secondary constituents – depending whether or not they have an essential role in
plant metabolism and are universally present in all plants. Primary constituents
include the common sugars, proteins, amino acids, the purines and pyrimidines of
the nucleic acids, chlorophyll, and so on. Secondary constituents make up all the
remaining plant constituents, which varied in their distribution from plant to plant.
Allelochemicals are secondary metabolites produced by plant. There are various
types of allelochemical.
2.1
Phenolic Compounds
Phenolic compound contains hydroxyl group directly attached to aromatic
ring. It contains aromatic phenol, tannins, some flavonoids, cinnamic acid
derivatives, hydroxyl and substituted benzoic acids, and quinones. The
most common allelochemicals of plant origin are benzoic acid and their
derivatives [16]. One research report discussed the effect of aqueous extract
of Delonix regia on the growth of lettuce (Lactuca sativa) and Chinese
cabbage (Brassica chinensis) and found that aqueous extract inhibited the
growth of plant. Chlorogenic acid, protocatechuic acid (3,4-dihydroxybenzoic
acid), gallic acid, 3,4-dihydroxybenzaldehyde, p-hydroxybenzoic acid,
caffeic acid (3,4-dihydroxycinnamic acid), and 3,5-dinitrobenzoic acid were
the major compounds present in aqueous extract responsible for its allelopathy
effect [17].
Research study revealed that phenolic compound from Chenopodium murale
affects the growth and macromolecule content in chickpea and pea. Protocatechuic (12.8 5), ferulic (30.4%), p-coumaric (20.2%), and syringic acid (33.6%)
are the four phenolic allelochemicals present in Chenopodium murale when analyzed
by HPLC [18]. Two glucosides of cis-cinnamic acid, 1-O-cis-cinnamoyl-β-Dglucopyranose and 6-O-(49-hydroxy-29-methylenebutyroyl)-1-O-cis-cinnamoyl-βD-glucopyranose, are present in the leaves of Spiraea thunbergii Sieb [19] and show
plant growth inhibitory effects (Fig. 2).
The allelopathic influence of Eucalyptus globulus is due to generation of
many volatile terpenes and phenolic acids [20, 21] and is responsible for the
allelopathic effect on germination and seedling growth of various crops.
To determine the allelopathic chemical in different parts of Eucalyptus
tereticornis, E. camaldulensis, E. polycarpa, and E. microtheca, a study was
performed and confirmed the presence of phenolic compounds p-coumaric, gallic,
gentisic, p-hydroxybenzoic, syringic, and vanillic acids and catechol [20]. Other
reports are available which ensure the allelopathic effect of Eucalyptus species
[22–25]. Study on allelopathic activity of fermented and unfermented wheat and
corn straw extracts was performed [26]. Allelopathic activity was tested against seed
germination of Abutilon theophrasti, Asclepias syriaca, and Chenopodium album.
Crude straw extracts show more inhibition on seed germination and seedling growth
as compared to fermented extract. The allelopathic effect of root exudates and
residues of Ageratum conyzoides on Oryza sativa was studied which concluded
444
A. Bachheti et al.
plant metabolism and are universally present in all plants. Primary constituents
include the common sugars, proteins, amino acids, the purines and pyrimidines of
the nucleic acids, chlorophyll, and so on. Secondary constituents make up all the
remaining plant constituents, which varied in their distribution from plant to plant.
Allelochemicals are secondary metabolites produced by plant. There are various
types of allelochemical.
2.1
Phenolic Compounds
Phenolic compound contains hydroxyl group directly attached to aromatic
ring. It contains aromatic phenol, tannins, some flavonoids, cinnamic acid
derivatives, hydroxyl and substituted benzoic acids, and quinones. The
most common allelochemicals of plant origin are benzoic acid and their
derivatives [16]. One research report discussed the effect of aqueous extract
of Delonix regia on the growth of lettuce (Lactuca sativa) and Chinese
cabbage (Brassica chinensis) and found that aqueous extract inhibited the
growth of plant. Chlorogenic acid, protocatechuic acid (3,4-dihydroxybenzoic
acid), gallic acid, 3,4-dihydroxybenzaldehyde, p-hydroxybenzoic acid,
caffeic acid (3,4-dihydroxycinnamic acid), and 3,5-dinitrobenzoic acid were
the major compounds present in aqueous extract responsible for its allelopathy
effect [17].
Research study revealed that phenolic compound from Chenopodium murale
affects the growth and macromolecule content in chickpea and pea. Protocatechuic (12.8 5), ferulic (30.4%), p-coumaric (20.2%), and syringic acid (33.6%)
are the four phenolic allelochemicals present in Chenopodium murale when analyzed
by HPLC [18]. Two glucosides of cis-cinnamic acid, 1-O-cis-cinnamoyl-β-Dglucopyranose and 6-O-(49-hydroxy-29-methylenebutyroyl)-1-O-cis-cinnamoyl-βD-glucopyranose, are present in the leaves of Spiraea thunbergii Sieb [19] and show
plant growth inhibitory effects (Fig. 2).
The allelopathic influence of Eucalyptus globulus is due to generation of
many volatile terpenes and phenolic acids [20, 21] and is responsible for the
allelopathic effect on germination and seedling growth of various crops.
To determine the allelopathic chemical in different parts of Eucalyptus
tereticornis, E. camaldulensis, E. polycarpa, and E. microtheca, a study was
performed and confirmed the presence of phenolic compounds p-coumaric, gallic,
gentisic, p-hydroxybenzoic, syringic, and vanillic acids and catechol [20]. Other
reports are available which ensure the allelopathic effect of Eucalyptus species
[22–25]. Study on allelopathic activity of fermented and unfermented wheat and
corn straw extracts was performed [26]. Allelopathic activity was tested against seed
germination of Abutilon theophrasti, Asclepias syriaca, and Chenopodium album.
Crude straw extracts show more inhibition on seed germination and seedling growth
as compared to fermented extract. The allelopathic effect of root exudates and
residues of Ageratum conyzoides on Oryza sativa was studied which concluded
444
A. Bachheti et al.