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Crime Scene Investigation (CSI) with Powdery Mildew Fungi

LESSON PLAN

Learning objectives:

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.

Exercise description:

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.

Time frame:

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.

Study questions:

Forensic Conclusions: Innocent or Guilty?

1. Compare the forensic plant pathology observations you have recorded for the two different samples. Are the appendages observed on the two different samples the same or are they different?
   
   
   
   
2. If the appendages you observed on the cleistothecia found on the plant material taken from your shoelaces (murder suspect) are different from appendages on the cleistothecia found on the plant material taken from the murder victim, what does this evidence suggest?
   
   
   
   
3. If the appendages on the cleistothecia found on the plant material taken from your shoelaces (murder suspect) are the same as the appendages on the cleistothecia found on the plant material taken from the murder victim what does this evidence suggest?
   
   
   
   
4. Do you need an alibi as to where you were when the murder took place? Explain.
   
   
   
   

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