Ex.
No. 5 Study
of Oomycetes fungi
Domain:
Eukarya Kingdom: Chromista /
Straminopila
Division:
Oomycota
Class:
Oomycetes Oomycetes /Straminopila (Water
mould fungi)
Order: Pythiales Peronosporales
Sclerosporales
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 Sclerosporaceae |
(Family)Pythiaceae (Family)
Albuginaceae (Family)
Peronosporaceae
Damping
– off White rust of Amaranthus Downy mildew cereals Downy mildew
Late
blight of Potato
Pythiaceae
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Disease name
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Causal Organism
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Symptoms
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Damping – off
In ginger –
Rhizome rot
In Papaya –
Foot rot
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Pythium aphanidermatum
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1.
Pre emergence damping – off : Failure
of seed germination
2.
Post emergence damping – off : Dark
brown lesions/ spots are formed on the collar region of the stem and affected
tissues are soon become rotten condition
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Previously
Pythiaceae family, at present in Peronosporaceae family
Late blight of
potato
Citrus
gummosis, Cardamom Azhukal, Pepper Quick wilt
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Phytophthora infestans
Phytophthora sp.
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Brown to black
coloured water soaked lesions are formed on the tip or margin of the leaves
and corresponding lower surface of the leaves, white coloured mycelial growth
are appear. Potato tubers show dry rot symptoms.
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Albuginaceae
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Disease name
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Causal Organism
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Symptoms
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White rust or
White blisters of Amaranthus
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Albugo bliti
/ Albugo candida
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White rust
pustules appear on the lower/abaxial surface of the leaves. It produces knob
shaped Haustoria. (Obligate parasite)
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Peronosporaceae
Downy
mildew (Obligate parasite / Biotroph) : White colour mycelial growth is appear
on the lower/ abaxial surface of the leaves and corresponding upper/ adaxial
surface they can produce chlorotic/ yellow spots are appear
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Disease name
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Causal Organism
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Symptoms
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Downy mildew
of grapes
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Plasmopara viticola
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Fruit
infection: Infected berries become harden, leathery and
wrinkled (Mummified)
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Downy mildew
of cumbu or Green ear of cumbu
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Sclerospora graminicola
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Flowers are malformed
into green leaf like structures
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Downy mildew
of sorghum or Sorghum leaf shredding
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Sclerospora
sorghi
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The leaves are
converted into thread like structures
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Downy mildew
of maize or Crazy top of Maize
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Peronosclerospora sorghi
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Malformed
flower buds are called as Crazy top
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Lettuce downy
mildew
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Bremia lactucae
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Downy mildew
of cucurbits
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Pseudoperonospora cunbensis
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Tobacco blue
mould
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Peronospora tabacina
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Downy mildew
of ornamental plants (aster)
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Basidiophora endospora
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Downy mildew
of Impatiens
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Bremiella sphaerosperma
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Life cycle of Pythium aphanidermatum
Taxonomic
position
Kingdom:
Fungi
Division:
Eumycota
Class:
Oomycetes
Order:
Peronosporales
Family:
Pythiaceae
Genus:
Pythium
Species:
aphanidermatum
Disease
name: Damping – off / Seedling rot
Anamorphic stage:
1. The
hyphae are both intercellular and intracellular and there is no Haustoria are
produced.
2. The
sporangia are globose and are produced terminal or intercalary on the hyphae.
3. The
sproangiophore consists of sporangia with a bubble like structure called as
vesicle.
4. On
maturity the vesicular wall is burst out like a soap bubble and the zoospores
are released.
5. The
zoospores are asexual spore, kidney shaped and has two lateral flagella. (Whiplash
& tinsel).
6. After,
Zoospores comes to rest, encyst and germinates by germ tube.
Teleomorphic stage:
1. Paragynous
antheridium, the Oogonium is globose with a multinucleate oosphere surroundly
by a layer of periplasm and the antheridium is a club shaped.
2. Upon
gametangial contact, a fertilization tube develops fertilization tube develops
and penetrates the oogonial wall and the periplasm,
3. In
the mean time, meiosis has taken place in both the gametangia. The male nucleus
now passes through the tube into the oosphere, approaches the female nucleus,
unites and forms the zygote.
4.
Oosphere develops into a thick walled
oospore and it germinates after undergoing a rest period.
Life cycle of Phytophthora infestans
Taxonomic
position
Kingdom:
Fungi
Division:
Eumycota
Class:
Oomycetes
Order:
Peronosporales
Family:
Pythiaceae
Genus:
Phytophthora
Species:
infestans
Disease
name: Late blight of potato
Mitosporic stage:
1. The
Sporangiophores are symboidally branched and hyaline multinucleate lemon shaped
papillate sporangia are produced.
2. In
the presence of water the sporangium germinates either by a germ tube or
zoospore formation.
3. After
the zoospores are comes to rest they encyst and germinates produces by germ
tube, produces an Appressorium.
4. After
penetrating the germ tube develops into a profusely branched, hyaline,
Coenocytic, intercellular mycelium and haustoria are produced.
5. Low
temperature favours zoospore production and high temperature favours germ tube
formation.
Meiosporic stage:
1. heterothallic
fungus, the oogonia penetrates ad grow through the antheridium and form a
globose structure above the antheridium (Amphigynous antheridia)
2. Both
gametes are multinucleate are initially, but they mature only a single nucleus
is left that probably undergoes meiosis before fertilization.
3.
Migration of the male nucleus occurs
through the oogonial wall and fusion takes place and after a rest period of
several weeks the oospore germinates and produces sporangium.
Sporangiophore characters of
Peronosporaceae
1. Basidiophora
2. Sclerospora
3. Plasmopara
4. Peronospora
& Pesudoperonospora
5. Bremia
6. Bremiella
Basidiophora: The
Sporangiophore is club shaped with swollen head over which the sporangia are
borne. Ex. Basidiophora entospora
Sclerospora: The
Sporangiophore is long, stout with upright branches bearing sporangia at the
tips.
Ex. Sclerospora
graminicola
Plasmopara :
Sporangiophore branched at right angles with blunt tips. Ex. Plasmopara viticola
Peronospora
& Pseudoperonospora : The
sporangiophores are dichotomously branched on which sporangia are borne singly.
Ex. Peronospora destructor & Pseudoperonospora cunbensis
Bremia:
They are similar to Peronospora except the tip of branches are cup shape
with four sterigmata from which sporangia are borne. Ex. Bremia lactucae
Bremiella :
Tip of its branches inflated into bulbous apophysis. Ex. Bremiella sp.
