Marker assisted selection: a strategy for wheat improvement Bhakti Rana1, Preeti Rana 2, Manoj K. Yadav1, Sundeep Kumar1

Resistance to abiotic stress
Traditional approaches at transferring resistance to crop plants are limited by the complexity of stress tolerance traits, as most of these are quantitatively linked traits (QTLs). The direct introduction of a small number of genes offers convenient alternative and a rapid approach for the improvement of stress tolerance. Although, present engineering strategies rely on the transfer of one or several genes that encode either biochemical pathways or endpoints of signalling pathways, these gene products provide some protection either directly or indirectly against environmental stresses. Drought is a major abiotic factor that limits crop productivity, thereby causing enormous loss.
Low temperature (LT) tolerance is a complex quantitative character that is expressed in anticipation of and during exposure of plants to temperatures that approach freezing. This environmentally reduced character is determined by a highly integrated system of structural and developmental genes that are regulated by environmentally responsive complex pathways. The superior LT-tolerance genes have been tagged using molecular markers that allow plant breeders to select hardy genotypes without having to wait for a test frost in the field (Fowler and Limin 2007).
Quality traits
Other than reporter genes, perhaps the most targetted trait for genetic engineering in wheat is quality. Seed storage proteins (SSP) are contained in the seed of higher plants. These proteins have been classified as albumins, globulins and glutenins on the basis of their solubility in solvents. The high molecular weight glutenin subunits (HMW-GS) genes in wheat are located on the long arm of the homeologous chromosomes 1A, 1B and 1D. Bread-making properties are particularly associated with variation at the Glu-D1 and Glu-A1 loci. The HMW-GS 1Ax1, 1Ax2, 1Dx5 and 1Dx10 have been shown to be associated with stronger dough, better elasticity and, hence, improved bread-making quality. Many elite wheat varieties lack the desired studies have demonstrated that the introduction of one or two HMW-GS genes results in a stepwise increase in dough elasticity. The transgenic lines produced so far have also demonstrated a very high level of expression and stability over several generations. This may imply that native genes are more tolerated by a plant genome.subunits and, thus, many research groups are attempting to introduce these via genetic engineering (Shewry et al. 1995; Altpeter et al. 1996; Barro et al. 1997; Vasil and Anderson 1997). In addition to increasing the bread-making quality, altered amino acid composition of the SSP is feasible and could result in improved nutritional properties. For example the insertion of genes for proteins such as zeins or albumins, could lead to an increase in the desired amino acid. Other approaches are also being considered such as reducing the level of anti-nutritional factors and modifying starch and oil composition and content.