10/31/12
Basic Plant Pathology Training
Central Disease Concepts
Kevin Ong, PhD.
Associate Professor and Extension Plant Pathologist
Director – Texas Plant Disease Diagnostic Laboratory
College Station, TX
MG series module 1
What is a PLANT DISEASE?
Any alteration of a plant that
interferes with its normal
appearance, function, or value and
renders it unfit for its normal use.
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TWO kind of disease
•  Infectious
–  Transmissible from plant to plant
–  Caused by biotic (pathogenic) agents
•  Non-infectious
–  Disorder caused by unfavorable physical
environmental (physiogenic) effect
What can make plants sick?
Baudoin, A.B.A.M. 2007. The Plant Disease Doughnut, a Simple Graphic to Explain what is Disease and what is a Pathogen. The Plant Health Instructor. DOI: 10.1094/PHI-T-2007-1221-01
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How many/much of the
plant can be affected by
disease pathogens?
1.  Fruit
2.  Roots
3.  Leaves
4.  Branches
5.  All of the above
CONCEPT #1: Disease triangle
V
EN
DISEASE
NT
ME
HO
ST
ON
IR
PL
AN
T
•  Three factors:
PATHOGEN (disease causing agent)
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The Disease Triangle
V
EN
PL
AN
T
y
Dr
Disease Occurs
NT
ME
HO
ON
ST
IR
t
We
Susceptibility
PATHOGEN (disease causing agent)
CONCEPT #2: Disease Cycle
Management
Overseasoning/
Overwintering
Management
Host (inoculation)
Management
Management
Reinfection
Disease
Infection
Management
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Disease Cycle
•  Example of a pathogen: cedar – apple Rust
Host
(inoculation)
Infection
Disease
Overwintering
Disease Cycle: Peach Brown Rot
Host
(inoculation)
Infection
D
i
s
e
a
s
e
Overseasoning
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Disease cycle: Alternaria (early) blight
Host (inoculation)
Overseasoning
Infection
Disease
Review
Importance of Disease Triangle
1.  Identifies the factors critical in disease
development
2.  Helps to determine the interactions between
the factors involved in disease development
3.  Reminds and enables a logical approach to
diagnosing a pathogenic problem
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Review
Disease cycle
1.  Identifies/documents how a pathogen
lives and causes diseases.
2.  Enables the development of proper and
effective management approaches.
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