WHEAT, the chief ingredient in everything from Ethiopian flat breads and Indian chapattis to French baguettes and American doughnuts, faces a crisis. Unless something drastic is done, climate change, disease and drought will ravage the crop that is the main source of food for 2 billion people.
Fortunately, a strategy is emerging to save wheat from oblivion. It involves neither genetic engineering nor subtle changes to farming techniques. Instead, the plant is being recreated over again from scratch. And test plantings of these 鈥渟ynthetic鈥� wheats are raising hopes they will be resilient enough to feed billions of people well into the next century.
As plants go, wheat is a bit of a freak, originating some 30,000 years ago in the Fertile Crescent of Mesopotamia, in what is now Iraq, when two unrelated wild grasses Triticum urartu and Aegilops speltoides came together in a genetic accident, hybridising to create 鈥渆mmer wheat鈥�, the forerunner of durum wheats used to make pasta today. Some 20,000 years later, a third wild plant, the goat grass Triticum tauschii, joined the party, creating Triticum aestivum, the type of wheat suitable for making bread.
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鈥淭he synthetics are ugly things but they contain valuable genes. One variety digs deep into the soil to find water鈥�
This serendipitous coming together produced a hexaploid plant 鈥� one that contains three pairs of chromosomes. But hexaploidy contains the seeds of wheat鈥檚 current problems: such plants cannot be cross-bred with other species, which usually have only one or two pairs of chromosomes. This makes it almost impossible to introduce new traits such as tolerance to salt or drought. An inefficient method called genetic introgression can be used to fuse chunks of chromosomes of related plants into wheat, but it is not very successful. Instead, plant breeders have focused on maximising wheat鈥檚 own genetic potential, which, in the main, has meant selecting for new wheat varieties with progressively higher yields.
Now even this limited room for manoeuvre is running out. As the natural genetic variability of wheat becomes exhausted, the crop has been left exposed to a rapidly changing environment. New fungal diseases are emerging and in the American Midwest, the country鈥檚 bread basket, farmers are suffering the worst drought for more than a century. History reminds us how calamitous such events can be. In the 1930s, the 鈥淒ust Bowl drought鈥� wreaked havoc on American agriculture. During the 1950s a fungal disease called stem rust 15b devastated the nation鈥檚 pasta wheat crop.
Scientists raced to head off another catastrophe. A breakthrough came 15 years ago, when scientists at the International Wheat and Maize Improvement Center (CIMMYT) in Mexico discovered a way to cross a wild variant of emmer wheat with a wild variant of goat grass. Normally, the result of such crosses is triploid, with just three chromosomes, each lacking the twin it needs to be fertile (the hexaploidy that made Triticum aestivum fertile was a lucky genetic accident). But by exposing the triploid plants to the chemical colchinine, each chromosome could be tricked into making the twin it needed to become fertile, and thus crossable with modern hexaploid wheats.
This technique has since been used to create more than 1000 varieties of synthetic wheat from the many thousands of wild varieties of emmer wheat and goat grass that have spent the past 10,000 years adapting to new conditions. 鈥淭hese relatives have carried on evolving in very hot, dry places,鈥� says Jonathan Crouch, head of the genetic resources programme at CIMMYT. The new synthetic wheats obtained by crossing tough wild strains can be cross-bred with conventional wheat to introduce new traits. 鈥淭he synthetics are ugly things, but they contain valuable genes,鈥� says Richard Trethowan, senior wheat breeder at CIMMYT.
They are now beginning to show their worth. Last December, Crouch told a conference in Cambridge, UK, that one artificial variety has just produced yields 50 per cent greater than normal wheat in drought conditions in Mexico. Yields proved 5 to 40 per cent higher than with normal wheat in test plantings in India, Pakistan, Ecuador, Australia and Argentina. In a paper submitted to The Journal of Experimental Biology, the researchers say the success of this synthetic wheat lies with its unusually deep roots, which dig into the soil to find water.
Other synthetic wheats tested show tolerance to extreme heat, with varieties coping well with temperatures of up to 40 掳C in Mexico鈥檚 Sonora desert. Such heat-tolerant strains will be vital if climate change leads to higher temperatures. A 2 掳C rise depresses wheat yields by up to 15 per cent in warm countries such as India and Pakistan, Trethowan says. 鈥淚f wheat production fails in these countries, you鈥檙e talking about considerable social and economic instability.鈥�
Synthetic wheats are also appearing that are resilient to a range of emerging crop diseases. In east Africa, the Ug99 strain of stem rust has been causing wheat to wither in the field, while elsewhere a disease known as Take-all, caused by a soil fungus that damages roots, can cut yields by 40 per cent. Another, fusarium head blight, not only attacks the ears of growing wheat plants but contaminates the harvest with toxins that render the crop dangerous to eat. Synthetic wheats resistant to these and other fungal diseases have been identified, and researchers are working to turn these into commercial crops.
Last month the National Institute of Agricultural Botany, in Cambridge, UK, signed a contract with CIMMYT to co-develop new varieties. Wayne Powell, the institute鈥檚 chief executive, says he hopes it will become a model for developing crops without genetic modification.
鈥淚f wheat production fails, you are talking about considerable social and economic instability鈥�
The new strains could have many desirable traits, such as extra mineral content. CIMMYT has identified synthetic wheats with 50 per cent more iron than usual and 80 per cent more zinc. The new varieties could help farmers as they try to adapt to climate change. As temperatures change, wheat will grow at other latitudes, where the length of day is different. 鈥淲e can鈥檛 change that, but we can change the way wheat responds to it,鈥� says Powell, who envisages synthetic wheats that develop at the right times in unfamiliar environments.
