Club root of cabbage

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Club root of cabbage Plasmodiophora brassicae
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hairy flagella
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Hyphae of Oomycetes
Hypha
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Spore Type Oospore
Oospores
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Oomycetes Sexual Reproductive
Antheridium
Oospore
Oogonium
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Oomycete Antheridium and Oogonium
Hyphae
Antheridium
Oogonium
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Asexual Reproductive Structures of Oomycetes
Sporangia
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Zoospores

• Single cell, but membrane bound
• Product of mitosis
• Released from sporangium
• Motile
• Not long lived

Zoospores
Sporangium
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Sporangia Borne on Single or Branched
Sporangiophores
Lemon to globose shaped structures are sporangia
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Germination of Sporangium
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Zoospores attracted to infection court
Plant surface
Flagellum
Body of zoospore
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Germination of Zoospores
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Sporangia of Downy Mildew Fungi
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Oomycetes Pythium, Phytophthora Aphanomyces
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Diseases caused by OomycetesSeed rots and
Seedling Damping-off
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Diseases caused by OomycetesDamping-off
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Diseases Caused by OomycetesRoot rots
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Phytophthora Root andCrown Rot Symptoms
Leaves are small, yellowish, and sparse fruit
are small often turn red prematurely.
Bark and wood at crown is orange to brown and
water-soaked margin between diseased and healthy
tissue is usually distinct.
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Alfalfa root rot caused by Phytophthora
megasperma
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Diseases Caused by Oomycetes

• Maple Decline

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Diseases Caused by OomycetesMaple DeclineRoot
and Crown Rot
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Pythium Blight of TurfgrassesDiagnosis based on
microscopic signs
Oospores
Coenocytic hyphae
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Control Fungicides - mefenoxam, propamocarb,
fosetyl Al
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Diagnosis based on symptoms and macroscopic signs
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Oomycetes Aphanomyces
Spores
Sporangiophore
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Oomycetes Aphanomyces
Exit pore
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Life Cycle of an Oomycete
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OomycetesAphanomyces

• Sporangium is a modified hypha
• Primary spores exit and aggregate at end of
  sporangium
• Primary spores release zoospores

Spores
Sporangiophore
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OomycetesAphanomyces

• Primary spores
• Two means to resume growth
• Germinate to germ tube
• Release zoospore through pore

Exit pore
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What are Zoospores?

• Single cell, but membrane bound
• Motile
• 2 flagella propel zoospore in liquid environment
• Move to host

Flagellum
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Phytophthora compared to Downy Mildew Fungi
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B
A B
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Phytophthora compared to Downy Mildew Fungi
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B
A Phytophthora B Downy mildew fungus