Natural Cure for Sugar Beet Leaf Spot
By Don Comis
May 21, 2003
Agricultural Research Service scientists
have applied for a patent on their discovery of a "good" fungal
enzyme that may prevent leaf spot, a widespread disease of sugar beets that
reduces beet yields and sugar content.
This biocontrol discovery is especially timely because scientists now
believe that Cercospora beticola, the fungus that causes leaf spot
disease, is beginning to develop resistance to some fungicides. The researchers
envision possibly applying some form of the enzyme to sugar beet leaves to
starve the "bad" fungus.
In 2001, U.S. farmers grew more than 25 million tons of sugar beets,
providing about half of the country's sugar supply. They also applied thousands
of pounds of fungicide to sugar beet leaves to battle leaf spot.
Plant pathologist Robert Lartey and microbiologist TheCan Caesar-TonThat of
ARS' Northern Plains Agricultural
Research Laboratory in Sidney, Mont., discovered an enzyme called laccase
in the beneficial fungus Laetisaria arvalis. This fungus is well known
as a wood- and leaf-decay fungus of forests. But it is also found in farm soils
where sugar beets grow.
Laccase is one of many enzymes produced by the fungus to break down deadwood
and leaves. In lab experiments, it was very good at detoxifying the toxin
produced by the leaf spot fungus. The toxin, called cercosporin, kills plant
leaf cells. Leaf spot gets its name from the spots on leaves that are actually
colonies of fungi feeding on leaf tissue killed by the toxin.
Next, Lartey and Caesar-TonThat will test the enzyme on potted sugar beet
plants in a greenhouse. If that goes well, they will move on to sugar beets
growing in the field.
More information about this natural biocontrol research can be found in the
May issue of
Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.