The shape-shifting blight that threatens our spuds

ANOTHER LIFE:A MURKY, MIDGE-BITTEN morning in the last days of May found me out with the sprayer, pumping a mist of fungicide across my ridges of potato plants. It was the earliest Met Éireann warning I can remember of imminent conditions for the spread of blight. Its solicitude stemmed, perhaps, from the commercial toll of recent muggy summers, but also, I would like to think, from concern for all the new gardeners growing their first potato crop.

"What can they do to you, really," I once asked rhetorically of the world's darker fortunes, "if you have enough land to grow a half-tonne of spuds?" Most people don't, of course, but even a few back-garden ridges can seem precious, and their destruction by Phtyophthora infestansa foul calamity. On the other hand, rushing out with a fungicide every couple of weeks through the summer can be tiresome, not to mention the cost or possible harm to wildlife or even oneself.

The quest for blight-resistant potatoes has intensified as the world’s food crisis deepens. Across poorer nations, land planted with potatoes is increasing faster than that for any other staple crop. Of the 213 million tonnes grown every year, more than half are harvested in developing countries, and China alone accounts for 70 million tonnes.

Meanwhile, strains of blight have been developing resistance to sprays, and new forms of the fungus that persist for years in the ground have spread west in Europe to reach Ireland. Finding potatoes with genes for blight resistance will be helped by the work of an international consortium that is sequencing the plant’s complete genome.

Teagasc scientists have joined those of a dozen other nations in the project, including China, Russia and the US, and the consortium meets next week at Teagasc’s plant biotechnology unit at Oak Park, Co Carlow.

Here, the Irish team are tackling Chromosome 4, a sizeable chunk of the 840 million nucleotides in the potato’s full chain of DNA.

Teagasc has already bred highly successful and tasty potatoes (the red-skinned Rooster, for example, has become the most popular variety in Ireland). But finding out which genes control which traits in plants is still a huge challenge. When key sequences in the full genome are found, they can be used as markers to identify wild potatoes (nearly 4,000 varieties in the Andes alone) that can bring disease resistance into strains conventionally bred for cultivation.

Selective breeding for resistance has an elaborate history. Since every tuber is a clone, an exact genetic copy, of the plant it was harvested from, breeding turns to the potato’s often beautiful flowers (pictured above), transferring pollen to cross-fertilise and produce the potato berry (like a small, green – and, as it happens, toxic-to-humans – tomato). One berry can hold up to 200 seeds, each genetically different and a potentially new variety of potato.

NEAR LAKE BALATONin Hungary, more than 40 years ago, the Sárvári family began breeding hardy potatoes for a Soviet research station, using wild potato strains from South America and Mexico. Initially, they achieved resistance to common potato viruses and later a high resistance to blight. In the 1990s, a chance glimpse by a Scottish grower of healthy plants in an otherwise blighted Hungarian field, led him to the Sárváris.

Today, this family sends promising strains of potato to the Sárvári Research Trust, a non-profit company set up near Bangor in Wales and led by Dr David Shaw, a research associate of the University of Wales. This has developed the two red-skinned, blight-resistant potatoes, the early-maturing Sarpo Mira and maincrop Sarpo Axona, that are nationally listed in the UK and finding rapid popularity with back-garden growers both there and in Ireland (where Dublin’s Mr Middleton offers them).

They have been my choice now for three years, producing vigorous, weed-smothering thickets of leaves and splendid crops of potatoes.

Why, then, hurry out to spray them when the Met office murmurs of blight? Because I’m paranoid, that’s why, and can’t quite trust in all the good reports. Next year, I may be bolder.

Meanwhile, a new type of Phytophthorathreatens potato growing in Ireland.

Until now, the blight organism has spread in Ireland as wind-born spores produced asexually, landing on the potato leaves and infecting only the plant tissue. But a new genotype, A2, which has swept through Britain from Europe and recently arrived in Northern Ireland, boosts the risk of sexual reproduction. This could produce spores that survive in the soil for years, infecting potato crops before the plants even emerge.

A joint project by Teagasc and farming scientists in the north is now on the trail of this shape-shifting blight. So, one imagines, are proponents of GM potatoes artificially engineered for resistance.