2. General Characters Of Order
Saprolegniales-
Systematic Position-
Kingdom-Chromista
Phylum-Oomycota
Class- Oomycetes
Order-Saprolegniales
Majority of the saprolegniales are aquatic hence called
“water moulds”, few species are found in moist soil.
Most of these fungi are saprobic i.e grow on dead plants
and animals.
Cellulose is present in the cell wall.
Mycelium is profusely branched and coenocytic.
3. Reproduction in Saprolegniales-
Reproduction
in
Saprolegniales
Asexual
Reproduction
(During favourable
conditions)
By Zoospores
Monoplanetic
(Producing a
single type of
zoospore) e.g
Dictyunchus
Diplanetic
(Simultaneous
production of
both zoospores )
e.g Saprolegnia.
Polyplanetic
(Repeated
encystment and
germination of
secondary
zoospore.)
Sexual Reproduction
(During Unfavourable
Conditions)
Oogamous type
i.e By Antheridia
and Oogonia.
On the basis of zoospore type ,life
cycle can be-
4. Asexual Reproduction-
• Zoospores are produced in
elongated zoosporangia.
• These are heterokont i.e
posses one whiplash and one
tinsel (straminipilous) type
flagellum.
• Two types of zoospores are
produced in some species like
Saprolegnia and Achlya.
• Two types of zoospores are
produced-
1-Primary zoospore.
2-Secondary zoospore.
Electron micrograph of
primary zoospore of
Saprolegnia.
Electron micrograph of secondary
zoospore of Saprolegnia.
5. Comparison between Primary and
Secondary Zoospore-
Secondary Zoospore
Kidney shaped.
Laterally inserted flagella.
Encystment by shedding of flagella.
Can swim for hours (vigorous
swimmer)
In some species of Saprolegnia the
encysted zoospore shows boat hook
hairs for attachment.
Primary Zoospore
Pear shaped.
Apically inserted flagella.
Encystment by withdrawal of
flagella.
Can swim for about few minutes.
It consist of tuft of flagella during
encysted condition called tripartite
tubular hairs (TTHs)
Encysted zoospore of Saprolegnia
ferax showing TTHs.
6. Vegetative reproduction in
Saprolegnia and Achlya.
By Fragmentation-Small fragments of hypha
accidently break up and give rise to new mycelium.
By Gemmae (Chlamydospore) formation- Tip of
hypha swells and becomes thickened and separated by
a septa.
Vegetative Reproduction in Saprolegnia by
Gemma.
7. Asexual reproduction in
Saprolegnia ,Achlya and Dictyuchus
Saprolegnia – Dimorphic, diplanetic with swimming
periods of equal duration.One of the most
characteristic feature is proliferation of
zoosporangium.
Achlya – Dimorphic, diplanetic but primary
zoospores encyst just outside the sporangium.
Dictyuchus – Monomorphic, polyplanetic, no
primary spores are liberated. Primary spore encysts
in the sporangium, each cyst releases a secondary
zoospore that can swim and encyst repeatedly.
11. Sexual Reproduction in Saprolegnia
and Achlya
Sexual Reproduction is of Oogamous
type i.e male reproductive organ is
antheridia and female reproductive
organ is oogonia.
Meiosis is gametangial i.e takes place
in antheridia and oogonia just before
gamete formation. The mycelium is
always diploid.
Saprolegnia-In S.litoralis the
antheridial branch develop from the
oogonial stalk showing androgynous
condition or monoclinous condition
while when develops on different
hyphal branch .(diclinous)
Achlya- sexual reproduction is
controlled by hormones.
Arrangement of ooplast and
lipids in Oospore of
Saprolegnia.
12. Antheridium and Oogonium of
Saprolegnia
SEXUAL REPRODUCTION IN SAPROLEGNIA
Saprolegnia growing on
dead insect.
14. Hormone Produced By Affecting Specific action
A (Antheridiol) Vegetative hyphae Vegetative hyphae Induces formation of
Antheridial branches
B (Oogoniol) Antheridial branches Vegetative hyphae Induces formation of
Oogonial initials
C (Antheridiol) Oogonial initials Antherial
branches
1-Attracts antheridial
branches
2-Induces
thigmotropic
response and
delimitation
antheridia.
D Antheridia Oogonial initials Induces delimitation
of oogonium by
formation of basal
septum.
Role of hormones in Oomycota : Achlya ambisexualis.
15. Role of hormones in
sexual reproduction of
Achlya ambisexualis.
B) Hormone A produced by
vegetative hyphae affecting
vegetative hyphae.
C) Hormone B produced by
antheridial initial induces the
formation of Oogonial initial.
D) Hormone C produced by
Oogonial initial that attracts
the anthredial branches.
E) Hormone D produced by
Anthredial branches that
causes the formation of
septum between oogonia
and vegetative hyphae.
