Features Agronomy Genetics/Traits
Plan in place to prepare for arrival in Canada

Ug99 wheat stem rust threat is being monitored closely around the world

Dr. Duane Falk of the University of Guelph contends that developing resistance must include gene insertion as well as accumulating minor genetic resistance, to ensure longer-term success.

A form of wheat stem rust known as Ug99 is sending shockwaves of alarm in wheat producing areas around the world. However, with proper implementation of federal and provincial planning, it is hoped that the threat to Canadian wheat will be kept to a minimum.
At present, this virulent strain of black stem rust fungus, Puccinia graminis, has spread from Kenya and Ethiopia in Africa to Yemen and Iran in western Asia. It originated in Uganda in 1999, hence the Ug99 designation. Parts of the Indian subcontinent also are at risk.
Iran is considered a flashpoint in Ug99’s spread. The fungus normally reproduces asexually, releasing billions of spores. These spores are not identical, and there can be mutations in asexual populations of spores. If the spores drift onto a barberry bush, Berberis vulgaris, which is common in Iran, sexual reproduction, gene mixing with other stem rusts could occur. The resulting offspring could be much more virulent than their parents.

Even on its own, Ug99 continues to evolve. New derivatives of Ug99 were isolated in Kenya in 2006 and 2007. 

There is general consensus that Ug99 will eventually arrive in North America. Albert Tenuta, crop pathologist and field crops program lead with the Ontario Ministry of Agriculture, Food and Rural Affairs, says, “The concern of course is that our varieties have little protection and today would be susceptible. We’ve probably seen more stem rust this past year than I’ve ever seen. It’s the same across North America.”

Although a lot of attention is on Ug99, there is also the possibility that a new stem rust race could develop in North America,” Tenuta also points out. “Our resistance genes have been effective for 44 plus years, and it’s only a matter of time until they’re overcome by stem rust.”

Despite that outlook, Tenuta is nonetheless optimistic. “One of the main differences between the 1940s and 1950s, when we last saw stem rust outbreaks, and now is the fact that we have some preparation time. We will hopefully have new high-yielding resistant varieties available. We also have fungicide products which are very effective against not only stem rust but other cereal rusts such as stripe and
leaf rust.”

There is little time to lose for developing resistance. The standard amount of time to cross disease-resistant lines with wheat varieties adapted to local conditions in wheat-growing areas around the globe is generally considered to be at least five years. Mark Etienne of Hyland Seeds says “rust tolerance is one thing, but in Ontario and Canada, we are working with a quality crop that must ‘yield’ and be competitive within our current marketplace.” He adds, “We have been working on fusarium for more than twenty years in Ontario and are still striving to incorporate tolerance to infection and DON within our varieties. Based on fusarium, finding tolerance and resistance can be a long-term, frustrating and somewhat expensive process.”

Taking action
To mitigate the global threat of Ug99, the Bill and Melinda Gates Foundation has provided a grant of $26.8 million for three years of research into the extent of resistance in current varieties, and develop resistance in new varieties. The project, entitled “Double Rust Resistance in Wheat,” is based at Cornell University in Ithaca, NY, and directed by Dr. Ronnie Coffman, an international professor of plant breeding and director of International Programs at Cornell’s College of Agriculture and Life Sciences.

Program partners include research labs in Kenya, Ethiopia, US, Canada, China, Australia, and South Africa. Project support also will be provided by the Food and Agriculture Organization of the United Nations (UN-FAO). Three international agricultural research centers will also take part: the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, the International Center for Agricultural Research in the Dry Areas (ICARDA) in Syria, and International Rice Research Institute (IRRI) in the Philippines.

In the project’s executive summary, Coffman states that “about 90 percent of the wheat grown around the world is vulnerable to severe damage to the new types of stem rust disease emerging out of East Africa.” It also has been reported that up to 75 percent of all spring and winter wheat varieties grown in the US are susceptible to Ug99. In terms of Canadian wheat resistance, Dr. Tom Fetch can give the most accurate answer. As Canada’s leading stem rust expert and a crop pathologist with Agriculture and Agri-Food Canada in Winnipeg, Fetch has sent about 70 spring cultivars for Ug99 field testing in Kenya, and found that about 10-15 percent have intermediate resistance and about five per cent have high levels of resistance.

Coffman states that the Cornell project, of which Fetch is the lead Canadian, will use multiple approaches to achieve long-lasting stem rust resistance including a small group of elite high-yielding breeding lines. Other sources, particularly from wild relatives, need to be “cleaned up” by having linked deleterious traits removed before they can be used effectively in wheat breeding programs. Marker assisted technologies
can speed up these breeding approaches.

Dr. Duane Falk, associate professor of plant agriculture at the University of Guelph, hopes that the high-tech strategy of inserting resistance genes, while considered “cutting edge,” is not the primary focus. “It’s short-sighted,” he says. “We must accumulate minor resistance genes in breeding programs, so that resistance doesn’t break down. It’s a much better long-term solution. Once you’ve done it, you’ve done it
for good.”

In the search for resistance, 10 to 15 percent of spring cultivars from North America exhibit intermediate resistance with five percent showing high levels of resistance.

Canadian concerns
There are two ways Ug99 could spread to North America, according to Fetch. “Wind is the natural way rust spores move,” he says. “If it went to western Africa, if we could confirm it was on the west coast, in August there are hurricanes and tropical storms that move across the Atlantic that could bring it here.”

“The other direction is to the East,” Fetch notes. “If it gets to China, we know there have been events where dust particles have blown across to North America. A rust spore is equal to or even lighter than these particles.”

The second manner Ug99 could turn up in North America is through human transfer. “Rust spores can be transported on clothes,” says Fetch. “We think that this is how stripe rust was introduced into Australia. We don’t know how soon Ug99 could be introduced into North America in this manner, but the more Ug99 spreads, the greater the chance that someone could bring it over here.”

Although Ug99 is not considered an immediate threat to Canadian wheat fields, Tenuta sees the global threat as a positive force, by raising awareness. “We have a whole new generation of growers that haven’t seen stem rust and aren’t aware of the impact it could have on crops,” he says. “The more people looking out there, the better.” Tenuta says OMAFRA has incorporated Ug99 information into many recent presentations, and will be producing a stem rust brochure that will assist producers in Ontario and beyond.

In terms of Canada-wide preparedness, Fetch is leading the creation of a national action plan. “There are three things that we’re going to try to do,” he says. “One is basic pathology work, part of the Cornell project, where the fungus is and how much it is mutating. We know the original isolate has mutated at least twice to slightly more dangerous forms. This is very important to know for breeding programs.”

The second part of the national plan, says Fetch, is to identify resistance in Canadian wheat lines and incorporate known resistance genes. “There are not a lot of lines within the bread wheats with significant resistance,” he says. “That’s where we’re focussing our work.”

“In tandem with that,” Fetch says, “the third thing we want to do is ensure new cultivars have at least two effective resistance genes and then use them in a field program.” The action plan will finalized by the end of the year. “In the meantime,” he says, “I am doing what I can on my own. This plan will enhance the work.”