Strategies for Improving Abiotic Stress Tolerance

Many strategies undertaken for improving abiotic stress tolerance in a particular genetic background have included screening of diverse genetic resources, wide crossing and subsequent recurrent backcrossing; identification and selection of the major conditioning genes through linkage mapping and quantitative trait loci (QTL) analysis; the production and screening of mutant populations and the transgenic introduction of novel genes (Fig. 1.1). Although some success has been achieved in introducing tolerance traits into crop varieties from wild relatives (i.e. barley; Forster et al. 2000 and tomato; Foolad et al. 2001), in

Fig. 1.1 Integrated components in the development of improved germplasm for abiotic stress tolerance

general there has been very little success reported in achieving high abiotic tolerance into elite ger-mplasm (Flowers 2004).

As previously mentioned, breeding for, or induction of, abiotic stress tolerance traits is almost always limited by the genetic complexity of the underpinning mechanisms as well as potential interaction among genetic determinants. Also, differential selection of a particular stress may be affected by additional environmental factors, plant development stage, poor or irreproducible selection techniques, and the logistical constraints of physiological screening of large breeding populations on a field scale (Flowers et al. 2000) . In this regard, the identification of discrete chromosomal regions that have a major effect on the specific tolerance trait through quantitative trait loci (QTL) mapping and marker-assisted selection remains a valuable option for many breeding programs (Cushman 2009; Cuartero et al. 2010). This is particularly so when whole genome knowledge is lacking and no candidate tolerance genes are known.

For accurate selection of the related phenotype, reliable and realistic screening techniques are required. However, uniformity and reliability of field-based screening may suffer from heterogeneity in the stress across the site (i.e. boron or salinity level) as well as the potential compounding environmental factors (i.e. disease, rainfall, temperature). Also, when the starting material is genetically wide, heterogeneity among the genetic backgrounds may also impact on the ability to accurately select the most superior or different tolerances. As an alternative, cellular-based mutant induction and subsequent selection initially under controlled in vitro conditions offers a method to quickly screen large populations with homogeneous backgrounds for novel fortuitous changes related to tolerance. Subsequent field screening then ensures adequate performance of the tolerance trait under the external potentially mitigating factors previously mentioned. Unsurprisingly, this method has generated great interest in selecting for abiotic stress tolerances in several crop species (Suprasanna et al. 2008).

Table 1.1 Some examples of osmoprotectant genes used in transgenic studies for engineering abiotic tolerance


Gene source


Crop species engineered



Moth bean

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