BioEd Online

The average human being eats more than 500 calories worth of wheat every day it is a staple among staples. Now, a strain of fungus that threatens most of the world's wheat crop has spread from its origin in Africa, across the Red Sea to Yemen.

Prevailing winds will probably start moving the fungus spores eastwards, experts say. The fungus could be in South Asia in four years, where wheat is the number-one crop in Pakistan and the number-two crop in India.

"It's like it just got on the highway," says Rick Ward, coordinator of the Global Rust Initiative, a group started by the International Maize and Wheat Improvement Center, based near Mexico City, to deal with this strain.

The fungus is a kind of stem rust (Puccinia graminis), so called because it gives the stems and sometimes heads of the grain a rusty look. The stem rust penetrates the plant and gorges itself, leaving little for humans and sometimes breaking the head off altogether. Crop losses start at 40% and keep going up.

Fifty years ago a similar strain of rust ransacked the wheat fields of North America, but since that time wheat growers have not maintained genetic resistance to the blight. To be resistant, the plant must have genes that code for proteins that recognize the incoming rust and kill the first plant cells it infects, so that its march through the plant is stopped. The best resistance is a mixture of several genes, which seems to give a more generalized resistance, rather than a single gene that matches a single protein on the fungus.

The race is on

Almost none of the now-popular wheat varieties have any resistance to the current strain, known as Ug99 (for Uganda 1999, the time and place of its discovery). It will take time for the few crops that do have resistance to be bred into large numbers of plantable crops. Meanwhile, fungicides lie outside the realm of financial possibility for most of the world's wheat farmers.

What results is a race between wheat breeders and the windborne spores. Experts are grasping for monetary figures to put on the likely damage. They agree that it will be at least several billion dollars by the time the fungus can be stopped, although they emphasize that neither the percentage of crop destruction, nor the fungus's exact speed and pathway, is certain.

"This is the equivalent of a slow-motion tsunami," says Ward. "The earthquake happened in central-eastern Africa where Ug99 arose, and the damaging waves are moving out."

Norman Borlaug, who won the 1970 Nobel Peace Prize for his work on improving food crops, bemoans the fact that past experiences with disease strains are often lost. "As we forget what a disease epidemic can look like, the impetus to maintain certain lines of research and types of international collaboration also weakens," he says.

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