Oomycota

Question 1

Phylum oomycota common names

Answer 1

Water molds

Downy mildews

Question 2

Are oomycota true fungi

Answer 2

Nope

Question 3

What group of algae are in the same group as oomycota

Answer 3

Heterokonts

Question 4

Why are oomycota treated as fungi?

Why are oomycota treated as Heterokonts?

Answer 4

Fungal like properties like filamentous thallus called hyphae

Flagella of zoospores occur in pairs (one long with hairs-tinsel, other short and smooth-whiplash)

Question 5

How are oomycota distinct from other true fungal groups

Answer 5

-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

Question 6

Coenocytic

Answer 6

Cell with many nuclei or a filament without septa between nuclei

Question 7

Oomycota range from _______ to highly branched ______, and ______ forms

Answer 7

Unicellular
Coenocytic
Filamentous

Question 8

Two lifestyles of Oomycota

Answer 8

1. Saprotrophs: important in freshwater and terrestrial systems as decomposers
2. Parasite: parasitize freshwater protozoa, invertebrate and vertebrate animals, algae and terrestrial plants

Question 9

Order Saproleginales
-habitat
-lifestyle

Answer 9

Fresh water and soil
Saprotrophs or obligate parasites of plants and animals -> water molds

Question 10

Saprolegniasis

Answer 10

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.

Question 11

Saprolegniales asexual reproduction

Answer 11

-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

Question 12

Saprolegniales sexual reproduction

Answer 12

-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)

Question 13

In Saprolegniales sexual reproduction, self fertilization can occur in ______ species, while two strains of opposite mating types are required for fertilization in ______ species

Answer 13

Homothallic
Heterothallic

Question 14

How can you tell oospheres from oospore?

Answer 14

Oospheres are light strucures (unfertilized eggs)

Oospores are darkly stained

Question 15

How long can oospores survive in soil?

Answer 15

10-15 years in soil

-produced in infected plant tissue and released into soil as the plant tissue degrades

Question 16

Encysted zoospores of Saprolegniales

Answer 16

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

Question 17

Primary zoospores of Saprolegniales

-sharpe
-movement

Answer 17

Pear-shaped, flagella emerge anteriorly, “sluggish” movement and develop into primary cysts (spherical)

Spherical to aid in dispersal by water

Question 18

Secondary zoospores of Saprolegniales
-movement

Answer 18

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

Question 19

Order Peronosporales
-lifestyle
-what do they cause
-how do they cause it?

Answer 19

-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

Question 20

What habitat do Peronosporales not live in

Answer 20

-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

Question 21

In foliage pathogens of Peronosporales, sporangia germinate directly on _________

What dispersion is common in this case

Answer 21

Plant surface by the formation of germ tube (conidium)

Wind dispersion of sporangia

Question 22

Human impact of Peronosporales

Answer 22

-late blight destroy potato populations ( Irish potato famine)
-destroy grape populations
-destroy impatiens populations

Question 23

What can help prevent decimation of an entire crop by disease?

Answer 23

Genetic variety

Question 24

How were grape vineyards saved from the fungus?

Answer 24

-liquid fungicide developed (Bordeaux mixture): copper duplicate and lime used as a fungicide
-copper prevents germination of fungal spores