Central Luzon State University
Science City of Muñoz 3120
Nueva Ecija, Philippines
Instructional Module for the Course
PPATH 3305 – MYCOLOGY
Module 2
Topic 1 Phylum Oomycota
Objectives
1. Illustrate fungal structures representing the Phylum Oomycota 2.
Explain the economic importance of each group of Lower fungi 3.
Explain the development/life cycle of Phylum Oomycota 4. Equip with
the different genera and structures of Phylum Oomycota.
Phylum Oomycota
Stramenopilous Fungi
∙ Tinsel flagellum
∙ Tubular mitochondrial cristae
∙ Cellulose in cell walls
∙ Lysine synthesis by diaminiopimelic acid pathway (DAP)
∙ 1 class (Oomycetes), 8 orders, 92 genera and 800 species
∙ Orders to cover:
o Saprolegniales
▪ Holocarpic thallus
o Pythiales
▪ Filamentous thallus
o Peronosporales
▪ Filamentous thallus
Life cycle
, Characters
∙ Cell walls composed primarily of beta-glucans with small amounts of
cellulose ∙ Filamentous species generally produce coenocytic hyphae
∙ Principal storage compounds are water-soluble mycolaminarins (beta-
glucans) ∙ Haustoria formed by plant parasitic species
Zoospores
∙ Primary zoospores
o First formed
o Pip-shaped
o Flagella emerging from anterior
o Poor swimmers, encyst readily
∙ Secondary zoospores
o Reniform or bean-shaped
o Flagella emerging from lateral groove
∙ Dimorphic
o Primary and secondary zoospores present in life cycle
▪ Primary zoospores formed in zoosporangium
▪ Secondary zoospores formed upon germination of primary zoospores ∙
Monomorphic
o Secondary-type of zoospores formed inside zoosporangium
Sexual Reproduction
∙ Mostly heterogametic (morphologically differentiated gametangia):
o Hyphal-like antheridia
▪ Attracted to oogonium by hormones and develop fertilization tubes
o Large, globose oogonia
▪ One or more oospores in oogonium
∙ Simultaneous meiotic divisions occur in antheridia and oogonia prior to
fertilization ∙ Karyogamy occurs in oosphere to form oospore that matures inside
oogonium
Oogonia & Oospores
∙ Oospore wall consists of 3 parts:
o Exospore
o Epispore
o Endospore
∙ Periplasm = residual protoplasm
o Plerotic = periplasm present
o Aplerotic = lacking periplasm
Oogonium (female gametes) & Antheridium (Male
gametes)
∙ Hypogynous
o Antheridium formed in oogonial stalk
∙ Paragynous
o Antheridium attaches laterally to oogonium
▪ Monoclinous—branch off oogonial stalk
▪ Diclinous—branch off separate hypha
Science City of Muñoz 3120
Nueva Ecija, Philippines
Instructional Module for the Course
PPATH 3305 – MYCOLOGY
Module 2
Topic 1 Phylum Oomycota
Objectives
1. Illustrate fungal structures representing the Phylum Oomycota 2.
Explain the economic importance of each group of Lower fungi 3.
Explain the development/life cycle of Phylum Oomycota 4. Equip with
the different genera and structures of Phylum Oomycota.
Phylum Oomycota
Stramenopilous Fungi
∙ Tinsel flagellum
∙ Tubular mitochondrial cristae
∙ Cellulose in cell walls
∙ Lysine synthesis by diaminiopimelic acid pathway (DAP)
∙ 1 class (Oomycetes), 8 orders, 92 genera and 800 species
∙ Orders to cover:
o Saprolegniales
▪ Holocarpic thallus
o Pythiales
▪ Filamentous thallus
o Peronosporales
▪ Filamentous thallus
Life cycle
, Characters
∙ Cell walls composed primarily of beta-glucans with small amounts of
cellulose ∙ Filamentous species generally produce coenocytic hyphae
∙ Principal storage compounds are water-soluble mycolaminarins (beta-
glucans) ∙ Haustoria formed by plant parasitic species
Zoospores
∙ Primary zoospores
o First formed
o Pip-shaped
o Flagella emerging from anterior
o Poor swimmers, encyst readily
∙ Secondary zoospores
o Reniform or bean-shaped
o Flagella emerging from lateral groove
∙ Dimorphic
o Primary and secondary zoospores present in life cycle
▪ Primary zoospores formed in zoosporangium
▪ Secondary zoospores formed upon germination of primary zoospores ∙
Monomorphic
o Secondary-type of zoospores formed inside zoosporangium
Sexual Reproduction
∙ Mostly heterogametic (morphologically differentiated gametangia):
o Hyphal-like antheridia
▪ Attracted to oogonium by hormones and develop fertilization tubes
o Large, globose oogonia
▪ One or more oospores in oogonium
∙ Simultaneous meiotic divisions occur in antheridia and oogonia prior to
fertilization ∙ Karyogamy occurs in oosphere to form oospore that matures inside
oogonium
Oogonia & Oospores
∙ Oospore wall consists of 3 parts:
o Exospore
o Epispore
o Endospore
∙ Periplasm = residual protoplasm
o Plerotic = periplasm present
o Aplerotic = lacking periplasm
Oogonium (female gametes) & Antheridium (Male
gametes)
∙ Hypogynous
o Antheridium formed in oogonial stalk
∙ Paragynous
o Antheridium attaches laterally to oogonium
▪ Monoclinous—branch off oogonial stalk
▪ Diclinous—branch off separate hypha
