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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)

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slide1

Phylum :OomycotaClass:Oomycetes

Order

Pythiales

Peronosporales

Families

Families

Pythiogetonaceae

Peronosporaceae

Pythiaceae

Albuginaceae

classification
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)
general characters
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
sexual reproduction
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
asexual reproduction
Asexual reproduction
  • Zoosporangia variable in shape and size
  • Sporangiophore type delimits families:
    • Pythiaceae: indeterminate sporangiophores
    • Peronosporaceae: determinate sporangiophores
    • Albuginaceae: club-shaped sporangiophores, catenate sporangia
pythium pringsheim 1858
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
pythium
Pythium

Zoosporangia (above)

Oogonium/oospore (right)

slide9

vesicles

zoosporangia

phytophthora de bary 1892
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
slide12

lemon-shaped

infestans

Phytophthora

  • Sporangia ovoid, obpyriform tolemon-shaped
diseases caused by phytophthora species
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
family peronosporaceae
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
sexual reproduction1
Sexual reproduction
  • Oogonia larger, antheridia paragynous, broader relative to Pythiaceae
  • Formed inside host tissue
  • Periplasm forms thick, sculptured wall
sclerospora sclerospora
Sclerospora Sclerospora
  • Bulbous sporangiophores with short terminal branches
  • Most species with indirect germination
  • Restricted to monocots
  • Forms digitatehaustoria
plasmopara
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
peronospora
Peronospora

Sporangiophores and direct germination of sporangia

peronospora1
Peronospora
  • Elongated, curved, dichotomously branched sporangiophoresclaw shape
  • Sporangia germinate directly

From Webster, 1980

pseudoperonospora
Pseudoperonospora
  • Sporangiophores similar to Peronospora except branching more delicate and not dichotomous
  • Sporangia germinate indirectly
bremia
Bremia
  • Dichotomously branched sporangiophores with enlarged tips bearing ring of sterimata. Sauccer shape.
  • Sporangia germinate indirectly
family albuginaceae
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
slide26

Albugo

haustoria

Release of zoospores

Club-shaped sporangiophores and chains of sporangia

From Webster, 1980

white rust of crucifers caused by albugo candida
White Rust of Crucifers Caused by Albugo candida
  • Symptoms of White Rust on Shepherd's Purse
white rust
White rust

Host plant :

Protulacaolearacea