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Title: Occurrence of Late Blight caused by Phytophthora infestans on Potato and Tomato in Alaska

Author
item Winton, Loretta
item LEINER, R - UNIVERSITY OF ALASKA
item Krohn, Andrew
item Deahl, Kenneth

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2007
Publication Date: 5/20/2007
Citation: Winton, L.M., Leiner, R.H., Krohn, A.L., Deahl, K.L. 2007. Occurrence of Late Blight caused by Phytophthora infestans on Potato and Tomato in Alaska. Plant Disease. 91:634.

Interpretive Summary: Potato late blight, the disease which caused the Irish potato famine, is a recent, sporadic problem for commercial growers in Alaska. Since the 1930’s potato has been the main vegetable crop produced in Alaska, however late blight outbreaks have occurred only recently in 1995, 1998, and 2005. The more recent outbreaks in 1998 and 2005 were caused by the same genotype of the pathogen and resulted in significant economic impact. In the 2005 outbreak, disease was found in 10 commercial potato fields and greenhouse tomato at two locations. Isolates of the pathogen were found to be resistant to a fungicide commonly used to control disease. This information will be used by extension agents and growers who should be aware that late blight can gain entry into Alaska via retailers of table potatoes and tomato starts.

Technical Abstract: Potato late blight, a disease caused by the plant pathogen Phytophthora infestans, is a recent, sporadic problem for commercial growers in Alaska. Since the 1930’s potato has been the main vegetable crop produced in Alaska, however late blight outbreaks have occurred only recently. The 1995 outbreak was caused by the US-7 allozyme genotype of the pathogen. The more recent outbreaks in 1998 and 2005 were caused by the US-11 genotype and resulted in significant economic impact. In the 2005 outbreak, disease was found in 10 commercial potato fields and greenhouse tomato at two locations. Isolates of the pathogen were found to be mating type 1, mitochondrial haplotype IIB, and metalaxyl resistant. This information will be used by extension agents and growers who should be aware that late blight can gain entry into Alaska via retailers of table potatoes and tomato starts.