New Variety of Wheat Resists Ancient Disease : Agriculture: Scientists declare victory over leaf rust, the age-worn fungus that this summer caused an 18% drop in yield on premier U.S. farmland.

After more than two decades of research, scientists in Mexico City say they have finally won the battle against leaf rust, a fungus that has plagued wheat fields since Roman times.

The plant specialists developed a variety of wheat that is high-yielding and shows long-term resistance to the leaf rust disease, said lead researcher Sanjaya Rajaram. The work was done at the Centro Internacional de Mejoramiento de Maiz y Trigo (International Maize and Wheat Improvement Center), the world’s foremost center for wheat and corn research.

Center officials are scheduled to proclaim their victory over leaf rust next week in Washington at a meeting of the 18 worldwide plant research centers that make up the Consultative Group on International Agricultural Research.

The announcement comes at a time when U.S. wheat farmers are particularly worried about leaf rust. California wheat farmers lost as much as 20% of their wheat crops to the fungus this spring. More significantly, in wheat fields throughout Kansas and upper Oklahoma--the heart of America’s breadbasket--the disease caused an 18% drop in yield in this summer’s harvest, for an estimated $90 million in losses.

“Our No. 1 problem is leaf rust,” said Bikram Gill, a wheat researcher and plant pathologist at Kansas State University.

Wheat is still the staff of life for many of the world’s people. It is the second most important food crop, after rice, and is grown in nearly every part of the world. And where wheat grows, so does the leaf rust--so named because the yellow spores of the fungus give the leaves a rusty appearance. The fungus coats the leaves of the plants, blocking the plant’s ability to absorb nutrients.

The leaf rust is such a facile disease that each time breeders develop a variety of wheat that resists the fungus, the rust mutates into a strain that overcomes the resistance. That’s why the development of long-term resistance is “very significant,” Gill said.

The key to the resistance, Rajaram said, is that it involves several genes working together to fend off the fungus. Actually, the wheat is not totally resistant to the fungus; instead of killing off the leaf rust, it disables the fungus and reduces the damage to a negligible level.

“When there is complete resistance, the (plant) doesn’t let the fungus grow at all, and the automatic response in the fungus is to mutate and survive,” Rajaram said. “When there is only partial resistance, there is no need for the fungus to mutate. So that’s why we believe this (partial) resistance will be more durable.”

The center can make the resistant wheat available to farmers on all continents, but it may take several years for breeders to fine-tune it to local environments.