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New blackleg threat to British crops

26 August 2011

One of the seminars at British Potato 2009, at the Yorkshire Event Centre, Harrogate, on November 25 and 26, will bring growers valuable information of a new Dickeya pathogen. The symptoms of the seed-borne bacterial disease make it potentially a more aggressive form of blackleg, warn scientists.

Growers attending the BP2009 seminars will be guided through a major new disease threat to crop production. Scientists have discovered a new bacterial pathogen in the genus Dickeya, that causes plants to wilt and rotting in tubers. Symptoms are almost indistinguishable from ‘traditional’ blackleg (Pectobacterium atrosepticum) but the disease appears to be more aggressive and causes damage in a wider range of conditions and at lower bacterial loadings.

“We’re urging all growers to find out about this new disease that is potentially a more serious form of blackleg,” says AHDB Potatoes head of seed and export Mark Prentice. “We are already hearing of findings in some ware crops in Britain. The fear is that its apparent ability to cause problems in both warm and cooler conditions could make it a far worse problem than the blackleg we know and have managed”. 

The pathogen, currently referred to as ‘Dickeya solani’, has only been identified as a separate species in the last six months and has yet to be formally named. It is a close relative of Dickeya dianthicola, previously known as Erwinia chrysanthemi, that has caused damage to crops on the continent since the 1970s. But unlike D. dianthicola, the new pathogen thrives under a range of conditions, according to SASA’s head of diagnostics and analytical services, Dr Gerry Saddler, who will be presenting the seminar at BP2009.

P. atrosepticum, the form of blackleg most growers are aware of, is well-suited to the cooler, damper conditions in the UK, while D. dianthicola tends to be more of a threat in warmer years. ‘D. solani’ is certainly adapted to warmer temperatures but can also cause disease under cooler conditions typically found in Britain. It is likely to cause more losses in the southern counties, but growers in the northern half of the country should not be complacent. Symptoms have been observed under Scottish conditions and the disease, if it was to become more wide-spread, would damage our seed exports.”

Of most concern is its aggressive nature. “Observations from The Netherlands indicate that once established, the new species will rapidly displace others and take over as the principal cause of wilting and blackleg-like symptoms in potato crops. Symptoms closely resemble blackleg: wilting can be rapid, with black soft rotting extending internally up the vascular system of the stem from the infected seed tuber. Even mild symptoms in the plant can lead to severe rots in the tubers.”

What’s more, very low levels of infection on the seed – the principle source of disease transmission– will develop into full-blown symptoms, Gerry warns. “Growers must think very carefully about where they source their seed. The best way for growers to keep this disease out of their crops is to buy Safe Haven-accredited seed.”

It is unlikely that growers will be able to distinguish the disease from traditional blackleg, he notes. “Be vigilant for symptoms in the crop and arrange a diagnostic test if you suspect Dickeya.”

SASA is compiling more information and guidance on the disease and a leaflet for growers will be available at BP2009. Experts from SASA and the Food and Environment Research Agency (FERA) will be on hand to address specific queries, while there’ll be opportunities to discuss the new threat during Gerry’s seminar.

Mark Prentice is keen for seed growers in particular to use the event to help establish an adequate defence strategy. “The high health of British seed is a huge selling point. At the heart of our high health status lies the Safe Haven Certification Scheme. 60% of the British seed area is in the scheme and seed growers who are members of the scheme can now have the logo printed directly on to their seed bags. It is important that we continue to raise awareness of the plant health benefits that Safe Haven seed brings.”

Examples of seed bags with the logo will be on show at BP2009 and members of the team will be keen to discuss seed health issues with growers at the event.

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