Two Fungal Discoveries Will Save Your Bread

Wheat stem rust isn't just ugly, it can destroy the crop that accounts for 20 percent of humanity's food. Robert Park/University of Sydney

Even if worrying about global catastrophes keeps you up at night, wheat rust probably doesn't rank with climate change, nuclear war, and antibiotic resistance. However, with one-fifth of the world's food coming from a single crop, the re-emergence of a disease that threatens it gives agricultural scientists nightmares. So the announcement of two developments to keep this threat at bay brings real Christmas cheer to the few who are actually aware of the danger.  

Wheat rust is a fungal disease caused by members of the Puccinia genus. It has plagued farmers at least since Roman times, and outbreaks continue to threaten lives and livelihoods. Human history has been a race between crops bred to be resistant to diseases and mutations that overcome this resistance. The Irish Famine shows what happens when we fall behind, although in that case a fungal disease infected potatoes.

In recent years, the Ug99 strain of Puccinia graminis has caused losses of up to 100 percent in wheat crops in parts of Africa and the Middle East, contributing to famines in places with little margin for error. So far Ug99 has only just begun to affect the world's largest wheat producers, but Professor Robert Park of the University of Sydney does not think this is something we should be taking for granted.

Park has tackled one of the major obstacles to fighting wheat rust, the long delay before an outbreak can be identified. It currently takes weeks to tell whether an outbreak of stem rust is a strain that poses a major threat, requiring at best expensive fungicides and at worst destruction of the crop and expensive decontamination procedures, or one we can live with.

Although it is called stem rust, the Ug99 strain can infect the leaves and grain as well. Karanjeet Sandhu, University of Sydney

"For the first time it will be possible to do DNA testing to identify whether a rust in a wheat crop anywhere in the world can overcome a rust-resistance gene, called Sr50, which is being introduced in high-yielding wheat varieties," Park said in a statement. More importantly, the analysis techniques Park has announced in Science can be done in hours. Co-author Dr Peter Dodds noted demand for wheat in the developing world is expected to increase 60 percent by 2050, something we have no hope of meeting if we can't get rust under control.

Park and Dodds' work reveals mutation of the gene AvrSr50 led to Ug99 producing a peptide that overcomes defenses bred into wheat to defeat previous rust attacks. The same edition of Science carries another paper showing that a different peptide disables a separate part of the wheat immune system.

Besides swift identification of outbreaks, the two discoveries will help plant breeders develop strains of Ug99-resistant wheat, and possibly even predict the appearance of future dangerous strains.

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