A24—Lancaster Farming, Saturday, November 1,1980
Genetic engineers discover
BELTSVILLE, Md. - A
viroid the smallest agent
known to cause an infectious
disease, has become the sub
ject of genetic engineering
by U.S. Department of
Agriculture scientists.
By making DNA com
plementary to potato spindle
tuber viroid, which causes a
troublesome potato disease,
and then cloning it, research
chemist Robert A. Owens
and geneticist Dean E. Cress
made possible the develop
ment of a test for detecting
PSTV in potato seed and
breeding stock.
Such a test could help
boost world food supplies
considerably, by allowing
greatly increased production
of the highly nutritious
potato m tropical and sub
tropical regions where viroid
jvernor recek .(y signer iuse :o
with the Governor are, left, Rep. Reno Thomas, chairman of the Agriculture and
Rural Affairs Committee and Rep. Noah Wenger, vice-chairman and prime
sponsor. Standing are representatives from the Pennsylvania farm community.
Governor signs HBI6OB
HARRISBURG - A
measure that would help
preserve family farms has
been signed into law by the
Governor.
Rep. Noah Wenger, prime
sponsor, noted the new law
will exempt family farm
corporations from the state
capital stock and franchise
tax.
“The tax discouraged
many farm families from
incorporating their hold
sing,” Wenger said. “In
corporating, in some cases,
will make it easier to pass
the farm from one
generation to the next.”
Wenger, vice chairman of
the Agriculture and Rural
Affairs committee said this
type of corporation will now
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Cloning this DNA will also
help scientists study how
viroids multiply in host cells,
say Owens and Cress
Theodor 0. Diener, a
USDA research plant
pathologist who discovered
the first viroid, says that the
cloning success of Owens
and Cress is providing the
basic ingredient for a sen
sitive and reliable test for
PSTV which will aid potato
breeders and seedsmen
around the world. The potato
disease caused by PSTV
threatens to hamper current
efforts to increase potato
production m warm coun
tries. Warm climates en
courages viroid replication.
Testing potatoes and other
crops for the presence of
PSTV is currently a time
consuming, inefficient pro
be exempted from the stock
tax and therefore, encourage
families to benefit from the
advantages of being in
corporated.
“This law will help keep
Pennsylvania as one of the
major food producers by
preventing family farms
from splitting up and the
land being used for non
farming purposes,” Wenger
said.
A family farm cor
poration, as defined in the
bill, must be organized and
operated for agricultural
land use.
In addition, 75 percent of
the corporation’s stocks
must be owned by members
of the family and at least 75
test, based on a technique
called nucleic acid
hydndization, can probably
be automated, much like
current tests that quickly
and reliably screen plant
material for the detection of
plant viruses.
Viroids are one-fortieth
the size of the smallest
known virus. Viruses
themselvs are directly visi
ble only with an electron
microscope. They are very
simple structures, consisting
of a core of nucleic acid sur
rounded by a protein coat or
coats. The nucleic acid is
either deoxyribonucleic acid
(DNA) or ribonucleic acid
(RNA), the two kinds of
molecules that carry the
genetic information for liv
ing 0) Until Diener
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viroids, potato disease test
' 1.
were considered the
smallest infectious agents
capable of replicating
themselves within living
cells.
Although viroids are
smaller and have an even
less complex structure than
viruses, they can replicate
independently within in
fected cells. Actually,
viroids are merely small
bits of RNA that appear as
short strands or rods m the
electron microscope.
Owens and Cress used
recombinant DNA techn
mques (genetic engineering)
to clone this specific DNA.
They first made DNA which
was complementary to the
RNA of PSTV. They inserted
this complementary DNA
into plasmids (circles of
DNA from a bacterium) by
biochemical methods and
then put the plasmids back
into a bacterium called E.
coli. As the bacterium
reproduced, the plasmid
DNA containing the PSTV
related sequences was also
reproduced. The DNA
complementary to PSTV
was then purified and
radioactively labeled.
The final product is a large
number of homogeneous,
labeled DNA molecules that
can be used as molecular
probes' in experiments to
learn how to prevent potato
spindle tuber disease and
possibly other diseases
caused by the elusive
viroids.
Two earlier studies were
essential to the successful
completion of this USDA
project. In 1962, USDA’s
William B. Raymer and
Muriel J. O’Brien discovered
that the (as yet) unknown
causal agent of potato
spindle tuber disease could
be propagated in tomato
plants - thus, the first
bioassay for PSTV was
discovered. In 1978, German
scientists at the Max-
Planck-Institute for
Biochemistry and at the
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