A devastating fungus is stalking the world’s wheat crops, placing millions at risk of famine. Now, in a renewed commitment toward eliminating the wheat stem rust pathogen called Ug99, the UK’s Department of International Development (DFID) and the Bill & Melinda Gates Foundation have pledged $40 million to Cornell University’s plant research program.
“[Stem rust] is the source of the great biblical plague,” says Ronnie Coffman, principal investigator of the Durable Rust Resistance in Wheat project at Cornell University. Plants affected by Ug99 erupt in rust-colored pustules on the stem. Clouds of red spores take to the wind, spreading their disease to distant nations.
In Kenya last year, Ug99 destroyed around 80% of the wheat crop. Spores have spread to Kenya, Ethiopia, Sudan, Yemen and Iran. Scientists fear the other major wheat-growing regions of the world, including North America, will be next.
Stem rust is not new; it has been wiping out crops for millennia. But for a brief period following the green revolution, it looked like modern science had defeated the threat. Stem rust is the most severe of the three types of rust diseases affecting wheat. Yellow or stripe rust, and leaf rust are prevalent but more manageable threats.
Scientists have been working diligently against stem rust for decades, carefully cultivating genes that make wheat resistant to the fungus. Each time, the fungus has evolved with remarkable speed. As Norman Borlaug, pioneer of the green revolution, noted, “Rust never sleeps.”
Then in the 1960s, crop scientists had a remarkable breakthrough. While the fungus is able to overcome single resistance genes in wheat, a combination of many resistance genes is difficult to overcome. Such a crop was duly created. With the introduction of major resistant gene Sr31 and a number of other minor genes, stem rust became a distant memory. Borlaug won the Nobel Peace Prize for his efforts in 1970. Already scarce plant research funding was directed elsewhere.
Then in 1998, a crop researcher in Uganda noticed a strain of stem rust in his test plot that was capable of overcoming Sr31. The fungus had evolved and become virulent again. Stem rust was back, quite aggressively, and researchers had few tools to fight it.
Since then, CIMMYT (the international maize and wheat improvement center in Mexico), and other partners have identified new resistance genes and created wheat varieties that can resist Ug99. The seeds have been distributed to agricultural research services in a number of at-risk nations, including Nepal, Bangladesh, Ethiopia, Kenya, Egypt, Pakistan and Afghanistan. It is somewhat of a quick fix, however.
“We are concerned that this resistance will be overcome in a fairly short time,” says Coffman. “Sometimes it lasts longer than the others.” Borlaug’s resistance lasted for 30 years. Ug99 is still mutating, and new variants can overcome to a number of resistance genes. (See Nature’s previous coverage.)
Cornell University and its many partner organizations are looking for a more durable solution to the problem. The $40 million in funding should help them in this quest, says Coffman. Over the next five years, the DFID will contribute $15 million, and the Gates Foundation a further $25 million.
The money will go toward better surveillance, breeding of new variants and cultivars, as well as pre-breeding programs that identify new sources of resistance, according to Coffman.
New techniques such as genome wide selection, as well as older, tested techniques such as marker-assisted breeding will help. Stacking many resistance genes together will make it is impossible for the fungus to overcome resistance, says Coffman.
“We’ve been at work for 3 years, and we’ve had real progress,” he says.
Image: photo by jayneandd via Flickr under Creative Commons