Note: These experiments are very basic. For more experiments and in-depth exercises check out the Lessons and Laboratories in Plant Pathology.
Recognition of healthy and diseased plants is important. It is also essential to know the difference between a sign and a symptom
The objective of this exercise is to find some plant diseases. The first step in this process is to familiarize yourself with diseased plants that may be in your area. Look online or in a plant disease book beforehand to find some possible plant diseases that may be in your area. Pictures can be saved for reference later.
Materials needed: pen or pencil, paper, and a 10X hand lens or magnifying glass. (Hand lenses can be found at bookstores or online.)
Procedure: Now go outside and begin walking around, whether it is in your backyard, a field, or a park. Look at the plants around you from the grass on the ground to the trees in the sky. Begin by looking at healthy plants. It is important to know what a healthy plant looks like to help determine when you have a sick one. Once you have found a healthy plant look for one that is out of the ordinary, such as one that is wilted or has yellowing leaves. Wilting can be associated with the plant’s inability to move water in the vascular system (xylem). Note the differences between the healthy and sick plants. Be sure to examine many different plant types. As you study these plants, list 5 symptoms you observed and 5 signs you examined. If you have a hand lens, look very closely at the plant specimen (maybe a leaf or stem). You may be able to see fruiting bodies and if you see fruiting bodies then you may have found a sign of the disease.
Over the next few days note in your journal any changes with the diseased plants that you saw on your walk. Ask yourself some questions. “Have they changed in color or shape?” “What do you think the cause of the sickness is?” “Is it related to weather, such as being too cold or too hot?” “Is only one plant sick or many plants?” Be sure to also take pictures throughout the exercise to help show what the plant looked like when you first saw it and what it looked like a few weeks later.
Signs and Symptoms Point the Way
Plant Parts and Their Diseases
The most difficult challenge in diagnosing the cause of a sick plant is not deciding which pathogen is responsible for the disorder, but rather whether the disorder is abiotic or biotic. In cases where no evidence of a pathogen is found, most plant pathologists assume the disorder to be caused by an abiotic factor if the symptoms and conditions fit. This exercise will focus on the impact of light versus shade.
Materials needed: 4 Styrofoam or plastic pots or cups, 10 corn seeds, 10 soybean seeds, 4 labels, potting soil and a large plastic container (dark in color) or cardboard box. If you do not have corn or soybean seeds, cucumber or pea seeds work great too.
First, poke holes in the bottom of the plastic pots/cups for drainage purposes. (Figure 1)
Then fill each pot with potting soil leaving about ½ inch of space at the top of the pot (Figure 2).
Plant five seeds per pot (two pots with five corn seeds each and two pots with five soybean seeds each) (Figure 3).
Label the pots as follows: 1- corn light, 2- corn dark; 3- soybeans light, 4- soybeans dark (Figure 4). Include the date on each label.
Place the two pots for light on a windowsill or in a place where there is direct sunlight (Figure 5). Place the two pots labeled dark in the same area but with the plastic container/box covering them to block the sunlight (Figure 6).
Water the plants as needed. Be sure to have something under the pots to collect the extra water the plants do not absorb.
Write in your journal how you think the dark plants will differ from the plants in the sunlight.
Observe your plants twice a week for two weeks. Measure and record the plant height and color and any other data you believe would be useful at determining the role of light on plant growth. At the end of the initial two-week period, move the dark plants to the same location as your light plants (remove the plastic container/box) and continue making observations for an additional week. Record your observations and conclusions regarding the influence of light on plant health.
Plants need water and are actually made up of 70% water. Plant roots pick up or absorb water and transport it to the stems and leaves. When plants are watered too much, they will become weak. If plants are not watered enough, they will wilt and dry up. This is why it is essential that plants receive the proper amount of water.
Materials needed: One small clay flower pot (4 inches in diameter) with holes in the bottom, planter box or 9 in. x 12 in. baking pan, potting soil, lima beans, string, one paper towel, and water.
Fold the paper towel and place it in the bottom of the clay flowerpot. This will help to reduce the flow of water out of the pot.
Place the clay flowerpot in the corner of the planter box or baking pan (Figure 7). The clay flowerpot will be empty but fill the rest of the box/pan with around 2 inches of tightly packed potting soil (Figure 8).
With the string mark off four rows with the first being very close to the clay pot. Each additional string will be around 3 inches apart from one another (Figure 9).
Plant the first row of seeds very close to the clay pot by pushing the seed with your finger into the soil. Plant each additional row between the string lines (Figure 10).
Now fill the clay pot with water. Do NOT water the potting soil (Figure 11). Keep the clay pot filled with water so that the soil next to the pot is moist.
Predict what will happen by taking notes in your journal. Ask yourself a few questions. “Which row of seeds will grow and which will not?” “Why is this?” Take pictures and keep a record in your journal of what happens each day for the next few weeks.
Pathogens are everywhere! They are in places that you would never guess. Because we cannot see most pathogens without a hand lens or microscope, we often think there is nothing to worry about. This is not the case. Just look at your local grocery store.
Materials needed: pen and pencil, paper, and a hand lens or magnifying glass.
Procedure: This exercise will be much like the disease plant walk you did outside. Go to your local grocery store and head towards the produce section. Examine the different fruits and vegetables and look for symptoms and signs of disease.
Record your observations, but also think of the big picture. What are some things that you do not see? You didn’t get to see how this food was grown in the field, who handled it, how it was shipped there, or where it came from. Most of the diseases you get on your produce are from cross-contamination from being handled by workers who have handled many different types of produce. There may be a vegetable that comes into the grocery that is healthy, but if a worker or other shoppers that have handled diseased produce handle it, then contamination occurs. This is why it is important to thoroughly wash all produce you get at the grocery store.
Note in your journal any observations and also take pictures of your trip to the grocery store. Visit this website to gain information on food safety practices: http://www.fightbac.org.
Vegetables and fruits are often wounded during harvesting, transportation, and storing processes. These wounds are entry points for bacteria or fungi that cause soft-rot. Soft rot bacteria and fungi cause plant cells to “slide apart” causing a soft, mushy feeling and often a strong, unpleasant odor. The goal of this exercise is to determine the role of the environment in the development of bacterial soft rot.
Materials needed (adult supervision): one carrot, one potato, one cucumber, water, paper towels, one paring knife, six one gallon Zip-lock bags, and an electric fan.
Procedure: Cut each of the vegetables into six separate pieces. Place one piece of each vegetable (cut side up if possible) into each bag so that you have one carrot, one potato, and one cucumber section in each bag. Then dampen a paper towel and place one in each bag. Seal three of the bags and leave the other three open. Place one open bag and one closed bag on the kitchen counter at room temperature. Put one open bag and one closed bag in the refrigerator. Place the last open and closed bags on a counter or in another location at room temperature and place a fan in from of the bag so air is blown across the vegetables. Write in your journal your thoughts on which vegetables will rot the least. Those on the counter, in the refrigerator, or in front of the fan? What impact will sealing the bags have on soft rot?
Over the next 7 days, observe your vegetables and take notes in your journal. Use the following rating scale to show the amount of soft rot observed, in which 1= no rot and 5= complete rot. Display your results in a graph showing the amount of rot (vertical axis of graph) and time (horizontal axis of graph). List any characteristics you see. Ask yourself these questions: “What happened to each bag of vegetables?” “What do they look like?” “What could you do to help prevent soft rot?” Determine what the best storage conditions are for preventing bacterial soft rot and come to a conclusion. Take pictures when setting up the exercise and when rating the results.
The American Phytopathological Society: http://www.apsnet.org
APS Education Center: http://publish.apsnet.org/edcenter/Pages/
The Microbiology Information Portal: http://www.microbes.info
United States Department of Agriculture- Animal and Plant Health Inspection Service (APHIS): http://www.ars.usda.gov
Introduction to Plant Diseases Fact Sheet Series: http://ohioline.osu.edu/hyg-fact/3000/index.html
For voice-overlaid PowerPoint files on plant pathology that are downloadable to your MP3 player, I-Pod, or computer, visit:
Introduction to Plant Pathology
What is Plant Pathology?
Plants Get Sick Too! a brief video introducing plant diseases and plant pathology, http://www.youtube.com/watch?v=VzvIuhiPkc8