Hot potatoes

Saturday 25 February 2012

Taste and cooking quality are paramount when choosing seed potatoes, and enthusiasts often like to select varieties not found in supermarkets.

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Dave Allan

Finding potatoes that won't succumb to blight, however, is becoming vital. Put simply, potato blight – Phytophthora infestans – turns spuds to mush. Tiny brown circles on leaves and withering round the edges are often hard to spot at the beginning, but within a week all the foliage, the shaws, collapse in a rotting heap. The disease then spreads down to the tubers and turns them to a stinking, watery mess.

The potato famines which struck Ireland and the Highlands in the 1840s are all-too well known and late blight has stalked the vegetable garden ever since. Potato breeders developed varieties such as Cara that had some resistance to the disease, but nearly 40 years ago a second blight strain was accidentally imported to the UK, then both strains bred new hybrids. Scientists were faced with the task of keeping up with these hybrids by constantly producing new blight-resistant varieties, such as Stirling.Over the past few years, an especially virulent hybrid has arrived on the scene and proceeded to knock the stuffing out of the traditionally disease-resistant potatoes. Superblight, or Blue 13, now causes 80% of blight damage. Most varieties that once had good resistance, like Sante, are now as susceptible as Maris Piper or Pink Fir Apple, which wilt at the first sign of the disease. Despite what mail-order catalogues often claim, most recent tests have shown blight resistance for varieties including Lady Balfour and Setanta have been halved by Blue 13. Some potatoes are so tasty gardeners insist on growing them, but, year on year, fungal attack is more and more likely.The only potatoes that reliably withstand blight are the Sarpo (pronounced "sharpo") group. They were pioneered 40 years ago by Dr Sarvari at the Keszthely Research Institute in the Soviet Union at the request of the authorities, who wanted a potato with optimum disease resistance. Potato varieties are all members of one species, Solanum tuberosum, but Sarvari crossed his potatoes with genes of other wild South American and Mexican species which belonged to the plant collection amassed nearly 100 years ago by the outstanding geneticist Nikolai Vavilov.Via a complicated route, these potatoes were introduced to the UK and the Sarvari Research Trust was established. Sarvari's sons still work on Sarpo potatoes in Hungary and the most hopeful specimens are sent to the trust for further rigorous testing. From his base at Bangor University, the trust's director, Dr David Shaw, oversees exhaustive trials in several locations throughout the UK. Each variety is assessed over eight to 10 years before being added to the National Potato List.Six varieties are now available. The first Sarpos, maincrops Sarpo Mira and Sarpo Axona, are good for baking and cooking with fat. Early maincrop Sarpo Shona is a general-purpose spud, and the slow-growing Kifli is very tasty. Blue Danube has spectacular blue skin and, unlike the others, Sarpo Una, a first/second early, is a waxy salad potato which I've earmarked for my garden this year. Another four varieties will be available fairly soon.For best results, Sarpo potatoes need to be treated a little differently to other potatoes. You plant them in the usual way, 45cm apart in a trench one spit (spade's depth) deep. Rake the soil over the tubers to make a ridge along the row, then earth up the potatoes as the foliage grows. Traditional potatoes reach a certain size, produce a predictable harvest and stop. Sarpos, on the other hand, keep on going, just like cordon – or indeterminate – tomatoes. "I'd like to have a trial where we plant Sarpos next to 40ft-high poles and see how high they climb," says Shaw.Left alone, Sarpos keep growing till the frost kills the foliage, but unfortunately the skin becomes hard and the potatoes are difficult to cook: they stay solid for ages then collapse. When left too long in the ground, they also suffer from "hollow heart" – where a cavity at the centre of the potato is surrounded by brown rot. It's easy to prevent all this by harvesting them when they're no larger than baking potatoes. As Shaw explains: "Growers must learn to stop them when the size of tuber is just right. Even maincrops [Mira and Axona] will mature in August." You can also treat Sarpos like new potatoes – dig what you want for a meal and leave the rest in the ground. Kifli is ideal for this; even its largish tatties taste good.Astonishingly, Sarpos are still not commercially grown as widely as they should be. They require no synthetic chemicals to combat late blight, so they're cheaper to produce and much better for the environment. Their taste alone makes them an excellent choice. nVisit www.alanromans.com and www.thompson-morgan.com.

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