The application of molecular markers in the process of selection

Molecular markers are modern diagnostic tools, which may help breeders to solve practical problems. They facilitate cultivar identification, the determination of genetic similarities among breeding stocks and enable the calculation of polymorphism level, heterozygosity or self-pollination rate. But the main expectation with respect to molecular markers is their potential use in marker-assisted selection (MAS). There are four major strategies of finding a molecular marker tightly linked to a target gene of agronomic importance. The first approach takes advantage of the nearly isogenic lines (NILs) which are differentiated only by the allelic sets in the gene of interest and in the adjacent chromosomal region. The second strategy involves bulked segregant analysis (BSA) for identification of markers linked to a single gene. The third involves the genetic dissection of more complex traits, which leads to the identification of quantitative trait loci (QTL) and their markers. The fourth strategy of marker identification includes computer databases (sequence and mapping data). The usefulness of these strategies is discussed in this paper. Some consequences of the application of BSA for gene tagging are described.