General mycology laboratory the powdery mildew fungi




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GENERAL MYCOLOGY LABORATORY

THE POWDERY MILDEW FUNGI

November, 11 2003
PURPOSE: To become familiar with the overall morphology of the powdery mildew fungi and to observe their haustoria in host material.
Order Erysiphales
The ascoma of the Erysiphales is completely closed and is called a cleistothecium. Some mycologists, consequently, prefer to classify such forms with the Plectomycetes in spite of the fact that the asci are not scattered within the cleistothecium as they are in the typical Plectomycetes. The cleistothecia of the Erysiphales have a pseudoparenchymatous wall which generally bears long appendages or bristles of various types. The asci are globose or broadly oval and rise from the base of the ascoma. The mycelium is superficial in all but a few species, and obtains nourishment by means of haustoria. The Erysiphales are specialized, obligate parasites of plants.
For each of the species for which there are prepared slides, examine the slides for the followings structures: 1. Cleistothecium wall ornamentation; 2. Centrum structure; 3. Number of asci; 4. Ascus morphology; 5. Ascospore morphology; 6. Conidial morphology; and 7. Haustorium morphology.
For two of the species for which there are dried specimens, examine the specimen with the dissecting microscope and describe the type of appendages. Mount some dried ascomata on a slide in KOH and crush by pressing on the coverslip with a needle. Describe the anatomy of the ascomatal wall. Count the number of asci and describe the ascospores.
Dried Specimens Prepared Slides

Microsphaera alni Microsphaera alni

Phyllactinia corylea Erysiphe graminis

Podosphaera oxyacanthe Uncinula salicis

Sphaerotheca sp.

Uncinula salicis
1. Describe the relationship of the vegetative hyphae of the Erysiphales to their hosts.

2. Draw a life cycle diagram typifying the Erysiphales.



3. Discuss ascoma development in the Erysiphales.

4. How are the Erysiphales dispersed?


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