`Micro Bugs' Harnessed To Replace Plant Pesticides

Friendly microbes, used as an alternative to chemical treatments, are being reintroduced to American farmlands to combat plant diseases

It's the Timex watch of microbes: Boil it, dry it, deprive it of oxygen, and it keeps on ticking - fighting plant diseases.

UW85, recently discovered by a team from the University of Wisconsin at Madison, combats a strain of algae that specialists say is responsible for causing millions of dollars in damage to crops and ornamental plants.

It contains a powerful new class of naturally occurring plant antibiotics that scientists are trying to harness in their quest to come up with biological alternatives to chemical treatments.

The move may represent good news for consumers, who are increasingly demanding chemical-free foods.

``Soil communities have been destroyed through years of intensive farming,'' says Cindy Schaffer, a microbiologist in the US Environmental Protection Agency's Pesticide Program Office. In effect, she says, scientists are rediscovering useful microbes that once were prevalent in farmland.

Biological control, as the approach is known, has been harnessed for more than 100 years in the fight against insect infestations. But the field is still in its infancy when dealing with plant diseases.

Researchers give two reasons for the lag: Bugs and bug damage are relatively easy to spot, and so have drawn more attention; and plant diseases involve microbes in soil, an environment with highly complex interactions, many of which are not well understood. Conditions must be right

``You're dealing with living organisms,'' says Arthur Nethery, vice president for research and development at Liphatech, Inc., the company licensed to commercialize UW85. ``Conditions must be just right for organisms to grow and have their intended effect.'' Hence success rates at dealing with plant diseases have been lower using biocontrol methods.

Yet biocontrols for plant maladies are beginning to edge their way into the marketplace. Four years ago, the EPA had registered only six biocontrol products; as of this year, the figure has risen to 10, according to Jack Lewis, a soil scientist with the US Agriculture Department's Biocontrol of Plant Diseases Laboratory in Greenbelt, Md. Indeed, this week, the EPA's biopesticides and pollution-prevention division opens for business.

According to acting director Janet Anderson, the division will serve as an advocate for the use of safer pesticides, including biocontrol agents. It also will try to streamline the registration and reregistration process for these products.

The work on UW85, conducted by University of Wisconsin biologist Jo Handelsman and colleagues, illustrates both the potential and the challenges in discovering and marketing new biocontrol agents.

The villain in this bio-melodrama, according to Dr. Handelsman, is a genus of algae-like organisms known as Phytophthora, which includes a species now thought to have been responsible for the Irish potato famine. In the realm of plant pathogens, Phytophthora is one of the most difficult to control, he notes, adding that ``the chemicals that have been used against it are being phased out.''

In Wisconsin, the problem was manifest in soybeans, particularly under cool, wet conditions. Handelsman's team took samples of healthy soybean roots from around the state and developed pure cultures of more than 1,000 different bacterial organisms. They treated soybean seeds with the organisms, and then exposed them to Phytophthora. One strain of bacteria (UW85) shielded the young plants with 100 percent effectiveness. When used in field trials on soybean test plots, UW85 increased the yield by 40 percent over the untreated control group.

The researchers have tested UW85 on a range of crops and diseases, with encouraging results. In one instance, the bacteria successfully warded off a mold that can quickly turn stored cucumbers into a mass of green goo - a potential benefit to Wisconsin's pickle industry.

What's more, in isolating the active component of UW85, the group discovered a new class of antibiotic that targets a wide range of water-mold diseases in plants. As the researchers sought soil samples from sites around the world, they found a variety of bacteria that produce this antibiotic. Regional effectiveness

The issue now, Handelsman said at recent briefings in Madison, Wisc., sponsored by the Council for the Advancement of Science Writing, is to determine the geographic range over which UW85 and its relatives are effective. Her team found, for example, that while UW85 was highly successful in the Midwest, it's results were less spectacular in the South.

One of the unknowns: the size of the region in which UW85 and similar bacteria are effective. Tailoring might be a challenge to marketing and distribution, particularly when compared with the broad applicability of chemicals. The most appropriate avenue for commercializing site-specific products may be agricultural cooperatives.

``Co-ops have a lot of unused labor in the winter,'' Handelsman says, adding that this labor could be put to use producing and distributing biocontrol agents like UW85.

Critical to the continued development of biocontrols is adequate research.

``Soon we may be caught between a rock and a hard place,'' says the USDA's Dr. Lewis, who is concerned about the prospect of declines in federal research budgets. ``Chemicals are being taken off the market and not enough research is being done on biocontrols'' to replace them, he says.

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