cultivars to compete with weeds (Berkowitz 1988) that are sources of organic plant
breeding approaches for a pollution-free and cleaner environment. Plant height is
often labeled as one of the best important traits in the overall competitive capability
of a crop and accounts for a similar percentage of total competitive ability (Gaudet
and Keddy 1988). Practically, weed control will be a challenging task because of a
wide range of susceptible weed species, and, thus, incorporation of allelopathic traits
appeared to depend on combining genes for diverse allelochemicals in one cultivar,
or choosing cultivars that already have such genes will be an appropriate approach.
In the recent past, the rice germplasm screening bestowed valuable insights into crop
allelopathy and its application in weed management and identified elite allelopathic
genotypes, predominantly Asian rice lines, which have been utilized to commence
traditional breeding programs to improve allelopathy in rice (Gealy et al. 2005). In
wheat, screening of allelopathic varieties and further improving the allelopathic
potential at the genetic level are studied to identify new potent wheat varieties, to
analyze the allelopathic impact of wheat on weeds, and to isolate and identify the
allelopathic compounds and their collegial and combined effects on physiological
mechanisms of plants ((Bertholdsson 2010).
4.3.2 Molecular Breeding for Improving Allelopathic Traits
The allelopathic genetic traits are knitted with environmental and ecological conditions expressed in genotype by environmental interactions, causing different expressions in a different environment. The allelopathic potential of crops is weakly
associated to yield and yield-related characters due to its polygenic nature
(Olofsdotter et al. 1999). In the identification of genes regulating allelopathy,
without insight knowledge about the genetics, breeding allelopathic cultivars is
practically impossible. Generally, allelopathy is a quantitative trait because of the
genetic variability in allelopathic strength within a plant species (Dilday et al. 1998).
Recently, DNA marker-assisted selection has been understood to detect QTLs
responsible for the synthesis of allelochemicals in various crops. Identification of
allelic loci governing the production of allelochemicals would assist in improving
cereals for augmenting the release of these biochemical compounds. Successful
genetic manipulation of allelopathic traits has been validated for crops, such as
rice (Olofsdotter et al. 1999, 2002; Amb and Ahluwalia 2016), sorghum (Shehzad
and Okuno 2020), and wheat (Wu et al. 2000). In sorghum, QTL mapping found
nine QTLs (three for deterring germination and six for the length of roots in lettuce),
and a total of 17 QTLs (seven for inhibiting germination and ten for the length of
roots in lettuce) were identified in a linkage study.
The previous scientific reports have shown the existence of several
allelochemicals and the multigenic nature of allelopathic traits in sorghum (Shehzad
and Okuno 2020). The quantitative trait loci (QTL) regulating allelopathic effects in
rice have been identified (Xu et al. 2002; Xu et al. 2003). The ISSR (inter-simple
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H. Palanivel et al.
breeding approaches for a pollution-free and cleaner environment. Plant height is
often labeled as one of the best important traits in the overall competitive capability
of a crop and accounts for a similar percentage of total competitive ability (Gaudet
and Keddy 1988). Practically, weed control will be a challenging task because of a
wide range of susceptible weed species, and, thus, incorporation of allelopathic traits
appeared to depend on combining genes for diverse allelochemicals in one cultivar,
or choosing cultivars that already have such genes will be an appropriate approach.
In the recent past, the rice germplasm screening bestowed valuable insights into crop
allelopathy and its application in weed management and identified elite allelopathic
genotypes, predominantly Asian rice lines, which have been utilized to commence
traditional breeding programs to improve allelopathy in rice (Gealy et al. 2005). In
wheat, screening of allelopathic varieties and further improving the allelopathic
potential at the genetic level are studied to identify new potent wheat varieties, to
analyze the allelopathic impact of wheat on weeds, and to isolate and identify the
allelopathic compounds and their collegial and combined effects on physiological
mechanisms of plants ((Bertholdsson 2010).
4.3.2 Molecular Breeding for Improving Allelopathic Traits
The allelopathic genetic traits are knitted with environmental and ecological conditions expressed in genotype by environmental interactions, causing different expressions in a different environment. The allelopathic potential of crops is weakly
associated to yield and yield-related characters due to its polygenic nature
(Olofsdotter et al. 1999). In the identification of genes regulating allelopathy,
without insight knowledge about the genetics, breeding allelopathic cultivars is
practically impossible. Generally, allelopathy is a quantitative trait because of the
genetic variability in allelopathic strength within a plant species (Dilday et al. 1998).
Recently, DNA marker-assisted selection has been understood to detect QTLs
responsible for the synthesis of allelochemicals in various crops. Identification of
allelic loci governing the production of allelochemicals would assist in improving
cereals for augmenting the release of these biochemical compounds. Successful
genetic manipulation of allelopathic traits has been validated for crops, such as
rice (Olofsdotter et al. 1999, 2002; Amb and Ahluwalia 2016), sorghum (Shehzad
and Okuno 2020), and wheat (Wu et al. 2000). In sorghum, QTL mapping found
nine QTLs (three for deterring germination and six for the length of roots in lettuce),
and a total of 17 QTLs (seven for inhibiting germination and ten for the length of
roots in lettuce) were identified in a linkage study.
The previous scientific reports have shown the existence of several
allelochemicals and the multigenic nature of allelopathic traits in sorghum (Shehzad
and Okuno 2020). The quantitative trait loci (QTL) regulating allelopathic effects in
rice have been identified (Xu et al. 2002; Xu et al. 2003). The ISSR (inter-simple
108
H. Palanivel et al.