Neuchâtel, Switzerland
August 3, 2009
Restoring a natural root signal
helps to fight a major corn pest
| |
|
| |
 |
| |
The
Western corn rootworm (insert) is a devastating pest of
maize roots. By emitting the volatile compound
E-beta-caryophyllene in response to rootworm feeding,
maize plants naturally attract insect-killing nematodes.
Using genetic transformation, the signal was restored in
an American line and in field tests it was shown that
this dramatically increased the protection that the
plants received from the nematodes.
Credit: Matthias Held and Sergio Rasmann, University of
Neuchâtel, Switzerland |
| |
|
The
University of Neuchâtel, Switzerland, together
with contributions from colleagues in Munich and the US, has
produced another first: the successful manipulation of a crop
plant to emit a signal that attracts beneficial organisms.
Genetic transformation of maize plants resulted in the release
of the naturally active substance (E)-beta-caryophyllene from
their roots. The substance attracts nematodes that attack and
kill larvae of the Western corn rootworm, a voracious root pest.
In field tests, the enhanced nematode attraction resulted in
reduced root damage and considerably fewer surviving rootworms.
Further fine-tuning of this natural defense strategy will allow
for an environmentally friendly growing of maize with minimized
use of synthetic insecticides. The project was carried out
within the framework of the Swiss National Centre of Competence
in Research (NCCR Plant Survival). (Proc. Natl. Acad. Sci. USA,
Early Edition, August 3, 2009)
The Western corn rootworm (Diabrotica virgifera virgifera) is
the most damaging maize pest in the US and is responsible for
enormous financial losses. Current methods to control the
rootworm pest include insecticides, crop rotation and transgenic
Bt maize lines that are not yet approved in Europe. After first
invading the Balkans, the pest has since 2007 also been found in
southern Germany. The corn rootworm larvae feed on root hairs
and bore themselves into the maize roots. The results are
devastating: The plants take up less water and nutrients, and
with the root mass severely reduced the plants lodge and
collapse. In areas in Germany where the corn rootworm is a
potential threat, the Federal Office of Consumer Protection and
Food Safety (BVL) establishes safety zones and enacts the use of
the insecticide chlothianidine. In spring 2008 this insecticide
was directly applied on the seeds, but during sowing it was
unintentionally emitted as dust from abraded seeds, contaminated
flowers, and poisoned 330 million honey-bees.
"Instead of using insecticides, the use of natural enemies of
the corn rootworm could be much more environmentally friendly,"
says Jörg Degenhardt, who was recently appointed professor at
the University of Halle. While working in the group of Jonathan
Gershenzon at the Max Planck Institute for Chemical Ecology in
Jena he had already contributed to a key discovery four years
ago by Sergio Rasmann in the group of Ted Turlings at the
University of Neuchâtel. They found that maize roots attacked by
rootworm attract nematodes by releasing (E)-beta-caryophyllene
(EβC). One striking finding was that, after decades of breeding,
most North American maize varieties no longer emitted EβC and
had lost the ability to attract protective nematodes.
Therefore the research group in Jena and Neuchâtel teamed up
again in an attempt to restore the EβC signal in a variety that
normally does not emit the substance. Jörg Degenhardt, with the
help of Monika Frey at the Technical University of Munich,
transformed a non-emitting maize line with a gene that encodes
an EβC generating enzyme, resulting in continuous emissions of
EβC. Next, the Turlings group in Neuchâtel sent Ivan Hiltpold to
Missouri, where, under the guidance of Bruce Hibbard of the
United States Department of Agriculture, the transformed plants
were tested in the field.
"Our study showed that the re-established natural EβC signal
greatly enhanced the effectiveness of nematodes in controlling
Western corn rootworm", Hiltpold reports. In rows with
EβC-producing maize plants root damage was greatly reduced; 60%
fewer Diabrotica beetles emerged as compared to rows with
non-transformed maize plants. This control efficiency approaches
that of conventional synthetic insecticides used to fight
Diabrotica. Subsequent laboratory studies confirmed that
transgenic plants attracted significantly more nematodes than
the non-transformed equivalents.
"The use of this indirect defense is an attractive strategy to
increase plant resistance against herbivores and to reduce the
use of chemical pesticides," Degenhardt says. "The transgenic
corn plants used in these experiments have no commercial value
and the experiments simply served a 'proof of principle' that
the EβC emission helps to protect the plants against underground
infestation." The EβC trait is present in other, mainly
European, corn varieties as well as in the maize ancestor
species. The trait could be reintroduced into deficient plants
by conventional breeding. On the other hand, generating EβC
emitting maize varieties by means of gene technology may have
advantages: it is faster and prevents the loss of other
important traits.
In further experiments the researchers want to determine the
most effective way the nematodes and their response to the EβC
can be applied. Moreover, the diffusing properties of
caryophyllene make it an ideal belowground signal that could
also serve to protect other crop plants. A patent for this
approach has been filed.
Citation:
Restoring a maize root
signal that attracts insect-killing nematodes to control a
major pest
Jörg Degenhardt, Ivan Hiltpold, Tobias G. Köllner, Monika
Frey, Alfons Gierl, Jonathan Gershenzon, Bruce E. Hibbard,
Mark R. Ellersieck and Ted C. J. Turlings
Proc. Natl. Acad. Sci. USA, Early Edition, August 3, 2009,
DOI: 10.1073/pnas.0906365106
Other news
from the University of Neuchâtel |
|
