Bacteria May Turn a Weed into a Weakling

Leafy spurge, one of the worst weeds on western ranges, is doing some good for a change--and doing itself a disservice, scientists hope.

As a “lab rat” at the Agricultural Research Service, spurge is helping scientists ferret out which root-dwelling bacteria might have potential as commercial bioherbicides to thwart this pesky weed and perhaps others. ARS is the chief scientific research agency in the U.S. Department of Agriculture.

Rhizobacteria live on or within a few millimeters of roots. As roots grow through the soil oozing juices in their wake, the microbes feed on the substances. Some of these microbes, called deleterious rhizobacteria (DRB), also produce toxins. These trigger cells of some plants to produce excessive hormones. The hormonal flood may keep seeds from germinating or damage plants by putting their life processes in “overdrive.”

Weeds weakened by DRB toxins are less able to compete with other plants, such as field crops and forage plants, for soil nutrients, moisture and sunlight. Wimpier weeds are also more vulnerable to other controls.

Leafy spurge, a Eurasian native, infests at least 29 states. It costs four of them--Montana, Wyoming and North and South Dakota--an estimated $144 million annually.

Using half-gram samples of leafy spurge tissue culture, ARS microbiologist Robert J. Kremer at Columbia, Mo., developed a time- and labor-saving procedure to screen DRB for further testing on whole plants.

So far, Kremer and colleagues have tested thousands of strains of DRB at the agency’s Cropping System and Water Quality Research Unit. About 30 percent are highly toxic to leafy spurge. Many have reduced root growth in preliminary field tests. Some DRB may prove better suited than others for mass production and commercial use.

This month’s Agricultural Research magazine contains an article about the DRB research--and a related story on the agency’s special 5-year anti-spurge project. The stories are also online at:

http://www.ars.usda.gov/is/AR/archive/oct98/rhizo1098.htm

Scientific contact: Robert J. Kremer, ARS Cropping System and Water Quality Research Unit, Columbia, Mo., phone (573) 882-6408, fax (573) 884-5070, [email protected]