Minimising Scottish potato crop's growing pains

EVERY year, during the early summer about 100 trainee potato inspectors are to be found walking through numbered rows of plants in a large field on the outskirts of Edinburgh. Sometimes the inspectors will stop and gather round an instructor, who points out features in the luxuriant foliage.

At the end of their course at Gogarbank Farm outside the capital, the inspectors are able to identify at least 30 of the varieties they are likely to encounter when they later visit the seed potato fields of Perthshire, Angus, Aberdeenshire, Moray, the Black Isle, Caithness, the Lothians and the Borders to help in the fight against diseases in the vegetable. Each field is inspected at least twice.

Lumpers are one of more than 1,000 different potato varieties grown in the collection at Gogarbank. These seemingly innocuous plants have a dark history, being generically identical to the variety that in the 1840s was wiped out by the devastating fungal disease known as late blight.

Much of Europe was thrown into "the great hunger", with Ireland worst affected. In the Scottish Highlands, crofters were ruined when the potatoes on which they relied fell victim to the blight.

Although, these days nobody grows Lumpers commercially, blight remains a threat in other varieties. The inspectors are trained to look out for signs of this, and other diseases that affect the susceptible potato – signs of viral disease the inspectors are taught to look for include barely perceptible marks on foliage to stunted plants with crinkled, discoloured leaves.

The July round of field inspections is one highly visible aspect of a scheme co-ordinated by Science and Advice for Scottish Agriculture (Sasa) that protects against all the threats. The organisation mobilises the efforts of farmers, government scientists and inspectors and agronomists.

The Scottish potato seed crop is thus remarkably healthy, this being achieved mainly in the early stages of propagation long before the ware potatoes – the ones we get to eat – appear on our tables.

Robert Doig's family owns 50 hectares at Old Fargie Farm, near Glenfarg in Perthshire and rents another 200 closer to the Fife border. On site, he points out the rows of pre-basic seed potatoes in a field 700 feet above sea level with a distant view of the Lomond Hills. The plants grow in a shallow field, with occasional rocky outcrops. Yet this is actually a good place to grow the high grades of potato plant since even at that modest altitude there is less risk of attack by virus-carrying aphids. Other farmers use the same fields for other purposes – mainly livestock or cereals – in the other six years of the crop rotation cycle.

Doig is licensed to grow pre-basic potatoes from mini-tubers supplied by one of seven specialist companies in Scotland. There is zero tolerance for disease during the inspection of the mini-tubers, but they are vulnerable as soon as they are planted.

The mini-tubers do not come cheap, so Doig's task is to continue to grow their daughter plants as pre-basics, multiplying them annually in a four-year sequence. He continues to grow the progeny for a further two or three years as what are called "super-elites". After six or seven years, the numbers are so prolific that the high initial costs are diluted and the potatoes can then be sold on commercially.

Doig continuously monitors for any sign of disease, his efforts being complemented by the July inspections and by consultations with the Scottish Government's agricultural officers based in Perth.

For pre-basics, spraying against blight and aphids is an absolute necessity and has to be done every seven or ten days. Regular and frequent walking inspections of the fields means that any diseased plants can be spotted early and removed.

Some 20 years ago, Doig and his father joined forces with Jack Dunnett, a legendary potato breeder from Caithness who was looking for experienced farmers to collaborate in producing new varieties. The Caithness venture has succeeded and now there are 15 different varieties of potatoes, many being exported to countries such as Egypt and Israel with hotter climates.

These days, Robert Doig's special interest is in the painstaking work of plant breeding in which he builds on Jack Dunnett's original achievement.

John Mackay represents the fourth generation at Fletcher's Field near Kirriemuir in Angus. He farms 530 hectares in his own right and another 1,000 through contract farming and leasing from neighbours.

His family has grown seed potatoes as far back as he can remember and he also grows cereals and raises livestock. Mackay cultivates his own fields every year of the crop cycle, with potatoes in the seventh year.

He has no set pattern, but typically grass, barley, wheat and a crop of vegetables (peas, broccoli or carrots) will be grown in the other years.

The seed potatoes are mostly super-elites, along with some ware, in well-established brands such as Maris Piper, King Edward and Desiree. Apart from ware stocks, the total seed production is 4,000 tonnes a year, with about 70 per cent going to farmers and merchants in the south, 5 per cent sold in Scotland and 25 per cent being exported.

On the wall of his farm office, Mackay has a set of colour-coded maps showing what is growing where, in 140 fields, all numbered but also carrying traditional names such as the Shift, Balbegno, the Roundel and Hatton's Field.

The clean boxes in which the potatoes are stored after they have been harvested are marked with the grade, variety and the field in which they were grown. The chemical agronomy is managed with the help of a computer-based programme called "Muddy Boots", augmented by the advice of an agronomist.

But in the end, it all comes down to husbandry and the passion for the job – whatever the weather. On a day of pouring rain we drive out and met the roguers, the people employed to walk the long rows of potatoes looking for signs of disease in the plants and for any varieties that should not be growing there. These potatoes are known as "groundkeepers" or "rogues". The roguers' mantra is: "If in doubt, have it out!"

Among the roguers was Edinburgh University graduate James Mackay, representing the fifth generation of his family at Fletcher's Field.

There is a consensus among the people I have spoken to that, as Mark Prentice of the Potato Council expresses it, Scottish seed potatoes are not just a commodity but a brand because of a high health status.

This is important for exports, having done better in 2007 than in any previous year. For Robert Doig, the scheme is pivotal and gives growers an edge in the highly competitive export markets.

John Mackay agrees. To his mind the protection scheme is not just another example of time consuming bureaucracy but a model of co-operation, with everybody pulling on the same side.

Kevin O'Donnell, who heads up Sasa's Rural Scientific Services, shares this opinion: "For those of us who are involved through government it is not just a job but a privilege to be part of a Scottish success story."

• THE Scottish Seed Potato Classification Scheme is seen as vital for maintaining the very high standard of plant health.

All growers, of which nearly 300 have three or more hectares, are registered on the scheme. Each year, they declare the different varieties and grades of potatoes they are growing as well as the fields in which they are grown. This is complemented by inspections and by a rigorous laboratory-based process at Science and Advice for Scottish Agriculture (Sasa).

There is much to protect against. One of the pathogens is the virulent A2-13 strain of the blight (known as Blue 13).

However, the impact of nine separate viruses, carried by aphids, is minimised, partly by Scotland's climate and partly by vigilance and preventive measures. Scotland is free from other diseases by the work of Sasa's quarantine unit.

In any field intended for potatoes, Sasa tests the soil for the minute organism known as Potato Cyst Nematode or eel worm. If it is found, no seed potatoes may be grown on that land.

In addition, Sasa tests for any infection in the "nuclear stock". This represents the earliest stage in the propagation of seed potatoes.

Sasa's continuous monitoring of the seed potatoes as they grow is complemented by the research carried out into blight and other diseases by the Scottish Crop Research Institute.

• Sasa is part of the Scottish Government's Rural Payments and Inspections Directorate.