Marker-Assisted Selection

Abstract

Conventional plant breeding has been very successful in developing improved cultivars with desirable traits. However, it has not been as successful in improving traits with low heritability, e.g., abiotic stress resistance, horizontal disease resistance, etc. Molecular marker technology can effectively supplement the crop improvement programs in a variety of different ways, including indirect selection for all kinds of traits. Marker-assisted selection (MAS) makes selection independent of the phenotypic expression of the traits. As a result, it allows efficient utilization of greenhouse/off-season nursery facilities so that up to three generations of the breeding populations can be grown each year. In addition, it also permits the use of the selected plants for hybridization in the same crop season, in which the selections were done. These together greatly expedite the development of new cultivars with higher yields and improved stress tolerance. Markers are being used for marker-assisted backcrossing (MABC) to achieve the introgression of oligogenes as well as QTLs, and efforts are being made to combine oligogenic disease resistance with horizontal resistance. In MABC, MAS has been generally used for foreground selection, but it has also been used for background and recombinant selections. A specialized scheme of MAS, called marker-assisted recurrent selection, is designed to accumulate favorable QTLs in cross- as well as self-pollinated crops. In addition, innovative breeding approaches have been proposed to take full advantage of the marker data and increase the efficiency of the breeding strategies. MAS is being routinely used in several crops, and many crop varieties developed through MAS have been released for cultivation. In this chapter, the various aspects of MAS, including the successful examples of crop improvement, have been discussed in some detail.