Vital Signs of Animals Presentation By Aftab Ahmed Rahimoon
Albugo
1. (CYSTOPUS)
Classification:
Kingdom : Mycota / Fungi
Division : Eumycotina
Subdivision: Mastigomycotina
Class : Oomycetes
Order : Peranosporales
Family : Albuginaceae
Genus : Albugo By:
Dr P B MALLIKHARJUNA
GFGC YELAHANKA BANGALORE - 64
Infected mustard leaf with white pustules
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Ploidy state is controversial : Diploid / Haploid
2. Introduction: Albugo is an obligate parasitic fungal genus. It consists
of about 45 species. All these will infect higher plants and cause leaf spot
/blister diseases. Some of these are ;
Albugo candida: infects the crucifers/ mustard family and cause white
rust disease (misnomer) ,a leaf spot disease in more than 300 species.
Albugo ipomae-panduranae: infects the plants belonging to the family
Convolvulaceae
Albugo bliti: infects the Amarantheceae members.
Albugo occidentale: infects spinach- (Spinacea oleracea, phalak)
Albugo portulacea: infects Portulaca oleracea
Albugo oleracea: infects the Asteraceae members
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3. Albugo species can be identified based on the host specificity, oospore
ornamentation and conidial characteristics.
Albugo candida is the common and widely distributed fungus, which
infects the crucifer members such as mustard, cabbage, radish,
horseradish and Capsella bursa-pastoris (Shepard purse).
It causes white rust/blister disease especially on the leaves.
This fungus causes two types of symptoms. The primary symptoms will
occur on the leaf surface in the host plants, indicating the predominant
phase/stage of the fungus called the asexual stage.
Whereas, the systemic (infection) symptoms may appear at later stage as
the hypertrophied and hyperplasia structures, appears as tumours on the
entire aerial parts of the plants (such as stem, leaves, petioles and veins)
indicating the sexual stage of Albugo.
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4. Habit and Habitat:
• Albugo candida is an obligate parasitic plant pathogen that infects primarily
the leaves and finally spreads into the different aerial parts, especially, the
cortical tissues of the petiole , stem and floral parts.
It is an aseptate mycelial form and highly branched, siphon like mycelial
fungus.
It will grow intercellular in the host tissues and absorbs the nutrients from the
host by producing the characteristic knob or button shaped haustoria.
Further, the mycelium is coenocytic (multinucleate) due to the no cross
septa formation in the hypha. The cytoplasm with all cell organelles mainly
confined to the peripheral region. Its wall is made of cellulose.
Albugo will undergo both the asexual and sexual reproduction soon after
establishing in the host vegetatively.
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6. Asexual reproduction: is the most predominant type of
reproduction of Albugo, that occurs during favourable
conditions.
It occurs due to the formation of sporangiospores
Some of the mycelial hyphae terminal tips are going to
accumulate as a palisade like structures just below the
lower epidermis of leaf.
These hyphae tips will protrude vertically as the club
shaped conidiophores/sporangiophores due to the
accumulation of more nutrients and nuclei. Further, they are
with thick lateral walls and thin apex.
The terminal tip of each sporangiophore produces a bulged
structure, which metamorphoses into a sporangium.
The developmental
stages of sporangia
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7. VS of mustard leaf showing the asexual reproduction of Albugo
In the permanent slide under microscope
micrograph
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8. Both these structures create pressure over the leaf lower epidermis, and
hence ruptures, so as the tuft of club shaped sporangiophores along with
the sporangial chains is being exposed.
The tip of sporangiophore is continuously produce sporangia, and hence
these are arranged in the form of a chain in an basipetal manner i.e, the
earliest (older) spore at the tip and young one at the base.
All the spores/conidia are colourless and multinucleate. Further, the young
spores are spheroidal while the matured spores are hexagonal in shape.
In-between these conidia, there will be hygroscopic intercalary discs
called disjunctors, which help in the spore dispersal.
The matured sporangia/conidia are get detached from the conidial chain
and there by germinate on the same leaf or different host plant.
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9. The germination of these sporangia is of two
types based on availability of water/ moisture
content.
Usually under favourable conditions (sufficient
water) each sporangium will produce 8
zoospores due to cytokinesis.
Each zoospore is small, motile, biflagellate
(heterokont), naked and uni-nucleate structure.
Whereas, under unfavourable conditions rarely
the sporangia directly germinates and
establishes the daughter mycelia.
The entire asexual reproduction is completed
within 10 days. The germination of Sporangium
Zoospore
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10. Sexual reproduction: in Albugo occurs during unfavourable conditions
like the end of host season.
This process occurs in the host plant deeper tissues like the petiolar or
the stem cortex, which is indicated by the hypertrophied (tumour)
structure.
Sexual reproduction in Albugo is the Oogamous and gametangial
contact. Further, it is a eucarpic, and the homothalial or
heterothalial fungus.
Antheridium is male sex organ, which is a tubular or club shaped
structure. Further, it is a long slender and multinucleate (6-8) structure,
rich with nutrients.
Oogonium is the female reproductive structure. It is a large and
conspicuous globular structure with distinct Periplasm and Ooplasm.
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11. The Ooplasm is present at the centre with dense cytoplasm and egg nucleus and
other nuclei.
Whereas, the periplasm is a vacuolated cytoplasm that surrounds the ooplasm.
The antheridium and oogonium usually produced by the two different individual
mycelia and lay side-by-side (Perigynous) or the antheridium surrounds the
oogonium.
The fertilization takes place due to the gametangial contact. Both sex organs
undergo meiosis and produce haploid nuclei.
The antheridium makes a contact with the oogonium at receptive papilla.
Further, the antheridium penetrates into the oogonium by producing the
fertilization tube.
Meanwhile, some visible cytological changes occurs in the Oogonium. Two distinct
regions develops namely the vacuolated periplasm and the multinucleated dense
cytoplasm in the centre called Ooplasm.
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12. The centre of the ooplasm is denser
and multinucleated structure
generally referred as the
coenocentrum.
The tip of the fertilization tube
ruptures and the functional male
nucleus and some amount of
cytoplasm discharged into the
oogonium.
The male nucleus fuses with the
one egg nucleus called Oogamy
and produces a diploid oospore
(zygote). The sequential events occurring in the sexual reproduction
of Albugo
Gametangial
contact GFGC Yelahanka 12
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13. The oospore is a diploid, resting spore
with trilayer thick wall, dark brown in
colour, spheroidal and highly resistant
structure, usually found in the soil or
infected plant debris.
During favourable conditions each
oospore will undergo mitotic divisions in
order to produce 32 to 64 zoospores
(reniform and biflagellate).
These spores germinate on the suitable
host plant and develops into individual
Albugo.
Resting
Oospore
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14. The life cycle of
Albugo
Asexual
Sexual
Diplobiontic life cycle
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