Marker-Assisted Selection Introduction

Conventional plant breeding is dependent on appropriate environmental conditions in which to identify and select desirable plants. Typically, breeders improve crops by crossing plants with desired traits, such as high yield or disease resistance, and selecting the best offspring over multiple generations of testing. A new variety could take 8 to 10 years to develop. Breeders are very interested in new technologies to speed up this process or make it more efficient. 

Molecular marker technology offers such a possibility. Marker-assisted selection involves selecting individuals based on their marker pattern (genotype) rather than their observable traits (phenotype) (Fig.1). Since the mid-1990’s, the term 'marker-assisted selection' has entered the working vocabulary of plant breeders and geneticists. As an example of its common usage, a bibliographic search via 'ISI Web of Science' for articles published in 2003 and having the key words 'marker-assisted selection' found 40 references for wheat, 41 each for rice and barley, and 35 for maize. Reflecting the state of the art, many of the references simply mention MAS as a potential application of the results of a marker-trait linkage study. However, compared to previous years, an increasing number of current articles now report the results of MAS implementation in a breeding program. 


Figure 1. Phenotypic and genotypic views of a corn plant. A. Conventional selection is based on direct measurement of important traits, such as yield, maturity, or disease resistance (their phenotype). B. In marker-assisted selection, plants are selected based on molecular marker patterns known to be associated with the traits of interest.

This lesson will describe the requirements for conducting a Marker-Assisted Selection (MAS) program in crop plants, discuss some of the advantages and drawbacks of MAS, and outline the methods used to select for markers linked to qualitative (single gene) or quantitative (multigenic) traits. The viewer is assumed to be familiar with DNA molecular markers and quantitative trait locus (QTL) analysis. For a review of these topics, please consult other lessons, including: