Transcript Plant Disease General Concepts

Plant Disease
General Concepts
 Signs
 Symptoms
 Etiology
 Epidemiology
 Pathogenicity
 Virulence
Photos used from various UF/IFAS Extension Publications or provided by UF/IFAS faculty and staff, unless otherwise stated.
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Signs vs. Symptoms
Sign of Disease
• observation of the organism causing
the disease (objective observation)
Symptom of Disease
• observation of how the host is
manifesting infection by a pathogen
and disease development due to a
pathogen
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Signs vs. Symptoms
Symptoms of Guinea worm disease or dracunculiasis
Dracunculus medinensis - nematode
Symptoms of Ganoderma Butt Rot
Ganoderma zonatum - fungus
Photos from The Carter Center
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Bacteria oozing from leaf
Rust spores on leaf
Signs of Disease
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Rust spores on leaf
Mycelia (cottony growth)
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Fungal sclerotia inside stem
Powdery mildew mycelia
Fungal mycelia and sclerotia
Signs of Disease
Fungal mycelia
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Pycnidia (fungal structures with spores) on branch
Pycnidia (fungal structures with spores) on orange skin
Signs of Disease
Fungal mycelia on roots (microscopic view)
Pythium oospores on roots (microscopic view)
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Plant
Organs
Disease
And
Symptoms
Functions
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Types of Symptoms
• spot – small, distinct lesion on leaf, fruit . . .
• blight – spots that have coalesced or merged
together; more tissue being affected
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Types of Symptoms
• rot – tissue is breaking down (fruit, roots);
usually mushy, but can be dry
• wilt – plant droops due to water stress; can be
systemic (xylem) or due to root rot
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Types of Symptoms
•canker – sunken lesions; usually on stems or
woody tissue; but can occur on fruit
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Types of Symptoms
• gall – masses of undifferentiated growth; usually
on stems or woody tissue (branches) but
can be on roots
S. Browning, University of Nebraska, Lincoln
http://hortupdate.unl.edu/peach-leaf-curl
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Types of Symptoms
• patches, decline – terms often used in
association with grasses (turf, grain crops)
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Symptoms Caused by Bacteria
• leaf spots and blights – water soaked, greasy
• soft rots of fruits
• wilts (systemic – xylem)
• cankers
• gall (overgrowths/cell proliferation)
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Symptoms Caused by Fungi/Oomycota
• leaf spots and blights (including rust and
powdery mildew)
• soft or dry rots of fruits, bulbs . . .
• root rots
• wilts (systemic – xylem)
• overgrowths/cell proliferation –
clubroot, galls, warts, witches’-broom
• scabs, cankers, patches and decline
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Symptoms Caused by Viruses
• dwarfing or stunting to some degree
• mosaics – light green, yellow or white
areas intermingled with green – leaves
or fruits
• ring spots – chlorotic or necrotic rings –
leaves, fruits or stems
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Symptoms Caused by Viruses
Dwarfing
Mosaic
Ringspot
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Plant Pathology Terms
• Pathogenicity: the pathogen either does
or does not cause a disease; a question
with yes or no answer
• Virulence: relative capacity of pathogen to
cause disease; range from minimal damage
to dead plant
• Etiolgy: determining the cause of disease
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Etiology and Pathogenicity Testing
1) Consistent isolation of a pathogen from
symptomatic host tissue
2) Pathogen is grown in pure culture and its
characteristics documented
3) Inoculation of a healthy plant with the pure
culture of the pathogen, and inoculated plant
must then develop symptoms similar to those
observed initially
4) Recovery of the same pathogen used for
inoculation purposes
This is general scheme; non-culturable plant pathogens have special rules.
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Etiology and Pathogenicity Testing
Example: Fusarium Wilt of Queen Palm
The “potential” pathogen isolated consistently
from symptomatic tissue was Fusarium.
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Etiology and Pathogenicity Testing
Example: Fusarium Wilt of Queen Palm
Isolated Three Fusarium Species
(sometimes from the same tissue piece)
1) F. incarnatum-equiseti species complex (6 isolates)
isolated from Fusarium wilt symptomatic palms in Australia
2) F. oxysporum (43 isolates)
known Fusarium wilt pathogen of palms worldwide
3) F. proliferatum (9 isolates)
known pathogen of palms; can cause wilt symptoms
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Control
F. oxysporum
F. incarnatum-equiseti
F. proliferatum
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Plant Pathology Terms
• Epidemiology: study of the factors
influencing the initiation, development and
spread of infectious disease
But, how do pathogens enter
the plant?
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How do pathogens enter plant?
•Viruses and Viroids and Fastidious Bacteria
most require vectors; a few mechanical entry
•Bacteria – most enter through natural
openings or wounds
•Fungi & Oomycetes – enter through natural
openings, wounds; by mechanical pressure
or enzymes they produce; a few by vectors
•Nematodes – stylets used to gain entry
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How do pathogens enter plant?
Plants have natural openings:
stoma or stomata (plural)
Plant Epidermis
Stoma
(plural=stomata)
Plant Epidermis
Stoma
(plural=stomata)
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How do pathogens enter plant?
Leafhopper
(insect vector)
Use mouth parts to
penetrate
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How do pathogens enter plant?
Leafhopper
Bacteria
(insect vector)
on water film,
Use mouth parts to
enter
penetrate
through stoma
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How do pathogens enter plant?
Leafhopper
Bacteria
(insect vector)
on water film,
Use mouth parts to
enter
penetrate
through stoma
Fungal Spore
entering
through stoma
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How do pathogens enter plant?
Leafhopper
Bacteria
(insect vector)
on water film,
Use mouth parts to
enter
penetrate
through stoma
Appressorium
fungal structure from Fungal Spore
entering
spore for direct
through stoma
penetration
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How do pathogens enter plant?
Leafhopper
Bacteria
(insect vector)
on water film,
Use mouth parts to
enter
penetrate
through stoma
Appressorium
fungal structure from Fungal Spore
entering directly
spore for direct
through stoma
penetration
Fungal Hyphae
can grow between
cells or penetrate cells
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Disease Development
• pathogen comes in contact with plant
• pathogen infects plant – penetration, can be
direct or indirect; with or without vector
• incubation period – time between penetration
and first appearance of symptoms
• pathogen increases within plant, uses host to
grow and reproduce
• symptoms observed continue to increase
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Disease Development
Environmental conditions influence each and
every step in disease development process!!
Susceptible
Host
Favorable
Environment
DISEASE
Pathogen
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Disease Development
Susceptible
Host
Nematode
Fungus
W. Deacon, Univ. of Edinburgh
Vector required for
some pathogens!
DISEASE
Favorable
Environment
Pathogen
Mite
Insect
USDA/ARS
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How do plant pathogens move
from plant to plant if they are
not moved by a vector?
• Wind dispersal of spores
• Splash dispersal of spores – rain, irrigation
• Physical movement of soil-borne pathogens
that don’t produce spores – ex: soil tillage
• Nematodes swim or move with soil
• Seed associated – internal or external
• Plant associated – cuttings, grafting
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How do plant pathogens move
from plant to plant if they are
not moved by a vector?
Time to have some fun!
Cheap, easy way to demonstrate
spore dispersal without
water or spores!
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Splash Dispersal of Spores
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