lookKIT 02/2011 - PKM - KIT

0211
Ways 39
Information
Downy mildew is a dreaded plant disease in
viniculture. Following infection, leaves and
young berries putrefy, ripeness of the fruit is
delayed, the fruit sugar content is reduced,
and the taste is spoiled. Actually, the different
types of downy mildew are not fungi,
but related to brown algae and diatoms.
Pilzabwehr
durch
Mundgeruch
KIT-Forscher bekämpfen
Parasiten der Weinrebe
“To reduce the spraying volume, we urgently need
new concepts for improving crop protection,” says
Professor Nick. A successful approach consists of
crossbreeding fungus-resistant genes from American
wild vines into the cultivated vines. The resulting
vines are immune to the fungus, but unfortunately
also taste of wild vines. It took nearly 100
years to cultivate vines that are both resistant and
tasty. Thanks to modern gene maps and highly developed
molecular biology methods, cultivation today
is much more efficient than it was in the past.
The new method invented by Nick now represents
a rather promising, environmentally compatible approach
that is associated with relatively low costs
and minimum time expenditure. The idea is based
on chemical communication of the plant with other
organisms. By means of attractants, plants can attract
pollinating insects. By releasing volatile scents,
the vines defend themselves against pests. This
strategy is used by Nick and his team.
When they studied wild vines from China and Japan
in more detail, the researchers found that these species
were resistant against downy mildew even when
they had never been in contact with this pathogen.
Infection experiments revealed that the pathogen
obviously does not find the stomata of the Asian
wild vine. To determine the reason, Nick and his
team went to the laboratory of Professor Wilhelm
Boland at the Max Planck Institute of Chemical Ecology
in Jena, which has specialized in the detection
of volatile attractants. With gas chromatographs –
highly sensitive chemical noses – even the smallest
amounts of these attractants can be detected. In
this way, the scientists from Karlsruhe proved that
the vines produce a type of “bad breath;” volatile,
smelling substances, so-called aldehydes, such as
hexenyl acetate and nonanal are released from the
stomata.
To verify their hypothesis, the researchers confronted
the mildew pathogen with the Asian wild vine
attractant and observed that the “fungus” indeed
moves to the source of the scent. With the help
of an attractant, the pathogen can orient well and
rapidly finds the stomata of Müller-Thurgau vines. In
this case, the “bad breath” unintentionally tells the
fungus where the weak point of the vine is.
Nick thinks that Asian wild vines release the attractant
in a decentralized manner, i.e. not only via stomata,
but also from other openings of the plant. This
obviously confuses the fungus so it cannot find the
stomata. Infection experiments of Müller-Thurgau
vine leaves with downy mildew confirmed that the
pathogen does not find the stomata of the leaves, if
large areas of the plant are sprayed with the attractant
nonanal. Hyphae are formed on the leaf surface
only. The fungus is isolated from the supply vein of
its host and condemned to die out.
Nick and his team have also started to solve another
problem. They are now developing a scent that does
not volatilize so rapidly, but is as effective as nonanal.
The next hot summer will certainly come. Covered
by the new biological fungicide, the cultivated
vine will have good chances to win the fight against
downy mildew.
Forscher vom Botanischen Institut des KIT haben
einen wirksamen Weg gefunden, die Weinrebe
vor „Schadpilzen“ wie dem falschen Mehltau
biologisch zu schützen – ohne Pestizide und
Genmanipulationen. Das Team um Professor Peter
Nick identifizierte mithilfe asiatischer Wildreben
eine Substanz, mit der man den Pilz davon
ablenken kann, in die Spaltöffnungen einzudringen
und die Blätter zu infizieren.
Der Falsche Mehltau, ein pilzähnlicher Parasit,
der weltweit große Schäden im Weinbau verursacht,
wurde im 19. Jahrhundert aus Amerika
eingeschleppt. Er gelangt in ihr Inneres, breitet
sich großflächig aus und ernährt sich vom Lebenssaft
seines Wirtes. Weil Pflanzenschutzmittel
schnell vom Regen weggespült werden, sind
13 bis 15 Spritzungen pro Saison nötig. Etwa 70
Prozent der Fungizidproduktion gehen allein auf
das Konto des Weinbaus.
„Damit wir weniger spritzen müssen, brauchen
wir dringend neue Konzepte für die Verbesserung
des Pflanzenschutzes“, fordert Professor
Nick. Ein erfolgreicher Weg besteht darin, pilzresistente
Gene amerikanischer Wildreben in die
Kulturrebe einzukreuzen. Man bekommt dann
durchaus Reben, die gegen den Pilz immun
sind. Dank moderner Gen-Karten und hoch entwickelter
molekularbiologischer Techniken ist
Züchtung heute deutlich effizienter als früher.
Die von Nick ersonnene neue Methode stellt
nun einen vielversprechenden, umweltschonenden
Ansatz dar mit relativ geringen Kosten und
minimalem Zeitaufwand. Die Idee beruht auf der
Erforschung der chemischen Kommunikation
der Pflanze mit anderen Organismen. So können
Pflanzen mittels Signalstoffen bestäubende Insekten
anlocken oder sich durch Abgabe flüchtiger
Duftstoffe gegen Fraßfeinde verteidigen.
Michael Rauhe