Set by Phil Taylor (CABI).
It will soon be time for those of us in the UK to start planting potatoes. There are certain aspects of potato production that are unique and others that relate to root crops in general. This quiz is centred around the pathogens and pests of potato.
#1. This is the symptom of tobacco rattle virus on a peeled potato. Viruses are a common pathogen of potato; what can be done to remove a virus from a potato that you are about to plant?
The correct answer is:
None of the above will work.
Once a tuber is infected with a virus it is not possible to rid the potato tuber of the virus; a virus infected plant will develop. Note; it is unusual to see symptoms of a virus in the tubers.
Photo credit; Whitney Cranshaw, Colorado State University, Bugwood.org
#2. Traditionally potatoes are ridged up (or earthed up) which means that the soil is raised near the developing plant. Why is this done?
The correct answer is:
All of the answers are correct.
It prevents spores of late blight dripping onto the tubers and prevents light from turning the potatoes green, it extends the stems from which the potatoes develop, and it also protects from frost and allows the soil to warm up quickly.
#3. PVX is a virus of potato that is common but often not extremely damaging. Under what circumstances can it be very damaging? Photo shows PVX particles as viewed under a scanning electron microscope.
The correct answer is:
When co-infected with another virus
All of the stresses mentioned will not help the situation but when PVX is part of a viral complex infecting the plant, the symptoms are often much more severe than either virus in isolation.
Photo credit: D.-E. Lesemann creative commons.
#4. Meristem culture is a technique used by those in the seed industry to do what?
The correct answer is:
Remove viruses from the planting material
The tiny bundle of cells at the very tip of the plant is the only area that remains free of virus. The removal, sterilisation and then growth (on nutrient media) of the tips is the only way to eradicate viruses from potatoes. The small plants are multiplied in the field many times before being sold as ware potatoes.
#5. What is this disease?
The correct answer is:
Potato wart disease:
These dramatic symptoms are due to Synchytrium endobioticum a chytrid fungus. It is seldom seen as it is a notifiable disease in many countries and it is illegal to grow potatoes on infected land. Believe it or not these symptoms are mild compared to some infections.
Photo credit: Central Science Laboratory, Harpenden, Bugwood.org
#6. These symptoms are caused by Alternaria solani and the disease is often referred to as “Early blight”. How can the symptoms be distinguished from late blight?
The correct answer is:
Small discrete spots with no yellowing around the necrosis:
In this case there is a clear line between the healthy and the diseased tissue, the spots do not appear to be spreading rapidly and there is almost no yellowing. All these symptoms (along with the concentric circles within the spots which cannot be seen here) are indicative of early blight.
Photo credit: Howard F. Schwartz, Colorado State University, Bugwood.org
#7. Rust mite damage is an unusual symptom of potato and does not occur in many areas? Why are rust mites so often misdiagnosed?
The correct answer is:
The mites are so tiny they cannot be seen.
Most pests can be seen with the naked eye or at least with a hand lens. Inspection of plants infested with rust mites will reveal nothing, often leading to a misdiagnosis.
#8. This photo show ozone damage on a potato leaf. Which leaves are most likely to show damage by ozone?
The correct answer is:
Older leaves
In all crops it is the older leaves that show symptoms of ozone toxicity. The most susceptible crops are beans although potatoes are mildly susceptible. Note how clearly defined and lifeless the spots appear indicating an abiotic cause.
Photo credit: Gerald Holmes, Strawberry Centre, Cal Poly San Luis Obispo, Bugwood.org
#9. Contrast the yield from the infected plant with the healthy on the right. What kind of problem would cause these symptoms.
The correct answer is:
Viral infection
These are the symptoms of Potato spindle tuber viroid (PSTVd). A viroid is effectively a virus that does not have a protein coat and survives as naked nucleic acid. It is spread via mechanical transmission on tractor wheels and trousers. It can be spread by aphids but only when plants are also infected with Potato leaf roll virus (PLRV).
Photo credit: European and Mediterranean Plant Protection Organization , Bugwood.org
#10. Few plant diseases are caused by Actinomycetes, but Common scab caused by Streptomyces scabiei is a good example. 3-6 weeks after tuber initiation is a critical period in the development of this disease. What should be done to control this disease at this stage?
The correct answer is:
Keep the developing tubers moist.
There are few examples where keeping the plant wet will prevent disease, but this is one of them. Crops should be irrigated at this critical period if there is insufficient rainfall to keep the surface of the tuber moist.
Results
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
