2
Rich Sources of Allelochemicals
2.1
Allelopathic Crops
Various crop species have shown allelopathic potential that can be used to manage
weeds in field crops by using them as cover crops, surface mulch and/or residue
incorporation, intercropping, and rotation and using crop extract with reduced dose
of herbicides [7]. Researchers have screened various crop cultivars with strong
allelopathic traits. Common field crops including rice (Oryza sativa L.), wheat
(Triticum aestivum L.), sunflower (Helianthus annuus L.), maize (Zea mays L.),
canola (Brassica napus L.), sorghum (Sorghum bicolor L.), millet (Pennisetum
glaucum (L.) R.Br.), and buckwheat (Fagopyrum esculentum Moench) possess
variety of allelochemicals that can be used to suppress weeds [1, 7]. Alfalfa
(Medicago sativa L.) a common fodder crop cultivated worldwide provided significant control (up to 80%) to various weeds of rice ecosystem [8]. Rice a major cereal
also possess various herbicidal compounds; Xuan et al. [9] reported that rice
allelopathy can provide up to 88% control of weeds. Similarly, buckwheat residues
caused up to 80% weed control in rice field [10]. Furthermore, allelochemicals
released from sunflower, rye (Secale cereale L.), wheat, and sorghum could be
utilized to provide effective weed control in various crops [1, 11–19]. Allelopathic
potential of crops against weeds varies among crop species. For example, Batish
et al. [91] tested the weed control potential of 35 crops; all tested crops showed weed
suppression potential; some common crops including rice, wheat, maize, sugarcane,
alfalfa, and vegetable crops (cucumber (Cucumis sativus L.), soybean (Glycine max
[L.] Merr.), fennel (Foeniculum vulgare Mill.), and carrot (Daucus carota L.))
showed strong allelopathy and even caused autotoxicity under some conditions.
Various allelochemicals having inhibitory effects against the weeds have also been
identified from different common crop species [7, 20].
Different genotypes of the same crop may have different allelopathic potential.
Thirty eight wheat cultivars were tested for their allelopathic effect on Lolium rigidum
Gaud. Wheat cultivars showed differential allelopathic potential [84]. The above
discussion indicates that the allelopathic potential of a number of field crops has
been established in the last decades. These crops can be potentially used to manage
weeds in agroecosystems in different ways to ensure sustainable weed control.
2.2
Allelopathic Weeds
A large number of allelochemicals that can suppress the growth of other plant
species have been identified in various weeds. Similar to crops, weed species also
produce allelochemicals; these allelochemicals are supposed to be more toxic
because weeds normally grow under stress conditions. Different weed species
including Chenopodium album L., Medicago denticulata L., Melilotus indica L.,
Convolvulus arvensis L., Vicia hirsute L., Lathyrus aphaca L., and Rumex acetosella L.
21 Allelopathy for Weed Management
507
Rich Sources of Allelochemicals
2.1
Allelopathic Crops
Various crop species have shown allelopathic potential that can be used to manage
weeds in field crops by using them as cover crops, surface mulch and/or residue
incorporation, intercropping, and rotation and using crop extract with reduced dose
of herbicides [7]. Researchers have screened various crop cultivars with strong
allelopathic traits. Common field crops including rice (Oryza sativa L.), wheat
(Triticum aestivum L.), sunflower (Helianthus annuus L.), maize (Zea mays L.),
canola (Brassica napus L.), sorghum (Sorghum bicolor L.), millet (Pennisetum
glaucum (L.) R.Br.), and buckwheat (Fagopyrum esculentum Moench) possess
variety of allelochemicals that can be used to suppress weeds [1, 7]. Alfalfa
(Medicago sativa L.) a common fodder crop cultivated worldwide provided significant control (up to 80%) to various weeds of rice ecosystem [8]. Rice a major cereal
also possess various herbicidal compounds; Xuan et al. [9] reported that rice
allelopathy can provide up to 88% control of weeds. Similarly, buckwheat residues
caused up to 80% weed control in rice field [10]. Furthermore, allelochemicals
released from sunflower, rye (Secale cereale L.), wheat, and sorghum could be
utilized to provide effective weed control in various crops [1, 11–19]. Allelopathic
potential of crops against weeds varies among crop species. For example, Batish
et al. [91] tested the weed control potential of 35 crops; all tested crops showed weed
suppression potential; some common crops including rice, wheat, maize, sugarcane,
alfalfa, and vegetable crops (cucumber (Cucumis sativus L.), soybean (Glycine max
[L.] Merr.), fennel (Foeniculum vulgare Mill.), and carrot (Daucus carota L.))
showed strong allelopathy and even caused autotoxicity under some conditions.
Various allelochemicals having inhibitory effects against the weeds have also been
identified from different common crop species [7, 20].
Different genotypes of the same crop may have different allelopathic potential.
Thirty eight wheat cultivars were tested for their allelopathic effect on Lolium rigidum
Gaud. Wheat cultivars showed differential allelopathic potential [84]. The above
discussion indicates that the allelopathic potential of a number of field crops has
been established in the last decades. These crops can be potentially used to manage
weeds in agroecosystems in different ways to ensure sustainable weed control.
2.2
Allelopathic Weeds
A large number of allelochemicals that can suppress the growth of other plant
species have been identified in various weeds. Similar to crops, weed species also
produce allelochemicals; these allelochemicals are supposed to be more toxic
because weeds normally grow under stress conditions. Different weed species
including Chenopodium album L., Medicago denticulata L., Melilotus indica L.,
Convolvulus arvensis L., Vicia hirsute L., Lathyrus aphaca L., and Rumex acetosella L.
21 Allelopathy for Weed Management
507