An obscure variety of potato grown in Hungary is being hailed as the way to a boom in organic farming, because it does not need fungicide.
The purple-skinned tuber has been bred by the Sarpo family of Hungary to have a natural resistance to potato blight, but for years has been ignored in western Europe.
Farmers have instead used synthetic pesticides, fungicides, or fertilisers to prevent blight, the fungal disease which by rotting their staple food killed up to 1m people in the Irish famine of 1845-47.
The fungus can be held at bay with copper-based fungicides but the crop cannot then be labelled "organic".
Researchers at the University of Newcastle tested seven strains of blight on the Sarpo potato at a plot near Hadrian's Wall in Northumberland. They found that, while the fungus was picked up - as shown by tiny lesions on the leaves - the plants, and the potatoes themselves underground, continue to thrive. Though the Sarpo tuber's skin is dark purple when ready to harvest, the flesh is as white as traditional varieties.
Its blight resistance was achieved not by modern genetic modification but by the age-old method of tweaking genes through cross-breeding.
"This is extremely promising for organic farmers and consumers," said Carlo Leifert, professor of ecological agriculture at the university. "A potato which can be grown commercially without chemicals would be an important breakthrough for the organic movement worldwide."
There was a shortage of organic potatoes in shops, and a lack of varieties, because of blight that destroyed millions of pounds worth each year and put farmers off trying.
In addition to its immunity, the Sarpo variety appeared to thrive in poor soil, said Prof Leifert. "I'll not say they're the answer to everything, but when cooked we couldn't tell the difference between Sarpo potatoes and bog-standard Tesco varieties."