Fusarium Wilt May be Controlled by Other Fusarium Strains

By Sharon Durham
July 14, 2000

Agricultural Research Service scientists and cooperators are searching for environmentally-friendly ways to control plant diseases. In the case of Fusarium wilt, beneficial stains of Fusarium are being used to control plant pathogenic strains. In tests so far, some of the beneficial Fusarium are winning--and that’s good news for tomato growers who need an alternative to the chemical fumigant methyl bromide.

The scientists’ enemy is a pathogenic strain of Fusarium oxysporum that causes Fusarium wilt. Fusarium wilt afflicts many vegetables, melon and other crops such as basil, causing severe losses. Fusarium wilt, however, is a particular problem for tomatoes since there is a new race of the pathogen that attacks tomatoes. For now, methyl bromide is used to keep this pathogen at bay. But by 2005, methyl bromide will be phased out, because it is identified as an ozone-depleting chemical. So scientists are studying alternatives that are environmentally safe while still effective against the pathogen.

Deborah R. Fravel, a plant pathologist at ARS’ Biocontrol of Plant Diseases Laboratory in Beltsville, Md., and George Lazarovits, research scientist and team leader with Agriculture and Agri-Food Canada in Ontario, Canada, are working in a cooperative study to find methyl bromide alternatives. In their studies, they’re pitting harmless Fusarium species and other “good guy” biocontrol organisms against the wilt-causing F. oxysporum.

The scientists tested several beneficial strains of F. oxysporum against the wilt-causing strain. They found one strain, CS-20, reduced wilt by 49.6 percent. They also mixed beneficial strains of a fungus (Trichoderma virens strain G1-3) and a bacterium (Burkholderia vietnamiensis strain Bc-F). The fungus/bacterium treatment reduced wilt incidence by 41.6%. Also, CS-20 and the fungus/bacterium combination treatment significantly increased both the weight and number of tomatoes on the plant.

Now, researchers must figure out how the biocontrol mechanisms work. Some biocontrol agents work by competing with the pathogenic strains for nutrients and space. CS-20 seems to pump up the plants’ natural defenses against pathogens, a reaction called “induced systemic resistance,” according to Fravel.

Scientific contact: Deborah Fravel, ARS Biocontrol of Plant Diseases Laboratory, Beltsville, Md.; phone (301) 504-5080, fax (301) 504-5968; fraveld@ba.ars.usda.gov.