3. powdery mildew of
hardwood trees
• There are number of species of
genus Phyllactinia. P. dalbergiae is
commonest species found growing
on the leaves of Dalbergia
sissou (shnharn).
• The specimens can be collected in
abundance during the winter on
the fallen leaves of shisham. This
fungus is an obligate parailte.
4. habitat
It is a plant pathogen distributed in
temperate regions, P. gultata causes
a powdery mildew on leaves and stems on a
broad range of host plants.
5. Structure
• Its mycelium grows on the surface of
leaves forming a whitish con ring.
The hyphae send their short
branches or haustoria through
stomata of host in the epidermal or
other mesophyll cells. Haustoria are
used to absorb food form the host
tissues. Its hyphae are hyaline,
• much branched and septate. These
form a whitish mat on the surface of
leaves.
7. Asexual reproduction
unicellular, hyaline conidia
Structure of conidia
The wall of conidia is two layered. The outer
layer is smooth and thin. But the inner layer
is comparatively thick!.. There are ‘toted
marking on its surface. These conidia are
formed at the tips of short or
long conidiophores.
8. Powdery mildew
• Thus conidia are formed singly and no
conidia chain is formed. The conidia
are produced in abundance.
Therefore, the leaf surface appears to
be covered by a white powdery mas.,
• Therefore, this disease is known by
the name of Powdery Mildew. The
conidia form germ tube after
germination. This germ tube infects
new leaves of the host.
9. Sexual
reproduction
• Sexual reproduction occurs in
later summer.
• The hyphae
produce ectophytic mycelium.
• The conidia production stops
during sexual reproduction.
Young cleistothecia start
developing on the ectophytic
mycelium.
• The colour of cleistothecia
changes from white to black.
The fruit-bodies are produced
as a stimulus of sexual
reproduction.
• Therefore, these cleistothecia
represent the perfect stage.
10. sexual reproduction
• It takes place under unfavourable conditions.
The fungus is heterothallic and the gametangia
are formed on two closely lying hyphae. The
male gametangium is antheridium and the
female gametangium is ascogonium.
• (a) Antheridium is small clavate, one celled and
uninucleate structure.
• (b) Ascogonium is thick, ovoid, one celled,
uninucleate and closely applied to or coiled
around the antheridium.
• (c) Plasmogamy- When mature, the wall
between the two sex organs dissolves and the
nucleus from the antheridium migrates into the
ascogonium. Plasmogamy takes place followed
with nuclear pairing.
11. Cleistothecium:
• The mature cleistothecium is brown or black in
colour, globose with several layered wall and
bears appendages.
• The appendages are of two types:
• (a) An equatorial group of radiating appendages
with bulbous swollen bases and
• (b) A crown of repeatedly branched mucilage
secreting appendages which help in adhesion of
cleistothecium to the substratum.
• After completion of dormancy, the
cleistothecium ruptures irregularly by elongation
of asci. The asci come out and the ascospores
are liberated from the asci.
• The ascospores are ovate to elliptical, haploid,
uninucleate and smooth walled. Upon reaching a
suitable host, the ascospore germinates to form
new mycelium which soon becomes ready to
produce conidiophores and conidia.
12. Rupturing of cleistothecium
• The base of bulbous appendage is thick
walled above and thin walled below.
The appendages bend downward on
drying. Thus thin part buckles inwards.
It causes downward pressure of the
appendages tips. It frees the
cleistothecium from the mycelium. Now
cleistothecium attach to leaves.
• The ascospores become mature in the
asci. Now the inner cells of the
cleistothecium absorb water. It swells to
rupture the cleistothecium. Asci also
burst. Thus ascospores are discharged.
