Biological Control of Microbial Plant Pathogens

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Biological Control of Microbial Plant Pathogens

• Introduction to the Microbial World of Biological
  Control
• Ent 447/547, Fall 2005
• http//www.agls.uidaho.edu/ent547biocontrol/
• wchun_at_uidaho.edu
• AgBiotech 109/TLC 231
• 5-5708/5220

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Plant Disease

• Plants can become "sick" due to some infectious
  agent, such as fungi, bacteria, nematodes, or
  viruses.
• In some instances insects and vascular plants may
  be considered as plant pathogens.
• These agents are capable of infecting plants
  and disrupting their normal functioning,
  resulting in disease.
• Thus, Plant Disease is considered to be the
  abnormal physiological response of a plant to the
  chronic association with a primary causal agent.

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Plant Disease Expression

• Diseased can be manifested in many ways.
• Blemishes, or lesions, on the leaves, stems,
  flowers, or fruit.
• Reductions in growth
• Loss of color loss or abnormal growth of leaves,
  flowers, or fruit.
• Browning or dieback of leaves and shoots
  wilting.
• Death of the plant.
• Organisms that cause disease in plants generally
  do not cause disease in humans or animals.
• The science of studying diseases of plants, their
  causes, effects, and control, is called Plant
  Pathology.

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Plant Pathogens

• Bacteria
• Fungi
• Insects
• Nematodes
• Viruses
• Weeds

Stemphylium fruit spot of papaya caused by
Stemphylium lycopersici
Photograph courtesy W. T. Nishijimafrom the
Compendium of Tropical Fruit Diseases
Plant Damage destruction of plant tissue due to
a single, non-recurring event.
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Fungal Etiology of Late Blight Identified1853 -
Anton de Bary firmly established the fungal
etiology of plant disease. Describes
Phytophthora infestans as the causal agent of the
Irish Potato Famine. Went on to describe the
etiology of many other important diseases of the
time.
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Similarities and Differences (Insect, Plant,
Microbial)

• Similarities
• Employs many of the same principles of biological
  control for insects and plants.
• Best success with integrative use of control
  agents.
• Utilizes parasites.
• Utilizes conservation, augmentation, and
  importation.
• Differences
• Employs ecological management at the microbial
  level.
• Uses competitors, tricksters and parasites.
• Usually focuses more on conservation and
  augmentation rather than importation.

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Challenges Facing Microbial Agents
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The Nature and Practice of Biological Control of
Plant Pathogens Baker and Cook

• Favor the Antagonist
• Adding Amendments - antagonist stimulation
• Alter pH
• Tillage - modify soil structure or aeration
• Planting date selection escape
• Apply organic amendments increase background
  flora
• Add antagonists
• Trick the Pathogen
• Crop Rotation - lower inoculum density
• Trap plants
• Irrigation Practices

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EPA Biopesticides

• Microbial Pesticides
• Plant-Incorporated Protectants (PIPs)
• Biochemical Pesticides

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Microbial Pesticideshttp//www.epa.gov/pesticides
/biopesticides/

• Microbial pesticides  consist of a microorganism
  (e.g., a bacterium, fungus, virus or protozoan)
  as the active ingredient. Microbial pesticides
  can control many different kinds of pests,
  although each separate active ingredient is
  relatively specific for its target pests. For
  example, there are fungi that control certain
  weeds, and other fungi that kill specific
  insects.

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Plant-Incorporated Protectants (PIPs) (EPA)

• PIPs used to be called Plant-pesticides are
  pesticidal substances that plants produce from
  genetic material that has been added to the
  plant. For example, scientists can take the gene
  for the Bt pesticidal protein, and introduce the
  gene into the plants own genetic material. Then
  the plant, instead of the Bt bacterium,
  manufactures the substance that destroys the
  pest. Both the protein and its genetic material
  are regulated by EPA the plant itself is not
  regulated.

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Biochemical Pesticides

• Biochemical pesticides Biochemical pesticides are
  naturally occurring substances that control pests
  by non-toxic mechanisms. Conventional pesticides,
  by contrast, are generally synthetic materials
  that directly kill or inactivate the pest.
  Biochemical pesticides include substances, such
  as insect sex pheromones, that interfere with
  mating, as well as various scented plant extracts
  that attract insect pests to traps. Because it is
  sometimes difficult to determine whether a
  substance meets the criteria for classification
  as a biochemical pesticide, EPA has established a
  special committee to make such decisions.

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Early Microbial Biological Control was Accidental
The Aztecs were a warring people who came to the
central valley of Mexico around 1200 AD from the
southwestern United States
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Aztec Microbial Biological Control

• According to legend, a special sign from the gods
  would show them the site for their new
  settlement. This would be an eagle with a serpent
  in its mouth, perched on a large cactus. Sometime
  around 1325, they saw such an eagle on an island
  in the middle of a lake and settled there. This
  site, where Mexico City is located today, became
  the center of the Aztec world
• Tenochtitlán.

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Aztec Microbial Biological Control

• By 1519, an estimated 200,000 people lived in
  Tenochtitlán
• Had developed an agricultural system farming
  adjacent marshy but rich land
• Built floating islands of dirt piled on bound
  weeds, surrounded by canals, fertilized with
  aquatic weeds and animal manure

http//www.xochimilco.df.gob.mx/turismo/chinampas.
html
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Aztec Microbial Biological Controlhttp//www.silv
ervizion.com/lewis/aztecs/content/foodfarm/chinamp
as.htm
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Vile Concoctions for Tree Wounds

• Nectria galligena a fungus, European Apple
  Canker
• Austen, 1657 - treat fresh pruning wounds with
  cow dung and urine to prevent apple canker

Twig canker
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Vile Concoctions for Tree Wounds

• Forsyth, 1791 - fresh cow dung, lime, wood ashes,
  and sand
• Le Berryais, 1785 - fresh mud
• MacDonald et al., 1979 - soil applied to American
  chestnut caused Endothia parasitica cankers to
  heal - Trichoderma sp.?

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The Discovery of Antibiotics Was A Turning Point
In Biotechnology and Plant Pathology

• Roberts, W. 1874
• Penicillium broth inhibitory to bacteria
• Antibiotics, antibiosis
• Sir Alexander Fleming, 1928, penicillin
• Most of the antibiotics discovered since then are
  from soil saprophytic microorganisms

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Biological Control With Microbes First Described

• Hartley, 1921
• Autoclaved soil with Pythium debaryanum nearly
  100 pine seedling death
• Non-sterile soil P. debaryanum 38.5
  damping-off.
• Added Phoma, Chaetomium, Rhizopus, Trichoderma,
  Aspergillus, Rosellinia, Penicillium - 11
  damping-off.
• Mixed non-sterile soil and 13 microorganisms
  together, 16.9 damping-off.

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Second Direct Application

• Millard and Taylor, 1927
• Common scab of potatoes, Streptomyces scabies

• Added green grass cuttings and Streptomyces
  praecox in sterilized soil in pot tests
• Starving out

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Still on History

• Sanford and Broadfoot, 1931 - first used
  Biological Control in plant pathology
• 40 bacteria, 24 fungi
• Organisms or culture filtrates in sterile soil
• Found organisms more effective against
  Gaeumannomyces graminis var. tritici

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First Demonstration of a Toxin from a BC Agent

• Weindling, 1931 to 1941
• Trichoderma viride antagonistic to soil pathogens
• Purified viridin, gliotoxin (Gliocladium virens)
• 1/300,000 dilution active against Rhizoctonia
  solani

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Suppressive Soils

• Reinking and Manns, 1933
• Central America soils
• Fusarium oxysporum f. sp. cubense - Panama
  disease of banana
• Pathogen isolated from sandy soil but not from
  clay soils
• Sandy soil plantings last 10 years (conducive)
• Clay soil planting last 20 years (suppressive)

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Suppressive Soils Have a Microbiological Reason

• Gerlagh, 1968
• 4 successive crops in soil increased suppression
  of Gaeumannomyces graminis var. tritici
• Steaming destroys antagonists

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Biological ControlA Microbiologists Perspective

• Pest suppression with biological agents operating
  in a background of integrated control that does
  not depend on host resistance, sterilization of
  the target pathogen, or modification of pest
  behavior

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Biological Control Mechanisms

• Competition
• Antibiosis
• Parasitism
• Induced resistance
• Disease agent transfer

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Microbial Control Results inA Microbiologists
Perspective

• Destruction of the propagative units or biomass
  of the pathogen
• Prevention of inoculum formation
• Weakening or displacement of the pathogen in
  infested residue
• Reduction of vigor or virulence of the pathogen
  by agents such as mycoviruses or hypovirulence
  determinants
• Nothing

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Agrobacterium radiobacter Galltrol-A, Nogall,
Diegall, Norbac 84C Bacillus subtilis Epic,
Kodiak , Rhizo Plus , Serenade , System_3
Burkholderia cepacia Intercept Pseudomonas
fluorescens BlightBan A506, Conquer, Victus
Pseudomonas syringae Bio-save100, Bio-save 110
Streptomyces griseoviridis Mycostop
Ampelomyces quisqualis AQ10 Candida oleophila
Aspire Coniothyrium minitans Contans , KONI
Fusarium oxysporum Biofox C, Fusaclean
Gliocladium virens SoilGard Gliocladium
catenulatum PreStop, Primastop Phlebia
gigantea Rotstop, P.g. Suspension Pythium
oligandrum Polygandron Trichoderma harzianum
and other spp. Bio_Fungus, Binab_T, RootShield,
T-22G, T-22 Planter Box, Bio-Trek), Supresivit,
Trichodex, Trichopel, Trichoject, Trichodowels,
Trichoseal , Trichoderma 2000
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Reasons Why Biological Control is not Very Popular

• Wait until something is wrong.
• Chemicals are faster and less complicated and
  usually give better results.
• Active grower engagement.
• Marketing
• Extension pathology.
• Decline in interest in ecology.
• Poor biological control products (haste).

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Final Points

• Finding biological control organisms
• Suppressive soils
• Old world
• Plant pathogens
• Strange and unusual places
• How do you use microorganisms as BC agents?
• Application methods
• In IPM programs