Marker-assisted breeding in crops.

Attaining global food security by means of increased crop productivity will require an increase in gains from selection achieved through conventional breeding. To this end, the identification of molecular markers associated with loci controlling traits of agronomic interest coupled with the exploitation of marker-assisted breeding (MAB) approaches provides the opportunity to accelerate gain from selection. In particular, marker-assisted selection (MAS) and marker-assisted backcrossing have been widely adopted to improve resistance to diseases and other relatively simple traits. Notwithstanding these remarkable achievements, the improvement of yield and other complex quantitative traits via MAB has been marginal, mainly due to the difficulty in identifying major quantitative trait loci (QTLs) with an adequately stable effect across environments and genetic backgrounds. Additionally, the effect of most QTLs affecting yield is too small to be detected with either biparental mapping or association mapping. Genomic selection (GS) circumvents this problem by using an index for the selection of unmapped QTLs of small individual effects but with otherwise sizable effect at the whole plant level when selected together. GS is already having a positive impact on the improvement of crop yield, mainly in the private sector where high-throughput infrastructures allow breeders to handle the large number of molecular datapoints that are required for effectively deploying GS. Ultimately, an effective exploitation of MAB to enhance crop performance will rely on a closer integration between molecular approaches and conventional breeding.