please & Appease
History
• Homer, 1000 B.C., Sulfur
• Democritus, 470 B.C., Ground Olives
• Theophrastus, 300 B.C., Lowlands Effect
• Thoullier, 1670, Ergotism
• Prevost, a Frenchman, 1807:
• “A Fungus Causes Wheat Smut.”
• “Bull!” – Academy of Scientists
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Late Blight of Potato
Spontaneous Generation
• Microorganisms
• The Little People
• The Devil
• Fiendish 20 mph
Locomotives
• Punishment from God
Produced
Spontaneously by
Dying & Dead
Plants & Animals
Phytophthora infestans
Pasteur & Microbes
• Early 1860s
• “Microbes Are Involved
in Fermentation &
Disease.”
• deBary, German, 1861
• “The fungus
Phytophthora infestans
is responsible for the
blight of the foliage &
the rot of the tuber.”
• Proved It!
Germ Theory
• This (FINALLY) Signals End of Belief of
Spontaneous Generation of Disease, in
Favor of Germ Theory of Disease
Diagnosis of
Plant Diseases
Diagnosis of Plant Diseases
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5-Step Program
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ID the Plant
CSI Time!
Describe Symptoms
Who Done It? Consult Resources
Koch‟s Postulates
How Do You Diagnose the Cause
of a Plant Disease?
• Sometimes You Get Lucky
– Symptoms
– Signs
• Sometimes You‟re Not Unlucky
– Know the Plant
– References
• Most Times You Are Unlucky
– Examine
Brown spot on soybean & early
blight on tomato
– Explore
Examine Symptoms &
Search for Pathogens
Look on Surface
Look Inside Plants
What Do You Look With?
• Naked Eye or Magnifying Lens
• Microscope
• More Sophisticated Technology
Bacterial Wilt on Zea mays
Where Do You Look?
• Margins of Affected Tissues
Downy Mildew
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•Vascular Tissues
•Base of Plant
Verticillium Wilt on Maple
--Oregon State photo
•On or In Roots
What Are You Looking For?
Common Root Rot
Caused by a Complex of Soil-Borne Fungi
--Photo by Manitoba Agriculture & Food
Bacteria
Fungi
• Identify with Microscope
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• Visual Observation
Mycelium
Fruiting Structures
Spores
May Need to Induce
Spores
Insufficient
• Identify By
– Symptoms
Claviceps purpurea
– Constant Presence in
Affected Area
--Photo by J.D. Watkins, Univ. of Nebraska
– No other Pathogens
• Culture to Confirm
(Erwinia on Cyclamen)
http://janus.state.me.us/agriculture/plantind/hortweek/erwinia.htm
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Spiroplasmas & Phytoplasmas
Viruses & Viroids
• Wall-Less Bacteria that Live in Phloem
• Symptoms
– Stunting, Leaf Yellowing or Reddening
• Sometimes Symptoms Distinctive
• Usually Symptoms not Distinctive
– Shoot or Root Proliferation
– Abnormal Flowers
– Eventual Decline & Death
• Cannot Culture
Impatiens
• Diagnose by Symptoms, Grafting, Electron
Microscopy
cosmos
cyclamen
dahlia
delphinium
exacum
forget-me-not
gaillardia
geranium
gladiolus
gloxinia
hydrangea
impatiens
lobelia
marigold
phlox
poppy
primrose
ranunculus
salvia
sinningia
snapdragon
stock
tiger lily
verbena
zinnia
Vegetables
broad bean
cauliflower
celery
eggplant
lettuce
pepper
potato
snap bean
spinach
tomato
Weeds
beggar ticks
black nightshade
morning glory
burdock
chickweed
galinsoga
lamb's quarters
shepherd's purse
sowthistle
purslane
yellow clover
Virus Identification
• Transmission
• Molecular Techniques
• Electron Microscopy
Parasitic Higher Plants
• Presence of Parasite Sufficient to Diagnose
Cineraria
http://www.umass.edu/umext/programs/agro/floriculture/floral_facts/insvtswv.htm
Some Species Susceptible to INSV
Ornamentals
ageratum
amaranthus
amaryllis
anemone
aster
baby's breath
begonia
calceolaria
calendula
calla lily
campanula
china aster
chrysanthemum
cineraria
coleus
columbine
coreopsis
Gloxinia
Nematodes
•If
– Plant Shows certain Symptoms
– Nematodes Are on or in Plant
– Nematodes Are in Rhizosphere
•Then
– Maybe Nematodes
•Check Resources
http://www.ppru.cornell.edu/nematology/Bigpicture. htm
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Multiple Pathogens
• Recognize additional Pathogens
• Use Above Procedures to ID Pathogens &
Diagnose Diseases
Noninfectious (Abiotic) Diseases
• Usually the Cause if no Pathogen can Be
Found, Cultured or Transmitted
• Usually Interfere with Normal Physiological
Processes
• Usually Difficult to Diagnose
What Resources Do You Use?
• Plant ID Books
• Textbook
• American Phytopathological Society
• University & Extension Publications
• Online Resources
Koch‟s Postulates
• Procedures to Isolate & Identify
Cause of a Microbial Disease
1. A specific organism must be
always be observed in association
with the disease.
2. The organism must be isolated from an
infected host & grown in pure culture in a lab.
3. When organisms from the pure culture are
inoculated into a susceptible host organism, it
must cause the disease.
4. The infectious organism must be re-isolated
from the diseased organism & grown in pure
culture.
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