Future Perspectives in MAS

Abstract

MAS can be simply defined as selection for a trait based on the genotype of an associated marker rather than the trait itself. In essence, the associated marker is used as an indirect selection criterion. The potential of MAS as a tool for crop improvement has been extensively explored in different plant species. Major applications of MAS include (1) tracing favourable alleles and pyramiding them in desirable genetic backgrounds (foreground MAS), (2) eliminating unwanted genetic backgrounds (background MAS) or undesirable plant material in early breeding generations and identifying the most desirable gene combinations or individuals in segregating populations and (3) breaking the undesirable linkages between favourable and unfavourable alleles (reducing linkage drag). The success of MAS in plant breeding is often assessed on the basis of these three components. In theory, MAS can reduce the cost and increase the precision and efficiency of selection and breeding. However, MAS is not a ‘silver bullet’, and it can be more effective than conventional phenotype-based selection only under certain situations, including when (1) trait-based selection is not feasible (e.g. lack of selection environment or pathogen), (2) such selection is costly or ineffective, (3) trait expression is developmentally regulated or phenotypically not obvious until late in the season, (4) the trait is governed by recessive or incompletely dominant gene(s), (5) trait heritability is low rendering conventional phenotypic selection is ineffective, (6) there are too much G × E interactions, (7) multiple trait selection is desired, (8) conducting gene introduction/pyramiding from different sources and (9) transferring genes/QTLs from wild genetic backgrounds. Furthermore, in a backcross-breeding programme, MAS allows reduction of linkage drag by selecting against the undesirable donor genome and for desirable recurrent parent genome (background selection) while also selecting for desirable donor alleles (foreground selection). Moreover, with MAS, it is possible to conduct multiple rounds of selection in a year, allowing approximately two generations of selection per year, compared to one in phenotypic selection methods.