Stem rust outbreak potentially the largest to hit Europe
An unusually destructive strain of stem rust fungus may devastate European wheat crops this year, according to warnings from epidemiologists at the University of Cambridge. The fungus decimated tens-of-thousands of hectares of crops in Sicily in 2016. Cambridge Professor Chris Gilligan led a team which found that stem rust spores from the Sicilian outbreak may have drifted to other parts of the Mediterranean. Tests by the Global Rust Reference Center have also revealed that the fungus can now infect dozens of lab-grown strains of wheat.
The stem rust fungus damages wheat, leaving a characteristic brown stain.

An infection that struck wheat crops in Sicily last year is a new and unusually devastating strain of fungus, researchers say — and its spores may spread to infect this year’s harvests in Europe, the world’s largest wheat-producing region.

“We have to be careful of shouting wolf too loudly. But this could be the largest outbreak that we have had in Europe for many, many years,” says Chris Gilligan, an epidemiologist at the University of Cambridge, UK, who leads a team that has modelled the probable spread of the fungus’s spores.

In alerts released on 2 February, researchers revealed the existence of TTTTF, a kind of stem rust — named for the characteristic brownish stain it lays down as it destroys wheat leaves and stems. The alarm was raised by researchers at the Global Rust Reference Center (GRRC), which is part of Aarhus University in Denmark, and the International Maize and Wheat Improvement Center (CIMMYT), headquartered in Texcoco, Mexico.

Last year, the stem rust destroyed tens of thousands of hectares of crops in Sicily. What’s particularly troubling, the researchers say, is that GRRC tests suggest the pathogen can infect dozens of laboratory-grown strains of wheat, including hardy varieties that are usually highly resistant to disease. The team is now studying whether commercial crops are just as susceptible.

Adding further concern, the centres say that two new strains of another wheat disease, yellow rust, have been spotted over large areas for the first time — one in Europe and North Africa, and the other in East Africa and Central Asia. The potential effects of the yellow-rust fungi aren’t yet clear, but the pathogens seem to be closely related to virulent strains that have previously caused epidemics in North America and Afghanistan.

The Food and Agriculture Organization of the United Nations (FAO) in Rome issued similar alerts about the three diseases on 3 February.

Severe wheat damage in Europe could affect food prices, inflation and the region’s economic stability, says James Brown, a plant pathologist at the John Innes Centre in Norwich, UK.

But researchers hope that by putting out alerts before European wheat crops have started to grow this year, they will give farmers enough warning to monitor fields and apply fungicides, halting the disease’s spread. Plant breeders can also start to ramp up efforts to produce resistant varieties. “Timely action is crucial,” says Fazil Dusunceli, a plant pathologist at the FAO.

Return of stem rust

In the mid-twentieth century, devastation caused by stem rust spurred efforts to breed wheat strains that could resist the fungi. That research — led by agronomist Norman Borlaug — famously led to the Green Revolution in agriculture, increasing crop yields around the world.

But stem rust returned in the late 1990s and 2000s, with a variety called Ug99 that spread through Africa and parts of the Middle East. It ruined harvests and caused international concern because, says Dusunceli, more than 90% of wheat crops were susceptible to it. So far, however, it hasn’t hit large wheat-producing regions such as Europe, China and North America. Researchers are developing resistant crops.

Stem rust epidemics haven't been seen in Europe since the 1950s, says Mogens Hovmøller, who leads the GRRC’s testing team. “It’s not a challenge plant breeders have faced for many years,” agrees Brown.

But the outbreak that hit Sicily in 2016 suggests that the disease has now returned. Unusually, even the hardy durum wheat, used to make pasta, is susceptible to it, says Hovmøller. But it’s too early to say whether the new infection could be as devastating as Ug99.

Models based on wind and weather patterns, conducted by Gilligan's team at Cambridge University together with CIMMYT and the UK's Met Office in Exeter, suggest that stem-rust spores released during the Sicilian outbreak may well have been deposited throughout the Mediterranean region. That doesn’t mean the infection will spread — the spores may not have survived the winter, for example — but it is worrying enough for researchers to raise the alarm.

The yellow-rust strains are also a concern, says Hovmøller. For Europe, perhaps the most alarming is one provisionally called Pst(new), which was spotted in Sicily, Morocco, Italy and northern Europe in 2016. The fungus is related to a virulent strain that hit North America in the 2000s, but it is not clear how aggressive it is.

Early-warning system

Researchers are accustomed to finding one or two new wheat-rust strains each year in Europe; these must be guarded against but are not usually dangerously virulent. But since 2010, the region has experienced a greater influx of wheat pathogens, says Hovmøller.

He doesn’t know why, but speculates that it could be down to warmer autumns and milder winters attributable to climate change, combined with changes in farming practices, such as sowing wheat earlier in the season. Increases in international travel — potentially spreading spores on clothing — could also be a factor, speculates Brown.

Hovmøller and others will in the next few weeks ask the European Research Council for funds to establish an early-warning system. That will help partners including breeders, scientists and agrochemical companies in Europe to share diagnostic facilities and information about potential outbreaks.