1 / 30

Phylum : Oomycota Class: Oomycetes

Phylum : Oomycota Class: Oomycetes. Order. Pythiales. Peronosporales. Families. Families. Pythiogetonaceae. Peronosporaceae. Pythiaceae. Albuginaceae. Classification. Order Pythiales Families Pythiaceae (9 genera, 230 species) Pythiogetonaceae (2 genera, 8 species)

jabir
Download Presentation

Phylum : Oomycota Class: Oomycetes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Phylum :OomycotaClass:Oomycetes Order Pythiales Peronosporales Families Families Pythiogetonaceae Peronosporaceae Pythiaceae Albuginaceae

  2. Classification • Order Pythiales • Families • Pythiaceae (9 genera, 230 species) • Pythiogetonaceae (2 genera, 8 species) • Order Peronosporales • Families • Peronosporaceae (8 genera, 600 species) • Albuginaceae (1 genus, 45 species)

  3. General characters • Mostly parasitic with intracellular haustoria • Narrow diameter hyphae • Trend towards terrestrial habitats • Loss of primary zoospore stage • Trend towards loss of secondary zoospore stage. • Inability to synthesize sterols

  4. Sexual reproduction • One oospore/oogonium • Oospores formed in host tissue • Unifactorial mating system • A1 and A2 mating types • Selfing may occur • Relative sexuality • Bisexual strains

  5. Asexual reproduction • Zoosporangia variable in shape and size • Sporangiophore type delimits families: • Pythiaceae: indeterminate sporangiophores • Peronosporaceae: determinate sporangiophores • Albuginaceae: club-shaped sporangiophores, catenate sporangia

  6. Pythium Pringsheim 1858 • Type species P. monospermum • 127 species • First invaders of plant tissue, not good competitors with other organisms • Major components of damping-off disease of seedlings, collar rot of apples, foliar and stem blights, snow rot of winter wheat • Sporangia of various shapes, sizes • Zoospores cleaved out and released from vesicle • Oogonia fertilized by one to many antheridia • Oogonial wall smooth or with spiny or blunt projections • Chlamydospores present in some species

  7. Pythium Zoosporangia (above) Oogonium/oospore (right)

  8. vesicles zoosporangia

  9. Zoospore cleavage and release in Pythium

  10. Phytophthora de Bary 1892 • Type species P. infestans (Montagne) de Bary • 65 species • Wide range of diseases • Sporangia ovoid, obpyriform tolemon-shaped • Sporangia papillate, semipapillate or nonpapillate • Zoospores cleaved out inside zoosporangium • Oogonium fertilized by one antheridium

  11. lemon-shaped infestans Phytophthora • Sporangia ovoid, obpyriform tolemon-shaped

  12. Diseases caused by Phytophthora species • P. infestans— late blight of potato, tomato • P. cinnamomi— root rot of avocado, eucalyptus and > 1000 hosts • P. cactorum— fruit rots (>154 host genera) • P. ramorum— Sudden Oak Death

  13. Family Peronosporaceae • Obligate biotrophs of vascular plants • “downy mildews” • Sporangiophores aerial, determinate, up to 750 microns tall • Sporangia deciduous, released by drying • Sporangia germinate directly or indirectly

  14. Sexual reproduction • Oogonia larger, antheridia paragynous, broader relative to Pythiaceae • Formed inside host tissue • Periplasm forms thick, sculptured wall

  15. Sclerospora Sclerospora • Bulbous sporangiophores with short terminal branches • Most species with indirect germination • Restricted to monocots • Forms digitatehaustoria

  16. Plasmopara • Random branching of sporangiophores, branches at ~ 90 degrees • Sporangiophores cross shape stiff and erect, with short terminal branches • Sporangial germination indirect • Cassed downy mildew of vitis

  17. PeronosporaparasiticaDowny mildew infection on leaf

  18. Peronospora Sporangiophores and direct germination of sporangia

  19. Peronospora • Elongated, curved, dichotomously branched sporangiophoresclaw shape • Sporangia germinate directly From Webster, 1980

  20. Pseudoperonospora • Sporangiophores similar to Peronospora except branching more delicate and not dichotomous • Sporangia germinate indirectly

  21. Bremia • Dichotomously branched sporangiophores with enlarged tips bearing ring of sterimata. Sauccer shape. • Sporangia germinate indirectly

  22. Bremia

  23. Family Albuginaceae • One genus, Albugo • “white rusts” • Sporangia formed in basipetal succession, dispersed by wind • Germinate to form 8 zoospores • Oogonia develop in host, oospores develop thin vesicle similar to Pythium sporangium

  24. Albugo haustoria Release of zoospores Club-shaped sporangiophores and chains of sporangia From Webster, 1980

  25. Albugo candida conidra tjv

  26. White Rust of Crucifers Caused by Albugo candida • Symptoms of White Rust on Shepherd's Purse

  27. Albugo oospores

  28. White rust Host plant : Protulacaolearacea

More Related