barley, decreases the growth of wild mustard (Sinapis arvensis L.) and wild barely
(Hordeum spontaneum L.) saplings through increase in the lipid peroxidation
[40, 41]. The application of non-sterile aerial parts of wheat and water foxtail
(Alopecurus aequalis L.) increases the ROS (reactive oxygen species) activity and
leaf malondialdehyde contents in the seedlings of non-transgenic and transgenic
potato (Solanum tuberosum L.) owing to leakage of biological membranes [42]. The
use of lemongrass (Cymbopogon citratus L. (DC) Stapf) essential oil enhanced the
lipid peroxidation and thus caused damage to the biological membranes in barnyard
grass (Echinochloa crus-galli (L.) P. Beauv) [43]. The exposure of cucumber
seedlings to cinnamic acid enhanced the ROS production, thus enhancing the lipid
peroxidation and reducing the membrane H
+
-ATPase activity [44].
2.4
Impact on the Plant Growth Regulatory System
Allelochemicals may cause imbalances to the several phytohormones or change the
plant growth regulator contents, which reduce the plant growth and development
including the germination of seed and growth of seedling. The phenolic
allelochemicals may cause increase in the activity of indole acetic acid (IAA)
oxidase and may decrease the reaction among peroxidase and IAA [45]. In barnyard
grass, application of aqueous extracts of rice (Oryza sativa L.) negatively affected
the growth of seedling through reducing the IAA levels with immediate increase in
IAA oxidase activity [46]. In tomato (Lycopersicon esculentum L.), the application
of cyanamide (1.2 mM) caused an imbalance in two plant hormones, viz., auxin and
ethylene [47]. In another study, the exposure of seedlings of wheat to ferulic acid
(1.50 mM) decreased the seedling growth through accumulation of cytokinins, IAA,
and gibberellic acid [48].
In rice seedlings, Yang et al. [49] investigated the impact of two different
allelochemicals (i.e., DTD and HHO) on the abscisic acid, ZR contents and IAA.
Both of these allelochemicals were extracted from the Ageratina adenophora
Sprengel weeds. The application of the DTD allelochemical, at higher concentrations (i.e., 1.5 mM), increased the abscisic acid contents in rice root which was
followed by a sharp decline in its contents after 96 h of the application of DTD
allelochemical. The application of HHO allelochemical enhanced the abscisic acid
contents for 48/96 h. Nonetheless, the HHO and DTD application reduced the ZR
and IAA contents in rice roots.
2.5
Influence on Photosynthesis Process
The main effect of allelochemicals on plant photosynthesis process can be visualized
through decrease in photosynthesis or destruction of the photosynthetic machinery.
Subsequently, the pigment contents of photosynthetic apparatus are reduced, which
lumps the power and transfer of electron, and reduce the ATP synthesis, enzyme
activity, and disturbs the stomata which eventually reduce the process of
23 Ecological Management of Agricultural Pests Through Allelopathy
547
(Hordeum spontaneum L.) saplings through increase in the lipid peroxidation
[40, 41]. The application of non-sterile aerial parts of wheat and water foxtail
(Alopecurus aequalis L.) increases the ROS (reactive oxygen species) activity and
leaf malondialdehyde contents in the seedlings of non-transgenic and transgenic
potato (Solanum tuberosum L.) owing to leakage of biological membranes [42]. The
use of lemongrass (Cymbopogon citratus L. (DC) Stapf) essential oil enhanced the
lipid peroxidation and thus caused damage to the biological membranes in barnyard
grass (Echinochloa crus-galli (L.) P. Beauv) [43]. The exposure of cucumber
seedlings to cinnamic acid enhanced the ROS production, thus enhancing the lipid
peroxidation and reducing the membrane H
+
-ATPase activity [44].
2.4
Impact on the Plant Growth Regulatory System
Allelochemicals may cause imbalances to the several phytohormones or change the
plant growth regulator contents, which reduce the plant growth and development
including the germination of seed and growth of seedling. The phenolic
allelochemicals may cause increase in the activity of indole acetic acid (IAA)
oxidase and may decrease the reaction among peroxidase and IAA [45]. In barnyard
grass, application of aqueous extracts of rice (Oryza sativa L.) negatively affected
the growth of seedling through reducing the IAA levels with immediate increase in
IAA oxidase activity [46]. In tomato (Lycopersicon esculentum L.), the application
of cyanamide (1.2 mM) caused an imbalance in two plant hormones, viz., auxin and
ethylene [47]. In another study, the exposure of seedlings of wheat to ferulic acid
(1.50 mM) decreased the seedling growth through accumulation of cytokinins, IAA,
and gibberellic acid [48].
In rice seedlings, Yang et al. [49] investigated the impact of two different
allelochemicals (i.e., DTD and HHO) on the abscisic acid, ZR contents and IAA.
Both of these allelochemicals were extracted from the Ageratina adenophora
Sprengel weeds. The application of the DTD allelochemical, at higher concentrations (i.e., 1.5 mM), increased the abscisic acid contents in rice root which was
followed by a sharp decline in its contents after 96 h of the application of DTD
allelochemical. The application of HHO allelochemical enhanced the abscisic acid
contents for 48/96 h. Nonetheless, the HHO and DTD application reduced the ZR
and IAA contents in rice roots.
2.5
Influence on Photosynthesis Process
The main effect of allelochemicals on plant photosynthesis process can be visualized
through decrease in photosynthesis or destruction of the photosynthetic machinery.
Subsequently, the pigment contents of photosynthetic apparatus are reduced, which
lumps the power and transfer of electron, and reduce the ATP synthesis, enzyme
activity, and disturbs the stomata which eventually reduce the process of
23 Ecological Management of Agricultural Pests Through Allelopathy
547