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2-Plants: Some European maize varieties exibit natural rootworm resistance

   "Plants under attack by arthropod herbivores often emit volatile
    compounds from their leaves that attract natural enemies of the
    herbivores. Here we report the first identification of an insect-
    induced belowground plant signal, (E )-b-caryophyllene, which
    strongly attracts an entomopathogenic nematode. Maize roots release
    this sesquiterpene in response to feeding by larvae of the beetle
    Diabrotica virgifera virgifera, a maize pest that is currently
    invading Europe. Most North American maize lines do not release
    (E)-b-caryophyllene, whereas European lines and the wild maize
    ancestor, teosinte, readily do so in response to D. v. virgifera
    attack. This difference was consistent with striking differences in
    the attractiveness of representative lines in the laboratory. Field
    experiments showed a fivefold higher nematode infection rate of
    D.v.virgifera larvae on a maize variety that produces the signal
    than on a variety that does not, whereas spiking the soil near the
    latter variety with authentic (E)-b-caryophyllene decreased the
    emergence of adult D.v.virgifera to less than half. North American
    maize lines must have lost the signal during the breeding process.
    Development of new varieties that release the attractant in adequate
    amounts should help enhance the efficacy of nematodes as biological
    control agents against root pests like D. v. virgifera."
                                            NATURE, VOL 434, 7 Apr 2005

-------------------------------- GENET-news -------------------------------

TITLE:  Corn roots out unwanted pests
SOURCE: swissinfo, Switzerland, by Scott Capper
DATE:   7 Apr 2005

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Corn roots out unwanted pests

Researchers at Neuchâtel University have demonstrated that the roots of
some varieties of corn send out a chemical signal to help ward off pests.

Their results could lead to more efficient pest control and solve a
billion-dollar problem faced by maize growers around the world.

The study focused on how corn plants react to damage inflicted on them by
the larvae of a beetle called the Western Corn Rootworm.

The female lays eggs beneath the soil near a plant, and when they hatch,
the larvae start feeding on the roots. The damage they inflict is enough
to make a corn stalk collapse, reducing harvest yields.

The scientists found that some varieties of maize won't give up without a
fight. Their roots emit a compound that attracts a tiny parasitic worm -
a nematode - that lays its own eggs inside the corn's attacker,
eventually killing it.

"The rootworm is the most important maize pest in the United States, and
it reached Europe during the Bosnian war in the 1990s," said the head of
the research team, Ted Turlings.

The beetle was probably carried to the Balkans as part of a corn
shipment, before spreading further afield, including southern Switzerland.

Identical mechanism

The discovery comes a few years after scientists showed an identical
mechanism in corn leaves.

"We found at the time that when a caterpillar eats the leaves of maize,
the plant emits a smell that attracts a parasitic wasp," Turlings told
swissinfo. "We wanted to see if the same thing happened underground."

Besides determining the actual compound involved in fending off the
rootworm - caryophyllene - the researchers also confirmed that not all
corn varieties act the same way.

"Some types do not produce the compound, and these are usually the most
popular American varieties," added Turlings. "This seems to be the first
example whereby artificial selection to improve maize plants has wiped
out an important property."

This incapacity to produce the compound carries a huge cost for North
American farmers. They spend around $1 billion (SFr1.21 billion) each
year just to pay for insecticides and cover for lost crops.

The problem is spreading to Europe, where not all varieties of corn are
resistant to the rootworm either.


Another team of researchers at Germany's Max Planck Institute is now
looking at the genetic make-up of the varieties that do produce the chemical.

Reintroducing the gene thought to be responsible for the compound into
types of maize that lack it, although fairly simple, isn't on the cards

According to Turlings, besides raising issues related to the use of
genetic engineering, it would also be cheaper to consider varieties that
can defend themselves.

The researchers are still unsure whether this form of biological pest
control is cost-efficient. Producers would have to purchase the nematodes
needed to ward off rootworms.

Results from field tests in Hungary seem to indicate some cost benefit,
but more trials will have be carried out to find out if pest-resistant
maize varieties have high enough yields.


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