Introduction to Diseases

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Introduction to Diseases
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Introduction to Diseases

• What disease is
• What causes disease
• Disease diagnosis
• Control Concepts

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Introduction to Diseases

• Disease Abnormality

Horsfall and Cowling "The term plant disease is
properly applied to any deviation from normal
growth or structure of plants that is
sufficiently pronounced and permanent to produce
visible symptoms or to impair quality and
economic value." Stakman and Harrar Any
disturbance of a plant that interferes with its
normal growth and development, economic value, or
aesthetic quality a continuously, often
progressively affected condition in contrast to
injury, which results from momentary damage."
Schumann Any disturbance brought about by a
pathogen or a consistent environmental factor
which interferes with normal manufacture,
translocation, or utilization of nutrients
Failure to reach full genetic potential due to
the activities of another organism or
environmental factor.
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Introduction to Diseases
Agrios A malfunctioning of host cells and
tissues that results from their continuous
irritation by a pathogenic agent or environmental
factor and leads to the development of symptoms.
Disease is a condition involving abnormal changes
in the form, physiology, integrity or behavior of
a plant. Such changes may result in partial
impairment or death of the plant or its
parts.

• Disease Abnormality

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Causes of Disease

• Abiotic (Non-infectious)
• Biotic (Infectious)

Pathogen an agent that causes disease
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Causes of Disease

• Abiotic (non-infectious)
• Extremes of temperature
• Oxygen deficiency
• Soil moisture
• Air pollutants
• Biotic (Infectious)

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Causes of Disease

• Abiotic (non-infectious)
• Extremes of temperature
• Oxygen deficiency
• Air pollutants
• Soil moisture
• Biotic (Infectious)
• Bacteria - Mycoplasmas
• Fungi - Nematodes
• Mistletoes

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Fungi

• Characteristics
• Produce hyphae (structural unit)
• Produce spores (reproductive unit)
• Heterotrophic obtain food from -
• Dead organic matter (saprophytic)
• From other living organisms (parasitic)

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Fungi

• Characteristics
• Produce Hyphae (structural unit)
• Produce Spores (reproductive unit)
• Heterotrophic
• Beneficial
• Decompose dead plants and animals
• Important industrially
• Mycorrhizae

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Bacteria

• Characteristics
• Single-celled
• Microscopic
• Lack chlorophyll

Bacterial canker of cherry
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Seed Plants

• Characteristics
• Flowering plants
• Most have chlorophyll
• Establish root like haustorial connections with
  vascular elements of the host

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Mycoplasmas (MLOs)

• Characteristics
• Microscopic smaller than bacteria
• Single-celled membrane rather than
• cell wall
• Lack chlorophyll
• Associated with yellows
• disorders

Elm Yellows
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Viruses

• Characteristics
• Obligate, intracellular parasites
• Non-living
• Named according to symptoms produces

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Disease is the result of an interaction between a
host, a potential pathogen, and the environment.
If any one of these factors is missing then
disease will not occur.
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Classifying Tree Diseases

• Symptoms
• Rots
• Blights
• Decays
• Type of Pathogen
• Fungal
• Bacterial
• Parts of Tree Affected
• Roots
• Stems
• Foliar

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1. Leaf spots - a foliage disease 2. Twig dieback
- evidence of cankers and/or stress and
decline 3. Mistletoe - a parasitic seed plant 4.
Wilt - evidence of moisture deficiency, vascular
wilt disease or root rot 5. Fruiting bodies of a
canker fungus - signs of canker infections  6.
Vascular streaking (internal) - evidence of
vascular wilt disease 7. Branch canker at a
branch stub 8. Heart rot (internal) and
sporophore of a heart rot fungus at a broken
branch stub 9. Sporophore of a butt-rot fungus at
base of tree 10. Sporophores of a root rot fungus
arising from a damaged root 11. Crown gall - a
gnarled swelling ("tumor") caused by a
bacterium 12. Severed root resulting from
construction damage - site of entry for root and
butt-rot  fungi 13. Nematode damage to small tree
roots  lesions (upper) and galls (lower)
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Effects of Disease

• Death
• Growth Loss
• Malformation
• Predisposition

Predisposition the influence of the environment
on the susceptibility of the host to disease
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Disease Diagnosis

• Signs
• Symptoms

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Clues Used in Diagnosis

• Signs
• Symptoms
• Stand Conditions
• Cultural Practices

Related Circumstances are often extremely
important in properly diagnosing a tree disease
problem. For example, has the tree been exposed
to severe or unusual weather conditions? Has
there been a history of site disturbance such as
building or road construction near the tree? What
is the history of tree removal or thinning in the
area? Has the tree been fertilized lately? What
are the predominant soil and/or drainage features
in the area? Have any chemical spills occurred in
the area? Has a herbicide been used? Is there a
source of an air pollutant nearby?
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Steps in Diagnosis

• Identify the Host
• Examine Site Conditions
• Pattern of occurrence
• Area affected
• Weather conditions
• Soils
• Examine Affected Trees
• Analyze Accumulated Information

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Kochs Postulates

• Pathogen must ALWAYS be associated with disease
  in ALL diseased plants. There are no exceptions
  allowed.
• 2. Pathogen must be isolated and established in
  PURE culture. This may be difficult with obligate
  parasites, but methodologies have been developed
  to fulfill this requirement even with obligate
  parasites.
• 3. Inoculation of a healthy plant of the same
  variety must reproduce EXACTLY the same
  symptom(s). Inoculation must be of a healthy
  plant of the same species and cultivar. The
  symptoms must be reproduced essentially identical
  to the initial diseased plant.
• 4. Pathogen must be reisolated from inoculated
  plant and its identity confirmed as the same as
  the original isolate. The organism recovered must
  be the identical to the original isolate. There
  are no exceptions.

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Types of Disease Control

• Exclusion
• Eradication
• Protection
• Chemicals
• Cultural Practices
• Host Resistance

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Cultural Practices Examples

• Modifying the environment
• Choice of site
• Reduce competition
• Increase tree vigor
• Avoiding tree wounding
• Separating the tree and the pathogen
• Utilizing the tree
• Pathological rotations
• Sanitation clauses

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Prevention
Prevention is usually more effective, and cost
efficient, than attempting to suppress the
problem after its started.
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