“the effect of one plant on the growth and development of other plant, comprising
microorganisms, through the release of the chemical substances in the neighboring
environment.” Farooq et al. [6] defined allelopathy as “the phenomenon in which
fungi, viruses, other microorganisms and plants produce secondary metabolites that
affect the biological and agricultural systems.”
Indeed, the allelochemicals are the byproduct of the primary metabolism and are
thus called as secondary metabolites. The allelochemicals are present in different
plant parts (e.g., seed, leaves, stem, flowers, rhizomes, pollen, and roots pollen)
which enter to the agroecosystems through the exudation from roots, residue decomposition, and volatilization from the aerial plant parts. The microorganisms also
modulate the production and transformation of secondary allelochemicals [5, 7].
The important allelochemicals are categorized into phenolics, steroids,
amino acids, alkaloids, terpenoids, flavonoids, carbohydrates, etc. [8]. Among
plant secondary metabolites, phenolic compounds are the most prevalent and are
involved in plant developmental cascades under optimal and suboptimal conditions.
The phenolics also act as defense agent against the attacking organisms and work
as a signal molecule thus impacting the plant/cell growth and development [9]. The
process of germination, growth, and development may be affected when a susceptible plant is exposed to allelochemicals of some other plants. Inhibition of
the germination of seeds, elongation of coleoptile, and development of root/shoot
are the most evident effects of allelochemicals on other plants [8].
For field crops, the phenomenon of allelopathy may be exploited through crop
rotations, as green manure crops, as cover crops, intercrops, and the use of allelopathic water extracts and allelopathic powders (either alone or in combination with
reduced doses of pesticides) [7, 10–18].
In this chapter, the role of crop rotation, allelopathic mulches, allelopathic cover
crops, intercrops, and allelopathic water extracts (alone or with reduced doses
of herbicides) in weed management has been described. The role of allelopathic
water extracts and powders for the management of crop insect pests and diseases in
agronomic and horticultural crops has also been discussed.
2
Mechanism of Action of Allelochemicals for Agricultural
Pest Management
Upon release of allelochemicals in the environment, they may affect the physiological and biochemical processes in other plants and organisms present in the vicinity [19, 20]. In the following lines, mechanism of action of allelochemicals for
agricultural pest management has been described.
2.1
Changes in the Micro- and Ultrastructure of Cell
The allelochemical present in different plant parts affects the cell structure and its
shape. The root cells can widen or shorten by the volatile allelochemical (e.g.,
23 Ecological Management of Agricultural Pests Through Allelopathy
545
microorganisms, through the release of the chemical substances in the neighboring
environment.” Farooq et al. [6] defined allelopathy as “the phenomenon in which
fungi, viruses, other microorganisms and plants produce secondary metabolites that
affect the biological and agricultural systems.”
Indeed, the allelochemicals are the byproduct of the primary metabolism and are
thus called as secondary metabolites. The allelochemicals are present in different
plant parts (e.g., seed, leaves, stem, flowers, rhizomes, pollen, and roots pollen)
which enter to the agroecosystems through the exudation from roots, residue decomposition, and volatilization from the aerial plant parts. The microorganisms also
modulate the production and transformation of secondary allelochemicals [5, 7].
The important allelochemicals are categorized into phenolics, steroids,
amino acids, alkaloids, terpenoids, flavonoids, carbohydrates, etc. [8]. Among
plant secondary metabolites, phenolic compounds are the most prevalent and are
involved in plant developmental cascades under optimal and suboptimal conditions.
The phenolics also act as defense agent against the attacking organisms and work
as a signal molecule thus impacting the plant/cell growth and development [9]. The
process of germination, growth, and development may be affected when a susceptible plant is exposed to allelochemicals of some other plants. Inhibition of
the germination of seeds, elongation of coleoptile, and development of root/shoot
are the most evident effects of allelochemicals on other plants [8].
For field crops, the phenomenon of allelopathy may be exploited through crop
rotations, as green manure crops, as cover crops, intercrops, and the use of allelopathic water extracts and allelopathic powders (either alone or in combination with
reduced doses of pesticides) [7, 10–18].
In this chapter, the role of crop rotation, allelopathic mulches, allelopathic cover
crops, intercrops, and allelopathic water extracts (alone or with reduced doses
of herbicides) in weed management has been described. The role of allelopathic
water extracts and powders for the management of crop insect pests and diseases in
agronomic and horticultural crops has also been discussed.
2
Mechanism of Action of Allelochemicals for Agricultural
Pest Management
Upon release of allelochemicals in the environment, they may affect the physiological and biochemical processes in other plants and organisms present in the vicinity [19, 20]. In the following lines, mechanism of action of allelochemicals for
agricultural pest management has been described.
2.1
Changes in the Micro- and Ultrastructure of Cell
The allelochemical present in different plant parts affects the cell structure and its
shape. The root cells can widen or shorten by the volatile allelochemical (e.g.,
23 Ecological Management of Agricultural Pests Through Allelopathy
545