As climate change makes tropical wheat environments less favorable, new varieties and conservation agriculture will help wheat beat the heat.

Excess heat hurts wheat yields on more than 9 million hectares globally. This number will increase, as the Intergovernmental Panel on Climate Change predicts that global temperatures will rise by 1.8°C to 4.0°C by the end of the century. Current heat-stressed areas, which include some of the world's poorest regions, will likely suffer yield losses.

"To maintain food security, we have to increase the yield potential of staple crops by 1.5% to 2% a year," says Matthew Reynolds, a wheat physiologist at the International Maize and Wheat Improvement Center (CIMMYT), adding that crop productivity is currently increasing annually by around 1%. "Climate change reduces yield potential, so not only do we have to go from less than 1% to at least 1.5%, but climate change is making that much more difficult to achieve."

South Asia's Indo-Gangetic Plains will be among the areas hardest hit by warmer temperatures, water scarcity and heightened soil salinization. A productive wheat-growing area that includes India, Pakistan, Nepal and Bangladesh, this region is home to more than 1.2 billion people, many of whom are farmers growing annual rotations of rice and wheat. By 2050, over half the region is expected to suffer heat stress and possible desertification. If wheat yields fall as a result, the situation for the region's 480 million poverty-striken people will become even worse.

Climate change brings more than heat and drought. Variation in precipitation patterns will likely dry out some places while flooding others. Hotter and more humid conditions will encourage pests, diseases and weeds. In the tropics, heat is expected to shorten the grain-filling period for wheat, damaging product quality, according to the recent CIMMYT publication Wheat Facts and Futures .

But there is some good news. Wheat is planted on 240 million hectares worldwide. As some areas become hostile to wheat, others will become more receptive, such as the high latitudes, where a temperature increase of a few degrees is expected to boost wheat yields. Cool, high-latitude spring wheat environments, as in Canada and Siberia, will benefit most, as farmers will be able to plant earlier and replace current cultivars with high-yielding winter wheats, according to the report. And higher atmospheric carbon dioxide can enhance photosynthesis, which will likely boost plant growth and yields.

However, areas with shaky food security are unlikely to benefit. To help farmers in developing countries deal with climate change, researchers in an international network that includes CIMMYT and the International Center for Agricultural Research in the Dry Areas are developing new varieties suited to warmer, drier environments and promoting resource-conserving farming practices. At CIMMYT, scientists have been breeding for heat-stressed areas for several years, and these resources can be deployed to newly heat- stressed regions. However, regions that are already hot and dry will require tougher varieties. Targeted breeding and strategic physiological characterization used to select varieties that display traits associated with heat and drought tolerance (such as cooler canopies and the ability to store starch in the stem) will help these areas. The varieties can be crossed with landraces that are particularly heat tolerant to increase wheat's genetic diversity. Wild relatives are also used in wide crossing to introduce exotic traits not found in wheat. The resulting synthetic wheats have been bred for disease resistance and more stress-adaptive root systems.

Breeding and crop management research under the Cereal System Initiative in South Asia (CSISA), a large collaborative project led by the International Rice Research Institute and funded by the United States Agency for International Development and the Bill & Melinda Gates Foundation, should also help farmers cope with climate change. The goal of CSISA is to use new science and technologies to boost cereal production and productivity, particularly for rice and wheat, in South Asia's most important grain baskets. Physiological approaches are incorporated with conventional breeding to increase genetic diversity, even as the CSISA target area suffers dramatic temperature increases and constricted water resources.

Agronomic practices play an important role in the ability of wheat to withstand climate change. Conservation agriculture encompasses a set of cropping practices that includes reduced soil tillage, the retention of crop residues and crop rotation. This optimizes the root environment and the availability of essential nutrients and water, permitting cultivars to achieve their genetic potential. The adoption of conservation agriculture has been slow in developing countries, but it is key to solving the climate change puzzle.

"You need different strategies to improve agriculture productivity, especially in terms of climate change," said Reynolds. "You need to think about other species, about the soil, about genetics, about economic imperatives - everything. In the end, we must look beyond our own expertise and focus on how different technologies can be complementary to avert a major catastrophe."