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United States Department of Agriculture

Agricultural Research Service

Title: The Occurrence of Late Blight in North America

Authors
item Deahl, Kenneth
item Jones, Richard

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 16, 1999
Publication Date: N/A

Interpretive Summary: It is now over 150 years since the Irish Potato Famine. Unfortunately, in spite of increased knowledge of the disease and advances in fungicides available for control, late blight continues to be a major constraint to potato production in extensive numbers of diverse environmental areas of North America. Few areas where potatoes are grown are unaffected. New pathogenic forms seem to be present throughout the continent. New molecular techniques have brought to light dramatic changes which have occurred within the fungal population over the last ten years. The dramatic increases in disease severity in North America correspond with great genetic changes in the fungal pathogen. This information will be greatly beneficial to potato farmers and scientists.

Technical Abstract: Late blight, caused by the fungus Phytophthora infestans, remains the greatest threat to the potato crop world-wide. It occurs everywhere potatoes are grown in North America and is especially important in traditional potato-producing areas, e.g. in the semi-arid western regions of the United States. Within the scope of this article, it is only possible to summarize briefly the current status in a rapidly evolving field, but from the data it is apparent that a major genetic upheaval is taking place. The initial evidence was provided by the use of allozyme markers, especially glucose-6-phosphate isomerase and peptidase. Studies using these indicated that the 'old' blight population, designated US-1, was being displaced by new types. A range of other molecular techniques were brought into play. These have included DNA fingerprinting, mitochondrial DNA haplotyping, RAPD's and microsatellites. Analyses with these molecular markers unveiled the primary cause of late blight epidemics to be new immigrant strains of the fungus, most probably from northwestern Mexico.

Last Modified: 11/27/2014
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