Mutant Wheat Fungus Continues To Frustrate Food Experts

Wheat stem rust, also known as wheat black rust, is often referred to as the “polio of agriculture.” The rapidly mutating fungal disease can travel thousands of kilometers and wipe out crops, and outbreaks of the deadly fungal disease in wheat crops in Germany and Ethiopia in 2013 have had the scientific community up in arms trying to figure out how to stop it from spreading to other regions of the world.

Wheat farmers and scientists at a recent summit hosted by the Mexico-based International Maize and Wheat Improvement Center (CIMMYT ) have been examining outbreaks of different strains of wheat stem rust in the two countries to identify any similarities.

In Germany “the occurrence of stem rust was favored by a period of unusually high temperatures… and an unusually late development of the wheat crop due to cold spring and early summer temperatures,” explained Kerstin Flath, senior scientist at Germany’s Federal Research Center for Cultivated Plants at the Julius Kuehn-Institut. The outbreak occurred in June in central Germany, a mainly wheat producing area, and was the first in the country in several decades.

Scientists noted that the rust came so late that even the fungicides sprayed earlier to prevent leaf rust epidemics proved ineffective.

Then in November 2013 the disease struck a popular variety of wheat in Ethiopia called digalu, used to make bread, said Bekele Abeyo, a senior scientist and wheat breeder at CIMMYT.

What was particularly disconcerting for the scientists was that digalu had been bred with inherent resistance to certain strains of stem rust and another wheat disease called “yellow rust” or “stripe”.

The fact that the fungus has been rapidly mutating has prompted scientists to study the two cases with a view to helping with the preparation of new wheat varieties.

David Hodson, a senior scientist with the Global Cereal Rust Monitoring Program at CIMMYT, says the analysis presented on the German outbreak showed “there were some clear specific differences between the races present in Germany compared to Ethiopia, although the races were similar and fitted into the same race group.”

Fungicides are the first line of defense, but a longer term solution is replacing the world's entire wheat varieties with those that contain several minor rust-resistant genes, which are pooled together to counter the infection, giving them an edge over single rust-resistant genes in combating various mutated variants of the fungus. Digalu contains single rust-resistant genes.

There are 20 new stem-rust-resistant varieties of wheat available. But getting the new seeds to farmers has been a problem, mainly due to poor distribution networks and cost.

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