(glucosinolates) are produced by Brassica spp. in soil microenvironment of soil
which can be useful for the reduction of fungal pathogens [177] and soil nematodes.
Application of canola (1%), barley, oat, and lentil extracts (each 2% and 4%)
significantly decreased the germination of sclerotia than control. However, ascospore germination was controlled by the application of 2 and 4% barley and lentil
extracts, respectively, while ascospore germination was encouraged by these similar
applications of wheat, canola, sweet clover, lentil, and rye extracts [178]. The root
rot disease in cumin (Cuminum cyminum L.), caused by Fusarium oxysporum
and other Fusarium spp. (e.g., F. moniliforme, F. lateritium, F. equiseti, F. solani,
and F. dimerum), was controlled by oil extract from cumin (Cuminum cyminum L.),
basil (Ocimum basilicium L.), and the rose geranium (Pelargonium graveolens L
[179]). Similarly, plant pathogens, such as Fusarium verticillioides, Bipolaris
sorghicola, Trichothecium roseum, F. solani, Alternaria alternata, Curvularia
lunata, Cladosporium cladosporioides, F. oxysporum, A. strictum, Aspergillus
flavipes, etc., were controlled by seaweed extract (0.3%) in sorghum seeds. They
also increased the activities of defensive enzymes such as ammonia lyase, peroxidase, phenylalanine, β-1, 3-glucanase, and chitinase [180]. In another study, the
application of seed meal of Ethiopian mustard (Brassica carinata L.) at 2.5 t ha
À1
enhanced the yield of tomato and reduced the root knot [181]. Two fungal
pathogens including Rhizoctonia solani Kühn and Pyricularia oryzae (Cavara)
were controlled, through inhibition of spore germination. There had been proposed
another important component of the defensive system of rice against diseases and
weeds by two allelochemicals present in rice, i.e., the 3-isopropy l-5-acetoxycyclohexene-2-one-1 and 5,7,40-trihydroxy-30,50-dimethoxyflavone [182]. The use
of crop allelochemicals is, thus, a cheap and environment-friendly way for managing
crop diseases (Table 6).
6
Conclusion
Various plants such as rice, sorghum, wheat, sunflower, eucalyptus, mulberry,
and neem have great allelopathic potential which can be exploited to reduce weed
pressure and control the insects and diseases in field and horticultural crops. For
weed control, the allelopathy can be exploited through crop rotation, use of allelopathic water extracts alone or in combination, intercropping and use of cover crops.
Nevertheless, special care is required to avoid any damaging influence of the
allelopathic phenomenon on the agricultural systems. The future research strategies
should include the breeding of crop cultivars with higher allelopathic potential to
cope with biotic and abiotic stresses. Although the allelochemicals extracted from
crop plants have been used for decades as eco-friendly pesticides, there have been
very few allelochemical-based pesticides available in the market across the globe.
Thus, due to increase in the area under organic crops, and to protect the environment
from the hazards of pesticides, the ecological and physiological mechanisms of the
allelopathy need greater attention in future studies with great emphasis on development of allelochemical-based pesticides. Although, the molecular mechanism of
564
A. Nawaz et al.
which can be useful for the reduction of fungal pathogens [177] and soil nematodes.
Application of canola (1%), barley, oat, and lentil extracts (each 2% and 4%)
significantly decreased the germination of sclerotia than control. However, ascospore germination was controlled by the application of 2 and 4% barley and lentil
extracts, respectively, while ascospore germination was encouraged by these similar
applications of wheat, canola, sweet clover, lentil, and rye extracts [178]. The root
rot disease in cumin (Cuminum cyminum L.), caused by Fusarium oxysporum
and other Fusarium spp. (e.g., F. moniliforme, F. lateritium, F. equiseti, F. solani,
and F. dimerum), was controlled by oil extract from cumin (Cuminum cyminum L.),
basil (Ocimum basilicium L.), and the rose geranium (Pelargonium graveolens L
[179]). Similarly, plant pathogens, such as Fusarium verticillioides, Bipolaris
sorghicola, Trichothecium roseum, F. solani, Alternaria alternata, Curvularia
lunata, Cladosporium cladosporioides, F. oxysporum, A. strictum, Aspergillus
flavipes, etc., were controlled by seaweed extract (0.3%) in sorghum seeds. They
also increased the activities of defensive enzymes such as ammonia lyase, peroxidase, phenylalanine, β-1, 3-glucanase, and chitinase [180]. In another study, the
application of seed meal of Ethiopian mustard (Brassica carinata L.) at 2.5 t ha
À1
enhanced the yield of tomato and reduced the root knot [181]. Two fungal
pathogens including Rhizoctonia solani Kühn and Pyricularia oryzae (Cavara)
were controlled, through inhibition of spore germination. There had been proposed
another important component of the defensive system of rice against diseases and
weeds by two allelochemicals present in rice, i.e., the 3-isopropy l-5-acetoxycyclohexene-2-one-1 and 5,7,40-trihydroxy-30,50-dimethoxyflavone [182]. The use
of crop allelochemicals is, thus, a cheap and environment-friendly way for managing
crop diseases (Table 6).
6
Conclusion
Various plants such as rice, sorghum, wheat, sunflower, eucalyptus, mulberry,
and neem have great allelopathic potential which can be exploited to reduce weed
pressure and control the insects and diseases in field and horticultural crops. For
weed control, the allelopathy can be exploited through crop rotation, use of allelopathic water extracts alone or in combination, intercropping and use of cover crops.
Nevertheless, special care is required to avoid any damaging influence of the
allelopathic phenomenon on the agricultural systems. The future research strategies
should include the breeding of crop cultivars with higher allelopathic potential to
cope with biotic and abiotic stresses. Although the allelochemicals extracted from
crop plants have been used for decades as eco-friendly pesticides, there have been
very few allelochemical-based pesticides available in the market across the globe.
Thus, due to increase in the area under organic crops, and to protect the environment
from the hazards of pesticides, the ecological and physiological mechanisms of the
allelopathy need greater attention in future studies with great emphasis on development of allelochemical-based pesticides. Although, the molecular mechanism of
564
A. Nawaz et al.