sequence repeat) molecular marker technique was used by Lin et al. (2005) to
evaluate the genetic diversity in rice and barley allelopathy. There are several
scientific reports on the successful usage of the RFLP technique to identify the
QTLs conferring the synthesis of phytochemicals in several crops. The similarities
among the allelopathic agents and these phytochemical-based features make it
probable to exploit the same research methodology to study the genetic control of
the allelochemical production in crops (Wu et al. 1999). The allelopathic research in
crops is still in its infancy. Further research along this line will offer a great prospect
for more understanding of the genetic control of allelopathy.
4.3.3 Genetic Engineering Approaches for Improving Allelopathic
Traits
Crop allelopathy has hardly ever been used effectually by farmers in weed management. Conventional breeding techniques have not been successful in developing
highly allelopathic crops coupled with higher yield potential. Genetic engineering
may perhaps have the potential for overcoming this bottleneck. Crops have been
developed resistant to pests, pathogens, and herbicides with transgenic technology,
but it has not evolved crops that hamper weeds with allelochemicals (Duke et al.
2003). The strategies for developing allelopathic crops by genetic engineering are a
quite complex process, usually involving multiple genes. One can select to enhance
the production of allelochemicals already present in a crop or to impart the synthesis
of new compounds. Several putative allelochemicals have been identified by observing for recognized phytotoxic chemicals in plant species; if a novel compound is
responsible for allelopathy, field screening will not be productive. The best accurate
method for the determination of prospective allelochemicals synthesized by a plant
is that of bioassay-directed isolation.
A molecular biology strategy for enhancement of prevailing biochemical pathways for allelochemical synthesis is restricted in several crops due to the dearth of
information or fragmentary knowledge of the biochemical pathways related to it. An
arduous strategy is the detection of genes encoding major and crucial enzymes for
allelochemical synthesis and to edulcorate the enzymes for elucidating the responsible genes (Canel 1999). Mutagenesis using transposable elements has been a
valuable technique for gene isolation for identifying the biochemical pathways
responsible for allelochemical production. In addition to this, an effective and
delineated transposable element is obligatory in the concerned plant species to utilize
this technique (Duke et al. 2001). Another potential genetic engineering-based
bioherbicidal weed management strategy is the improvement of cover crops that
are autotoxic after they have inhibited weeds, but already they start competing with
the crop. Stanislaus and Cheng (2002) established the proof of concept of this
strategy by expressing the Barnase gene cassette (which encodes a highly toxic
ribonuclease) in Nicotiana tabacum (tobacco) that is regulated by HSP81 heat-shock
5 Allelochemicals as Natural Herbicides for Sustainable Agriculture to Promote. . .
109
evaluate the genetic diversity in rice and barley allelopathy. There are several
scientific reports on the successful usage of the RFLP technique to identify the
QTLs conferring the synthesis of phytochemicals in several crops. The similarities
among the allelopathic agents and these phytochemical-based features make it
probable to exploit the same research methodology to study the genetic control of
the allelochemical production in crops (Wu et al. 1999). The allelopathic research in
crops is still in its infancy. Further research along this line will offer a great prospect
for more understanding of the genetic control of allelopathy.
4.3.3 Genetic Engineering Approaches for Improving Allelopathic
Traits
Crop allelopathy has hardly ever been used effectually by farmers in weed management. Conventional breeding techniques have not been successful in developing
highly allelopathic crops coupled with higher yield potential. Genetic engineering
may perhaps have the potential for overcoming this bottleneck. Crops have been
developed resistant to pests, pathogens, and herbicides with transgenic technology,
but it has not evolved crops that hamper weeds with allelochemicals (Duke et al.
2003). The strategies for developing allelopathic crops by genetic engineering are a
quite complex process, usually involving multiple genes. One can select to enhance
the production of allelochemicals already present in a crop or to impart the synthesis
of new compounds. Several putative allelochemicals have been identified by observing for recognized phytotoxic chemicals in plant species; if a novel compound is
responsible for allelopathy, field screening will not be productive. The best accurate
method for the determination of prospective allelochemicals synthesized by a plant
is that of bioassay-directed isolation.
A molecular biology strategy for enhancement of prevailing biochemical pathways for allelochemical synthesis is restricted in several crops due to the dearth of
information or fragmentary knowledge of the biochemical pathways related to it. An
arduous strategy is the detection of genes encoding major and crucial enzymes for
allelochemical synthesis and to edulcorate the enzymes for elucidating the responsible genes (Canel 1999). Mutagenesis using transposable elements has been a
valuable technique for gene isolation for identifying the biochemical pathways
responsible for allelochemical production. In addition to this, an effective and
delineated transposable element is obligatory in the concerned plant species to utilize
this technique (Duke et al. 2001). Another potential genetic engineering-based
bioherbicidal weed management strategy is the improvement of cover crops that
are autotoxic after they have inhibited weeds, but already they start competing with
the crop. Stanislaus and Cheng (2002) established the proof of concept of this
strategy by expressing the Barnase gene cassette (which encodes a highly toxic
ribonuclease) in Nicotiana tabacum (tobacco) that is regulated by HSP81 heat-shock
5 Allelochemicals as Natural Herbicides for Sustainable Agriculture to Promote. . .
109