Sept. 12 marked the one-year anniversary of the death of one of the greatest men of the 20th century, Norman Borlaug. He was the 1970 Nobel Peace Prize laureate and central figure of the “green revolution,” which transformed agriculture in the 20th century and saved millions from starvation. It is sad then that one of the greatest scourges that Borlaug seemed to vanquish in his day — wheat stem rust — is staging a comeback.
Wheat stem rust, Puccinia graminis, is a fungal pathogen of wheat that has been plaguing farmers for millennia. When a spore of the fungus lands on a healthy wheat plant it will multiply and form a reddish-brown pustule, which looks like rust on the stalk of the plant. This pustule will redirect the plant’s water and nutrients to its own growth and therefore deprive the grain, damaging its development. More spores will then be produced and the disease will spread like wild fire crippling a harvest. This rust destroyed 20 per cent of U.S. wheat crops several times between 1917 and 1935 with the last major outbreak in 1962 destroying 5.2 per cent of the U.S. crop. These frightening statistics are even more troubling when you realize that wheat is the most widely planted crop in the world, and that it accounts for an estimated 20 percent of the calories consumed by humans.
Despite its terrifying potential, wheat rust was thought to have been eliminated by the 1970s largely due to the work of Borlaug. Working with the Cooperative Wheat Research and Production Program in Mexico in the 1940s, he and his colleagues were able to crossbreed various strains of wheat until they identified a gene, Sr31, which resists wheat rust. In addition to this natural immunity from the rust, the Sr31 gene also boosted the yield of the wheat plant. New strains of wheat that possessed combinations of this and other resistance genes became ubiquitous until it was thought that wheat rust had vanished from the Earth.
In 1998 a researcher in Uganda discovered traces of wheat stem rust. Following confirmation of these findings, the new variant of wheat rust was named Ug99. It appears that Ug99 has mutated such that it can now overcome the Sr31 resistance gene and spread among once impervious fields. This is alarming given that all but a handful of the wheat strains grown today are vulnerable to Ug99. Ug99 quickly spread to wheat in Kenya and Ethiopia and in 2006 arrived in Yemen. In 2007 it was found in Iran and the fear is that it will shortly migrate into Pakistan and then to Punjab, India, one of the world’s great wheat producing areas.
The gravity of the threat Ug99 poses has prompted an immediate response by scientists to begin searching for new resistance genes. The most likely approach is to use four or five genes that independently are not as strong as Sr31 but which collectively grant resistance against the rust. To this end, researchers at the cereal disease laboratory of the U.S. Department of Agriculture have tested roughly 16,000 wheat varieties for resistance to the fungus.
Researchers elsewhere in the world are also working on the problem with India and Pakistan having released their own rust resistant varieties. In total, researchers have developed about 60 experimental wheat varieties with these low resistant genes.
While these discoveries have promise, they are not a cure-all. These new resistant strains often have lower yields than the Borlaug Sr31 strains. This is a trade-off that a hungry world can hardly afford. The green revolution was credited with saving millions of lives from starvation. Let’s hope that with the same determination and luck which Borlaug had we may stave off the dreaded stem wheat rust once more.
In memory of Norman Borlaug, reflect on what Jonathan Swift wrote in Gulliver’s Travels:
“And he gave it for his opinion, that whosoever could make two ears of corn or two blades of grass to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country, than the whole race of politicians put together.”