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Plant Disease and Environment Wilt on Pepper Seedling caused

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Plant Disease and Environment Wilt on Pepper Seedling caused by Pythium following Hurricane Frances, 2004 Temperature Affects growth rates Some pathogens adapted to ... – PowerPoint PPT presentation

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Title: Plant Disease and Environment Wilt on Pepper Seedling caused


1
Plant Disease and Environment
2
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

3
Plant Root Systems Damaged by Pythium Fungus
4
Causative Agents of Plant Disease Infectious
Agents
  • Fungi
  • Bacteria
  • Viruses
  • Nematodes
  • Mycoplasmas
  • Parasitic plants
  • Protozoa

5
Fungi
6
Fungi
  • Many different types (root rot fungi, leaf spots,
    rusts, seedling damp-off, vascular wilts, etc..)
  • Foliar vs soilborne
  • Many different and complex life cycles
  • Facultative organisms some may colonize live
    plant tissue and may grow and reproduce in dead
    tissue as well
  • May be many different isolates

7
Fungal Isolates
  • Different genotypes of the same pathogen
  • Can differ in their virulence (effect on plant)
  • Detect differences by DNA analyses

8
Fungi
Fragile structures need moisture to avoid
drying out
9
Choanephora Fruit Rot on Cucumber note white
fungal mycelium
10
Fusarium on Watermelon
11
Disease Invasion of Field following Heavy
Rainfall, 2003 season
12
Disease Symptoms on Seedling
Top wilted
Lesions and vascular tissue damage in lower stem
Roots not too bad
Isolated Fusarium spp. Pythium spp. Rhizoctonia
spp.
13
Early Blight of Tomato
14
Impatiens -- Root Knot and Rhizoctonia
15
Bacteria
  • Many different types (blights, leaf spots,
    cankers, crown galls, vascular wilts, soft rots,
    etc.)
  • Rapid exponential growth, many reproduce by
    fission, ultimate r-strategists
  • Often need lab analysis to diagnose whether
    problem is caused by fungi or bacteria

16
Many Beneficial Bacteria in Soil Rhizobacteria
from Cowpea Roots
17
Viruses need to enter plant tissue, transmitted
by
  • Seed
  • Tools used in pruning, grafting, etc.
  • Vectors

-- Insects (aphids, whiteflies, thrips, etc. --
Nematodes -- Mites
Viruses may have reservoirs in alternate plant
hosts
18
Cassava Mosaic
19
Corky Ringspot transmitted by nematode vector
20
Corky Ringspot
21
Causative Agents of Plant Disease Infectious
Agents
  • Fungi
  • Bacteria
  • Viruses
  • Nematodes
  • Mycoplasmas
  • Parasitic plants (dodder vs cranberry)
  • Protozoa

Usually studied in weed science or nematology
22
Causative Agents of Plant Disease Infectious
Agents
  • Fungi
  • Bacteria
  • Viruses
  • Nematodes
  • Mycoplasmas
  • Parasitic plants (dodder vs cranberry)
  • Protozoa

23
Mycoplasmas
  • Relative of bacteria
  • Needs a vector
  • Lethal yellowing of coconut (leafhopper vector)

24
Causative Agents of Plant Disease Non
Infectious Agents
  • Air pollution (ozone, N oxides, SO2)
  • Nutrient deficiencies
  • Toxic elements and chemicals
  • Chilling injury

25
Environment affects fungal and bacterial diseases
  • Incidence how many plants have the disease
  • Severity how bad the disease is on the plants
    that have it

26
Disease Triangle
Pathogen Host
Isolates ?
Cultivars ?
27
Disease Triangle
Environment
Pathogen Host
Must have correct combination of all 3 to have
disease
28
Exponential Growth from low initial inoculum if
environment is favorable
29
Predicting Plant Disease Progress
  • Exponential growth
  • Numerous other models are proposed for population
    growth (see Carroll et al., 1990, Ch. 9)
  • Weather forecasting (moisture, humidity)
    important in predicting disease progress and
    epidemics

30
Environmental and cultural factors affecting
buildup of fungal and bacterial plant pathogens
  • Moisture
  • Temperature
  • Dispersal agents
  • Soil pH
  • Other

31
Moisture
  • Activates resting stages
  • Affects germination of spores and penetration
    into host
  • Water on leaves
  • Humidity
  • Splashing water distributes inoculum
  • Leaf wetness best indicator but difficult to
    measure

32
Moisture
  • Activates resting stages
  • Affects germination of spores and penetration
    into host
  • Water on leaves
  • Humidity
  • Splashing water distributes inoculum
  • Leaf wetness best indicator but difficult to
    measure

Rainy, cloudy conditions important for spread
and growth of many diseases
33
Wilted area followed direction of earlier water
flow into field
34
Wilt on Pepper Seedling caused by Pythium
following Hurricane Frances, 2004
35
Temperature
  • Affects growth rates
  • Some pathogens adapted to certain temp. ranges
  • Refrigeration important for management

36
Dispersal Agents
  • Bacteria, fungi are limited in mobility, need to
    be moved by
  • Water
  • Wind
  • People, machinery
  • Insects, other animals

37
Environmental and cultural factors affecting
buildup of fungal and bacterial plant pathogens
  • Moisture
  • Temperature
  • Dispersal agents
  • Soil pH specific requirements for many
    soilborne pathogens
  • Other --

-- Widespread planting of genetically
homogeneous crops can favor epidemic -- N level
unclear depends on situation
38
Management of Plant Disease Strategies
  • Eliminate or reduce initial inoculum, or delay
    its introduction (preventive)
  • Slow the rate of increase, shorten exposure to
    favorable conditions

39
Management of Plant Disease
  • Sanitation
  • Fungicides
  • Host plant resistance
  • Crop rotation
  • Cultural practices
  • Temperature
  • Biological control
  • Organic amendments
  • Improved plant health and nutrition

40
Sanitation (aimed at excluding pest)
  • Avoid infested sites
  • Clean soil, planting material, tools, etc.
  • Inspection and quarantine
  • Remove infected debris
  • Tissue culture can provide disease-free planting
    material

41
Nematode Infection of Banana Planting Material
42
Fungicides
  • Bactericides, if target is bacteria
  • Dusts, sprays, fumigants, etc.
  • Foliar, soil, seed, wound, or post-plant
    application
  • Preventative slows rate of increase
  • Insecticides may also be useful for managing
    insect vectors

43
Host Plant Resistance
  • Caution pathogens can have multiple isolates
  • Vertical resistance against some genotypes of a
    pathogen
  • Horizontal resistance not limited to certain
    genotypes, across all isolates
  • Host genetic diversity is important to slow
    epidemics

44
Crop Rotation
  • Useful vs soilborne diseases
  • Residues of some plants (e.g. cabbage family) may
    be toxic to some pathogens

45
Cultural Practices to Minimize Spread of Disease
  • Favorable irrigation practices (drip vs overhead)
  • Timing of Planting
  • Wider row spacings
  • Eradicate alternate hosts for viruses

Moisture management
Important to minimize water and humidity to limit
disease spread
46
Snapdragon plant rows wiped out by soilborne
disease inoculum moved by water
Untreated border area
Direction of surface water flow
47
Temperature
  • Heat for soil sterilization
  • Hot water treatment of planting material
  • Solarization
  • Refrigeration to slow disease progress in
    harvested material

48
Solarization affects Rhizoctonia in Impatiens
49
Management of Plant Disease
  • Sanitation
  • Fungicides
  • Host plant resistance
  • Crop rotation
  • Cultural practices
  • Temperature
  • Biological control Rhizobacteria may interfere
    with colonization of plant roots by fungi and
    bacteria
  • Organic amendments (avoid diseased plants in
    mulch, etc.)
  • Improved plant health and nutrition

50
References
  • Text, pp. 187-196.
  • Agrios G.N. 1997. Plant Pathology. Academic
    Press, San Diego.
  • Carroll et al. 1990. Ch. 9.
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