The Durable Rust Resistance in Wheat project at Cornell University recently received $67 million in genetics funding from the Bill and Melinda Gates Foundation to design a wheat strain that can resist the devastating stem rust fungus.
Wheat stem rust has posed perhaps the greatest threat to the world food security in decades. Once thought to be completely contained, a new mutation of the fungus began tearing through previously immune crops around a decade ago. The new fungus, called Ug99, devastated crops in Uganda and soon spread to areas of Kenya, South Africa and Iran. Stem rust can kill up to half a harvest and has the potential to infect 90% of the wheat worldwide.
Since conventional forms of genetic resistance had failed to contain the fungus, a new approach was needed. The researchers at Cornell began working in partnership with Ravi Singh, a top wheat pathologist at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, to develop a new, more durably resistant form of wheat. This team of scientists rejected the current conventions of disease resistance genetics to design a wheat strain that would not be vulnerable to a slight mutation of the rust fungus.
There are two kinds of disease resistant genes: "major" genes which provide complete resistance to a disease by themselves, and "minor" genes which may slow a disease's progression but do not provide total immunity. The commonly accepted disease-resistance technique has almost exclusively used major genes. They are easily added to a wheat strain's genome and provide an easy and cost effective route to disease resistance. However, the simplicity of adding just one gene to provide total resistance proved to be this method's undoing. Pathogens, such as stem rust, can very likely mutate to overcome one gene. It usually requires only a few small changes in their DNA, which can likely happen just from normal, random gene mutations. This was the case with Ug99, which destroyed numerous crops with a "major" gene modification.
(image of stem rust courtesy of Wikipedia Commons)
Scientists have long known that it is more difficult for a pathogen to mutate to overcome numerous resistant genes. Therefore, Singh and the Cornell researchers employed a method that used several "minor" genes in combination to provide total resistance to Ug99. The researchers bred over 2 million varieties of wheat with numerous different combinations of Ug99 resistant "minor" genes. By the end of the first year they had 298 types of wheat with near or total resistance to the fungus. Many of these varieties had a 10% higher yield than current varieties being grown in Africa making the wheat more attractive to farmers and hopefully easier to distribute. However, the monumental task of distributing the new varieties to all the wheat farmers in Africa and the Middle East is a truly monumental task, and it still remains to be seen if the new genetically-modified wheat will provide a long-term solution to the rust problem.
Despite these difficulties this project remains as a glowing accomplishment for crop genetics. Ronnie Coffman, head of the DRRW project at Cornell University, summed up the project saying, “We are facing the prospect of a biological firestorm, but it’s also clear that the research community has responded to the threat at top speed, and we are getting results in the form of new varieties that are resistant to rust and appealing to farmers,”
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