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Introduction to Plant Pathology

Disease = disturbance from plant pathogen or environmental factor that interferes with plant physiology

Causes changes in plant appearance or yield loss

Disease results from:

• Direct damage to cells

• Toxins, growth regulators, or other byproducts that affect metabolism

• Use of nutrients and water or interference with their uptake

Plants Diseases Triangle

Pathogen Host Virulent pathogen: Susceptible

Fungi, Bacteria, -- Crop

Viruses, Nematodes, -- Cultivar

Nycoplasmas and

Spiroplasmas

Favorable Environment

Air temperature Soil fertility Rainfall

Soil Temperature Soil type Relative humidity

Soil pH Soil Moisture

Mazz’s Disease Pyramid

The interaction of components of plant disease can be expanded to include time and humans.

Time is often considered as the fourth component of plant disease development. The four components together can quantify the amount of disease.

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DISEASE

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The human equation can affect the three components of the disease triangle and should be considered as a fifth component in disease development.

Host Factors

All plants can be considered hosts Degree of genetic uniformity – crop plants – inbred lines Age – affects disease development depending on plant-pathogen interaction There are different levels of susceptibility, which include:

– Immune - cannot be infected. – Susceptible - can be infected. – Resistant - may or may not be infected, and is the plant able to prevent the

pathogen from killing it. ie. defense compounds

Pathogen Factors

Amount of inoculum Pathogen genetics Virulence of the pathogen

Type of reproduction:

– Monocyclic– polycyclic

Ecology and mode of spread

Air

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Soil Seed Vector dependency

Environmental Factors

Moisture Temperature Effect of human culture practice

– Monoculture– Amount of inoculum: seed quality, disease residues, rotation, alternate host– Introduction of new pathogens

Disease Development

Every infectious disease requires a series of sequential events in order for disease to develop.

Specific characteristics are unique for each disease.

General events are:

1. dispersal of the pathogen to the host2. penetration and infection of the host3. invasion and colonization of the host4. reproduction of the pathogen5. pathogen dispersal6. pathogen survival between growing seasons and/or in the absence of a host

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