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 thats good
news for tomato growers who need an alternative to the chemical fumigant methyl
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, theyre 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
Scientific contact: Deborah Fravel, ARS
Biocontrol of Plant Diseases Laboratory, Beltsville, Md.; phone (301) 504-5080,
fax (301) 504-5968; email@example.com.