Science News 07/06/2010

Alarm for new strains of Ug99

Four new mutations of Ug99, a strain of a deadly wheat pathogen known as stem rust, have overcome existing sources of genetic resistance developed

The new "races" have acquired the ability to defeat two of the most important stem rust-resistant genes, which are widely used in most of the world's wheat breeding programs.

The evolving pathogen may pose an even greater threat to global wheat production than the original Ug99.

The reddish-brown, wind-borne fungus known as Ug99 has decimated up to 80 percent of Kenyan farmers' wheat during several cropping seasons, and scientists estimate that 90 percent of the wheat varieties around the world lack sufficient resistance to the original Ug99. Starting five years ago, in response to evidence of Ug99's virulence, researchers expanded breeding programs and collaborated with each other in a kind of "shuttle breeding diplomacy" to identify wheat varieties that could resist the new strain. But the new mutations, identified last year in South Africa, will make wheat crops more vulnerable as pathogens now will find new wind trajectories for migration.

di S. C.