Demonstration of Plant Pathogen Dispersal Without Using Live Plants or Pathogens
APS Office of Public Relations and Outreach
Just like humans, plants are susceptible to diseases caused by microorganisms, including (from
smallest to largest in size) viroids, viruses, phytoplasmas, bacteria and fungi. Students are
repeatedly told to cough into their arm or tissue to prevent spread of human diseases such as flu
and colds, but they are seldom told how plant diseases are spread. This demonstration illustrates
one method of plant disease spread, water splashing of fungal spores or bacterial cells. Living
plants and pathogens are not required, and neither is water. Instead, coffee grounds are
substituted for spores or cells and polymer balls are used for water drops. Pathogen spread is the
result of velocity (magnitude and direction) of each polymer ball at the point of impact and the
amount of coffee grounds (spores or cells) it hits.
It is suggested that prior to the demonstration, a color illustration of a leaf spot or fruit spot
disease cycle is shown, along with fungal spore photographs. To enhance the demonstration, it is
useful to have a plant, plant part (e.g., large leaf) or fruit exhibiting leaf or fruit spot symptoms,
along with a healthy counterpart. If that is not possible, silk plants and artificial fruits can be
used. “Spots” are added to these substitutes using glitter glue.
For the demonstration, the following items are needed:
 Clear plastic storage container (~66 qt.; 13 in. high x 24 in. long x 16 in. wide)
 Round container, without lid (~6 in. high, 6 in. diam.; e.g., empty 34 oz. coffee container)
 Color leaf prints
 Embroidery hoop or very large rubber band
 Coffee grounds
 Orbeez™ (http://orbeezone.com)
 Colander
 Plastic bowl (>2 cup size)
 Measuring spoons
 Paper towels
 Laminated illustration of leaf spot or fruit spot disease cycle
Step 1:
Orbee are superabsorbent polymer balls that are initially the size of a pin head, but expand with
addition of water (maximum 14-mm diam.) and will be used to simulate rain drops in this
exercise. Final size depends on how long the Orbeez are left soaking in water. According to the
Orbeez™ website, 3/4 cup of Orbeez are obtained from one package (150 per package), after the
addition of 1 1/2 cups water and allowing expansion for at least 3 hr. After soaking to plump the
Orbeez, drain in colander and place in bowl.
Spore Movement Demonstration, Page 1
Step 2:
The color leaf print is placed on top of the empty round container (without lid) and held in place
with an embroidery hoop or rubber band (Fig. 1). The paper needs to be relatively tightly fitted
on the round container to allow the Orbeez to bounce and successfully simulate rain splash. The
container with leaf print is then placed inside the clear plastic storage container (Fig. 1A). This
larger container serves as containment for the bouncing Orbeez and can be the storage and
transport container for demonstration supplies.
Step 3:
About 1/4 tsp. of coffee grounds is placed on the color print, while explaining that the coffee
illustrates a “leaf spot” that is producing spores (Fig. 1B).
Step 4:
About 1 tbsp. of Orbeez (rain drops) are then dropped onto the coffee (spores), from at least 6 in.
above the coffee. The coffee (spores) spreads from the initial “leaf spot” to other portions of the
paper leaf (Fig. 1C).
Clean-up and care:
The paper leaf print will eventually become soggy and need to be replaced. We suggest having
multiple copies on hand. Also, the Orbeez will become coated in coffee after several
simulations, but they are reusable. They can be washed, dried and then stored in a container for
future use. They can also be thrown in the trash, or incorporated into soil. Do not wash them
down the drain.
Suggested question to enhance active learning:
“How can you prevent plant diseases that are spread by water splashing?” Answers include:
 No overhead irrigation (use drip lines)
 Place plants indoors or in greenhouses to prevent spread by natural rainfall
 Buy healthy plants, so the disease is not introduced (exclusion)
 Remove diseased plants or plant parts as soon as spot symptoms are observed
 Use plant cultivars/varieties that have been bred for disease resistance
Other questions that can be posed include:
 What are other methods of disease spread? Examples: wind, humans, insects.
 What is a fungus and fungal spore? Giant Microbes (http://giantmicrobes.com) sells plush
dolls (two sizes) of Penicillium chrysogenum and a plush toy that is a petri dish with
spores of this fungus.
 What is a bacterium and bacterial cell?
 What is a plant disease? And, how is it different from a disorder, such a nutrient
deficiency?
Spore Movement Demonstration, Page 2
Spore Movement Demonstration, Page 3