lives [79], and additionally the nature of allelochemicals, soil type, allelochemical
concentration, and soil enzymatic and microbial community are also important
[72]. Moreover, allelochemicals can be toxic to animals, e.g., fumonisin is toxic to
animals and sorgoleone causes dermatitis [77]. Furthermore, allelochemical concentration (10
À2
–10
À5 M) that causes herbicidal effect is higher than the ideal
concentration (10
À5
–10
À7 M) of natural herbicidal compounds according to environment safety standards [80]. In simple, issues regarding development of natural
herbicides that form allelochemicals are much complicated and uneconomical as
compared to synthetic herbicides. Additionally, less stability, low weed control
efficacy, poor selectivity, and high cost are major limitations for development
of natural herbicides by industries. However, the artificial modifications in
the structure of plant-released herbicidal compounds may help to increase their
selectivity and weed control efficacy. In addition, experiments considering
the change in allelopathic effects with application of nitrogen fertilizers,
activated charcoal, and environmental stresses may help to understand the fate
of allelochemicals in soil.
5
Future Directions
5.1
Germplasm Selection to Enhance Allelopathic Potential
Importance of crop cultivars with improved weed suppressive ability has highly
increased due to fast-increasing herbicide resistance in weeds and environmental
concerns of herbicide use. In this scenario, it is important to breed crop cultivars with
high allelopathic potential to suppress weeds and reduce herbicide usage. Different
crop species and even the cultivars within same crop species vary in their allelopathic potential [81]; this weed-suppressing potential can be used as an alternative to
herbicides. Studies on genetics of allelochemicals have not gained much attention in
the past. The variability in allelopathic traits can be used to breed crop cultivars with
more weed suppressive ability, e.g., rice produced from two inbred lines one with
allelopathic gene and second with restorative gene had strong suppressive ability
against E. crus-galli [82]. Crossing between old cultivars (having high allelopathic
potential) with new crop cultivars can also help to enhance allelopathic potential
[83]. Marker-assisted selection can help to develop crop cultivars with enhanced
allelopathic potential. For instance, two major QTLs linked with allelochemical
production were identified on 2B wheat chromosome [84]; thus allelopathic potential of wheat can be increased with the discovery of markers linked with the genes
that control allelopathic traits. Recently successful attempts have been made to
produce rice cultivars with high allelopathic potential in the United States (Arkansas), Asia, and Africa [85]. Bertholdsson [83, 86] also improved the weed suppressive potential of wheat and barley using breeding techniques; however the developed
cultivars showed low grain yield potential. Further studies are required to breed crop
cultivars with enhanced allelopathic potential and good yield potential for sustainable weed management.
21 Allelopathy for Weed Management
513
concentration, and soil enzymatic and microbial community are also important
[72]. Moreover, allelochemicals can be toxic to animals, e.g., fumonisin is toxic to
animals and sorgoleone causes dermatitis [77]. Furthermore, allelochemical concentration (10
À2
–10
À5 M) that causes herbicidal effect is higher than the ideal
concentration (10
À5
–10
À7 M) of natural herbicidal compounds according to environment safety standards [80]. In simple, issues regarding development of natural
herbicides that form allelochemicals are much complicated and uneconomical as
compared to synthetic herbicides. Additionally, less stability, low weed control
efficacy, poor selectivity, and high cost are major limitations for development
of natural herbicides by industries. However, the artificial modifications in
the structure of plant-released herbicidal compounds may help to increase their
selectivity and weed control efficacy. In addition, experiments considering
the change in allelopathic effects with application of nitrogen fertilizers,
activated charcoal, and environmental stresses may help to understand the fate
of allelochemicals in soil.
5
Future Directions
5.1
Germplasm Selection to Enhance Allelopathic Potential
Importance of crop cultivars with improved weed suppressive ability has highly
increased due to fast-increasing herbicide resistance in weeds and environmental
concerns of herbicide use. In this scenario, it is important to breed crop cultivars with
high allelopathic potential to suppress weeds and reduce herbicide usage. Different
crop species and even the cultivars within same crop species vary in their allelopathic potential [81]; this weed-suppressing potential can be used as an alternative to
herbicides. Studies on genetics of allelochemicals have not gained much attention in
the past. The variability in allelopathic traits can be used to breed crop cultivars with
more weed suppressive ability, e.g., rice produced from two inbred lines one with
allelopathic gene and second with restorative gene had strong suppressive ability
against E. crus-galli [82]. Crossing between old cultivars (having high allelopathic
potential) with new crop cultivars can also help to enhance allelopathic potential
[83]. Marker-assisted selection can help to develop crop cultivars with enhanced
allelopathic potential. For instance, two major QTLs linked with allelochemical
production were identified on 2B wheat chromosome [84]; thus allelopathic potential of wheat can be increased with the discovery of markers linked with the genes
that control allelopathic traits. Recently successful attempts have been made to
produce rice cultivars with high allelopathic potential in the United States (Arkansas), Asia, and Africa [85]. Bertholdsson [83, 86] also improved the weed suppressive potential of wheat and barley using breeding techniques; however the developed
cultivars showed low grain yield potential. Further studies are required to breed crop
cultivars with enhanced allelopathic potential and good yield potential for sustainable weed management.
21 Allelopathy for Weed Management
513