Rust never sleeps

From nuclear terrorism to Earth-killing asteroids, avian flu and global warming, these days you can choose to set aside every hour of the day for a specific worry and never repeat yourself.

To insure it stays that way, I’d like to introduce you to Ug99.

Ug99 is a strain of black stem rust that attacks wheat. It’s a fungus whose spores attach themselves to the plant. Once they germinate, the rust spreads inside the plant, sucking out nutrients, and eventually bursts out into the open, weakening the stem and shedding more spores. As the April 7 issue of New Scientist puts it (in a story subtly headlined “Billions at risk from wheat super-blight”), “It can reduce a field of ripening grain to a dead, tangled mass.”

Rusts aren’t exactly new: the Romans prayed to a stem rust god called Robigus. A 1916 epidemic in Saskatchewan in 1916 destroyed 100 million bushels of wheat, and a 1954 epidemic wiped out 40 percent of the North American wheat crop*.

Until recently, though, some people thought such epidemics were entirely of the past. That’s because of the successful development, after the 1954 epidemic, of rust-resistant wheat strains by the Mexico-based International Maize and Wheat Improvement Center (known as CIMMYT, its Spanish acronym). Rust resistance in wheat was a key element of the Green Revolution that boosted food production around the world in the 1960s.

Leading that work was Norman Borlaug, who won the Nobel peace prize in 1970. Now, at the age of 91, he’s leading the fight against Ug99, because when it comes to this new fungus, most rust-resistant strains aren’t.

The rust was first identified in Uganda in 1999 (hence the name), but the fight to stop it didn’t really get started until 2002, when it showed up in Kenya. Borlaug sounded the alarm, and finally the international research community moved into action. A Global Rust Initiative (GRI) has been formed at CIMMYT.

Ug99 was first noticed because it grew on crops that contained a gene complex called Sr31, the main source of rust resistance around the world. Then, just last year, it also started showing up on wheat with another gene complex providing resistance, Sr24. About 50 genes are known to provide rust resistance, but only 10 percent work even partially against Ug99, and they’re present in less than one percent of the crop.

CIMMYT has been taking the top-yielding varieties from various countries and crossing them with Ug99-resistant wheat from its seed collections, then testing the crosses in fields in Kenya and Ethiopia. Some of the resulting lines are now being grown in test plots in India, Afghanistan and Pakistan.

Resistant strains are important because fungicide is expensive and sometimes simply not available. Even the U.S. might not have enough if Ug99 were to show up right now, because the U.S. is already dealing with a soybean rust epidemic.

The soybean rust spores are thought to have ridden hurricane winds from Morocco. Ug99 could arrive here the same way (or arrive via air travel, or even be introduced deliberately by terrorists). In the meantime, the winds are spreading the fungus across the Middle East: it’s already jumped the Red Sea to Yemen and Sudan in the Arabian Peninsula.

Canada has some advantage because the rust resistance for most Canadian wheat varieties comes from different genes than those found to be ineffective against Ug99 (work is ongoing to determine exactly what genes do provide that resistance). About 100 Canadian wheat lines have been evaluated in Kenya, and while most were susceptible, some showed good resistance, and are being used in the effort to develop new rust-resistant strains for the rest of the world.

With luck, we’ll be ready when Ug99 gets here. For much of the developing world, however, specially since wheat stocks are at their lowest level since 1972, the threat is closer and the challenges greater.

So as you plan out your worry schedule for tonight’s insomnia, make room for Ug99.

There may not be a thing you can do about it, but when has that ever stopped anyone from worrying?

*UPDATE: David Mowbray, head of corporate communications for the International Maize and Wheat Improvement Center (CIMMYT), emailed me a slight correction: “In 1954 Canada lost about 40% of the harvest but in North America it was less because winter wheat planted in the southern US wheat belt was not so badly damaged. We think that 40% of spring wheat in North America is a better figure to use. Interestingly as well, Canada at the time had large surpluses in storage and that helped mitigate the scale of the problem.”

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    • David on May 14, 2007 at 10:36 am
    • Reply

    The spread of Ug99 and strategies to combat this are
    highlighted in a blog post Dangerous
    rust puts strain on food security
    , based on an article, “Current
    status, likely migration and strategies to mitigate the threat to wheat
    production from race Ug99 (TTKS) of stem rust pathogen
    ”, by Ravi P. Singh,
    David P. Hodson, Yue Jin, Julio Huerta-Espino, Miriam G. Kinyua, Ruth Wanyera,
    Peter Njau and Rick W. Ward, appears in CAB Reviews: Perspectives in
    Agriculture, Veterinary Science, Nutrition and Natural Resources 2006 1, No. 54.

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