MARKER-ASSISTED INTROGRESSION OF QUANTITATIVE TRAIT LOCI

The use of molecular markers for the introgression of one or several s uperior QTL alleles into a recipient line is investigated using analyt ic and simulation results. The positions of the markers devoted to the control of the genotype at the QTLs in a ''foreground selection'' ste p are optimized given the confidence interval of the QTL position. Res ults demonstrate that using at least three markers per QTL allows a go od control over several generations. Population sizes that should be r ecommended for various numbers of QTLs are calculated and are used to determine the limit in the number of QTLs that can be monitored simult aneously. If ''background selection'' devoted to accelerate the return to the recipient parent genotype outside the QTL regions is applied, the positions of the markers devoted to the control of the QTLs have t o be reconsidered. When several QTLs are monitored simultaneously, bac kground selection among the limited number of individuals resulting fr om the foreground selection step accelerates the increase in genomic s imilarity with the recipient parent, with only limited costs. Backgrou nd selection is even more efficient in a pyramidal backcross program w here QTLs are first monitored one by one.