In late summer or autumn collect leaves with mature (black) cleistothecia on plants that show signs (pale, dusty-white coating on leaves) of powdery mildew. The cleistothecia should be visible to your eye without the aid of a magnifying glass. Asters, azalea, cherry, filbert, grape, horse chestnut, lilac, oak, phlox, rose, zinnia, evening primrose (Oenothera spp., often called sundrops), viburnum, wheat, willow and many other shrubs, trees, flowers, weeds and garden plants are good sources of cleistothecia.
Leaves exhibiting abundant cleistothecia are good specimens for teaching purposes. Infected leaves should be pressed flat between pieces of newspaper. Pressed, dried, leaf specimens can be stored in envelopes for use over many years. Label the envelope with the pressed leaves giving the name of the plant, the powdery mildew genus (you will need to identify the genus with the forensic key and diagrams), and location of collection, for future reference. For your own purposes of cataloguing and ease of choosing teaching material for labs, you may want to number your envelopes and keep a separate list of the specific genera of powdery mildew found to be associated with each plant collected. You will find that several different genera of powdery mildew will infect the same host type. For example, Microsphaera and Phyllactinia may both be found on oak. This is why it is important to label your envelopes by powdery mildew genus and not host plant.
Powerpoint tutorial for class use
You are a suspect in a murder investigation. You must attempt to prove your innocence and clear your name using dissecting and compound microscopes, clear tape, petri dishes, forceps, microscope slides, a water dropper and a forensic key with the special characteristics of powdery mildew cleistothecia appendages.
You may work alone or in a group of three or four.
Repeat Sections B and C (Examination and Identification of Evidence) with the plant material in your petri dish labeled "Murder Victim" including the recording of results.
Appendages coiled or hooked at tip - UncinulaAppendages simple and straight with bulb-like base - PhyllactiniaAppendages branching dichotomously (antler-like at tip) Cleistothecium contains a single ascus - Podosphaera Cleistothecium contains several asci - MicrosphaeraAppendages simple or irregularly branched, often entangled Cleistothecium contains a single ascus - Sphaerotheca Cleistothecium contains several asci - Erysiphe
Locate the Forensic Evidence Data Table on the Case Study Sheet . Record and draw the type of appendages (arms) found on the surface of the cleistothecia (e.g. hooked tip; bulb-like base; antler-like dichotomous branching; or simple, string-like arms), the number of asci (one or several) contained within each cleistothecium, and the name of the powdery mildew genus.
Forensic Evidence Data Table
Characteristics of Cleistothecia
Types of Appendages
Number of asci (sacs) per cleistothecium (one or several)
Murder Suspect (YOU) #______
Images for class use.
Case Study Sheet