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Phytophthora infestans strains A2-Blue13 and A1- 6
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Spread of new strains of Phytophthora infestans in England


Name: Phytophthora infestans strains A2-Blue13 and A1- 6

Taxonomic Position:

Chromista : Oomycota : Oomycetes : Pythiales : Pythiaceae

Common Names:

potato late blight


Potato late blight, caused by Phytophthora infestans, is found in nearly all areas of the world where potatoes are grown. It is known as the most devastating disease of potatoes and one of the most devastating plant diseases of any crop. Phytophthora infestans is a heterothallic species with two mating types designated as A1 and A2. When both mating types are present sexual reproduction can occur leading to increased genetic variation from recombination and the formation long lived oospores. In North America both the A1 and A2 mating types are present.

A new strain of the A2 mating type, A2-Blue13, was found near Ipswich, England, in 2005 where prevalence is now almost 80 percent and has been recorded as some of the worst known potato blight (Abel, 2009). The A2 mating type, rare in the United Kingdom until 2005, is now dominant (Abel, 2009; Bretaña, 2008). In the UK, A2-Blue13 causes larger blight lesions and produces spores faster than other strains. In addition, A2-Blue13 can produce spores at lower temperatures,and has a shorter latent period (Abel, 2009; Bretaña, 2008). Growers are finding that some previously resistant varieties of potato are susceptible to the new strain, and some of their commonly used blight fungicides are not effective (Sárvári Research Trust, 2009; Sykes, 2008).

Also in England, a dominant strain of the A1 mating type is surfacing (Potato Council Ltd., 2009). This strain is called A1-6 or Pink 6. Potato researchers in the area report that regional differences in population diversity are no longer observed as strains like A2-Blue13 and A1- 6 continue to dominate. Use of clean planting stock and research aimed at resistance management strategies is critical to better control outbreaks.



Abel, C. 2009. New blight strain demands extra vigilance. Farmers Weekly Interactive. Last accessed April 9, 2009: [Also reported by ProMED-mail ( titled “Late Blight, Potato – United Kingdom, Bangladesh”, published online April 06, 2009]

Bretaña, G. 2008. Blight resistance - top of mind for potato growers. Argenpapa. Last accessed April 9, 2009,

Potato Council Ltd. 2009. Growers adviced to keep tight control on blight. Global Potato News. Last accessed April 10, 2009,

Sárvári Research Trust. 2009. Know Your Enemy - Blight. Last accessed April 9, 2009,

Sykes, L. 2008. Rethink needed on control tactics. Pages 30-31 in Farmers Weekly Academy.

Warning: The information in this alert has not been confirmed with the appropriate National Plant Protection Organization and is provided solely as an early warning. Please use the above information with caution.

Phytosanitary Alert System
Pest Alert
Prepared on: 04/16/2009
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