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How to Conduct a Visual Comparison

There has been an unexpected outbreak of powdery mildew in local wheat fields. Dr. Colleen Peterson, director of the Lawrence County Farming Agency, has asked you to analyze some samples she has collected. You will need to conduct a visual comparison of the unknown powdery mildew sample Dr. Peterson collected and known types of powdery mildew. Dr. Peterson has asked you to not only identify the sample, but to submit a justification for your findings.

The following step-by-step will guide you as you do your work.

1. Meet with your team and prepare to complete the task.
   
1. Together with your teammates, review the email from Dr. Peterson. Make sure you understand what you are being asked to do. You may find it helpful to print the email and highlight important instructions.
   
   
2. Download the email attachments. During this task you will need:
   1. Unknown Sample - Conidia
      
      
   2. Unknown Sample - Conidiophore
      
      
   3. Visual Comparison Template
      
      
3. Contact your mentor with any questions about your team assignment.
   
   
2. Organize your team to complete the task.
   
   1. Each time you are assigned a task, it is up to your team to develop a plan for completing it. You may want to use the strategy of "divide and conquer" so that team members split up the work, or you may want to help each other cover the same ground. If you decide to divide the work, it is important for you to meet regularly to touch base on your progress and share the information you have found. Regardless of how you decide to break up the work, each team will need to submit a single, unified document to the mentor for review.
   
   
   2. For help organizing your team, review the Teamwork resources in the General Skills Resources section of this rotation.
      
      
3. Conduct the visual comparison.
   
   1. Review your sample and describe its structure in the appropriate columns on the template.
      In the first column, describe the conidia of your structure. What do they look like? Are they a single cell or a chain of cells?
      
      
   2. Compare the unknown samples to the diagrams depicting Powdery Mildew located on the Resources page. Review the conidia of each genera of fungus.
      
      
   3. On the template, describe the conidia you see in each of the diagrams. As part of your description note whether it looks similar to or different from the conidia in your unknown sample.
      
      
   4. Determine which sample diagram most closely resembles your unknown sample.
      
      
   5. You will want to refer to the Fungi FAQ and the resources on powdery mildew, located on the Resource page, for more information on these structures.
      
      
   6. Consider the typical host range for each genus. (Consult the resource material to learn more about the concept of host range.) Does your finding fall within an expected host range for wheat? If not can you explain the atypical finding?
      
      
      • You will find it helpful to review the information on genetic mutation and resistance located on the Resource page of this task.
        
        
4. Together with your team, write a justification of your findings.
   In the findings section of the template, write at least one detailed paragraph justifying your decision. In your answer you should:
   • Detail which genus of powdery mildew you believe to be affecting the local wheat crop.
     
     
   • Describe the visual findings that justify your decision.
     
     
   • Discuss issues related to the host range of the powdery mildew you identify. Specifically consider:
     
     
     • Whether or not wheat falls into the typical host range for your finding.
       
       
     • If necessary, how you justify an atypical host range finding.
       
       
5. Review your work. Make sure your final document is well edited, cohesive and represents the work of all team members.
   
   
6. Submit your work. Review the checklist found in the Submit Your Work section of this task and submit the assignment to your mentor.

 

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Note: When referring to a Wikipedia resource, note that while Wikipedia is a valuable resource, unlike some other websites anyone can contribute to or modify the site (whether they're knowledgeable about the topic or not). As a result, the site is subject to constant change by questionable sources. Be sure to cross-check information on Wikipedia with other reputable sites to ensure accuracy.

Visual Comparison Samples

Arthrocladiella

Blumeria

Golovinomyces

Leveillula

Neoerysiphe

Pleochaeta

Podosphaera

FAQs

Fungi FAQ
This document will help you understand what fungi are and how some of them cause important plant diseases that reduce crop yields.

Resistance FAQ
This document addresses your questions about how genetic resistance comes about, and how we can improve crop plants by making them resistant to fungi and other pathogens.

Powdery Mildew - General Information

Powdery Mildew -Lancaster County Extension
This link offers overview information on powdery mildew, including favorable conditions for its growth and preventative techniques.

Plant Disease Facts: Powdery Mildew
This link is a straightforward explanation of powdery mildew. Be sure to click on the links under "Symptoms" to access pop-up photos of disease symptoms.

Powdery Mildew - Colorado State University
This link also describes the symptoms as found in other resources links presented here, but this link has specific information on plants with a resistance to powdery mildew as well as special facts about powdery mildew, like it being host range specific.

Powdery Mildew Fact Sheet- Cornell University
This link offers information on powdery mildew, including how it can be identified on plants, how it is spread and typical strategies for controlling powdery mildew.

Powdery Mildew - Wheat Information

Wheat Powdery Mildew - Virginia Tech
This link offers a brief description of Powdery mildew. It also includes pictures depicting what powdery mildew looks like on wheat.

Powdery Mildew of Wheat Fact Sheet - Ohio State University
This link includes information on the symptoms, disease cycle and controls of the kind of powdery mildew that typically affects wheat.

Role of Wheat in the World's Food Production

http://www.worldbank.org/html/cgiar/press/wheat3.html
This resource from the World Bank details the importance of wheat. The article includes information on who is consuming wheat and how wheat has been modified to make it a more productive crop.

http://en.wikipedia.org/wiki/Wheat
This link offers a comprehensive overview of wheat, including information on breeding, production and consumption.

Ask the Expert

How does a fungus hurt wheat?