PCN threat increasing for Scotland seed


23 January 2023
G pallida levels doubling every seven to eight years.

SCOTLAND's seed potato sector is becoming increasingly plagued by the potato cyst nematode (PCN) species, globodera pallida.

Certified Scottish seed represents 77% of all seed grown in Great Britain, and SASA data shows the Scottish land area recorded as infested with g pallida as doubling every seven to eight years. 

The two species of PCN (globodera rostochiensis and pallida) was among key topics discussed at the Cambridge University Potato Growers’ Association (CUPGRA) annual conference.

Agronomist Eric Anderson said: "It is a requirement of the Seed Potato Classification Scheme (SPCS) that crops must be grown on land with a valid PCN clearance certificate issued by SASA at the time of planting. A detectable PCN infestation in a statutory soil sample is a result of what has happened over the past 30-40 years. This means our industry needs a Plan B."

Some varieties are resistant to rostochiensis, but few have resistance or tolerance to pallida, Eric said. Authorisation for the nematicide Nemathorin (fosthiazate) ends on October 31st, 2004 and there are no guarantees for its renewal so the threat to Scottish seed and ware industries is very real.

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"The seed sector will potentially need to rapidly switch to multiplying new varieties while the ware, crisp and processing sector need to adapt and grow potatoes in the presence of PCN without the chemical crutch of nematicides," said Eric. "Integrated pest management (IPM) is useful but presents no silver bullet. Rotation length and groundkeeper control are of paramount importance as recent data indicated that PCN increased by 16-fold in the presence of volunteer potatoes."

When it comes to biofumigants, not enough is yet known about specific glucosinolate profiles and in Scotland the establishment of trap crops has been inconsistent. 
"We urgently need varieties that have both resistance and tolerance to PCN," Eric said, stressing that resistance restricted or inhibited the multiplication of PCN on the plant whereas tolerance reflects the ability of the plant to withstand damage by PCN and avoiding a fall in yield associated with infection.

There aren't currently any genetic markers for tolerance for pallida and one of the compounding factors is rented land, because land agents tend to maximise short term profits for landlords without taking a longer-term view on soil health.

"Land agents probably need greater appreciation and training on the vital importance of Integrated Pest Management and understanding of life cycles and control," Eric said.

Bespoke workshops for land agents involved with renting seed potato land to growers in Scotland are being planned as part of the ‘PCN Action Scotland’ programme. These will include discussions on measures aimed at proactively managing and protecting the land sustainably from PCN.

"Developing an integrated control programme, requires co-ordination at all levels: Growers, land agents, testing laboratories, agronomists, policy, research providers and consumers/processors," Eric said.

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