Biologists are warning that the resurgence of a plant disease in East Africa could destroy 10 percent of the world's wheat crops. The so-called wheat rust could seriously affect Africans, many of whom are already experiencing food shortages because of drought.

The world's most feared wheat disease is back. Puccinia graminis, also known as wheat rust or wheat rot, is a fast-spreading, wind-borne fungus that shrivels wheat stems so that they crumple over and die in the field. It's the equivalent of ebola virus for wheat.

Wheat rust caused huge grain losses in North America and famines in Asia in the first half of the 20th century. After a 50-year hiatus, it resurfaced in Uganda in 1999 and within three years spread to Kenya and Ethiopia, choking off tens of thousands of hectares of wheat crops.

Plant scientists are now raising the alarm that the disease, if unchecked, could spread to other parts of eastern Africa, which produces about 10 percent of the world's supply of wheat.

U.S. botanist and Nobel laureate Norman Borlaug helped develop resistant wheat varieties 50 years ago. Now, at 91 years old, he is leading the charge against the resurgence of this potentially devastating blight.

He says that wheat-rust fungus is like bacteria in that it protects itself by building up immunities to chemicals meant to kill it. The fungicides used 50 years ago no longer work today.

Mr. Borlaug spoke to VOA by telephone from Texas A & M University in College Station, Texas. "It's been 50 years without an epidemic, but in the biological world there are mutations and hybridizations going on in pathogens," said Mr. Borlaug.  "And it's true of wheat diseases, [or] any crop diseases. When penicillin first came out as an antibiotic, it controlled many diseases. But little by little it lost its effectiveness. This was because of changes in the microorganisms themselves to build up resistance."

Wheat, he says, is the world's most important cereal.  "Wheat, until the last 15 years, was the number one cereal in total tonnage produced. But in the case of maize a large part of it is used for animal feed," added the scientist.

More than 60 million tons of wheat is at risk of the wheat rot, or about $9 billion (U.S.) worth of grain, according to a report issued late last week by the International Center for Maize and Wheat Improvement.

East African farmers are desperately searching for wheat varieties that can withstand the fungus, says Mariam Kinyua, a director for Kenya's Agricultural Research Institute.  She is charged with developing those fungus-resistant wheat varieties.

"It's only time," she said.  "We can't tell how long it will take, but for sure it will spread, there's no question about that. It's not only spreading in East Africa, it stands to spread globally."

In Kenya, large-scale wheat farmers grow most of the country's wheat, and they have been spraying fungicide on their crops three times a year to control the blight, says Ms. Kinyua. But most small-scale farmers can't afford to spray, she says.

"The small-scale farmers stand to lose a lot," she said.  "The large-scale farmers of course also stand to lose in that they have to spray up to three times, and spraying of the fungicide is at a cost."

The cost of each spraying of fungicide is about $90 per hectare, a huge expense for the region's wheat farmers.

A Global Rust Initiative has been set up in Nairobi to monitor progress of the disease and identify and breed new rust-resistant types of wheat.

Scientists in Ethiopia and Kenya, testing thousands of wheat varieties, are confident that they can identify at least one that can resist the wheat rust by the end of November.

In the meantime, many of East Africa's small-scale farmers are forced to wait it out, hoping that the wheat rust will not damage too much of their harvest.