DS-Lancaster Farming, Saturday, November 28,1992
Predator
UNIVERSITY PARK, (Centre
Co.) Arnold Schwarzenegger
doesn’t have to worry, but if
you’re a fungus, watch out.
A predator bacterium, discov
ered by a Penn State researcher,
seems to be on the top of the bac
terial and fungal heap in respect to
predatory behavior and may pro
vide a biological control for com
mon fungal-caused plant diseases.
“About 12 years ago, I
stumbled onto a new group of bac
teria that I call non-obligate bac
terial predators,” said Dr. L.E.
Casida Jr., professor of
microbiology.
Non-obligate predators act like
other bacteria as long as soluble
nutrients are available in the soil,
but when nutrients are in short
supply, they attack other bacteria
or fungi for food.
“Over the years, I have found
several new predator bacteria, and
some of these bacteria would
attack other predator bacteria,”
said Casida. “Every time I discov
ered a new strain, I’d test it to see
which other predator bacteria it
would attack.”
With Pseudomonas strain
679-2, Casida finally found the
bacterium at the top of the hierar
chy. Nothing attacks strain 679-2
very quickly, and it attacks most
bacteria and many fungi.
Predator bacteria that eat other
bacteria are interesting, but one
that also consumes fungus has
potential for biological control of
the fungal diseases that attack
plants.
Current agricultural practices
use chemical fungicides to control
plant diseases. Everyone agrees
that a naturally occurring biologi-
direct®
Bacterium Protects Against
cal control agent for these prob
lems would be a good idea.
Casida and Dr. F.L. Lukezic,
professor of plant pathology,
report on field trials that test the
control of leaf spot diseases of
alfalfa and tomatoes using Pseu
domonas Strain 679-2, in the
December issue of Plant Disease.
Lukezic conducted initial trials
to ensure that the bacterium did
not damage the plants. A suspen
sion of the bacterium was then
sprayed on the plants growing in
test plots where fungal diseases
were endemic.
“Strain 679-2 greatly reduced
the incidence of fungal disease,”
said Casida.
While it may not be unusual to
test biological organisms to con
trol plant diseases, it is unusual to
use predator bacteria.
Other biological control
methods use organisms that
excrete antibiotics or other chemi
cals into the environment. Strain
679-2 actually targets the specific
bacteria or fungi and kills them.
Strain 679-2 controls bacteria
and fungi by attaching onto the
host cell and delivering a tiny
amount of a toxic compound. This
compound is water-soluble and
generated in such small amounts
that The researchers determined
there is no danger from this natur
ally produced substance and no
residual build up.
Laboratory tests of Strain 679-2
and its toxic compound show that
control of fungal diseases can also
occur at sublethal levels.
“It is not necessary for Strain
679-2 to kill the fungus outright,”
said Casida. “It only has to do
enough damage so that the fungus
does not sporulate.”
Inoculation of plants with
Strain 679-2 is also not a problem
because Casida can grow the bac
terial cells in a medium that nutri
tionally programs the organisms
for death. In the field trials, Strain
679-2 lasted for two to three
weeks, long enough to control the
fungal diseases, and then died out.
A change in the nutritional prog
ramming, however, can allow
Strain 679-2 to survive for pro
longed periods.
Unlike many other bacteria.
Strain 679-2 is highly resistant to
copper and can be used in con
junction with chemical fungicides
that are formulated with- copper
Beef Producers Say Mexican
Tariffs
WASHINGTON, D.C.
Reports of impending Mexican
tariffs on their live slaughter cattle
and beef imports is an outrage,
said NCA President Jimme Wil
son, Trout Creek, Mont, in letters
to Agriculture Secretary Edward
Madigan and U.S. Trade Rep
resentative Caria Hills.
A plan to impose a IS percent
tariff on live slaughter cattle and
carcass beef, a 20 percent tariff on
fresh or chilled beef, and a 25 per
cent tariff on frozen beef is
expected to be pulished in the
Mexican version of the federal
register, “Diario Official.”
The tariffs are reportedly the
results of internal pressure from
Mexican cattlemen who believe
they can not compete with U.S.
producers because of high feed
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Fungal Plant Diseases
containing compounds. These
fungicides will not hamper the
biological activity of Strain 679-2.
Pseudomonas Strain 679-2 in
nature is quite rare. It was found in
only one soil sample, and this
sample was taken in one corner of
one field in Pennsylvania. While it
grows well in the laboratory appa
rently, it can not be permanently
transferred to other soil areas.
“If you put it in soil, it will
attack other bacteria and multiply,
but eventually it dies out,” said
Casida. “It must be very sensitive
to something, but I don’t know
what.”
Casida is not sure why Strain
679-2 survives in one comer of
Are An Outrage
prices in Mexico, and an increase
in imports from other countries
such as Australia and the Euro
pean Community.
“Without question, this violates
the spirit of the North American
Free Trade Agreement (NAF
TA),” said Wilson. ‘Trade is a
two-way street, and the beef cattle
industries in both countries have
benefited enormously to date.
However, this recent tariff action
is contradictory and
unaccpetable.”
The Mexican market is an
important market for U.S. live
cattle and beef. In 1992, exports of
beef will exceed $225 million and
live cattle will be approximately
250,000 head, Wilson told
Madigan.
NCA is opposing the tariffs
one field and nowhere else.
Because only one strain of this
bacterium has been found, taxo
nomists are reluctant to name this
bacterium. Thus, it continues to be
called Strain 679-2 for Casida’s
679th experiment and the second
organism he looked at in that
experiment.
Penn State has applied for a
patent on Pseudomonas Strain
679-2. Its agricultural applications
as a biological control for leaf
fungal diseases are under con
tinued investigation by Lukezic.
Casida is continuing attempts to
figure out what holds Strain 679-2
in check in nature to explain why
its occurrence is so rare.
based on principle. The tariffs arc
expected to have limited impact
on the overall U.S. cattle market,
according to Cattle-Fax, a market
analysis firm. However, there may
be an impact on regional markets.
U.S. cattle producers are proud
of the trade relations that have
been developed with Mexico and
have been supportive of free trade
between two countires by
repeatedly testifying in favor of
negotiations for a NAFTA, Wil
son said.
The tariffs would be dropped on
U.S. beef and cattle imports if the
NAFTA agreement is signed next
year and implemented in January
1994.