Old wheat, new genetic engineering may protect crop from deadly pest

Wheat stem rust goes after its favorite meal.

Evans Lagudah and Zakkie Pretorius

Currently, roughly 20 percent of humanity's caloric intake comes from wheat. Agricultural strains, specialized for bread or pasta production, have been bred for high productivity and resistance to many agricultural pests. But over the past few years, one of those pests, a fungus called wheat stem rust, has evolved the ability to overcome wheat's defenses. Dangerous strains of wheat stem rust were first spotted in Uganda, but are now present elsewhere in Africa, in Yemen, and in some areas of Iran. That's set off an international scramble to find ways of generating a resistant wheat before the rust spreads any further.

By working with uncultivated relatives of agricultural wheat, two teams of scientists have identified a pair of genes, each of which provides partial resistance to the new strain of stem rust. Although each gene can be bred back into commercial wheat strains, the combination of the two is likely to be even more potent, so the researchers are considering putting them on a single DNA construct and then engineering that into various agricultural strains.

Wheat stem rust infections severely limit the plant's productivity and can kill it in severe infections. In the early 1900s, outbreaks in the US would routinely destroy a double-digit percentage of the nation's harvest. The breeding of resistant strains of wheat was therefore a major accomplishment. In 1999, however, researchers in Uganda discovered a new strain of stem rust (Ug99) that could infect resistant crops. Since then, the fungus has spread to other parts of Africa, and resistant strains have been spotted in the Middle East. Tests indicate that roughly 90 percent of the currently cultivated wheat strains are vulnerable to it. In 2005, a group was formed to coordinate international efforts to breed a resistant crop.