Science & Technology in Action

4th Edition

Potato Blight


This lesson outlines the life cycle of the potato blight organism, Phytophthora infestans, and outlines the various measures to control infection and improve crop resistance.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

No one knows exactly when or how potatoes first arrived in Ireland. Some claim they were brought by Sir Francis Drake or by Sir Walter Raleigh, both of whom visited Ireland on their return voyages from South America. Historical records refer to potatoes being grown in Co. Down in 1606 and to a toll (tax) on potatoes as early as 1623 in Youghal, Co. Cork. By the middle of the seventeenth century one can find many references to the potato as a source of food for the Irish. This would suggest, that even at that time, the potato was extensively grown in Ireland. This is still the case today.

The Irish potato crop occupies an area of 20,000 ha and was worth in excess of €140m in 2007. There are many different varieties of potato, including Golden Wonder, Kerr’s Pink, Record, Cara and Rooster. Rooster has been the most successful variety on the Irish market. It is very acceptable for boiling, steaming, mashing, roasting, baking, chipping and crisping.

Potatoes are grown by planting tubers in the soil. Shoots grow up above the ground from the tubers, eventually producing leaves and flowers.

This vegetatively propagated crop is subject to attack by viruses, bacteria, and fungi. Of these, late blight, caused by the fungus, Phytophthora infestans (Mont.) de Bary, is the most important.

This lesson will focus on late blight – its structure, significance, classification, life cycle and prevention.

The Search for the Cause of Late Blight Disease
In the mid-nineteenth century late blight disease was a major cause of famine here in Ireland, the effect of which lasted a hundred years. Although potato blight is unlikely to have such devastating effects today, it can still cause significant economic loss. Following the initial outbreak of the disease in 1845 there was a major search to establish the underlying cause. This led to a certain level of scientific controversy; one group maintained that it was due to natural causes such as the weather, while the others took the unpopular view that it was caused by a fungus. The full life cycle of the fungus was eventually unveiled by the German scientist Anton de Bary in the 1860s.

Classification and Structure
Although no longer considered to be a ‘true’ fungus Phytophthora infestans is classified as a eukaryotic Phycomycete which belongs to the class Oomycetes. It is made up of thread-like structures called hyphae that have many nuclei in the cytoplasm. A group of hyphae is known as a mycelium. The species is characterised by having a multi-nucleate mycelium and bi-flagellate motile zoospores.


True or False?

  1. Potatoes were first brought to Ireland from Italy. false
  2. The potato blight was a major cause of famine in Ireland in 1845. true
  3. Potatoes are roots swollen with food. false
  4. A mycelium is a collective term for a group of hyphae. true
  5. Potato blight is not a true fungus. true
  6. P. infestans is an example of a pathogen. true
  7. Sexual reproduction does not occur in potato blight. false
  8. A fungicide makes a fungus grow better. false
  9. It takes 15 years to produce a new variety of potato. true
  10. Resistant varieties of potato are susceptible to attack by blight. false