Sowing gene-altered antifungal bacteria.

Sowing gene-altered antifungal bacteria

Wheat take-all disease is aptly named. The take-all fungus invades the roots of wheat plants, causing a crop-devastating dry rot that costs U.S. farmers millions of dollars each year. With no chemical fungicides approved against take-all and no resistant varieties of wheat available, farmers in take-all areas must rotate their wheat crops with other plants that don't support the fungus -- or hope that a natural species of fungus-killing bacteria makes its home in their fields.

Scientists experimenting with genetically engineered bacteria hope to change that scenario. Researchers at Monsanto Co. in St. Louis have taken a naturally occurring, soil-dwelling species of the bacterium Pseudomonas that produces a chemical related to the antifungal phenazine, and added to its genetic material two genes that make the microbes easy to track in the soil. They plan to coat wheat seeds with the bacteria and plant them in test plots at Clemson (S.C.) University.

The Environmental Protection Agency recently granted approval for the bacterial release, based in part on data from ongoing experiments with similar gene-altered bacteria at Clemson. Scientists designed those experiments to see how far engineered bacteria might move from the test site, how long they would survive and whether they would transfer their genetic material to other bacteria. The bacteria, which had no fungicidal activity, were labeled with "market genes" that made them easy to find in soil.

According to Monsanto's David Drahos, results from those first experiments show that gene transfer with other bacteria "does not take place at all." And with the exception of "one guy that got between 7 and 14 inches," all the bacteria stayed within 7 inches of where they were planted.

In the new experiments, scientists will see whether wheat plants that grow from seeds coated with the fungicide-producing Pseudomonas prove resistant to take-all disease. Since the fungicidal bacteria have had marker genes inserted, it should be easy to correlate plant survival with the presence or absence of the fungus-killing bacteria. If the technique proves successful, researchers hope to engineer the bacteria to produce even more of the fungus-killing chemical and to apply the technique to other soil-borned pests.