Blight surveys in Scotland suggest the aggressive A2 mating strain, which is more difficult to control, is decreasing in frequency, in contrast to England and the rest of Europe.
Testing of 500 isolates collected from 51 farms and 31 gardens and allotments between 1995 and 1997 found 19% A2 isolates, which are formed by sexual recombination, says SCRI’s David Cooke.
But similar surveys in 2003 and 2004 found less than 2% A2 isolates.
“This is good news for Scottish growers,” says Mr Cooke.
The opposite has been found in England in British Potato Council surveys.
“A2 has been increasing there since 2003,” he adds.
“In 2005 over 30% of the isolates were A2 type.”
The reason for the difference is not readily apparent, says Dr Cooke.
“It is unlikely to be temperature – A2s have been found equally in the Nordic states.
It is rather mysterious.”