Molecular markers have proven to be invaluable tools for assessing plants’ genetic resources by improving our understanding with regards to the distribution and the extent of genetic variation within and among species. By using molecular markers, breeders can bypass traditional phenotype-based selection methods, which involve growing plants to maturity and closely observing their physical characteristics in order to infer underlying genetic make-up. Marker-assisted selection (MAS) provides opportunities for enhancing the response from selection because molecular markers can be applied at the seedling stage, with high precision and reductions in cost. MAS could be easily applied, but is often not necessary because the resistances are selected phenotypically. In quantitative disease resistances, MAS would be very useful, but the individual QTL often have small effects. Additionally, only a few monogenic resistances are durable and only a few QTL with high effects have been successfully transferred into elite breeding material. Further economic and biological constraints, e.g., a low return of investment in small-grain cereal breeding, lack of diagnostic markers, and the prevalence of QTL–background effects, hinder the broad implementation of MAS. The purpose of this article is to describe the available genetic marker types and provide the status of gene mapping and marker-assisted selection in important crop species. This review highlights how genetic markers have been used in mapping genes and discusses the importance of MAS and how it can be integrated into breeding programs for enhancing selection efficiency in developing disease resistant.
Keywords: Disease resistance; marker-assisted breeding; marker-assisted selection (MAS); molecular markers; quantitative trait loci (QTLs)