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 DiStudy of Plant Diseases:– Biotic, or living diseases– Abiotics disorders, or non‐,

infectious diseases– Sometimes referred to as 

PhytopathologyPhytopathologyHow Important?

– $220 billion crop value loss h d t dieach year due to diseases 

alone – Does not include 

i i i h hinteractions with other organisms

What is Plant Pathology?What is Plant Pathology?

An Interdisciplinary field:‐ Biology, horticulture, mycology, bacteriology, virology, plant physiology, entomology etcentomology, 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 (f ti )diseases (few exceptions)

– Either live with losses or prevent with culturalprevent with cultural practices

What is Plant Pathology?

A hi i l fi ld

What is Plant Pathology?

A historical field:– Studied since the advent of farming firstof farming – first recorded by the Greeks

– Field first defined in 1861 with the identification of the Potato Late BlightPotato Late Blight Pathogen

– Modern Plant Pathology gycombines Molecular and Field techniques

Historical Review of Plant PathologyHistorical Review of Plant Pathology

• Robert Hooke ‐ 1670

• Carl van Linne ‐ 1735

• Antonio Leeuwenhoek ‐16741674

• Charles Darwin ‐ 1859

A t d B 1861• Anton deBary – 1861

• Louis Pasteur – same time

• Robert Koch ‐ 1887

Koch’s PostulatesKoch s Postulates

1 O i t b1. Organism must be present in all plants showing symptoms.g y p

2. Agent must be isolated from diseased hosts

3 Th l i3. The pure culture is 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 Plant1. Carries out its 

Diseased Plant1. When the ability of cells of 

physiological functions to the best of its genetic 

t ti l

a plant or plant part is compromised 

potential

2. Cells divide and differentiate as needed

‐ Biological agent

‐ Environmental factor

2 Cells affected indicatesdifferentiate as needed and specialized cells fulfill dedicated tasks

2. Cells affected indicates type of physiological function lost.ded cated tas s u ct o ost

What is a healthy/diseased plant?y/ p

Agrios, 2005

Causes of Plant DiseasesCauses of Plant Diseases

Bi l i l A t• Biological Agents

1. Fungi2. Viruses3. Bacteria

d4. Nematodes5. Parasitic Plants6 Viroids6. Viroids7. Protozoans

Biotic Disease – Disease symptom caused by a y p y“living” organism

Agrios, 2005

Causes of Plant Diseases

E i l F

Causes of Plant Diseases

• Environmental Factors1. Temperature2. Moisture3. Inadequate Oxygen4 Li ht4. Light5. Air Pollution6 Nutritional Deficiencies6. Nutritional Deficiencies7. Herbicide Injuries

Abiotic disorder/noninfectious disease – Disease symptom caused by ancaused by an environmental factor.