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A genetic switch that makes certain fungi start producing aflatoxin has
been isolated for the first time. This discovery could lead to
improved resistance to the fungi in vulnerable cropscorn, cotton and
peanuts. ARS scientists located clusters of genes in the fungi
Aspergillus flavus and A. paraciticus for fungi growth and
aflatoxin production. They then found a way to disrupt the "master
switch" gene and shut it down, proving they had found aflatoxin's genetic
coding. For now, researchers are using the genetic code to search out
existing corn varieties that resist the fungi. A test has been developed
that tracks the activity of the aflatoxin master switch gene throughout a
corn seed sample using live A. flavus fungi. Where activity is
high, a bright blue stain appears. Corn seed with less stain shows a high
potential for fungal resistance.
Commodity Safety Research, New
Orleans, LA
Thomas E. Cleveland, (504) 286-4387
A genetically engineered tomato plant from ARS has a new natural shield
against cucumber mosaic virus. Worldwide, this viral disease can
inflict severe losses in tomato, cucumber, spinach and other vegetables.
Insecticides to kill aphids that carry the virus don't always control its
spread. Genes from a molecular enemy of the virus, transferred to
experimental plants, worked well as a defense in the first ARS field test
last year. A second test is underway. The virus rival, a molecule called
S-CARNA 5, is a string of gene material called ribonucleic acid, or RNA.
S-CARNA 5 subverts for its own purpose the virus' ability to multiply.
Thus, the virus can't cause symptoms. ARS scientists inserted the RNA
into a commercial tomato called UC28B. In virus-infected plots, the
plants yielded 50 percent more tomatoes than plants without S-CARNA 5
genes. S-CARNA 5 is harmless to humans, animals and insects. Additional
studies will further assess effectiveness and environmental safety of the
gene defense.
Molecular Plant
Pathology Laboratory, Beltsville, MD
Jacobus Kaper/Marie Tousignant, (301) 504-5745
A primitive fungus is the crucial carrier in a patented new biotech
process for moving desirable genes into plants. Use of the fungus
makes possible genetic transfers to a wide variety of plants. The
soil-dwelling fungus, Olpidium zoospore, is found in temperate
climates worldwide. ARS scientists are using it to help transfer traits
for qualities such as enhanced plant growth, improved seed and better
disease resistance. DNA-transfer methods usually rely on bacterial
vectors, but these are mostly limited to plants in the potato family,
including potatoes, tobacco and tomatoes. Olpidium's broader range
of hosts, from grasses to broadleaf plants, makes possible genetic
transfers to more types of plants. (PATENT 5,416,010)
Wheat, Sorghum and Forage Research, Lincoln, NE
William Langenberg/Lingyu Zhang, (402) 472-3162
Last updated: October 29, 1996
Return to: Quarterly Report
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