Part 2 Quiz

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This quiz will test your knowledge of the causes of seedling disease in soybean diversity, pathogenicity, and virulence.

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Question 1 of 15

1. Question
A seedling disease infects plants in one part of a soybean field. The organism responsible for this disease is…
- Phythophthora sojae
- Could be a number of Pythium species
- Rhizochtonia or Fusarium
- Could be any of the above.
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Hint

Hint: check out this reference
http://www.extension.umn.edu/agriculture/crop-diseases/soybean/soybeandisease.html
Question 2 of 15

2. Question
How could the species of organism causing the seedling disease observed above be identified?
- The organism responsible can be identified by close examination with the naked eye.
- A microscope taken to the field will be needed to identify the microbe causing the disease.
- The samples of diseased plants are taken to the lab, the organisms living on the plant cultured and DNA-based analysis can reveal the species.
- The above steps except the cultured organisms can be IDed based on how they appear in culture.
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Hint

Hint: Seedlings with the same disease symptoms can be caused by different microorganisms
Question 3 of 15

3. Question
Soybean plants showing seedling disease symptoms are sampled from locations shown above in 2011 and in 2012. Microorganisms are cultured from these samples with methods that promote Pyithium and Phytophthora growth. Hundreds of these cultures are analyzed by sequencing their DNA. How many different species will be cultured and identified?
- Two species
- Between 50 and 100 species
- Between 500 and 1000 species
- Over 1000 species
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Hint

HINT: Oomycetes form a community in the soil ecosystems.
Question 4 of 15

4. Question
The frequencies of the 30 most common oomycete species observed in the 2011 and 2012 growing seasons are shown in the figure above. Which statement below is NOT supported by this data?
- Pythium sylverticum was the most frequently sampled species in both years.
- Phytophthora sojae is the most abundant disease causing oomycete in both years.
- Numerous oomycete species are sampled in both years.
- When culturing methods are used that promote Phytophthora growth from these samples more than Pythium, the frequency of Phytophthora detection increases
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Hint

HINT: This figure provides information on both occurrence and abundence
Question 5 of 15

5. Question
What does the seed rot assay reveal about an oomycete species?
- Can the species infect the soybean seeds and cause disease under environmental conditions that promote healthy seeds to germinate?
- Does the severity of infection vary between species of Pythium?
- Both of the above
- None of the above
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Hint

HINT: Observe the range of seed health in these four germination plates
Question 6 of 15

6. Question
The best conclusion from the results of this seed rot assay is…
- Pythium species are not able to cause seed rot disease (not pathogenic)
- Pythium ultimum var. ultimatum is pathogenic but Pythium oopapillum is not.
- Pythium ultimum var. ultimatum is more virulent than Pythiumythium oopapillum
- Pythium irregular is pathogenic but not as virulent as Pythium oopapillum.
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Hint

Hint: What is the difference between pathogenic and virulent?
Question 7 of 15

7. Question
Which choice best ranks these oomycetes based on severity of disease?
- Pythium ultimum var. ultimatum is highest, then Pythium sylvaticum then Phytophthora sojae.
- Pythium ultimum var. sporangierum is highest, then Pythium oopapillum then Phytophthora sojae.
- Pythium ultimum var. ultimatum is highest, then Pythium oopapillum, then Pythium attrantheridium.
- All of the above show correct rankings based on the observations in the figure.
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Hint

Hint: Come up with a virulence scale based on visual comparisons.
Question 8 of 15

8. Question
Which statement below is the best conclusion based on the figure above.
- All Pythium have the same pathogenicity, or ability to cause the seed rot disease.
- The variety of soybean used had a resistance gene to prevent seed rot.
- The specific species of oomycete living in soil environment will make a big difference on the occurence of seed rot disease
- Seed rot will not tend to be a problem for farmers who have a variety of oomycete species in their soils.
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Hint

Hint: Compare these choices with the visual data
Question 9 of 15

9. Question
What is the best conclusion from the results of the seedling pathogenicity assays?
- Both Phytophthora and Pythium can cause seedling disease that stops or slows seedling development.
- Phytophothora but not Pythium can cause seedling disease.
- Pythium but not Phytophothora can cause seedling disease.
- Seedling disease caused by oomycete will not be a problem for soybean farmers compared with seed rot disease caused by oomycete.
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Hint

Hint: Justify the correct choice based on the visual data
Question 10 of 15

10. Question
Assume the assay shown above was repeated at a cooler temperature. Under those conditions, we would expect the seedlings living with Phytophthora sojae to look like…
- Pythium irregulare
- Pythium ultimatum var. sporangiferum.
- Pythium sylvaticum
- The control
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Hint

Hint: You need to know the results of the temperature impact experiment
Question 11 of 15

11. Question
The table above shows the seed rot disease severity (Y axis) for many different species of oomycetes (X axis). The disease severity assay was conducted at cooler (blue) and warmer (red) conditions. Which conclusion is best supported by this data?
- Disease severity is worse in cooler than in warmer temperatures.
- Disease severity is worse in warmer than in cooler temperatures.
- Disease severity response to temperature varies much among the different species.
- Disease severity is generally not responding to the change in temperature.
Correct

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Hint

Hint: Carefully compare and contrast the the temperature impact.
Question 12 of 15

12. Question
Which is the best statement that compares the seed rot severity caused by the species designated with the red, green and blue arrows?
- All three have more disease severity at higher temperatures.
- The species designated with the green arrow has higher severity with cooler temps which contrasts with the response of the red and blue arrow species.
- A farmer would rather have the blue arrow species in their field than the red arrow species.
- None of the above statements are supported by the data.
Correct

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Hint

Hint: Carefully compare and contrast the the temperature impact.
Question 13 of 15

13. Question
Assume that a farmer has in their field, several of the Pythium species from the group in the blue box from the graph above. They also have Phytophthora (red arrow). What should they expect to observe when they grow soybeans?
- They will observe reduced stand counts from seed rots in most years from the wetter parts of the field.
- Under low temperature springs, they will see almost no seed rot but will in warmer springs.
- If they use a seed treatment that works against Phythophthora (red arrow) they will avoid seed rot disease.
- ALL of the above would be expected.
Correct

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Hint

Hint: The species are arranged by disease severity
Question 14 of 15

14. Question
A farmer has numerous oomycete species in this part of their field. They could have a stand count reduced as a result of…
- seed rot caused by Phythium
- seedling disease caused by Phythium
- seedling disease caused by Phytophthora
- All of the above could result from the oomycete species in their field.
Correct

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Hint

Hint: Use the data shared in this part of the lesson
Question 15 of 15

15. Question
A reason why a farmer may benefit from knowing which oomycete species are living in their fields is….
- many oomycete species cause seed rot and seedling disease but the severity will vary with the species.
- if they have many species they are likely to get seed rot but not seedling disease
- one specific species causes seed rot and a different species causes seedling disease.
- All of the above are correct statements.
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Hint

Hint: Consider management choices available and remember, they are not all effective across oomycete species.