Irrigation water appears unlikely to be have been the source of infections in home-grown seed potatoes of the bacterial disease Erwinia chrysanthemi, tests suggest.

But seed growers should continue to take steps to avoid introducing the pathogen – which produces symptoms similar to blackleg and can cause soft rots in progeny tubers – into seed-growing areas, John Elphinstone of the Central Science Laboratory told Farmers Weekly after speaking at the Potato Council’s Seed Industry event.

Research had revealed that the disease was caused by at least six different species of dickeya bacteria, but within Europe, only one – Dickeya dianthicola – had been implicated in causing the disease in potatoes, he said.

First found in the UK on ware crops in 1990, Erwinia chrysanthemi infections are mostly associated with crops that are grown from seed brought in from outside the UK.

But it had also been found in two home-grown seed stocks, including one from Suffolk identified during testing of samples collected for a brown and ring rot survey in 2007.

There had been some suggestions that the source of the infection could have been irrigation water because Dickeya species have been detected in watercourses. But the strains found in watercourses were different, said Dr Elphinstone. “So it looks like it might not be through water.”

More research was being undertaken in a three-year Scottish government-funded project into the bacteria’s biology to help understand how the infection had moved into seed crops, with the aim of designing a better control programme, he said.

“At the moment it is difficult to recommend specific control measures for chrysanthemi,” he added.

Following guidelines for controlling soft rots and blackleg would be a good starting point for seed growers to help prevent its introduction, he suggested, particularly in Scotland, where the disease had never been found.

“Being a member of the Safe Haven scheme would also provide a barrier to introducing the disease on seed from outside the UK,” Dr Elphinstone added.