Introduction to Marker-Assisted Crop Improvement

Abstract

Crop cultivation has played an important role in human history and civilization. Agriculture began with the selection of some plant species to be grown in primitive fields. There would have been some form of selection of seeds with desirable features for planting the crop next season; this began to develop into the planned and systematic selection efforts around the beginning of the nineteenth century. With the rediscovery of Mendel’s laws of inheritance in 1900, the art of selection acquired a scientific framework and initiated the development of a new discipline called “plant breeding.” The basic necessity for selection is the presence of genetic variation for the traits to be improved; this variation can be created through hybridization, mutagenesis, somaclonal variation, and, more recently, recombinant DNA technology. The genetic variation for qualitative traits is easily and effectively exploited by selection. In contrast, selection for quantitative traits is much less effective due to their polygenic control and, more particularly, the confusing effects of the environmental influences on their phenotypic expression. Since most of the traits of biological and economic significance are quantitative in nature, an effective strategy for their selection needs to be devised. This need becomes more imperative in view of the increasing human population and the adverse impacts of the climate change, in view of which varieties combining higher yields with resistance/tolerance to abiotic and biotic stresses have to be developed in relatively shorter periods of time. The transgenic technology has generated some useful crop varieties, but their consumer acceptance remains one of the major issues. In contrast, the molecular marker technology does not have any consumer acceptance issues. In addition, it has several plant breeding applications, including detection and mapping of QTLs, and reliable indirect selection for target genes/QTLs (marker-assisted selection). The present chapter examines the contributions of conventional plant breeding, pinpoints its limitations, and surveys the strategies available for supplementing plant breeding activities. The usefulness of molecular markers is highlighted by summarizing their contributions to variety development and indicating the future research needs in this promising area.