August 22, 2013 | Vol. 117 -- No. 18

Scientists make progress in fighting wheat rust

Scientists have been hard at work in recent years combating a significant disease of wheat. Stem rust is caused by a group of nasty fungal organisms that can infect wheat plants and devastate yields. In some cases up to 100 percent of the crop can be lost.

The battle between stem rust and agricultural researchers isn’t new. Sometimes the tide runs in one direction, sometimes in another. At the end of the last century the advantage went to the fungus side. In Ethiopia and Uganda in 1998 and 1999, a new type of stem rust appeared. It’s known for short as “Ug99” for Uganda, 1999.

Luckily, Ug99 is apparently still limited in its occurrence to east Africa and possibly Iran. So far it’s not spread to places like Pakistan where it could devastate a food supply on which many millions of people depend. But time is ticking away, and the threat of Ug99 is very real.

Farmers in the developed world can combat stem rusts by spraying their crops with fungicides. But in the developing world, small farmers simply don’t have the economic resources to buy and apply fungicides. They are at the mercy of stem rust and can lose their crops to its many fungal strains.

To help farmers everywhere, agriculture researchers have been trying to give wheat genetically based resistance to stem rusts, including Ug99. If the plant itself could resist infection, the problem of Ug99 infection would be solved without the expense of sprays.

To help me understand the Ug99 threat I turned to Prof. Tim Murray, a plant pathologist at Washington State University. Murray talked me through two articles published this summer in the journal Science about Ug99 and resistance to the disease conferred by two genes.

Some 10,000 years ago ancient farmers started to bring about what became modern bread wheat. The first big step was taken with the crossing of two genomes or species of plants. Then another cross-pollination combining three genomes led to basic bread wheat, as we know it today.

“One of the techniques we have as researchers is to go back to wild relatives looking for useful genes,” Murray said.

Two such useful genes have now been identified, Sr33 and Sr35 (the Sr stands for “stem rust”). And those genes have been put into varieties of bread wheat not through GMO techniques but via traditional crossing.

The Sr33 gene gives wheat a relatively broad range of stem rust resistance but not excellent resistance to Ug99. Sr35 confers effective resistance for Ug99 but is vulnerable to other stem rusts.

“The next step is for researchers to combine Sr33 and Sr35 in one plant,” Murray said. “That’s not an uncommon strategy, combining multiple resistant genes into one variety of wheat.”

Murray explained to me more work must be done and Ug99 remains a serious threat. But the two recent articles mark real progress. And in such an important arena as the world’s wheat supply, it’s worth celebrating the victories that researchers are starting to make over major threats like Ug99.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

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