Link to home

​Chapter 1 Instructor Resources​

The Irish Potato Famine: The Birth of Plant Pathology

The famous Irish potato famine of the 1840s led to the first proof that an organism could cause a plant disease (late blight of potato), predating even Louis Pasteur’s germ theory. It was a time of scientific discoveries as people began to accept that the bacteria, fungi, and other pathogens were not the result of spontaneous generation, but the actual causes of diseases. It also was a time of worldwide movement of plants from their centers of origin to other areas where they could grow and flourish. People began to appreciate that many beneficial aspects of agriculture- monoculture, genetic uniformity, new crops- had their dangers.

  • Teaching Resources

    Teaching Resources​

    Late Blight and the Irish Potato Famine
    Digital Download & DVD available from the American Phytopathological Society

    Feeding the Future: Saving Agricultural Biodiversity
    A CNN Article

  • Chapter 1 Podcast

    Chapter 1 Podcast

    Listen to the Podcast (m​p3)

    The short podcast provided for each chapter includes a review of a major concept or issue, clarification of an important point that can be confusing to students, and questions for students to think about. This podcast uses the 1840s late blight epidemic in Ireland to demonstrate the plant disease triangle and the difference between a pathogen and a disease.

  • Demonstrations & Desktop Lab Exercises

    Demonstrations & Desktop Lab Exercises

    What is a Potato?

    Bring some potatoes to a class, and allow students to examine them to determine their structure and function. The purpose of this exercise is to have students determine that tubers are not roots by studying potatoes carefully. Use guiding questions.

    • Look at the eyes and notice the buds. (This works best with older tubers.)
    • Determine that only a potato piece with an eye (bud) will grow.
    • Determine that a single tuber can be cut up to produce several plants.
    • Note the genetic uniformity that will result.
    • Note that late blight destroys both the food supply and the planting material for the next crop.
    • Provide some white potatoes that have been left near a window for a couple of weeks and have turned green. Students usually know that potatoes should be stored in the dark but not why. Most will think this is to prevent sprouting. (So how do potatoes grow underground?) We don’t eat salads of potato leaves because of the alkaloids, and the same applies to green potatoes.
    • Buds and green photosynthetic tissue are evidence that a tuber is an underground stem, not a root.

    What is a "Water Mold"?

    Oomycota (oomycetes), or “water molds,” especially Saprolegnia spp., are found in almost any relatively clean surface water, such as a pond, lake, or moving stream. They will colonize carbohydrate sources, such as popped popcorn kernels (no butter or salt). Simply drop a few kernels into a jar of water collected from a natural water source. In 3–5 days, a mass of white mycelium will be seen growing on the popcorn. If a microscope is available, pull apart some hyphae on a microscope slide, and cover it with a coverslip. It is easy to observe nonseptate hyphae, zoospores, antheridia, oogonia containing several oospheres, and a variety of bacteria and aquatic protists.

    Grow your Own Fungus

    This exercise also applies to Chapter 2 but is recommended for Chapter 1, so that students have a fungus to look at when Chapter 2 is covered.


    • Water Agar (1 Petri Plate/Student)
    • Parafilm Cut into Strips to Seal Petri Plate
    • Razor Blades or Scalpels (To Cut Sclerotia off Potatoes)
    • Potatoes with Sclerotia of Rhizoctonia Solani (Available in Grocery Stores and Farmers' Markets)


    1. Each student should cut three or four small sclerotia from the surface of the potato tuber and distribute them on the water agar surface. Make shallow cuts. Avoid the underlying white potato tissue, which will support the growth of contaminating fungi and bacteria.
    2. Seal the plate with Parafilm.
    3. Observe the growth of hyphae from the sclerotial pieces for the next several days.


    This is a very easy way to demonstrate hyphal growth to students who are trying to understand how fungi and funguslike organisms grow. The feathery pattern of hyphal growth begins usually within 24 hours because of the radial growth of the hyphae seeking nutrients on the water agar. The water agar is low in nutrients and thus prevents the growth of most contaminants. Rhizoctonia Solani does not produce spores on the water agar, so mold allergies are not a concern.

  • Group Discussion

    Group Discussion

    Where did Important Crops Originate?

    Give small groups of 5–7 students a map showing the origins of some major crops (see following), and ask them to determine the origins of several of their favorite foods. Working in groups, have students determine if their preferences are concentrated in any particular geographical areas. Students also should discuss whether it is possible to make a meal from crops that originated in North America.

    After the group discussions, consider any questions or comments as a whole class. Follow up with a short writing assignment (see next section).

  • Short Writing Assignments

    Short Writing Assignments

    Notes: These assignments require each student to write a paragraph (introductory sentence, body, concluding sentence) and can be completed in 10–15 minutes in class. They provide a good way to check student comprehension and to improve student writing skills. Here is a simple grading system:

    ✓+ Good content and writing

    ✓ Problems with content or writing

    ✓– Problems with both content and writing

    If you use several short writing assignments over the course of the semester, you can reduce the number of grammar/spelling errors that you allow for a score of ✓+ each time.

    1) History & Plant Diseases

    This week, you learned about late blight and the Irish potato famine. Many different lessons can be learned from this historic plant disease epidemic and its consequences. In paragraph form, briefly describe two lessons you have learned from our first story.

    2) Disease Versus Pathogen

    An important concept for beginning plant pathology students to understand is the difference between a disease and a pathogen. In paragraph form, describe the distinction between a plant disease and a plant pathogen. List the three factors necessary for a plant disease to occur, and give a specific example of a plant disease and a plant pathogen that you studied this week.

    3) The Disease Triangle

    The first plant disease you have learned about is late blight, which caused the Irish potato famine in the mid-1800s. The components necessary for this epidemic are often depicted by plant pathologists as the plant disease triangle. Identify the three components of the plant disease triangle, and explain why each is necessary for a plant disease epidemic to occur. What is another component not included in your plant disease triangle that is necessary for some epidemics?

  • Longer Writing Assignments

    Longer Writing Assignments

    1) Where Did Important Crops Originate?

    This assignment follows the group discussion described earlier. Each student leaves with a map of the origins of some major crops.

    Follow-Up Writing Assignment (~350 Words):

    Answer these questions in a short essay (not individual answers to the questions):

    1. Did the origin of any major crop surprise you?
    2. Do the foods you prefer reflect the national origin(s) of your family, or do they mostly reflect the culture in which you grew up?
    3. Why might it be important to know where the major crops originated? (Speculate.)

    2) Media Report or Disease of the Week

    Notes: This Exercise Can Be Used in Various Ways:

    • One way is to have students start doing their reports about the fourth week of the semester, when they have some background. Each student turns in a written report and, if the class is small enough to accommodate this, gives a 5-minute summary report to classmates, so they all hear about additional topics.
    • Instructors can watch for media reports during the year and accumulate possible topics for students to choose from. These can include subjects that are not specifically plant pathology, such as the die-off of bats from a fungal disease.
    • In addition, it is possible to receive e-mail alerts about current disease outbreaks from the International Society for Infectious Diseases. This idea is summarized in a Teaching Note in the APSnet Education Center, but detailed instructions for students follow

    Directions to Students:

    These are the instructions if you signed up for either a media report or a Disease of the Week. This is a way to enrich the course with topics you find interesting. It is also a way for you to practice researching a scientific topic and determining a source’s accuracy and possible bias. When using a website resource, include the title of the site, as well as the URL.

    To prevent duplication and to ensure the selection of appropriate topics, you must have your topic approved at least one week before your presentation. (Do this as soon as possible, so you can be sure someone else does not select your topic.) Feel free to e-mail the instructor with your proposed topic: [insert instructor’s e-mail address]. The instructor may have some additional sources to suggest.

    Here are some sources of possible topics:

    1. American Phytopathol​ogical Society Website
    2. International Society for Infections Diseases - Search for plant types to see what new disease outbreaks are occurring.
    3. US Phytosanitary Alert System
    4. Science News Magazine
    5. EScience News

    You will make a 5- to 10-minute presentation to the class and turn in a written summary 3–4 pages in length. The class presentation should be a summary of your report—not a reading of the whole thing. Five minutes should be adequate to cover the key points, in most cases.

    Follow These Guidelines:

    1. Media Report
      • Find a report related to this course in the news media: a newspaper, news magazine, Internet, and so on. Read the report and summarize it for the class. Explain how the subject relates to the course. Also explain why this particular subject was of interest to you and why it should be of interest to students in this class. Some suggested topics to watch for in the media include loss of biodiversity, food safety, food supply, pesticide use, genetic engineering, and global warming.

        Analyze the report for bias and accuracy. Do not assume that because someone is a scientist, he or she is unbiased. An unbiased article may take a side on an issue but will include a fair appraisal of both sides. Include the source of the original report and at least two other sources related to this subject that you used to evaluate the content. These should be reliable, science-based sources, such as APS websites and journals, other scientific journals, and science magazines. List the questions and concerns you have related to the information. In the early weeks of the class, you are likely to have more questions than answers and opinions. Try to use the information learned in this course to speculate on possible answers/solutions.

        Your class report will be short, but your written report should demonstrate that you have learned about this topic and developed a science-based opinion on its controversial aspects.

        Evaluation of Media Report: 45 pts

        Presentation to class: clarity, accuracy, reason for interest10 pts
        Written Summary:
        Appropriate information sources5 pts
        Accurate Information about Subject10 pts
        Writing quality (includes correct grammar and spelling, correct use of scientific names: uppercase for first letter of genus, all lowercase for specific epithet; italics for name)5 pts
        Questions listed that were not answered by source5 pts
        Analysis of accuracy and/or bias of information (two other sources)5 pts
        Complete citations of sources5 pts
        Total: 45 pts

        Note: Please read your report and make sure it includes all of these elements before turning it in. If one of them is missing, you will not get the points for it.

    2. Disease of the Week
      • See the Internet resources listed in the syllabus and earlier in this section to find and research a plant disease. Choose a disease that has not been discussed in detail in class. Explain why the disease was of interest to you and why it should be of interest to students in this class. Try to determine the following:

      1. The significance of the disease
      2. The type of pathogen (e.g., bacterium, fungus, nematode, virus), its scientific name (uppercase for first letter of genus, all lowercase for specific epithet, italics), and some details about its biology (e.g., how does it spread? how does it survive when the plant is not around, as in winter?)
      3. What kinds of plants are affected (one species, many species)
      4. Where the disease is a problem (worldwide, North America, only in Wisconsin, only in New York etc.)
      5. What can be done to manage or prevent the disease (chemical or biological controls, genetic resistance, cultural practices such as irrigation or crop rotation)
      • List questions that come to mind as you try to find information about the disease. Use at least two sources (and cite them) for information on the disease. Also note if there is conflicting information between sources and how you determined which source was more accurate.

        Evaluation of Disease of the Week: 45 pts.

        Presentation to class: clarity, accuracy, reason for interest10 pts
        Written Summary:
        Appropriate information sources5 pts
        Accurate Information about Subject10 pts
        Writing Quality (includes grammar, spelling)5 pts
        Questions listed that were not answered by source5 pts
        Analysis for conflicting information and resolution5 pts
        Complete citations of resources5 pts
        Total: 45 pts

        Note: Please read your report and make sure that it includes all of these elements before turning it in. If one of them is missing, you will not get the points for it.

    3) Analysis of a Book Related to the Course

    Example: The Omnivore's Dilemma, by Michael Pollan


    • Many curricula emphasize critical thinking as an important component of core courses. It is very important in science courses, because students read media reports and websites every day that might look authoritative but are inaccurate.
    • The analysis of The Omnivore’s Dilemma has led to many interesting discussions. It will be helpful for instructors to prepare a set of questions for students to investigate in their assigned sections to help them identify where inaccuracies and/or bias occur. This book is particularly easy to use, because it is divided into three sections. The entire class can be assigned to write a short response to each section and one longer response at the end. This will encourage all students to engage in the weekly book discussions.
    • The last question on the last writing assignment asks students if they would recommend the book to their friends. Many students have said they would—but with the warning that they should not believe everything they read in it! A number of students have asked how a book can be published if some of the information it contains is not true.

    a) Book Chapter Discussions

    • Directions to Students:

      If you signed up to lead a book section discussion, you will work with a partner. Together, you will use the guidelines to prepare a 10-minute class discussion. The purposes of this discussion are to help the class focus on the key points, detect bias or inaccuracy, determine if there is missing or incomplete information, and compare the content of the reading to content in the textbook or other sources.

      All students will be writing on the three larger sections of The Omnivore’s Dilemma, so these discussions should help them prepare for those assignments. Your job is to stimulate thinking and discussion as the class moves through each section. It is expected that all students will have read the section at the time of the discussion, so they should be ready to respond to your queries and opinions.

      You will need to read your section in more detail and sometimes ahead of the class to be prepared for your discussion. You also should leave enough time to meet with your partner to discuss the section and prepare your presentation. Feel free to consult with the instructor if you have questions.

      Here are some items to consider for discussion:

      1. What are the most important points in your section of the book? (Keep this brief.)
      2. What information confused you or left you with questions?
      3. What are facts versus opinions? Do you agree or disagree with the opinions?
      4. What, if any, examples of inaccuracy or bias did you find?

      You will also be given some specific questions to consider for each section of The Omnivore’s Dilemma after you sign up. You will not have time in class discussions to go over all of these questions, but choose the ones you think will be most helpful to the class in understanding the section. Some of these questions were chosen because they point out inaccuracies in the book. Please research these issues to determine the correct answers. Each partner also will write his or her own more detailed response to the book section (3–4 pages).

      Evaulation of Book Analysis: 45 pts.

      Presentation of Material for Class Discussion
      Queries and opinions to provoke responses 5 pts
      Presentation of key points5 pts
      Identification of bias, missing information, opinions in reading5 pts
      Written Response:
      Summary of key points10 pts
      Writing Quality (grammar, spelling)5 pts
      Detailed discussion of bias or opinions in reading5 pts
      Answers to questions provided by instructor10 pts
      Total: 45 pts

    • b) Class Papers on Book Sections

      • Section I - Industrial/Corn (Chapter 1-7)

        This section of the book covers what the author calls “industrial” agriculture based primarily on corn (and soybeans). In your discussion, consider these questions:

        1. We are dependent on corn. How is corn dependent on us?
        2. How have corn yields grown in the last century? What energy inputs are required to obtain these yields? Is this sustainable? Can it be made sustainable? Where does ethanol production from corn for energy fit into this?
        3. “The free market has never worked in agriculture and it never will.” Do you agree or disagree with this statement? Consider both biological and economic reasons.
        4. After reading this section of the book, do you look at many common U.S. food products differently? If so, what particular aspects are of most interest/concern to you? If “fat is fat” and “protein is protein,” does it matter if you are eating a taco or a Twinkie?

        Section II - Pastoral/Grass (Chapter 8-14)

        This section of the book covers what the author calls “big organic” agriculture, as well as pasture-based, small farm agriculture. In your discussion, consider these questions:

        1. In what ways are “big organic” and “industrial” agriculture similar?
        2. What advantages and limitations do you see in local, small farm agriculture and pasture-based agriculture, in particular? Consider energy issues, food quality, distribution, ability to produce on a large scale, safety, etc.
        3. Was it possible for midwestern people to have a healthy winter diet before long-distance food distribution became the norm? What kinds of things did they eat, and how did they preserve these foods?
        4. Is it important to support local farmers? Would your eating habits have to change if you supported local farmers? Would you prefer to support organic farmers (as defined by the federal regulations—i.e., no synthetic chemicals or fertilizers and strictly organic feed for animals)? Or might it be better to encourage farmers who choose ecologically based practices using the most benign chemicals (fungicides, herbicides, insecticides—whether synthetic or not)? Would it be better to eat organic foods (which may be produced many hundreds of miles away) or locally produced foods (which may not be organic)?

        Section III - Personal/The Forest (Chapter 15-20) and Conclusions

        This section of the book describes the author’s attempt to return to hunting and gathering for food. In your discussion, consider these questions:

        1. The author suggests that both the first meal in the book—the industrial agriculture meal—and the last meal in the book—the hunter-gatherer meal—are unsustainable. Do you agree? Why?
        2. How have your views about food changed after reading and discussing this book?
        3. What changes would you like to see in American agriculture? Should we return to a U.S.-based agriculture completely, partially, or only if we can compete with the costs of importing food from other countries? What are the political, economic, and safety implications of relying on other countries for our food supply?
        4. How should we create sustainable agriculture? The following statement is printed on the grocery bags from Whole Foods: “We actively support organic farming—the best method for promoting sustainable agriculture and protecting the environment and farm workers.” See this website for a detailed statement on sustainable agriculture from the University of California. Read also Chapter 14 in the textbook.
        5. Consider some different kinds of agriculture in your answer—for example:
          • Would it be more efficient to grow our large field crops (e.g., corn, wheat) using herbicides (to reduce tillage) to preserve topsoil and synthetic fertilizers because of the difficulties of delivering large amounts of organic fertilizers to those large fields?
          • Should we use biodegradable, low toxicity synthetic fungicides to produce abundant, affordable fruits and vegetables?
          • Should we use genetic resistance as our preferred line of defense again pests and pathogens? If so, what do we need to do to preserve biodiversity?
          • hould we use modern tools to move genes along with traditional breeding?
        6. Would you recommend this book to your friends?