Agriculture Reference
In-Depth Information
28
Communication Between
Undamaged Plants by Volatiles:
the Role of Allelobiosis
Velemir Ninkovic, Robert Glinwood, Jan Pettersson
Abstract
Plant-plant signalling is discussed from a tritrophic perspective, with special
reference to results from experiments with a model system consisting of barley, aphids
and ladybirds. Experimental support for the following statements is discussed: (1) barley
plants communicate via volatile substances and, in certain combinations of genotypes, this
communication leads to changes in biomass allocation, (2) communication between barley
plants of certain genotypes changes the pattern of host plant acceptance by the bird cherry-
oat aphid,
Rhopalosiphum padi
, (3) odour stimuli from barley and common weeds affect the
searching behaviour of the seven-spotted ladybird,
Coccinella septempunctata.
The results
indicate that an active response of the barley plant to exposure to weed
Cirsium arvense
volatiles may be involved. The tritrophic effects of plant-plant communication in barley
add a new dimension to the term allelopathy. Thus, we use the term
allelobiosis
to denote
interactions in which exchange of plant chemicals has an informative value for the receiving
plant, and the response of the receiving plant affects its growth strategy, and relations with
herbivores and their natural enemies.
28.1
Introduction
Coexistence with other plants is the commonest type of biotic challenge
that an individual plant faces. With very few exceptions, plants have to stay
where the propagation unit, such as a seed, happens to start its development.
Thus, the survival of a plant depends on its capacity to meet challenges in
the growing environment, including competition with neighbouring plants.
One strategy for plants to deal with this may be to detect cues from their
neighbours, and to respond in a way that reduces the negative effects of
competition.
Onetypeofchemicalinteractionbetweenindividualplantscantakethe
form of 'chemical warfare', in which compounds that escape from one plant
into the environment may affect the growth and development of neighbour-
ing plants and their organs (Rice 1984). This was first described by Molisch
(1937) who named it 'allelopathy' after the Greek
allelon
'of each other',
and
pathos
,'tosuffer'.Theactivecompoundsareusuallynon-nutritional
chemicals whose effects on other plants depend upon their concentration
and the environmental conditions. Allelopathy has long been an important
issue in agricultural science, and has been shown to affect many aspects of
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