Mutant wheat fungus alarms food experts

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Outbreaks of a deadly fungal disease in wheat crops in Germany and Ethiopia in 2013 have had the scientific community buzzing over the threat posed to global food security.

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 kilometres and wipe out crops.

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 favoured 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 Centre 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.”

In Ethiopia, he said, the season had also been favourable for rusts, with above-average and well distributed rainfall - conditions similar to those in 2010 when wheat crops there were affected by yellow rust.

However, said Hodson, “the key factor was the presence of a suitable host and the appearance of a race that was able to attack this host.”

Flath said the big question on the German outbreak was whether it "was a unique situation or if it will repeat this year" - particularly because they had had a rather mild winter, so the spores might have survived.

She reckons a changing climate will "definitely" favour this thermophilic fungus. In the last two years two new aggressive variants of the yellow rust-causing fungus have made huge inroads in central and northern Europe.

Defense

Fungicides are the first line of defense. 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.

Industrialized countries have an edge in terms of resources, said Flath. But even developing countries, realizing that food security is at stake, are beginning to make massive investments, says Abeyo. For instance, after the outbreak in Ethiopia in 2010, the government invested US$3 in fungicides, which helped contain the fungus in 2013.

With global wheat supplies vulnerable to changing weather patterns, Abeyo says developing countries are realizing the need to become self-sufficient in grain.

"Countries are now making the investment in infrastructure and research to develop better varieties." But they still have a long way to go. Better partnerships with the developed world in sharing information and skills to monitor and protect their crops are also proving to be effective, he added.


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