Your Reading List

Heading off a stem rust pandemic

Only two older wheat varieties are resistant to Ug99, a devastating race of stem rust which threatens to spread around the world

Working under tight security in their plant science laboratory at Morden, Man., Tom Fetch and his scientific colleagues look as if they’re handling extremely hazardous material.

After changing into hospital scrubs in a locker room, Fetch and his team deactivate an alarm system and go through four doors to enter the laboratory. The Level 3 containment lab, certified by the Canadian Food Inspection Agency, operates under negative pressure so air cannot leave the room. The scientists work carefully with isolates from Africa obtained through CFIA import permits. Their work starts in November and lasts only during winter so cold will kill the agent should it accidentally escape from the lab. Before leaving, Fetch and his crew shower to wash away any spores that might be clinging to their bodies and hair.

Watching these extreme biosecurity measures, you’d think the scientists are dealing with a dangerous pandemic agent that, if it ever got out, could cause widespread devastation. And you’d be right.

Fetch leads a team of Agriculture and Agri-Food Canada research scientists racing against time to find genes with resistance to Ug99, a new race of wheat stem rust spreading through eastern Africa and central Asia.

Although Ug99 is currently confined to a distant corner of the globe, it has the potential to cross borders, even oceans, and infect wheat crops worldwide.

At AAFC’s research facility in Morden, Man., Tom Fetch and his colleagues study Ug99 in a hermetically sealed Level 3 containment lab, and only during the winter in case of a pathogen escape.

At AAFC’s research facility in Morden, Man., Tom Fetch and his colleagues study Ug99 in a hermetically sealed Level 3 containment lab, and only during the winter in case of a pathogen escape.
photo: AAFC

The stakes to develop resistant lines are high because, so far, over 80 per cent of the world’s wheat varieties have little or no resistance to Ug99.

The fungal disease is so virulent that crops, once infected, have been known to collapse completely in a few weeks.

Which means that Ug99, if it continues to spread, is a potential threat to wheat everywhere, including Western Canada.

“It’s almost like a forest fire,” said Fetch. “If it gets out of control, it just spreads so fast that, at that point, even with chemicals, it would be difficult to control if you had enough acres infected.”

On the move

First identified in Uganda in 1999 (hence the name), Ug99 is now present in 13 countries. Most are along Africa’s east coast from Egypt all the way down to South Africa. Ug99 has also been detected in Yemen and Iran.

Related Articles

Pathology experts worry Ug99, carried on the wind, could spread to Pakistan, India and China, where wheat is a staple crop. From there, spores could potentially ride trade winds over the Pacific Ocean to North America. This is not as far-fetched as it sounds. Dust particles have been known to blow across China to North America and a rust spore is no heavier than a speck of dust.

It’s also possible that spores could come over on the bodies of international travellers, which is how the SARS epidemic came to Canada from Hong Kong in 2003.

Even more worrying is the fact that new strains of Ug99 keep appearing, allowing the disease to stay one jump ahead of efforts to breed resistant varieties. Currently, there are 13 known strains of Ug99, including the original one. If a wheat variety contains only one resistant gene, a mutating Ug99 could pick it off and remain unchecked.

For that reason, Fetch and his colleagues are trying to use genes in combination to create multi-gene stacks of resistance. In that way, even if Ug99 overcomes one resistant gene, there are several others in the gene stack to counter it.

And there’s good news. Fetch said his group of roughly 15 scientists has found three new resistant genes and is currently identifying associated molecular markers to make sure those genes have actually been added to the lines they’re working with.

“The ideal system is to put multiple genes in a line so that, if Ug99 overcomes one gene, it still cannot attack the plant fully because there are other genes that are still effective,” says Fetch.

Resistant Canadian varieties

Currently, the two Canadian wheat varieties with the best resistance are AC Cadillac and AC Peace. Both are relatively old — Cadillac was registered in 1996 — so they may not be as good as the new high-yielding cultivars. But Cadillac is considered a gold standard for disease resistance and breeders have used it in crosses since 2005. In 2013, Agriculture and Agri-Food Canada released AAC Tenacious, a hard red spring wheat with Cadillac resistance to rust and fusarium head blight. Fetch says Tenacious contains two resistant genes — better than most wheat but still not quite enough to satisfy breeders.

There hasn’t been an epidemic of wheat stem rust on spring wheat in Canada for over 60 years. The last major one occurred in 1955 and caused hundreds of millions of dollars in losses. Since then, breeders have achieved durable resistance by stacking resistant genes into wheat varieties. Annual surveys in Canada and the U.S. monitor for changes in rust populations.

A successful North American campaign to eradicate the barberry early in the last century helped eliminate a host for cereal stem rust, but Fetch says eradicating the barberry in Africa and Asia is unrealistic, especially since its berries can be used for food or medicine.

A successful North American campaign to eradicate the barberry early in the last century helped eliminate a host for cereal stem rust, but Fetch says eradicating the barberry in Africa and Asia is unrealistic, especially since its berries can be used for food or medicine.

Most Canadian spring wheat varieties are resistant to current stem rust races in North America. But since Ug99 is not from North America, its arrival here could undo decades of progress in preventing rust outbreaks. Fetch says if Ug99 were to arrive in the southern U.S. in January, it could migrate northward along the so-called Puccinia pathway of spore movement into Western Canada within one growing season. Surveillance in the U.S. would give Canadian farmers advance warning. As a result, they could prepare for Ug99’s arrival by either planting the few available resistant wheat varieties or stocking up on fungicides.

Are fungicides an option?

But could chemical companies make enough fungicide available in such a short time to protect the millions of acres of wheat grown annually on the Prairies? It’s a big if.

“If you did not have fungicides available, it would cause some serious problems because (Ug99) is available on 80 per cent of our wheat,” Fetch says.

An added problem is that fungicides increase farmers’ input costs and their continued use could produce fungicide-resistant strains of stem rust.

Canada and the U.S. have one advantage over other countries in controlling the spread of Ug99. A common native shrub called the barberry, found throughout temperate and subtropical regions of Africa and Asia, acts as an alternate host plant, which allows rust spores to reproduce sexually. Normally, Ug99 reproduces asexually and releases spores that, for the most part, are genetically identical. However, when the barberry gets infected, sexual reproduction of spores can re-scramble the genes and produce new strains of the disease.

Widespread eradication programs throughout North America in the early 20th century largely eliminated barberry populations. But Fetch says eradicating the barberry in Africa and Asia is unrealistic, especially since its berries can be used for food or medicine.

Another concern is that the barberry is also present in South America, although it’s unclear if this shrub is the kind that gets stem rust. Fetch says a recently funded pro­ject in collaboration with scientists in Brazil, where barberry is native, will try to find out. If it turns out Latin America has rust strains which can infect barberry, that potentially brings Ug99 even closer to home.

Research into Ug99 is an international effort with scientific teams in various countries working co-operatively.

In 2011, the Bill & Melinda Gates Foundation and the U.K. Department for International Development announced a $40 million investment in a global project led by Cornell University to identify new rust-resistant genes in wheat and to distribute resistant seeds to farmers.

About the author

Comments

explore

Stories from our other publications