Marker-assisted-selection (MAS): a fast track to increase genetic gain in horticultural crop breeding.
Mapping and tagging of agriculturally important genes have been greatly facilitated by an array of molecular markers in crop plants. Marker-assisted selection (MAS) is gaining considerable importance as it would improve the efficiency of plant breeding through precise transfer of genomic regions of interest (foreground selection) and accelerate the recovery of the recurrent parent genome (background selection). MAS have been widely used for simple inherited traits than for polygenic traits, although there are few success stories in improving quantitative traits through MAS. They are been used to monitor DNA sequence variation in and among the species and create new sources of genetic variation by introducing new and favourable traits from landraces, wild relatives and related species and to fasten the time taken in conventional breeding, germplasm characterization, genetic mapping, gene tagging and gene introgression from exotic and wild species. The success of MAS depend on many critical factors such as the number of target genes to be transferred, the distance between the target gene and the flanking markers, number of genotypes selected in each breeding generation, the nature of germplasm and the technical options available at the marker level. The power and efficiency of genotyping are expected to improve with the advent of markers like single nucleotide polymorphisms (SNP). Although genetic maps have been developed for most important fruit and vegetables species and a number of horticulturally important gene loci have been tagged, only a few are reported. New, easy to perform allele testing methods are needed to bridge this large gap between marker development and application. This review discusses the basic requirements and the potential applications of MAS and the significance of integrating MAS into conventional plant breeding programmes.