1. ASCOMYCETES (CONT.) ERYSIPHALES
IB 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 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)

18. PODOSPHAERA

22. 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.

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