Transcript ASCOMYCETES (CONT.) ERYSIPHALES IB 371 - General Mycology Tuesday, November 11, 2003

ASCOMYCETES (CONT.)
ERYSIPHALES
IB 371 - General Mycology
Tuesday, November 11, 2003
ERYSIPHALES
All members of the order are
obligate parasites of above ground
parts of plants - usually the leaves.
Vegetative and reproductive
structures (except for haustoria) are
located on the surface of the host.
ERYSIPHALES COMES FROM THE
GREEK WORD FOR RUST
Powdery mildew on lilac leaf
Powdery mildew on lilac leaf
Erysiphales
Ascomata are non-ostiolate, dark
colored cleistothecia
Ascomata, conidia and hyphae are
superficial on the host
Asci are arranged in an irregular
hymenial layer within cleistothecia
Ascomata
ERYSIPHALES
Have a “phyllactinia type” centrum
development (sensu Luttrell).
Ascogonia and antheridia are single celled
and formed on superficial mycelium.
Cleistothecial wall is derived from hyphae
originating from stalk cells of ascogonia.
Wall cells become flattened, polygonal,
and thick walled.
ERYSIPHALES
Asci develop along a single irregular
layer in the middle of the cleistothecium.
Asci expand tremendously, crush the
sterile pseudoparenchyma cells of the
centrum and completely fill the cavity of
the cleistothecium.
Cleistothecia open by splitting.
Asci forcibly discharge ascospores into
the air.
SPLIT CLEISTOTHECIUM
Asci
ERYSIPHALES
 Asci are globose to pear-shaped, somewhat
thick walled and lack an apical apparatus.
 Ascospores are forcibly discharged when an
ascus is exposed to air and the ascus tip
explodes.
 Ascospores are single celled and hyaline.
 Powdery mildew fungi overwinter in the
ascomal state (cleistothecia), which is produced
toward the end of summer, and discharge
ascospores in the spring.
ERYSIPHALES
 Vegetative mycelium is hyaline, septate and
held to the host’s surface by appressoria
(lobed extensions of prostrate hyphal cells).
 Conidial states are in Acrosporium sp. (aka
Oidium).
 Conidia are hyaline arthrospores formed
basipetally in chains.
 Conidia are white in mass and look like
powder on the host, hence the name
“powdery mildews”.
CONIDIAL STATE
ERYSIPHALES
• Taxonomy of the group is based on
number of asci per single ascoma
and the morphology of the
cleistothecial appendages (see lab
material)
PODOSPHAERA
ERYSIPHALES
Found from the Arctic to the tropics, but
most common in temperate areas.
Occur mostly on cultivated plants,
attacking 7,187 hosts in 1,289 genera,
149 families and 44 orders of
Angiosperms.
Only one species, Erysiphe graminis, is
known to attack monocots.
90% of th hosts are dicots.
ERYSIPHALES
Biotrophic parasites - grow actively
only on their respective hosts and,
away from their hosts, are
encountered only as dispersal or
dormant spores
Get their nutrition from their hosts
through absorption by haustoria.
Haustoria
 Haustoria are formed from intercellular hyphae
that penetrate cell walls.
 Haustoria do not penetrate the host cell
membrane but act as a sink for nutrients
produced by the plant.
 Haustoria are important organs of absorption.
 Do not kill host but in the case of crop plants,
decrease overall yield.
LABOULBENIALES
• Mycelium mostly lacking
• Asci present but no hamathecial
structures
• Asci deliquescent
• Ascospores 2 celled with tips adapted
for attachment to hosts