maize [91], whereas in cotton sorghum mulch (3.5–10.5 t ha
À1 ) decreased the weed
by 23–65% [92] and, in aerobic rice, weed density reduced by 50% of total dry
biomass [93, 94]. Studies proved that mulching has effect on weed, fruit yield, and
economic returns of garden egg (Solanum melongena) in Okigwe, Southeastern
Nigeria. Different mulching materials, (1) two synthetic materials, polythene and
trampoline sheet, and (2) natural or organic materials, 6/ha sawdust and grasses,
were used. Results indicated that the plot mulched with sawdust had 7–76% and
6–72% greater fruit yield compared to the other mulching materials in both seasons.
3.2
Allelopathic Activity of Water Extract
Extracted water-soluble allelochemicals are used for controlling the weed [95]. Water
extract of sorghum has been effective in suppressing weeds [96–98], for example,
sorghum water extract showing allelopathic effect on wheat [98] rice [99], cotton
[100], canola [101], mung bean [97], sunflower [102], soybean [103], and maize [91].
Effect of rice straw extract on the growth of the microalga Chlorella species and the
cyanobacterium Anabaena species was evaluated [104]. Different rice straw extract
concentrations were prepared in water and methanol, and both extracts show inhibition
which was dose dependent. The main phenolic compounds present in water and
methanol extract were pyrogallol, gallic acid, and caffeic acid and were considered
for its allelopathic effect. This study shows that rice straw extract (aqueous) has a
potential to inhibit the growth of Anabaena species. Research study showed the
allelopathic effects of Solidago canadensis on the germination potential of seed and
seedling growth of Lactuca sativa under the salt stress condition [105]. Leaf extract of
goldenrod (Solidago canadensis) in high concentration effectively reduces root length,
germination percentage, leaf shape index, and germination rate index of lettuce (Lactuca
sativa). But interestingly at low concentration of leaf extract, there was enhanced leaf
width of lettuce (Lactuca sativa) and root length. Chrysanthemum coronarium aqueous
extract shows nematocidal activity against Meloidogyne incognita and Meloidogyne
javanica [106]. In the present scenario, abiotic stresses mainly drought and salinity are
one of the major constraints to agricultural productivity and growth of forest tree species
at seedling stages [107–114]. It has been suggested that the allelochemicals may
improve the resistance against abiotic stresses, for instance. Research studies showed
water extract from different plants which have shown the allelopathic potential in stress
mitigation. Authors have reported that the exogenous application of allelopathic water
extracts improved the stay green, proline accumulation, soluble phenolics, and glycine
betaine, which helped to stabilize the biological membranes and improved the tolerance
against terminal drought and heat stresses in Triticum aestivum [115].
3.3
Allelopathy for the Management of Phytopathogens
Natural compounds obtained from plants are secure and eco-friendly. Research
reports show that these natural compounds show allelopathic activity and
19 Plant Allelochemicals and Their Various Applications
453
À1 ) decreased the weed
by 23–65% [92] and, in aerobic rice, weed density reduced by 50% of total dry
biomass [93, 94]. Studies proved that mulching has effect on weed, fruit yield, and
economic returns of garden egg (Solanum melongena) in Okigwe, Southeastern
Nigeria. Different mulching materials, (1) two synthetic materials, polythene and
trampoline sheet, and (2) natural or organic materials, 6/ha sawdust and grasses,
were used. Results indicated that the plot mulched with sawdust had 7–76% and
6–72% greater fruit yield compared to the other mulching materials in both seasons.
3.2
Allelopathic Activity of Water Extract
Extracted water-soluble allelochemicals are used for controlling the weed [95]. Water
extract of sorghum has been effective in suppressing weeds [96–98], for example,
sorghum water extract showing allelopathic effect on wheat [98] rice [99], cotton
[100], canola [101], mung bean [97], sunflower [102], soybean [103], and maize [91].
Effect of rice straw extract on the growth of the microalga Chlorella species and the
cyanobacterium Anabaena species was evaluated [104]. Different rice straw extract
concentrations were prepared in water and methanol, and both extracts show inhibition
which was dose dependent. The main phenolic compounds present in water and
methanol extract were pyrogallol, gallic acid, and caffeic acid and were considered
for its allelopathic effect. This study shows that rice straw extract (aqueous) has a
potential to inhibit the growth of Anabaena species. Research study showed the
allelopathic effects of Solidago canadensis on the germination potential of seed and
seedling growth of Lactuca sativa under the salt stress condition [105]. Leaf extract of
goldenrod (Solidago canadensis) in high concentration effectively reduces root length,
germination percentage, leaf shape index, and germination rate index of lettuce (Lactuca
sativa). But interestingly at low concentration of leaf extract, there was enhanced leaf
width of lettuce (Lactuca sativa) and root length. Chrysanthemum coronarium aqueous
extract shows nematocidal activity against Meloidogyne incognita and Meloidogyne
javanica [106]. In the present scenario, abiotic stresses mainly drought and salinity are
one of the major constraints to agricultural productivity and growth of forest tree species
at seedling stages [107–114]. It has been suggested that the allelochemicals may
improve the resistance against abiotic stresses, for instance. Research studies showed
water extract from different plants which have shown the allelopathic potential in stress
mitigation. Authors have reported that the exogenous application of allelopathic water
extracts improved the stay green, proline accumulation, soluble phenolics, and glycine
betaine, which helped to stabilize the biological membranes and improved the tolerance
against terminal drought and heat stresses in Triticum aestivum [115].
3.3
Allelopathy for the Management of Phytopathogens
Natural compounds obtained from plants are secure and eco-friendly. Research
reports show that these natural compounds show allelopathic activity and
19 Plant Allelochemicals and Their Various Applications
453