Separation of Lanthanides/ Lanthanides and Actinides
Perenosporales
1. x
Agriculture and forestry university
Rampur, Chitwan
Presentation on
PERONOSPORALES
Submitted to:
Prof. Dr. Sundar Man Shrestha
Head of department
Department of plant pathology
AFU, Rampur
Prepared by:
Arjun Rayamajhi
Msc. Ag. 1st semester
Department of plant pathology
Exam Roll No: PLP-06M-2018
2. Introduction
• Most developed/specialized order of
class oomycetes
• An order comprising chiefly parasitic
lower fungi (class Oomycetes) that
have equally biflagellate zoospores
and conidia which either germinate
directly or act as sporangia and
contain the families
Albuginaceae, Peronosporaceae, and
Pythiaceae, (Merrim-webster
dictionary).
3. Characteristics
• Habitats and distribution:
aquatic, amphibious, and
terrestrial species
Many species are destructive
parasites of economically
important plants, frequently
causing epiphytotics.
The fungi of the order -
Peronosporales, cause damping
off, white rusts, downy mildews,
late blight diseases.
4. Characteristics continue…
• Food habits:
• Majority of the members are
the obligate parasites
(Albuginaceae and
Peronsporaceae) of higher
plants but some are aquatic or
semi-aquatic facultative
parasites (Pythiaceae).
• Some genera survive also
saprophytically on dead or
decaying vegetation and few
survive easily in soil or in mud.
5. Characteristics continue…
• General biology:
differs in fundamental ways
from the organisms in the
Kingdom Fungi – cell wall
chemistry, sterol biosynthesis
Cell wall composition – most
fungi contain chitin as the
major structural component
but oomycote contain cellulose
but no chitin
Sterol biosynthesis - Ergosterol
is characteristics sterol in true
fungi whereas peronosporales
donot need sterol to grow
Griffith et al., 1992).
6. Characteristics continue…
• Somatic Structures:
The mycelium is well developed, consisting
of coenocytic, stout hyphae that branch
freely.
The hyphae of parasitic species are growing
intracellularly in most of pythiaceae or
intercellularly in the downy mildew
parasites (perenosporaceae).
Those growing intercellularly produce
haustoria within the host cell which may be
either spherical in Albugo candida,
elongated in Phytophthora infestans and
Peronoospora pisi or branched.
8. Zoospores : Asexual reproduction
Asexual reproduction is through zoospores produced in
the sporangia which are reniform, biflagellate, and
monoplanetic. Diplanetism and polyplanetism occur in a
few species.
The sporangia are borne on somatic hyphae and remain
attached even after the zoospores are released but in the
more complex types the sporangia are borne on
sporangiophores and are deciduous upon maturity.
In this case, the whole sporangium acts as a spore and in
some species they germinate by a germ tube instead of
producing zoospores.
Majority of species produces zoospores, upon their
release from the sporangium, the zoospores swarm for
sometime, come to rest, encysts, and germinates each by
a germ tube that develops into the mycelium.
• Two types of flagella are found on zoospores
• Whiplash flagellum – smooth & tapers
• Tinsel flagellum – has lateral filaments
perpendicular to the main axis
9. Life cycle
Sexual cyle:
• Gametangia formed &
meiosis occurs–
• Homothallic &
heterothallic species
• Male gametangium –
antheridium- slightly
curved apical portion
• Female gametangium –
oogonium that contains
singleor multiple nuclei –
surrounded by periplasm,
globose
10. • Antheridium grows to oogonium
• Forms fertilization tubes to
oospheres
• Nuclei from antheridia migrate
through fertilization tubes
• Plasmogamy and karyogamy take
place
• Oosphere is now diploid
• Develops thick wall and becomes
an oospore
11. Oogonium
• Oospore can remain dormant
• Germinates to produce
zoosporangium or 2n mycelium
12. Pythiaceae
• Most highly evolved members
of the Oomycota
• Include aquatic, amphibious
and terrestrial forms
• Saprotrophs and parasites
• Oogonia produce only one
oosphere
13. Pythium
• Pythium – a large genus that includes saprotrophs (soil and water)
and facultative parasites of algae, fungi and plants
• One species causes “damping off” of seedlings – grows intercellularly
in stems and roots of seedlings and rots tissue
• Asexual reproduction by zoosporangia and zoospores (secondary
zoospores only)
14. Pythium
• Contents of zoosporangium
empty into a vesicle, cleave
and form zoospores outside
zoosporangium
15. Phytophthora
• Forms lemon shaped sporangia
that detach from
sporangiophore in asexual
reproduction – sporangia can
germinate by forming
zoospores or forming a germ
tube directly
18. Albuginaceae
• Albugo – obligate plant
parasite, causes white
rust
• Sporangia detach,
dispersed by wind
• If moisture available,
sporangia produce 4-12
zoospores
• Can germinate directly
with a germ tube
21. Peronosporaceae
• Peronospora and related genera
– obligate parasites of plants –
cause downy mildews
• In some species, sporangia
always germinate with a germ
tube, never form zoospores –
called conidia