23. Oomycota.pdf

Oomycota

1. (General Characteristics)
By
Hem Chander
Assistant Professor (Botany)
Career Point University Hamirpur(HP) 176041
[email protected]

2. •The division Oomycota, unlike the Chytridiomycota, is a
group of aquatic fungi that have cell walls composed
ofcelluloseand a diploid dominant lifecycle (=gametic
lifecycle).
•The mycelium iscoenocyticand produce septaonly to •The mycelium iscoenocyticand produce septaonly to
separate the reproductive structures from the
assimilative portion of the thallus.

3. •Asexual reproduction is byzoosporesthat are
produced inzoosporangia.
•The zoospores produced are biflagellatedwith one
flagellum of the whiplash type and the other of the
tinsel type.
•Zoospores have flagella that are anisokont(unequal) •Zoospores have flagella that are anisokont(unequal)
and heterokont(different) (straminipilous)
•The anteriorlydirected flagellum bears two rows of
tubular tripartite hairs
•The posteriorlydirected flagellum is a whiplash type

4. •Sexual reproduction is Oogamous.
•It isheterogamousand the male nuclei (=sperms) from
theantheridiumare inserted into the eggs contained in
theoogonium.
•A swimming sperm is absent in the Oomycota. •A swimming sperm is absent in the Oomycota.
•This type of sexual reproduction is referred to
asgametangialcopulation.
•The eggs and sperms are products of meiosis and the
only parts of the life cycle that are haploid.

5. •Female gamete (oosphere) produced by an
oogonium
•Depending on taxon, there may be one to many
oospheresper oogoniumoospheresper oogonium
•Male gamete is produced by antheridiumand
transferred to the oogoniumby gametangial
contact and migration of male nuclei

6. •There are more than 500 species in the Oomycota.
These include the so-called water molds (e.g.
Saprolegnia) and downy mildews (e.g. Albugo).
•They are filamentous fungiwhich must absorb their
food from the surrounding water or soil, or may
invade the body of another organism to feed. invade the body of another organism to feed.
•As such, oomycetesplay an important role in the
decomposition and recycling of decaying matter.
•Other parasitic species have caused much human
suffering through destruction of crops (e.g.
Phytophthora) and fish (e.g. Saprolegnia).

7. •Vegetative thallusfilamentous, coenocytic, in some
groups unicellular
•Cell walls lacking chitin (except for a few taxa), made of
glucans& cellulose
•Asexual reproduction by biflagellate zoospores•Asexual reproduction by biflagellate zoospores
•Sexual reproduction by oogonia(female) & antheridia
(male) -no motile gametes
•Sexual spore is the oospore
•Diploid life cycle