‘Stem rust’ fungus threatens global wheat harvest

The world’s leading crop scientists issued a stark warning that a deadly airborne fungus could devastate wheat harvests in poor countries and lead to famines and civil unrest over significant regions of central Asia and Africa.

Ug99 — so called because it was first seen in Uganda in 1999 — is a new variety of an old crop disease called “stem rust”, which has already spread on the wind from Africa to Iran. It is particularly alarming because it can infect crops in just a few hours and vast clouds of invisible spores can be carried by the wind for hundreds of miles.

Scientists meeting in Mexico this week at a summit on Ug99 worry it will continue travelling east and infect major wheat growing centres in Pakistan, India and Bangladesh, which produce nearly 15% of the world’s wheat and feed more than a billion of the world’s poorest people. Plant breeders are now racing against time to develop new resistant wheat strains and distribute the seeds around the world.

The fungus was thought to have largely disappeared since the 1960s when original disease-resistant varieties were developed and planted. But Ug99 has evolved to take advantage of those varieties, and it is now believed that 80-90% of all wheat varieties grown in developing countries are susceptible to the new fungus.

The Nobel prize-winner Norman Borlaug, who is credited with helping India and other countries avoid famines in the 1960s by developing high yielding crop strains, said: “This thing has immense potential for social and human destruction. It is capable of severely damaging virtually all of the world’s commercial bread wheat. It is a problem that goes far beyond wheat production in developing countries. Sooner or later it will be found throughout the world, including North America, Europe, Australia and South America.”

The new version of what scientists believe was one of the Biblical plagues has spread from Uganda to Kenya, and then to Ethiopia and southern Sudan. Where the spores attack, a wheat crop can be turned into a tangle of blackened and broken stems in a few days. Up to 80% yield losses were recently recorded in Kenya and Uganda, though fortunately neither of these countries wholly depends on wheat as a staple crop .

But in 2007, it jumped the Red Sea, possibly as a result of Cyclone Gonu, and is now widespread in Yemen and Iran. Wheat is a major crop in Iran, but its progress has been slowed by a long-term drought that has inhibited its growth.

“Kenya is having recurring epidemics, the situation is getting worse in southern Sudan and it is now widespread in Ethiopia,” said Rick Ward, co-ordinator of the Durable Rust Resistance in Wheat project, based at Cornell university. “The likelihood is that it has already spread beyond Iran. We would be foolish to believe that other countries in central Asia, such as Afghanistan and Pakistan, are not already at risk. Places like Kazakhstan, Turkey, Ukraine are all susceptible.”

Ward predicted that Ug99 would inevitably spread much further, potentially into regions where wheat is a staple crop for hundreds of millions of people. “It is a certainty that it will expand its area,” he said. “It will continue to move and wherever it is present and the crops are susceptible it will potentially lead to a disaster of catastrophic proportions, which will translate into widespread food insecurity and civil unrest.” Global wind models suggest the crop disease may next spread into Pakistan, Afghanistan and India.

Large wheat farmers in developed countries can buy expensive fungicides, which they must apply several times to protect their crops, but very few of the small farmers in Asia can afford the chemicals.
However, scientists at the meeting reported rapid progress in developing newly disease-resistant wheat varieties. According to plant geneticist Ravi Singh, a project leader at the International Wheat and Maize Improvement Centre in Mexico, 60 disease-resistant varieties have been developed via conventional breeding, some of which are thought to be not only resistant to Ug99, but higher-yielding than today’s most popular varieties. Countries such as Bangladesh and Pakistan are already being helped to multiply resistant seeds for future harvests, he said.

But it usually takes at least five years to cross disease-resistant lines with wheat varieties adapted to local conditions and then grow enough seed to plant fields. “We are making rapid progress but it will take years to distribute enough new varieties” said Ward.