Marker-Assisted Selection

Abstract

Marker-assisted selection (MAS) is a method of selecting desirable individuals in a breeding program based on molecular markers with or without consideration of their trait values. This allows indirect selection of specific characteristics of a plant based on the encoding genomic region. The introduction of next-generation sequencing technology and the availability of inexpensive and high-throughput marker systems have made molecular breeding more attractive. Marker-assisted breeding strategies such as marker-assisted backcross breeding, marker-assisted recurrent selection, and genomic selection were known to be successful in crop improvement. Nonetheless, conventional breeding and MAS are not mutually exclusive, instead they complement each other in most of the breeding methods, and therefore, in true sense they constitute integrated breeding. Definition and Background: The objective of plant breeding is to identify and develop superior individual(s) with desirable traits by selection, hybridization, heterosis, or mutation. Until twentieth century, plant breeding was based on the phenotypic selection based on yield, plant architecture preference, quality traits, ease of cultivation, and tolerance to biotic and abiotic stresses. Over the years, plant breeding technologies, such as pedigree, backcrossing, recurrent selection, and progeny testing, made an impact on crop improvement. With the discovery of molecular markers during the late twentieth century, the scenario of plant breeding started changing gradually. The fact that desirable lines can be selected based on molecular markers linked to the traits, at the seedling stage in a short time period is an attractive option for plant breeders, who in general spend about 5–8 years for the varietal release. Molecular markers are used as a substitute/supplement for the phenotypic selection to alter or improve the traits for crop improvement. In the initial years, breeders were reluctant to use the markers in their routine breeding program because of the high cost associated with genotyping and nonavailability of the high-throughput genotyping platforms. Although several publications reported mapping loci for important traits since the first quantitative trait locus report in tomato in 1988, there are very few instances where marker information has been utilized in plant breeding in public sector. In fact, most of the agronomically important traits are complex and are governed by polygenes. Hence, there was a notion that there should be cautiously optimistic vision to use the molecular breeding approaches in crop improvement.