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

Use of molecular markers in wheat improvement programme: conservation of genetic resources
Loss of genetic diversity has become a problem not only of the natural plant and animal population but also agriculturally important species. Ancient cultivars or landraces and wild relatives of domesticated species are being lost as modern varieties become adopted by farmers. This has led to calls for genetic conservation of crop germplasm (Frankel and Benett 1970). Microsatellites are commonly used to study genetic relationships among genotypes within species because of their high level of polymorphism (Devos et al. 1995; Roder et al. 1995; Korzun et al. 1997). Microsatellites markers are currently used to identify genotypes Quantitative trait loci (QTLs) and genetic diversity (Medini et al. 2005). Knowledge of genetic diversity of wheat varieties is a prerequisite for the successful management of conservation programs. The first microsatellite in wheat possessed 279 microsatellites (Roder et al. 1998) by now a total of 1235 microsatellite loci were developed and mapped (Somers et al. 2004). Recently 101 microsatellite markers derived from expressed sequence tags EST-SSRs were added into a set of microsatellites (Gao et al. 2004).
Resistance to biotic stress: gene pyramiding for multiple disease resistance
Development of resistant varieties for single disease is not enough to save plant product and to feed growing population especially in developing countries. In India, there are number of constraints in the successful production of wheat like leaf and yellow rust, powdery mildew and spot blotch. These all diseases together toll heavy yield losses and put us in the situation to redesign our experiments to develop multiple pest resistant varieties in wheat. The grown varieties on the market do carry some known disease resistance genes against powdery mildew and rusts and low levels of quantitative resistance against leaf spot diseases. However, most of the resistance genes against rusts and powdery mildew are already broken down. In the sustainable agriculture, which is economical both for the farmer and nature, multiple disease resistance is an essential tool against pathogens attack beside cultural practices like crop rotation. With the biotrophic fungi like rusts and powdery mildew, the only solution is the durable disease resistance.
In late 1980’s Fusarium head blight (FHB) become a world wide problem. Earlier, it was sporadic and localized to China, South America and a few European countries. Varieties resistant to FHB such as Wuhan 1, 2 and 3 and Shangai 7 and 8 and Suzhoe wheats were the product of generous collaboration between various Chinese institutions. Fusarium head blight is a serious disease of wheat (Triticum aestivum L) in humid and semi humid areas of the world. Evaluation of Fusarium head blight resistance is time consuming, laborious and costly as the inheritance of resistance is complex phenomenon. The most recent biotic threat to global wheat production is Ug 99, a virulent race of stem rust which has emerged from Uganda and has been confirmed at widely distributed testing locations in Kenya and Ethiopia. Yield losses of up to 71 percent have been recorded under experimental conditions (Dixon 2003).