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 SpecimensPrepared Slides