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 21st century. But the effects will not be uniform across all regions - and besides, the scientists have a few tricks up their sleeves.
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 CO2 stimulates 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.
Another significant threat posed by rising temperatures is water stress as transpiration rates in potato plants increase, leading to greater demand from the soil. Without adequate rainfall or irrigation systems, crop failure is a real danger. Despite this, potato is likely to become more important for food security as temperatures rise, since it has higher water productivity, yielding more "crop per drop" - than rice wheat and maize.
Seasonal changes are also a problem. In Bolivia, rains that used to arrive in October now come in December, but the rainy season still only lasts until March, meaning a shorter growing season. Potato farmers have traditionally hedged their bets by growing a number of different varieties in the hope of a better chance of a good harvest. Now, heat-tolerant potato varieties will become an essential weapon in their armoury.
Potato hybrids are one promising response to the threat of climate change, with hopes pinned on the development of early-maturing varieties with shorter growth cycles. CIP plant breeder Merideth Bonierbale is optimistic about these new potatoes: "Early-maturing varieties allow the crop to 'escape' stresses such as limited rainfall. They also ensure a harvest in the tropical highlands, for example, where the high incidence of frosts causes big losses," she says.
"One of the challenges now is to combine work on heat tolerance with current research into disease-resistance," continues Bonierbale. "This will enable the potato to produce in new environments under new conditions." If these traits can be combined, could a "super-potato" be on the horizon? She is confident: "Yes, and hopefully more than one of them." Other desirable traits being targeted by breeders include higher water-use efficiency, increased root length and disease resistance.
Since climate change presents challenges on many fronts it will require robust responses from potato growers and research organisations alike. As well as stress tolerance, disease resistance, early-maturation, improving irrigation and early-warning systems for severe weather will become important in adaptation strategies worldwide. When it comes to being prepared - as growers in Nepal, Mali and Peru will testify - there is certainly no time to lose.
Date published: September 2008
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Do not worry, God will always give us ways to survive. Potat... (posted by: Tatik Wardiyati)
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