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Joined up approach to tackle blackleg

29 September 2016

AHDB Potatoes will be using this year’s Seed Industry Event to help develop a pan-industry approach to reverse the recent increase in blackleg.

The bacterial disease, caused mainly by Pectobacterium species in the UK, has declined significantly since the 1960s, but in recent years has been rising again.

“The Scottish seed industry is facing some challenges with blackleg levels,” says Rob Clayton, AHDB Potatoes director. “We want to use the seed event to raise positive discussion about the sector’s collective responsibility to tackle the problem.

“Current controls are based on a mix of research, regulatory approaches and general best practice guidelines, incorporating a range of different views.

“We want to challenge the industry, carry out a stocktake of current best practice and find a consensus to reduce infection in our seed crops.”

The aim is to identify known best practice measures and separate them into those that are widely used and those that remain largely unadopted.

“Once we have identified those that are not being used, we need to find out what is preventing their uptake,” says Dr Clayton.

Practical challenges are often to blame, as with grader hygiene. “Cleaning graders can involve a considerable hassle factor, so getting the practice widely adopted is difficult to achieve.”

Two workshops will run concurrently at the event, each containing growers of pre-basic, basic and certified seed. “This will provide a range of perspectives and enable us to obtain a good stocktake on control strategies, barriers to uptake and what the next steps should be,” says Dr Clayton. “We hope some consensus will emerge from the two groups to indicate where the key challenges lie.”

The workshop approach marks a change in the way AHDB is delivering knowledge exchange, says Dr Clayton. “Rather than writing a brochure that people follow, we are looking to broaden the approach to blackleg management that involves every seed grower in the industry.”

Two areas of blackleg research will also be highlighted in the workshops to help guide decisions. The first is a study jointly funded by AHDB and the Scottish government led by Prof Ian Toth of the James Hutton Institute to understand routes of Pectobacterium contamination in high-grade seed. The second is a project carried out by SASA and AHDB to investigate social changes and industry practices that could be contributing to a rise in blackleg.

Routes of Pectobacterium contamination

Professor Ian Toth will highlight key points stemming from this recently completed three-year project, including interesting new biology that has implications for blackleg control.

“We have discovered that even when clean seed is planted it can still show significant levels of foliar disease in the field,” says Prof Toth. “Irrespective of hygiene, we now know seed can pick up contamination from soil and lead to diseased plants in the same season.

“We don’t yet know how to eliminate these soil-borne bacteria, but it could be that planting lower grade seed close to high grade seed increases the chance of contamination, so growing early generations in separate fields could help prevent the problem.”

Another finding is that blackleg tends to occur in hotspots of 5-25km diameters, which shift from year to year. While this shows blackleg outbreaks are not necessarily random events, it also suggests they are not necessarily related to any particular farm or farmer. 

“However, they may be spreading from a central source,” says Prof Toth. “If so, we need to get better at controlling and confining the disease through better more timely management to stop these clusters forming.”

Good hygiene of graders and machinery and other control measures such as planting and harvesting during dry weather, irrigating as little as possible and harvesting and grading high-grade stocks first, remain key.

The controversial third inspection of seed crops, introduced last year for any crop that shows more than 25% of allowable blackleg for its grade, could also be a useful addition, he believes.

“We know blackleg can get worse after the second inspection. A third inspection could make a big difference to seed quality. As the scheme involves all seed producers, it could be very powerful and we should see how effective it is pretty quickly.”

Factors leading to a rise in blackleg

Prof Gerry Saddler, head of potato and plant health at SASA, will talk about the results of the SASA/AHDB survey of 30 pre-basic seed growers carried out last year.

He will also update delegates on the second stage of the project which involves a postal survey of all commercial seed growers in the UK.

“We wanted to obtain views on why we seem to have more problems with blackleg compared with 10-15 years ago,” says Prof Saddler. “The results show that growers clearly are under much greater business pressure these days, particularly because numbers of pre-basic growers are dwindling.

“They are running bigger and more complex operations, which together with a shift to just-in-time deliveries puts them under even more pressure at one of the busiest times of year.”

The second phase of the project aims to gather views from commercial seed growers on the quality of purchased seed, their relationship with the seller and how seed is stored prior to planting.

“We think the period from leaving the producer to just before planting might be an Achilles heel,” says Prof Saddler. “Temperature and ventilation are both important for seed health at this time, and we want to identify the scale of the problem.

“We hope to complete most of the work in time for the seed event and have full results by the end of the year.”

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