• The Dutch perspective
• Effectiveness of pallida-resistant varieties

For spring 2015 planting, multi-purpose variety Maris Piper accounted for 15% of Britain’s 111,600ha of potatoes, but has a lowly pallida resistance score of 2.

Furthermore, of the other nine top-10 varieties, only fresh table variety Harmony trumps Piper with a score of 4.

ProCam technical director Tudor Dawkins says this is an important challenge that needs to be bridged in order to successfully manage a growing PCN problem.

“Piper is what causes us as advisers problems and differentiated varieties [for various markets] with resistance to pallida will represent a big step forward. The difficulty is, consumers like Piper.”

Tragedy

The concept and practice of using resistant varieties is not alien to the UK, with two varieties – Sante and Nadine – having had some commercial success until about a decade ago.

Shropshire-based Denis Buckley of Highfield Lodge Agronomy says although pre-pack variety Nadine fell foul of the market due to low dry matter, Sante was a good pre-pack option with decent resistance to pallida.

“With Sante and a nematicide you could crash a PCN population. It also had good common and powdery scab resistance, so it was a respectable all-round variety.

“It was a tragedy what happened [to Sante]. It [the flesh] was judged a little too yellow for British taste and the tubers were quite flat, so they spilled over the side of baker packs,” he explains.

The variety effectively disappeared and was largely replaced by Melody, which has no resistance to pallida, and few resistant types have managed to gain a strong foothold in the fresh market since.

Mr Buckley says the UK is now a decade or more behind the likes of the Netherlands, which has successfully used resistant varieties to slash pallida populations to manageable levels.

He points out that growers are well aware of the problem, as it is hurting their businesses, hammering their yields and driving up already high costs of production.

“They want to see pallida-resistant varieties, but they can only grow what the market wants.

“I find it very hard to believe that there aren’t any good pre-pack varieties with pallida resistance in the material breeders have churned out, but no one seems to have taken the time to work through it and test them in the market.”

Potato cyst nematode

Skin finish

The British potato market is made up of about 55% processing and 45% fresh, with both sectors having slightly different characteristic requirements from varieties.

Breeders have a complex array of characteristics to fit into a variety to suit each market, with dry matter, low sugars and storage characteristics most crucial for processors.

With fresh table potatoes, skin finish has become the number-one priority and Caithness Potatoes breeder Finlay Dale says emphasis on minor skin blemishes has gone too far, at the expense of PCN and blight resistance.

“It is supermarket driven and they are not too concerned about industry problems [such as PCN], but we should remember they have a business to run.

“Fresh potatoes are bulky and take up a lot of floor space for not a huge profit compared with other products, so they want to stock varieties they know will sell,” he explains.

In the processing sector, where skin finish isn’t so critical, companies such as McCain’s are making progress with resistant varieties, increasing its area of Royal – a variety with partial resistance to pallida in the field.

However, the fresh sector is lagging behind and Dr Dale says supermarkets need to be more open to trying out new varieties that could provide the grower with agronomic benefit.

“Packers could also invest more in marketing and how potatoes are packaged.

“People want more instant meals and new products that can take away the skin finish problem would allow breeders to concentrate on important traits such as PCN and blight resistance,” he explains.

Integrated approach

While growers wait for the market to swing in their favour and widely accept pallida-resistant varieties produced by the breeders, Dr Dawkins says all other tools must be used to reduce the effect of PCN.

This fully integrated strategy will use vigorous soil sampling, nematicides, trap crops and biofumigation to reduce the effect of PCN on crops and minimise its multiplication in the soil.

“Lengthening rotations will unquestionably help, but it is not always practical and it is difficult to convince people to do it,” adds Dr Dawkins.

In the Netherlands about one-third of seed and ware potatoes and almost 100% of starch potato tonnage is produced from highly pallida-resistant varieties.

This uptake has been a key part of the Dutch PCN management strategy in recent years and its growers have significantly reduced pallida populations as a result.

Wageningen University nematologist Thomas Been is surprised that British breeders haven’t taken the chance to use the pallida-resistance genetics to the extent of the Dutch.

He believes underlying the slow adoption of resistant varieties is the UK’s inadequate soil sampling protocol and laboratory infrastructure to provide growers with accurate information about their PCN problem.

“There is a tendency [in Britain] to blanket treat whole fields. In the Netherlands we have the precise information of where PCN is, so we can target those areas with resistant varieties.

“Why not do this in the UK? Then plant the rest of the field with a susceptible variety such as Maris Piper,” he adds.

Field trials carried out in 2014 by Science and Advice for Scottish Agriculture (Sasa) and Scottish Agronomy have shown the huge potential of available varieties for reducing pallida populations.

In a problem pallida field at Luffness, East Lothian, resistant and partially resistant varieties were planted in pallida hotspots alongside susceptible variety Maris Piper.

The soil was sampled and analysed for the initial pallida population (Pi) ahead of planting and again after harvest for the final population (Pf).

Jon Pickup

The Pf/Pi can then be calculated, which represents the change from the initial population to the final population.

The table below shows the results of laboratory egg and juvenile nematode counts for the variety plots, none of which were treated with nematicide.

Sasa’s head of virology and zoology, Jon Pickup, says he has heard comments that highly resistant varieties can only reduce PCN populations by 50%, similar to other control methods such as nematicides, trap crops and biofumigants.

However, reduction from methods such as nematicide application is only assessed at Pi and if you grow a susceptible variety afterwards it allows the multiplication of PCN in the soil, resulting in a very high Pf.

“In this instance, you can see Performer produces a Pf of 1.6, compared with Piper with 160, effectively giving the grower 99% control of PCN,” explains Dr Pickup.