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Pathogen List
High points on pathogens covered in lab
53
Pathology
10/24/2009

Additional Pathology Flashcards

 


 

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Term

Alternaria (Deuteromycete)

Definition

Symptoms: spots and occasionally blights, zonate lesions

Signs: generally not seen for most leaf spotting organisms

Life Cycles:

  1. Various species
  2. Anamorphic (Asexual)
  3. Distinctive, dark-colored multicellular spores
  4. can be controlled in greenhouses with UV-absorbing film (inhibits sporulation)

 

Term
Bipolaris maydis (corn blight) 1970's
Definition

Symptoms: spots and occasionally blights with dark borders

Signs: generally not seen for most leaf spotting organisms

Life Cycles:

  • Anamorphic
  • Bipolaris (formerly Helminthosporium) maidis =(Deuteromycete Name)
  • Cochliobolus heterostrophus = (Ascomycete Name)
  • Sexual stage a perithecium with filamentous ascospores
  • Genetic recombination led to 1970's blight epidemic

 

Term
Botrytis (Gray Mold) Deuteromycete
Definition

Symptoms: Diffuse blighting

Signs: hyphae and small sclertia can be seen for Botrytis under high humidity

Life Cycles:

  • Anamorphic
  • Gray mold most common disease of greenhouse crops and elsewhere
  • Favors cool, humid, conditions
  • Fungus often gains ingress through injury through decaying flower petals or damaged leaves and then advances towards healthy tissue
  • Produces gray mycelium, conidia, and flat sclerotia
Term
Cercospora (Deuteromycete)
Definition

Symptoms: Spots and occasionally blights

Signs: generally not readily seen for most leaf spotting organisms

Life Cycles:

  • Anamorphic
  • many species, many hosts both dicots and monocots
  • often lesion have black borders, tan centers
Term
Guignardia bidwellii (Black Rot of Grape) (Ascomycete)
Definition

Symptoms: Spots and occasionally blights (shothole appearance)

Signs: generally not readily seen for most leaf spotting organisms

Life Cycles:

  • Black rot is Florida's most serious grape disease
  • Sexual Stage (Guignardia bidwellia) perithecia air-borne ascospores
  • Asexual Stage (Phyllosticta sp.) pycnidia produces viscous conidia designed for spread by splashing water like anthracnoses
Term
Venturia inaequalis (Apple Scab)
Definition

Symptoms: Conspicuous, dry lesions

Signs: Acervuli with spores

Life Cycles:

  • Primary Cycle (one): Perithecia with asci (2-celled ascospores/disease forecasting)
  • Secondary Cycles (many): Acervuli with conidia
  • Transition: parasite become saphrophyte
  • Control: Genetic resistance or use of fungicides (time of fungicide application (disease forecasting/primary cycle)(spray immediately following rain)
Term
Monilinia fructicola (Brown rot of stone fruits)
Definition

Symptoms: Moist soft rots, decay

Signs: Sporodochia with conidia, apothecia, mummies
Life Cycles:

  • Primary cycle (one): Apothecia with asci (Ascospores discharged from mummies in Spring)
  • Secondary Cycles (many): sporodochia with conidia (especially fruits)
  • Transition: fruits mummify into a sclerotium-like structure
  • Control: Disking up mummies will eliminate as many mummies as possible (disrupt apothecia formation in spring) (Careful handling of fruit)
Term
Colletotrichum (Deuteromycetes)
Definition

Symptoms: Open, basil-like spores

Signs: Acervuli with spores

Spore Forms:

  1. Anamorphs (most common)
  2. Teleomorphs (less common)

Life Cycle:

  • Primary life cycle (usually conidia, plant debris)
  • Overlapping crops (e.g. papaya)
  • Vegetative (e.g. strawberry transplants)
  • Seed (e.g. bean anthracnose)

Control:

  • clean cultivation, crop rotation, timely sprays, certification programs, seed certification
Term

Erwinia tracheiphila (cucumber wilt)

Vs.

Ralstonia solanacearum (Southern bacterial wilt)

Definition

Erwinia

  • Vascular wilt caused by bacteria
  • very narrow host range (certain cucurbits)
  • Transmitted by flea beetles (disease forecasting)

Ralstonia

  • Vascular wilt caused by bacteria (viscous ooze in vascular system)= symptom
  • Some races infect solanaceous plants, other bananas (moko)
  • Mostly tropical, subtropical disease
  • Survives in plant debris, wild hosts
Term
Vascular wilt diseases
Definition
  1. Fusarium oxysporum
  2. Verticillium
  3. Erwinia tracheiphila (cucumber wilt)
  4. Ralstonia solanacearum (Southern Wilt)
  5. Ophiostoma ulmi (Dutch elm disease)
  6. Cryphonectria parasitica (Chestnut blight)
Term
Symptoms of Vascular Wilts
Definition
  1. Sudden wilt and death of plants
  2. Premature yellowing of lower leaves
  3. Vascular discoloration (for fungal wilts)
  4. Viscous ooze in vascular system (for bacterial wilts)
Term
Common Denominators of vascular wilts
Definition
  1. Most cause sudden wilt by plugging the xylem
  2. Most are soil-borne
  3. Some need vectors
  4. Most have restricted host ranges
Term
Fusarium oxysporum (Deuteromycete)
Definition
  • Similar to Verticillium
  • Trinomials
  • F. oxysporum f. sp. lycopersici (tomatoes)
  • F. oxysporum f. sp. cubense (banana)
  • Others infect coca, cannabis
  • Subspecies have races
  • Macroconidia, Microconidia, Chlamydospores
  • Teleomorphs are Ascomycota
Term
Ophiostoma ulmi (Dutch elm disease)
Definition
  • ascomycota
  • perithecia
  • conidia
  • introduced in the USA
  • exterminated respective native hosts
  • is a true vascular wilt disease
  • Quarantines for this disease failed because the entire life cycle is not understood.
  • Fungus thrives beneath bark
Term
Mechanism of Attack (Dutch elm disease)
Definition
  • Fungus mostly a saprophyte
  • colonizes bark beetle galleries
  • bark beetles emerge, feed on spring xylem
  • Lesser European elm bark beetle efficient vectore
  • Native American elm bark beelte inefficient vector because it feeds too early in the season
Term
Control of Vascular Wilts
Definition

Example: Dutch elm disease

  • Destroy infected trees
  • remove bark from dead trees
  • genetic resistance (oriental elms)
Term
Control of Vascular wilts
Definition

Example: Cucumber wilt

  • Disease forecasting
  • (spray for beetles when winters are mild)

 

Term
Control for vascular wilts
Definition

Southern bacterial wilt

  • used clean tools
  • crop rotation
  • fallow
  • use clean planting stock
Term

Fusarium oxysporum

vs.

Verticillium

Definition
  1. both attack the xylem
  2. Verticillium thrives under cool temps and high pH
  3. Fusarium oxysporum thrives under warm temps
Term

Ophiostoma ulmi (Dutch elm disease)

vs.

Cryphonectria parasitica (Chestnut blight)

 

Definition
  1. Both introduced in the USA
  2. Both exterminated respective native hosts
  3. chestnut blight is a canker disease while dutch elm disease is a true vascular wilt
  4. Both have perithecia and conidia
Term

Symptoms of:

Phytophthora infestans (late blight of potato) (Oomycete)

Definition

Symptoms:

  • seedling blight, damping-off fungi
  • Root necrosis (root rots)
  • stem cankers, stem girdling
  • foliar necrosis (blights)
  • tuber rot (potato late blight)

 

Term

Symptoms and Signs of:

Plasmodiophora brassicae (Myxomycete, a protozoan plant pathogen)

Definition

Symptoms:

  • causes clubroot; the causal agent is an obligate parasite
  • conspicuous root gall, no necrosis

Signs: not evident

 

Term

Symptoms and Signs of:

Sclerotium rolfsii (Deuteromycete)

Definition

Symptoms:

  • root necrosis (root rots)
  • stem cankers, stem girdling
  • Foliar necrosis (blights)
  • Tuber rot (potato late blight)

Signs:

  • white mycelium spherical sclerotia
Term

Symptoms and Signs of:

Fusarium solani (Deuteromycete)

Definition

Symptom:

  • root necrosis (root rots)
  • stem cankers, stem girdling
  • Foliar necrosis (blights)
  • Tuber rot (potato late blight)

Signs: signs not evident

 

Term

Common Features and Symptoms:

Seedling Diseases

Definition

Symptoms:

  • Pre-emergence damping off
  • Post-emergence damping off
  • Root rot
  • Above ground necrosis

Common Features:

  • Soils associated
  • Wide host ranges
Term

Symptoms:

Rhizoctonia solani (Basidiomycete) wide host range

Definition

Symptoms:

  • below ground (root rot, stem, cankers)
  • above ground (stem cankers, foliar blights)

 

Term

Symptoms:

Pythium spp. (Oomycete)(Chromistic Algae) wide host range

Definition

Symptoms:

  • below ground (root rot, stem, cankers)
  • above ground (stem cankers, foliar blights)

 

Term
Controlling Seedling Blights
Definition
  • Genetic resistance
  • Biological control (antagonists)
  • Chemical Control= sterilized soil (autoclaving, methyl bromide), seed treatments (mercury), sprays (copper sulfate, metalaxyl for oomycetes) Others for Rhizoctonia (Thiram, captan, PNCB)
  • Cultural Control= Hasten maturity (reduce nitrogen), avoid overcrowding, crop rotation, avoid contamination (pots, tools, irrigation)
Term

Symptoms:

Citrus greening (Huanglongbing) or HLB

Definition

Symptoms:

  • Yellow shoots

  • Twig die-back
  • Reduced fruit size and quality
  • Lopsided fruit
  • Bitter, inedible fruit
  • Leaf mottling or discoloration 
Term
What are Nematodes?
Definition

12,000 species of unsegmented, bilaterally symmetrical wormlike organisms abundant in marine and freshwater habitats, in soil, and as parasites of plants and animals

Term
What are Dorylaims?
Definition
  • the order of nematodes which have odontostylets (many parasites) for mouthparts
Term
What are tylenchoids?
Definition
  • the order of nematodes that have stomatostylets (many parasites) for mouthparts
Term
What are rhabditoids?
Definition
  • the order of nematodes that have a mouth with buccal cavity (saprophytes)
Term
What type of stylets do nematodes have?
Definition
  1. Stomatostylets- are hollow spears associated with tylenchoids (Order Tylenchida)
  2. Odontostylets- are solid, tooth-like structure associated with dorylaims (Order Dorylaimida)
Term
Stomatostylets
Definition
are hollow spears associated with tylenchoids (Order Tylenchida)
Term
Odontostylets
Definition
are solid, tooth-like structures associated with dorylaims (Order Dorylaimida)
Term
Symptoms of Nematodes
Definition
  1. Dwarfing, usually other symptoms of malaise, such as yellowing
  2. Some cause root symptoms (galls, stubby roots)
Term
What types of diseases do nematodes cause?
Definition
  1. Can cause wounds that increase incidences of fungal pathogens, such as Fusarium oxysporum
Term
Do nematodes transmit viruses?
Definition
  1. Can transmit certain viruses. Dorylaims in the genus Trichodorus transmit the tobravirus, tobacco rattle, which commonly infects potatoes, causing "corky ringspot" in Hasting, Florida.
Term
What type of life cycle do they have?
Definition
  • life cycle is complete within 3-4 weeks. Eggs hatch into larvae. There are four larval molts, after which the adults appear.
Term
Sporodochium
Definition
A fruiting structure consisting of a cluster of conidiophores woven together on a mass of hyphae
Term
AGDIA
Definition
A commercial company located in Elkhart, Indiana, that tests plants for specific viruses using serological techniques.
Term
Florida Index of Plant Diseases
Definition

The state organization responsible for publishing the "Index of Plant Diseases of Florida"

Florida Department of Agriculture & Consumer Services

Term

Control Methods:

Citrus greening (Huanglongbing) or HLB

 

Definition

  • Reducing psyllid population with natural enemies (parasitic wasp= Tamarixia radiata) can limit loss due to HLB
  • Pesticides will kill psyllids, but numbers of applications and quantities necessary to control populations are logistically, economically, and environmentally challenging.
Term

General Information:

Citrus greening (Huanglongbing) or HLB

Definition
  • Disease can be graft transmitted from apparently healthy budwood sources, because symptoms may take time to develop
  • limited knowledge of host range
  • Term

    Signs of:

    Phytophthora infestans (late blight of potato) (Oomycete)

    Definition

    Signs:

    • pale, moist mycelium
    Term

    Life Cyles and Structures of:

    Phytophthora infestans (late blight of potato) (Oomycete)

     

    Definition

    Life Cycles and Structures:

    • Facultative parasite
    • Moderate host ranges
    • prefers cool, wet conditions
    • sporangia (inoculum dispersal)
    • Will germinate directly or produce zoospores
    • Oospores (dormancy), Antheridia, Oogonia
    Term

    Life Cycles and Structures of:

    Plasmodiophora brassicae (Myxomycete, a protozoan plant pathogen)

     

    Definition

    Life cycles and Structures:

    • very restricted host range (and a disease of northern climates
    • produces an intracellular plasmodium
    • Plasmodium breaks up into zoospores
    • require acidic soils; can be controlled by raising pH to about 7.2 or higher
    Term

    Life Cycles and Structures of:

    Sclerotium rolfsii (Deuteromycete)

    Definition

    Life cycles and Structures:

    • like Rhizoctonia
    • very wide host range
    • mycelium white (no 90 degree branching)
    • truly a hot-weather pathogen
    • asexual stage without spores
    • sexual stage (Basidomycota) with no conidia
    Term

    Life Cycles and Structures of:

    Fusarium solani (Deuteromycete)

     

    Definition

    Life Cycles and Structures:

    • Moderately wide host range
    • asexual stages (macro-, microconidia, chlamydospores)
    • sexual stage (ascomycota)
    Term
    List of Seedling Diseases:
    Definition
    1. Rhizoctonia solani (Basidiomycete)
    2. Pythium spp. (Oomycete) Chromistic Algae
    3. (Aphanomycetes)
    Term

    Signs:

    Rhizoctonia solani (Basidiomycete) wide host range

    Definition

    Signs:

    • hyphae/mycelium (no spores, septate)
    • no asexual spores
    • sclerotia
    • sexual stage not common
    Term

    Signs:

    Pythium spp. (Oomycete)(Chromistic Algae) wide host range

    Definition

    Signs:

    • Hyphae/mycelium (coenocytic)
    • Zoospores/sporangia
    • sexual stage common
    • Oospores, Oogonia, Antheridia