Killer fungus spells disaster for wheat

“We advise at least two resistance genes,” says Ward. Wheat with the SR24 gene alone gives any Ug99 strains resistant to SR24 a huge advantage, just as misuse of antibiotics selects for antibiotic-resistant bacteria, says Ward. Farmers then switched to using wheat with other resistance genes and the same thing happened.

Ug99 is now resistant to the three major anti-rust genes used in nearly all the world’s wheat. “The real solution is disease resistance that relies on a number of genes,” says Ward. Wheat with multigene resistance does not so much destroy the fungus as slow it down. The hope is that with several genes involved it will be much harder for the fungus to become resistant and there will be less selection pressure for it to do so.

A breeding programme by CIMMYT and others has now uncovered some wheat types which “show promise” in tests against Ug99 in Kenya and Ethiopia, says Ronnie Coffman of Cornell University in Ithaca, New York, who chairs the programme. Funding has increased, as rich countries such as Canada and the US worry that Ug99 could hit their breadbaskets, accidentally or deliberately.

Without such fears, says Khouri, “it is hard to convince donors to take preventive actions, when people are not starving now”. But that may not be far off. “People will start starving if Ug99 cuts harvests enough to push up grain prices,” warns Ward.

The problem is that crop breeding is slow. It usually takes at least five years to cross disease-resistant lines with wheat varieties adapted to local conditions in the world’s wheat-growing countries, then grow enough seed to plant fields threatened by Ug99.

New Scientist has learned that China started a crash programme to breed resistance into Chinese wheat varieties last year, after an article on Ug99 in this magazine was translated into Chinese and circulated to top agriculture officials.

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