Application of Molecular Breeding for Development of the Drought-Tolerant Genotypes in Wheat

Abstract

Drought is one of the most important environmental challenges growers have to face around the world. Drought is the cause for large grain losses every year, especially in developing countries, and the current trend in global climate change will likely lead to further losses. The worldwide water shortage and uneven distribution of rainfall makes the improvement of drought tolerance especially important (Lou and Zhang, 2001). Breeding for drought tolerance is a major objective in arid and semiarid regions of the world due to inadequate precipitation, shortage of irrigation water and high water demand for crop evapotranspiration in such climates. Little progress has been made in characterizing the genetic determinants of drought tolerance, because it is a complex phenomenon (Tripathy et al, 2000). Breeding for water stress tolerance by traditional methods is a time consuming and considered inefficient procedure. Improving the drought tolerance of a crop is difficult for a breeder because yield usually has a relatively low heritability even under ideal condition and an unpredictably variable water supply reduces heritability (Blum, 1988). Drought tolerance is now considered by both breeders and molecular biologists to be a valid breeding target. In the past, breeding efforts to improve drought tolerance have been hindered by its quantitative genetic basis and our poor understanding of the physiological basis of yield in water-limited conditions (Passioura, 2002). Recently, Tuberosa and Saliva (2007) reported that genomics based approaches provide access to agronomically desirable alleles present at quantitative trait loci (QTLs) that affect such responses, thus enabling us to improve the drought tolerance and yield of crops under water limited conditions more effectively. Compared to conventional approaches, genomics offers unprecedented opportunities for dissecting quantitative traits into their single genetic determinants (QTLs), thus paving the way to marker-assisted selection (MAS) (Ribaut et al,2002; Morgante and Salamini, 2003) and eventually, cloning of genes at target QTLs (Salivi and Tuberosa, 2005).Recently, Tuberosa