1. Spore Type: Oospore Oospores

2. Oomycetes: Sexual Reproductive Antheridium Oogonium Oospore

3. Hyphae of Oomycetes Hypha Coenocytic hyphae

4. Asexual Reproductive Structures of Oomycetes Sporangia

5. Sporangia Borne on Single or Branched Sporangiophores Lemon to globose shaped structures are sporangia

6. Zoospores Single cell, but membrane bound Product of mitosis Released from sporangium Motile Not long lived Sporangium Zoospores

8. Germination of Zoospores

9. Oomycetes: Pythium, Phytophthora & Aphanomyces

10. Diseases caused by Oomycetes Seed rots and Seedling Damping-off

11. Diseases caused by Oomycetes Damping-off

12. Diseases Caused by Oomycetes Root rots

13. Bean root rot Pythium ultimum

14. Pythium Blight of Turfgrasses Diagnosis based on microscopic signs Oospores Coenocytic hyphae

15. Diagnosis based on symptoms and macroscopic signs

17. Control: Fungicides - mefenoxam, propamocarb, fosetyl Al

18. Phytophthora Root and Crown 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.

19. Alfalfa root rot caused by Phytophthora medicaginis

20. Stunting and yellowing Wet low area of field Disease resistance Black lesions http://ohioline.osu.edu/ac-fact/0013.html Alfalfa root and crown rot - Phytophthora medicaginis

21. Diseases Caused by Oomycetes Maple Decline

22. Diseases Caused by Oomycetes Maple Decline Root and Crown Rot

23. Phytophthora capsici on watermelon Plant Disease cover 2003

24. 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)