To learn about a specific method of identifying fungi, using a written key and an illustrated key. Powdery mildew fungi can be identified to genus by the morphology (appearance) of the sexual stage (cleistothecia).
To learn about scientific investigation using forensic techniques.
Plant leaves infected with powdery mildew disease are collected after the sexual stage, the cleistothecia, are visible on the leaf surface. Cleistothecia from leaf material are examined with a compound microscope to identify the type of appendages present. The fungi are identified to genus using the appendage type and the number of asci (spore-containing sacs) inside each cleistothecium using both a written and an illustrated key. The students, using forensic plant pathology techniques, must attempt to prove themselves innocent in this CSI lab. Images for class use are in the Supplementary Information and References section.
Infected leaves can be collected in late summer or autumn, pressed flat, and dried to preserve them until used. Fresh leaves also may be examined. Once you have a collection of powdery mildew infected leaves, the actual exercise takes little preparation and can be done at any time.
Forensic Conclusions: Innocent or Guilty?
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