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Supercharging the Wheat Plant

March 3, 2011

Wheat physiologists using a spectral radiometer to study photosynthesis in the spikes of wheat plants.

Against a worrisome background of unrelenting food price inflation and volatility, wheat researchers meeting in northwestern Mexico during the first week of March examined early evidence that shows the promise of a pioneering approach to achieve a quantum leap in the yield potential of this staple cereal. The group included some of the world’s top plant scientists, who gathered at Ciudad Obregón – the cradle of last century’s Green Revolution – for the First International Workshop of the Wheat Yield Consortium.

The approach they are pursuing focuses sharply on photosynthesis, the process whereby plants use sunlight to convert carbon dioxide into biomass. The wheat plant’s photosynthetic inefficiency, compared with that of some other crops, like maize and sugarcane, is the primary obstacle to improving its yield potential. Yet, modern wheat breeding, while improving many other important traits, such as disease resistance, has left this fundamental aspect of crop performance essentially unaltered since the work began.

“The world desperately needs a breakthrough in wheat photosynthesis,” said Thomas Lumpkin, Director General of the International Maize and Wheat Improvement Center (CIMMYT), who painted a grim picture of the “perfect storm” that is brewing, as sluggish yield growth, worsening water scarcity and exhausted soils steadily undermine global food security.

Evidence suggesting that it is feasible to ramp up wheat photosynthesis has come from seemingly unlikely sources. One recent result concerns the “stunning effect,” as Martin Parry of Rothamsted Research in the UK put it, of a single enzyme on biomass production in tobacco, which increased by 40 percent in the first 7 weeks of plant growth. Parry is now exploring whether the bacterial gene that produced this outcome in health-harming tobacco can have a similar effect on wheat, a critical staff of life.

Another piece of evidence derives from the results of CIMMYT wheat trials conducted during 2010 in South Asia. Among the best performers were new lines that were designed by combining traits that are known to improve plant performance under drought.

“Since this approach is successful for improving wheat performance in dry areas, we expect it to have a similar or even greater impact on yield potential under optimum conditions,” said Matthew Reynolds, the CIMMYT plant physiologist who is coordinating the Wheat Yield Consortium, which has received strong financial support from the Mexican government.

Based on a detailed knowledge of the physiological and genetic basis for plant performance, the approach aims to deliver a new and long-awaited breakthrough in wheat yield potential. Since the Consortium’s creation in late 2009, participating scientists have been pursuing three main lines of research.

The first aims to raise biomass production in wheat through genetic modification of the enzyme Rubisco, which plays a key role in photosynthesis but is relatively inefficient. A second group of researchers is concentrating on changing various traits to ensure that more biomass translates to higher grain yield but without weakening the stems and roots, which would cause plants to topple over, or lodge, as the grains ripen. Using a variety of plant breeding methods, a third group will assemble the combination of traits needed for higher wheat yields in superior lines that meet farmers’ other requirements, such as disease resistance and wide adaptation to diverse production environments.

This work marks the beginning of an exciting new chapter in wheat improvement, which promises to raise yield potential in favorable environments (where most of the world’s wheat is grown) by up to 50 percent within about two decades.

The last time an increase of that magnitude was achieved, it resulted from the work of Nobel Peace Prize Laureate Norman Borlaug, who developed disease-resistant, semi-dwarf wheat varieties in Mexico between the mid-1940s and 1960s. When fertilizer was applied, the new lines produced higher grain yields rather than lodge, as did the tall traditional varieties they replaced in Mexico and subsequently Asia. The result was the Green Revolution of the 1970s.

Since then, wheat yields have risen only gradually through a process in which breeders have selected the best lines in international yield trials without knowledge of the physiological basis for their superior performance. Within the last decade, the annual rate of wheat yield growth has slowed to less than 1 percent – far short of the 2 percent increase needed to keep pace with burgeoning demand (driven mainly by rapid population growth) and to ensure affordable wheat for poor consumers.

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