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Climate change - can potato stand the heat?

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Climate change - can potato stand the heat?

In Nepal's Kathmandu Valley, summer hailstorms in 2007 destroyed potato crops for the second consecutive season. Farmers are also struggling in the Sikasson region of Mali, where international agencies have spent years promoting and supporting potato production, but lower rainfall means farmers are moving away from potato. While this is not good news for the world's third-most important food crop, growers in other regions might be able to take advantage of cooler winters by planting potato out-of-season.

When it comes to the effects of climate change on potato, one thing is clear: production is changing and will continue to change around the world. Already it is migrating to higher, cooler altitudes in the tropics as some predictions put yield declines at up to 30 per cent in the latter half of the 21stcentury. But the effects will not be uniform across all regions - and besides, the scientists have a few tricks up their sleeves.Mixed messages

Potato is particularly vulnerable to global warming due to its narrow production "window": it needs mean daily temperatures of 18-20°C and night-time temperatures less than 15°C. Fluctuation outside the range of 10-30°C significantly inhibits tuber growth: this is what devastated potato crops in the Andean highlands of Peru in 2007, when a freak frost arrived in mid-February.

Meanwhile, other non-biological factors point to some advantages of climate change. Higher concentrations of atmospheric carbon dioxide (CO2), for example, may actually benefit potatoes as increased CO2stimulates the development of underground biomass in potato plants, with tuber weight and number both increasing significantly. Higher levels of atmospheric ozone (O3) also seem to benefit the crop, resulting in more of the antioxidant ascorbic acid in tubers.

Higher temperatures also mean longer growing seasons in more temperate areas. A greater number of frost-free days per year will lead to yield increases at high latitudes, including parts of Canada, Russia and Scandinavia. Winter cropping is expected to increase annual yields in parts of Algeria, Morocco, China and South Africa.

But where rainfall and humidity increases, so too will the threat of potato diseases, such as late blight (Phytophthora infestans), especially when combined with longer growing seasons. Bacterial wilt may also increase as the climate becomes warmer and wetter; and potato pests, including disease-carrying aphids, will survive at higher altitudes.

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