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ASCOMYCETES CONT' ERYSIPHALES

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ASCOMYCETES (CONT.) ERYSIPHALES. IB 371 - General Mycology. Tuesday, November 11, 2003 ... All members of the order are obligate parasites of above ground ... – PowerPoint PPT presentation

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Title: ASCOMYCETES CONT' ERYSIPHALES


1
ASCOMYCETES (CONT.) ERYSIPHALES
  • IB 371 - General Mycology
  • Tuesday, November 11, 2003

2
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.

3
ERYSIPHALES COMES FROM THE GREEK WORD FOR RUST
4
Powdery mildew on lilac leaf
5
Powdery mildew on lilac leaf
6
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

7
Ascomata
8
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.

9
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.

10
SPLIT CLEISTOTHECIUM
Asci
11
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.

12
ERYSIPHALES
  • Vegetative mycelium is hyaline, septate and held
    to the hosts 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.

13
CONIDIAL STATE
14
ERYSIPHALES
  • Taxonomy of the group is based on number of asci
    per single ascoma and the morphology of the
    cleistothecial appendages (see lab material)

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PODOSPHAERA
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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.

23
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.

24
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.

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LABOULBENIALES
  • Mycelium mostly lacking
  • Asci present but no hamathecial structures
  • Asci deliquescent
  • Ascospores 2 celled with tips adapted for
    attachment to hosts

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