Microorganisms used to fight fruit rot.

If you can't lick 'em, join 'em. That's the lesson agricultural researchers have been applying recently. Rather than fight mold on fruits and seeds with expensive and sometimes ineffective pesticides, plant pathologists have isolated naturally occurring bacteria, yeast, or fungi and used these microorganisms to control more harmful ones.

The beneficial microorganisms may work in several ways, says Wojciech J. Janisiewicz of the Department of Agriculture's Appalachian Fruit Research Station in Kearneysville, W. Va. They may outcompete pathogens for living space, he says, or use up available nutrients, thereby excluding the pathogens. The helpful microbes may also produce chemicals that kill or disable potential competitors.

Janisiewicz is now working with a pink yeast that can keep stored pears and apples from rotting. He scraped or bruised apples and then treated them with the pink yeast. The yeast reduced or completely prevented mold growth at wounds, he reports in the May PLANT DISEASE.

"The yeast worked as well as a fungicide on fruit removed from storage after 3 months," he says. "And in fruit stored for 6 months, yeast-treated fruit has less rot than fruit treated with fungicides." Because the pink yeast occurs naturally on most fruits, Janisiewicz adds, it should be safe to use on fresh produce.

"We really believe [such biocontrol agents] are going to be a major part of commercial pesticide control mechanisms," says Gary E. Harman, a plant pathologist at Cornell University who has recently started a company to exploit the new technologies. Harman and his colleagues are working with a fungus called Trichoderma, which acts both through simple competition -- not giving other fungi a chance to grow -- and by releasing enzymes that dissolve fungal cell walls.

Harman hopes to market biocontrol products for treating seeds and applying on soil by early next year. In addition, his company has isolated the fungicidal enzymes and the genes that code for them, he says. These may prove effective biocontrol agents and be easier to store and apply than the fungus itself. However, to be effective, enzyme solutions may require several applications.

Biocontrol agents that can be applied by conventional techniques should be on the market next year. Janisiewicz has patented a bacterium that prevents post-harvest diseases in apples, pears, and citrus fruits. This has been developed commercially by EcoScience Corp., based in Worcester, Mass.

Environmentally friendly biocontrol systems are looking more and more promising, says Janisiewicz, and should quickly acquire consumer support. "The public will have to be educated to accept [microorganisms] on fruit," he says. "They are already there . . . and [the public] just has to realize that some of them are good, and some of them are bad."