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Basic Plant Pathology
Master Gardener Training

• Karen L. Snover, Director
• Cornell University

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Why is my plant sick?

• Evaluate each situation.
• Diagnose some diseases.
• Understand why certain disease management
  situations are appropriate and others are not.
• Overall understanding of plant pathogens.

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Causal Agents of Disease.

• Living vs. Non-living factors

• Fungi
• Bacteria
• Nematodes
• Viruses
• Phytoplamas

• Nutrient deficiencies
• Mineral toxicities
• Lack/excess of
• soil moisture light
• Too low/high temperatures
• Air pollution
• Soil pH

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Definitions
PLANT DISEASE -- Any alteration in the
physiological processes of a plant, caused by
living organisms or nonliving agents, which
negatively affects the plant.
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PATHOGEN -- a pathogen is an organism that is
capable of changing the physiological processes
of a plant, thus causing disease.   PATHOGENIC
means "disease causing"
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History of Plant Pathology

• 700 B.C.- The Romans sacrificed red dogs and
  cattle to the Gods to rid their crops of rust.
• 470B.C.-Pliny reported that crushed olives
  sprinkled on plants prevented blight.
• 1844-1845-The Irish Potato Famine prompts the
  birth of modern plant pathology.

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History of Plant Pathology II

• 1885-Bordeaux Mixture.
• 1904-1940- Chestnut Blight- The disease wiped out
  all the mature American Chestnuts in the eastern
  North American states.
• The pathogen, Cryphonectria parasitica, was
  brought in form the Orient on infected trees and
  was first discovered at a zoo in NYC.

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Target canker
Diffuse canker
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History of Plant Pathology III

• 1930-present-Dutch Elm Disease. This disease
  devastated the street tree plantings across the
  country.
• The disease was named Dutch Elm Disease because
  it was first described in Holland in 1921.
• The pathogen, Ophiostoma novo-ulmi, was first
  discovered in the US in Ohio.

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Cost of Plant Diseases

• 4 billion dollars a year in crop losses.
• Commercial growers now average 4 for every 1
  invested in managing plant diseases.
• Homeowners find keeping ornamental plantings
  healthy yields a large return in increased
  property value and personal satisfaction.

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Wilting
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Vascular Wilts
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Tip Blights
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Leaf Spots
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Fruit Rots
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Cankers
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Root Rots
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Damping Off
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Reduced Growth
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Symptoms vs. Causal Agents

• Bacteria Fungi Viruses Nematodes
  Phytoplasmas
• Wilts ? ?
  ? ?
• Leaf Spots
• Blights ? ? ? 
• Fruit Rots ? ? 
• Root Rots ? ? 
  ? 
• Damping Off ?  
• Distorted
• Growth ? ? ?
  ? ?

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Parasites vs. Saprophyte

• Parasite- an organism that derives nourishment
  from another living organism.
• Saprophyte- an organism that derives nourishment
  from dead organic matter.

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DiseasePyramid
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Spread
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Overwintering strategy
survive within the host.
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Overwintering strategy
survive as sclerotia.
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Overwintering strategy
survive as rhizomorphs.
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Overwintering strategy
survive on perennial weeds.
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Overwintering strategy
move up from warmer areas.
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Overwintering strategy
introduced from other areas.
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Fungi

• A fungus is a non-photosynthesizing eukaryote
  that produces enzymes and absorbs its food
  usually producing and living inside a network of
  apically extending, branching tubes called
  hyphae. It produces reproductive structures
  called spores.

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Properties of Fungi

• Cause nearly all of the economically important
  diseases.
• Characterized by a mycelial (filamentous) growth
  habit.
• Live on organic matter.
• Identified on the basis of the morphology of
  their reproductive structures.
• Reproduce primarily by means of spores.
• Perennial inhabitants of all ecosystems.

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Fruit Bodies
conidiophores.
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Fruit Bodies
mushrooms.
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Fruit Bodies
pycnidia.
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Fruit Bodies
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Fruit Bodies
perithecia.
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Fungal Invasion
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Environment and Host Protection
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Moisture Favors

• Fungus Growth

• Spore Production

• Spore Germination

• Spore Dispersal

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Apple Scab
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Apple Scab Disease Cycle
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Bacteria

• A bacterium (bacteriaplural) is a prokaryotic
  single celled microscopic organism that multiples
  by division.

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Properties of Bacteria

• Tiny rod-shaped single celled microorganisms.
• 0.5-3.5 microns in length and 1.5-1.0 microns in
  diameter.
• Nearly 200 species cause diseases in plants.
• Identified on the basis of their physiology.
• Reproduce primarily by means of cell division.
• Perennial inhabitants of all ecosystems.

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Each colony contains thousands
perhaps millions of cells.
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Bacterial Infection Routes

• Bacteria can infect plants through natural
  openings and wounds.

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Fireblight
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Fire Blight Life Cycle
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Viruses

• A virus (virusesplural) is made up of small
  particles of genetic material encased in a
  protein coat. They can only reproduce in a
  living cell.

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Border Rows
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Weeds
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Virus Spread

• Insects
• Aphids
• Leafhoppers
• Planting Material
• Vegetative parts
• Mechanical Means
• Tools
• Plant Contact

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Virus Management Techniques

• Insecticides
• Border Plantings/Removal of Weeds
• Rogueing Infected Plants
• Resistant Varieties
• Clean Tools and Materials
• Avoid Wounds.

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Nematodes

• A nematode (nematodesplural) is a microscopic,
  worm-like animal that lives saprophytically in
  water and soil or as parasites of plants and
  animals

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Properties of Nematodes.

• Belong to the Animal Kingdom.
• Most nematodes are beneficial organisms that do
  not harm plants.
• Approximately 12 genera of nematodes are known
  parasites of turfgrasses.
• Obligate root parasites.
• Identified on the basis of their morphology.
• The greater the populations, the greater the
  damage.
• Perennial inhabitants of all ecosystems.
• Need to learn more to understand damage
  capabilities.

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Nematode Size
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Feeding Strategies

• Migratory Moving from plant to plant or from
  feeding site to feeding site.
• Sedentary Staying in one place, stationary.
• Ectoparasites A parasite feeding on a host from
  the exterior.
• Endoparasties A parasite which enters a host and
  feeds from within.

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RootKnot LifeCycle
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Nematode Management Techniques

• Avoid introduction of nematodes.
• Resistant varieties.
• Crop Rotation.
• Nematicides.

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Phytoplasmas

• Phytoplasmas are organisms that infect plants and
  cannot be grown in culture. Phytoplasmas cause
  the yellows diseases.

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Phytoplasmas

• Cause over 300 diseases.
• Are among the smallest organisms known.
• Are obligately parasitic and therefore are not
  culturable.
• Are vectored by phloem feeding insects,
  leafhoppers.
• Other methods of pathogen transmission my include
  grafting and dodder.

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History of Phytoplasmas

• 1967-Japanese researchers associated MLOs with
  yellows diseases.
• MLOs occupy sieve tubes.
• Graft and insect transmittable.
• Tetracycline causes remission and temporary
  disappearance of MLOs.

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Major Phytoplasmal diseases in North America.

• X disease of peaches and cherries.
• Lethal yellows of palm.
• Pear decline.
• Elm Yellows.
• Ash Yellows.
• Lilac witches broom.
• Aster Yellows.
• Blueberry witches broom.
• Bunch disease of pecan and walnut.
• Grapevine yellows.

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Phytoplasma-induced symptoms

• Slow to feeble growth
• Loss of apical dominance
• Witches broomes
• Dwarfing
• Sterility
• Yellowing

• Rootlet Necrosis
• Phloem Necrosis
• Phloem hyperplasia
• Leaf malformation
• Impaired gas exchange

Diagnostic symptoms can be absent!!
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Phytoplasma Vectors

• Primarily Leafhoppers.
• Other known vectors include planthoppers,
  psylids, a froghopper, and stinkbugs.
• Phytoplasmas circulate and multiply within their
  vectors.

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Phytoplasma Management Techniques

• Chemotherapy.
• Heat Treatments.
• Insecticides.
• Weed Control.
• Resistant Varieties.

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Abiotic Damage

• Herbicide Injury.
• Chemical Spills.
• Soil Compaction.
• Freeze Injury.
• Nutrient Deficiency.
• Air Pollution.
• Snow Damage.

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DiseasePyramid
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