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)