Introduction to Plant Pathology:
Introduction
to Plant Pathology:
A Master Gardener Short Course
David Doll
Farm Advisor, Merced County
Part 1:
Part
1:
Principles of Plant Pathology
What is Plant Pathology?
What is Plant Pathology?
St d f Pl t Di
Study of Plant Diseases:
– Biotic, or living diseases
– Abiotics disorders, or non‐
,
infectious diseases
– Sometimes referred to as Phytopathology
How Important?
– $220 billion crop value loss each year due to diseases h
d t di
alone – Does not include i
interactions with other i
ih h
organisms
What is Plant Pathology?
What is Plant Pathology?
An Interdisciplinary field:
‐ Biology, horticulture, mycology, bacteriology, virology, plant physiology, entomology etc
entomology, etc.
‐ Benefits from advances in Benefits from advances in
any other science
What is Plant Pathology?
What is Plant Pathology?
A Reactive Field:
– Plant can not communicate with us
– No curatives for plant di
diseases (few exceptions)
(f
ti )
– Either live with losses or prevent with cultural
prevent with cultural practices
What is Plant Pathology?
What is Plant Pathology?
A hi
A historical field:
i l fi ld
– Studied since the advent of farming first of farming –
first
recorded by the Greeks
– Field first defined in 1861 with the identification of the Potato Late Blight
Potato Late Blight Pathogen
– Modern Plant Pathology gy
combines Molecular and Field techniques
Historical Review of Plant Pathology
Historical Review of Plant Pathology
• Robert Hooke ‐ 1670
• Carl van Linne ‐ 1735
• Antonio Leeuwenhoek ‐
1674
• Charles Darwin ‐ 1859
• Anton deBary
A t d B
– 1861
• Louis Pasteur – same time
• Robert Koch ‐ 1887
Koch’ss Postulates
Koch
Postulates
1 O
1.
Organism must be i
tb
present in all plants g y p
showing symptoms.
2. Agent must be isolated from diseased hosts
3 The pure culture is 3.
Th
l
i
inoculated into a healthy host 4. The disease is reproduced
5. The same causal agent is re‐isolated from host
What is a healthy/diseased plant?
What is a healthy/diseased plant?
Healthy Plant
Diseased Plant
1. Carries out its physiological functions to the best of its genetic potential
t ti l
2. Cells divide and differentiate as needed
differentiate as needed and specialized cells fulfill dedicated tasks
ded
cated tas s
1. When the ability of cells of a plant or plant part is compromised ‐ Biological agent
‐ Environmental factor
2 Cells
2.
Cells affected indicates affected indicates
type of physiological function lost.
u ct o ost
What is a healthy/diseased plant?
y/
p
Agrios, 2005
Causes of Plant Diseases
Causes of Plant Diseases
• Biological Agents
Bi l i l A t
1.
2.
3.
4.
5.
6
6.
7.
Fungi
Viruses
Bacteria
Nematodes
d
Parasitic Plants
Viroids
Protozoans
Biotic Disease – Disease y p
y
symptom caused by a “living” organism
Agrios, 2005
Causes of Plant Diseases
Causes of Plant Diseases
• Environmental Factors
E i
lF
1.
2.
3.
4
4.
5.
6
6.
7.
Temperature
Moisture
Inadequate Oxygen
Li ht
Light
Air Pollution
Nutritional Deficiencies
Nutritional Deficiencies
Herbicide Injuries
Abiotic disorder/noninfectious disease – Disease symptom caused by an
caused by an environmental factor.