Heads Up for Soybean Rust

Four years ago, it was found lurking on soybeans growing on the Hawaiian island of Oahu. And some U.S. plant pathologists believe it's only a matter of time before this devastating fungus gets to the continental United States--hitchhiking on a traveler's clothing or in cargo or blown on the wind. 

It's the Asian species of soybean rust, known formally as Phakopsora pachyrhizi. And its potential for damage is enormous.

At a 1995 workshop convened to propose a plan for controlling a possible invasion of P. pachyrhizi, U.S. experts estimated that the fungus could cut soybean yields by more than 10 percent anywhere in the country. In the warm, moist Southeast, it could cause losses of up to 50 percent. In addition to soybeans,P. pachyrhizi naturally infects 31 legume species in 17 different genera. One of those plants is kudzu--a common weed pest in the Southeast--which might serve as a continual source of inoculum.

"All you need is one spore," says ARS plant pathologist Morris R. Bonde. Under the right environmental conditions, it could produce trillions of spores within weeks." Bonde was one of the experts at the workshop sponsored by the University of Illinois' National Soybean Research Laboratory.

Bonde is also one of the first U.S. scientists to study soybean rust, starting in 1974 when he joined ARS' Foreign Disease/Weed Science Research Unit in Frederick, Maryland. He says it was one of three foreign diseases the agency deemed necessary to prepare for.

He worked with the late Edgar E. Hartwig, an ARS soybean breeder in Stoneville, Mississippi, who developed some breeding lines with resistance to soybean rust. But as time passed and the virulent Asian species remained on the other side of the globe, interest waned.

Now Bonde and molecular biologist Reid D. Frederick and biologist Gary L. Peterson are gearing up this research. Bonde says there's a need for more germplasm with strong resistance to soybean rust. So he's searching for a laboratory method to rapidly evaluate wild germplasm and breeding lines that accurately reflects how the plants would react to the fungus in the field.--By Judy McBride, ARS.

Morris R. Bonde, Reid D. Frederick, and Gary L. Peterson are in the USDA-ARS Foreign Disease/Weed Science Research Unit, 1301 Ditto Ave., Fort Detrick, Frederick, MD 21702-5023; fax (301) 619-2880, [Bonde] phone (301) 619-2860. , [Frederick] phone (301) 619-7386. [Peterson] phone (301] 619-7313.

"Heads Up for Soybean Rust" was published in the July 1998 issue of Agricultural Research magazine. Click here to see this issue's table of contents.