spore type: oospore oospores. oomycetes: sexual reproductive antheridium oogonium oospore
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Spore Type: Oospore
Oospores
Oomycetes: Sexual Reproductive
Antheridium
Oogonium
Oospore
Hyphae of Oomycetes
Hypha
Coenocytic hyphae
Asexual Reproductive Structures
of Oomycetes
Sporangia
Sporangia Borne on Single or Branched Sporangiophores
Lemon to globose shaped
structures are sporangia
Zoospores
• Single cell, but membrane bound
• Product of mitosis
• Released from sporangium
• Motile• Not long lived
Sporangium
Zoospores
Germination of Zoospores
Oomycetes: Pythium, Phytophthora & Aphanomyces
Diseases caused by OomycetesSeed rots and Seedling Damping-
off
Diseases caused by Oomycetes
Damping-off
Diseases Caused by OomycetesRoot rots
Bean root rotPythium ultimum
Pythium Blight of TurfgrassesDiagnosis based on microscopic signs
OosporesCoenocytic
hyphae
Diagnosis based on symptoms and
macroscopic signs
Control: Fungicides - mefenoxam, propamocarb, fosetyl Al
Phytophthora Root andCrown Rot: Symptoms
Leaves are small, yellowish, andsparse; fruit are small; often turnred prematurely.
Bark and wood at crown is orangeto brown and water-soaked;margin between diseased andhealthy tissue is usually distinct.
Alfalfa root rot caused by Phytophthora medicaginis
Stunting and yellowing Wet low area of fieldDisease resistance
Black lesions
http://ohioline.osu.edu/ac-fact/0013.html
Alfalfa root and crown rot - Phytophthora medicaginis
Diseases Caused by Oomycetes
Maple Decline
Diseases Caused by OomycetesMaple Decline
Root and Crown Rot
Phytophthora capsici on watermelon
Plant Disease cover 2003
Figure 1. Typical symptoms of Phytophthora blight on cucurbits: (A) post-emergence damping-off of a pumpkin seedling;
(B) crown infection of a summer squash plant; (C) leaf spot of pumpkin; (D) fruit rot of processing pumpkin. (Courtesy M. Babadoost)