Oomycota Flashcards
Phylum oomycota common names
Water molds
Downy mildews
Are oomycota true fungi
Nope
What group of algae are in the same group as oomycota
Heterokonts
Why are oomycota treated as fungi?
Why are oomycota treated as Heterokonts?
Fungal like properties like filamentous thallus called hyphae
Flagella of zoospores occur in pairs (one long with hairs-tinsel, other short and smooth-whiplash)
How are oomycota distinct from other true fungal groups
-Have Oogonia and antheridia (oogamous), true fungi rarely are oogamous
-2 flagella (whiplash and tinsel) compared to no flagella or 1)
-diploid dominant
-cellulose compared to chitin
-coenocytic compared to a Duncan’s cross walls
Coenocytic
Cell with many nuclei or a filament without septa between nuclei
Oomycota range from _______ to highly branched ______, and ______ forms
Unicellular
Coenocytic
Filamentous
Two lifestyles of Oomycota
- Saprotrophs: important in freshwater and terrestrial systems as decomposers
- Parasite: parasitize freshwater protozoa, invertebrate and vertebrate animals, algae and terrestrial plants
Order Saproleginales
-habitat
-lifestyle
Fresh water and soil
Saprotrophs or obligate parasites of plants and animals -> water molds
Saprolegniasis
Cotton wool disease
External infection caused by water molds occurring in natural populations of fresh water fish. Exploited pre-existing illness, mechanical injury or environmental stress. Is highly fatal in aquaculture and aquarium trade.
Saprolegniales asexual reproduction
-apical hyphal cells swell to become a zoosporangium in which nuclear mitotic divisions take place
-the remainder of the supporting hypha is called a sporangiophore
-biflagellate zoospores
Saprolegniales sexual reproduction
-oomycetes spend most of their life as diploid thallus
-gametangia: only haploid stages in the life cycle are gametes
-sexual reproduction occurs between two dissimilar gametangia: a large round oogonium containing one to several eggs and a smaller antheridium that fertilized the oogonium.
-fertilization tube connects antheridium and oogonium-> release haploid nuclei near oosphere (plasmogamy)
-Karyogamy may be delayed until oospore has developed thick wall
-oospores=resting spores
-fertilization results in a thick-walled zygote = oospore (resting spore)
In Saprolegniales sexual reproduction, self fertilization can occur in ______ species, while two strains of opposite mating types are required for fertilization in ______ species
Homothallic
Heterothallic
How can you tell oospheres from oospore?
Oospheres are light strucures (unfertilized eggs)
Oospores are darkly stained
How long can oospores survive in soil?
10-15 years in soil
-produced in infected plant tissue and released into soil as the plant tissue degrades
Encysted zoospores of Saprolegniales
Encysted zoospores at end of the sporangium. Shortly after release primary zoospores will encyst.
-species of Saprolegnia have both primary and secondary zoospores
2 motile stages with a resting stage in between
Primary zoospores of Saprolegniales
-sharpe
-movement
Pear-shaped, flagella emerge anteriorly, “sluggish” movement and develop into primary cysts (spherical)
Spherical to aid in dispersal by water
Secondary zoospores of Saprolegniales
-movement
Flagella emerge laterally, swim vigorously (few hours) and then develop into secondary cysts (covered with spines= to attach to host)
-chemotaxis towards salts and amino acids
-chemotaxis of germinating hyphae of secondary zoospore towards amino acids
Order Peronosporales
-lifestyle
-what do they cause
-how do they cause it?
-obligate parasites of plants
-downy mildew disease
-haustoria grows between cells of the host plant, feeling through haustoria. Sporangiophores protrude through host stomata=appearance of “down”. Sporangia are formed at the tips of the sporangiophores and wind-disseminated
What habitat do Peronosporales not live in
-downy mildews do not occur in the aquatic habitat and typically the motile zoospore stage is limited to films of water on plant leaves and stems
In foliage pathogens of Peronosporales, sporangia germinate directly on _________
What dispersion is common in this case
Plant surface by the formation of germ tube (conidium)
Wind dispersion of sporangia
Human impact of Peronosporales
-late blight destroy potato populations ( Irish potato famine)
-destroy grape populations
-destroy impatiens populations
What can help prevent decimation of an entire crop by disease?
Genetic variety
How were grape vineyards saved from the fungus?
-liquid fungicide developed (Bordeaux mixture): copper duplicate and lime used as a fungicide
-copper prevents germination of fungal spores
