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DNA maps are being fashioned by ARS scientists to convict--or
free--insects of charges they spread bluetongue in livestock. This
virus disease, carried by biting midges, can cause severe illness in sheep
and abortions in cattle. A midge's DNA, however, may reveal that it's
unable to spread the disease. That detective work could prove that
livestock in the Northeast, where bluetongue has not been reported, can
safely be exported to countries free of the disease. Bluetongue's
presence in some U.S. regions now keeps the whole country from competing
in livestock markets overseas without the disease. Those markets are
valued at nearly $120 million annually. ARS entomologists are assembling
gene maps of different strains of biting midges called Culicoides
variipennis. Some strains are known to transmit the virus. So far,
scientists have identified 12 marker genes to compare midge strains. When
the DNA maps are complete, scientists can identify which genes signal that
a given strain won't carry the virus.
Arthropod-borne Animal Diseases Research Laboratory, Laramie, WY
Walter J. Tabachnick, (307) 766-3605
Biotechnology could enable tomorrow's vegetable crops to use a gene
from tobacco to ward off viruses. The gene attacks tobacco mosaic
virus that strikes tomato, eggplant, pepper and 150 other species.
Scientists with ARS and the University of California at Berkeley isolated
and cloned the gene. That's a scientific first for any plant-derived gene
for resistance to a plant virus. The researchers placed the gene, called
N, in a type of tobacco highly susceptible to the virus. The newly
fortified plants shrugged off attack. More recently, the scientists
slipped N into tomato cells to learn whether plants produced from
those cells resist the virus. If so, the N gene eventually may be
moved into other commercial crops. ARS is seeking a patent for the
N gene. And--with other researchers in the United States and
Australia--ARS has applied for a joint patent for two other, genetically
similar plant genes that defend plants against other kinds of microbial
attack. (PATENT APPLICATIONS 08/261,633 and 08/310,912)
ARS/University of California at Berkeley Plant Gene Expression Center,
Albany, CA
Barbara J. Baker, (510) 559-5900
ARS scientists and collaborating university researchers have
successfully inserted a new gene into Thompson seedless grapes--a
scientific first. They hope the new gene will give built-in
protection against a common grape virus. This genetic engineering advance
could decrease economic losses for grape growers and reduce the amount of
chemicals put into the environment. It paves the way for plant breeders
to improve disease and insect resistance of all major grape varieties.
Scientists from the University of Florida and Cornell participated in the
research.
Appalachian Fruit Research
Station, Kearneysville, WV
Ralph Scorza, (304) 725-3451
Horticultural Crops Research Laboratory, Fresno, CA
David W. Ramming/Richard L. Emershad, (209) 453-3160
A search among thousands of alfalfa plants has led to a new alfalfa
breeding line that resists a disease-causing fungus. Plant breeders
can use the new line to develop cultivars resistant to the fungus,
Sclerotinia trifoliorum. Sclerotinia causes one of the
worst alfalfa diseases in the southeastern and southcentral United States.
Severe outbreaks can wipe out entire fields. But no resistant varieties
currently are available to farmers who attempt to grow the legume for
high-protein forage. To develop the new breeding line, Mississippi
Sclerotinia-Resistant (MSR), ARS scientists propagated the most promising
candidates, then crossed and evaluated them several times to strengthen
resistance in offspring. In greenhouse-grown plants, the researchers
found less disease in MSR than in 26 commercial cultivars. In
fungus-infected field plots, the new line's yield averaged 83 percent of
plots free of Sclerotinia disease. Commercial varieties fared much
worse, yielding only 38 to 49 percent when infected with the fungus.
Crop Science
Research Laboratory, Mississippi State, MS
Robert Pratt/Dennis Rowe, (601) 323-2230
Hazelnut trees have a new, long-term genetic insurance policy.
Also known as filberts, hazelnuts are popular roasted and in baked goods.
Normally, hazelnut seeds won't sprout after long-term storage. But ARS
scientists showed that one part of the seeds--the axis, part of the
embryo--can survive storage while frozen in liquid nitrogen. A thawed
axis can be grown in tissue culture. That means that the genetic material
of the nine primary hazelnut species can be kept indefinitely, and may
someday be used to produce new commercial varieties with improved disease
or insect pest resistance.
National
Clonal Germplasm Repository, Corvallis, OR
Barbara M. Reed, (503) 750-8712
A light switch has been turned off, so to speak, in tropical sorghum
plants, so their valuable genes can be bred into varieties growing in the
United States and other temperate areas of the world. Tropical
sorghum varieties that have key genes for insect and disease resistance
could not be grown in temperate areas because days are too long in the
summer. Tropical sorghum needs at least 12 hours of darkness to begin
producing seed. And if planted during long summer days in the United
States, it won't produce seed. Scientists have overcome this problem by
genetically "switching off" this sensitivity to day length. After years
of breeding tropical and temperate plants, ARS and Texas A&M scientists
now have released 50 sorghum germplasm lines that begin to produce seed in
temperate areas in 60 to 70 days, regardless of day length. These lines
are four to five feet tall, and therefore can be harvested with combines.
Normally, tropical varieties can be up to 12 feet tall--too tall for
mechanical harvesting. Varieties developed from the new lines will widen
the genetic base of sorghum, which is grown on about 13 million acres in
the United States at an estimated value of $1.5 billion. Seed of the new
germplasm lines is available to breeders by contacting Texas Agricultural
Experiment Station, Route 3 Box 219, Lubbock, TX 79401.
Tropical
Agriculture Research Station, Mayaguez, PR
Jeffrey Dahlberg, (809) 831-3435
A biotech "vaccine" that protects peanut plants from deadly viruses
could be just around the corner. Virus diseases cost peanut growers
an estimated $10 million a year. ARS scientists for the first time have
genetically engineered virus resistance into peanut plants that remain
fertile and produce nuts. Until now, genetically engineering peanuts had
been unsuccessful because the resulting plants are usually sterile.
Scientists injected into peanut cells virus genes that make proteins from
the protective coating surrounding the virus. The coat proteins are
harmless to the plant, but trigger a reaction similar to a vaccine in
humans. The coat proteins alert the plant that an outside organism has
invaded, and the plant is then better able to protect itself from the
virus. Later this year in greenhouse tests, scientists will grow the
seedlings into mature peanut plants, spray viruses on them and see if the
plants continue to be resistant. The researchers injected virus protein
genes from two serious virus diseases of U.S. peanuts.
Plant
Genetic Resources Conservation Research, Griffin, GA
Robert Jarret, (404) 228-7303
Last updated: October 30, 1996
Return to: Quarterly Report
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