Molecular Approaches to Maize Improvement

Abstract

The presence of quantitatively inherited traits in a genotype can make the testing procedure complex, unreliable, and expensive. Under such circumstances, indirect selection using molecular markers becomes an efficient complementary breeding tool. When target traits can be easily identified and linked with one or more markers, the marker loci can be used as a surrogate for the trait, resulting in greatly enhanced breeding efficiency. Marker-assisted selection (MAS) involves the use of DNA markers instead of phenotypic selection to speed up the process of development and release of cultivars. Marker-assisted selection is useful for selecting quantitatively inherited traits that are difficult or expensive to measure, exhibit low heritability, and/or are expressed late during the developmental process. The approaches to MAS include marker-assisted backcrossing (MABC) and marker-assisted recurrent selection (MARS). Marker-assisted selection exploits the tight linkage between QTL and nearby markers and was proposed as easier, faster, and more efficient selection method. However, the use of marker-assisted selection has been limited in complex traits because of low power to detect QTL and bias in the estimated marker effects. The use of markers to track transgenes or pyramid favorable alleles determining a significant proportion of the phenotypic variance is possible for many crops, including maize. It is now generally accepted that the role of MB goes beyond the manipulation of elite alleles at a few loci in biparental segregating populations. There is a need for validation of genetic gain of favorable alleles so that markers could be developed and employed.