APSnet Image of the Week

Potato tubers displaying symptoms of potato late blight (Phytophthore infestans).

Sporangia and zoospores of P. infestans germinate and infect potato leaves causing necrotic lesions and collapse of leaves.

Click here to see a series of images portraying germination of the sporangia and zoospores of P. infestans.

Photographs courtesy Forrest W. Nutter, Jr.
Department of  Plant Pathology
Iowa State University, Ames 50011

Additional Information: It is hard to believe that such a small organism (Phytophthore infestans) was responsible for the "Great Potato Famine" that occurred in Ireland in 1845. This fungal pathogen of potato was responsible for the starvation of approximately 1 million of the 8.3 million Irish population as well as the emigration of an additional 1.5 million Irish peasants, mostly to the North American continent. The epidemic that occurred in the United Kingdom in the 1840's resulted in the repeal of protectionist trade laws that prevented the import of cheaper grain and the establishment of the first "work for food" welfare system in the United Kingdom. This fungus continues to wreak havoc, even today, as a new mating type required for sexual mating has been introduced into Europe and North America.

APS publication number:  IW00009

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