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ASCOMYCETES (CONT.) ERYSIPHALES

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.

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ASCOMYCETES (CONT.) ERYSIPHALES

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  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 host’s surface by appressoria (lobed extensions of prostrate hyphal cells). • Conidial states are in Acrosporium sp. (aka Oidium). • Conidia are hyalinearthrosporesformed basipetallyin 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)

  15. PODOSPHAERA

  16. 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.

  17. 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.

  18. 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.

  19. 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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