The combined use of marker-assisted selection (MAS) and recurrent backcrossing is a versatile method of plant breeding

and is known as marker-assisted recurrent backcrossing (MARB). Markers are used during recurrent backcrossing to select

for the presence of target gene (foreground selection), to select against donor genome contribution (background selection)

and to reduce the introgressed segment size and thus linkage drag. MARB reduces the number of backcrossing for recurrent

recovery by 3-4 generations if one or two genes are transferred. For foreground selection markers are most useful for traits

that are expensive and/or difficult to measure. Linkage drag when present is difficult if not impossible to remove by

phenotypic selection. The benefits of MARB were well demonstrated by theoretical and simulation studies, and confirmed by

empirical applications. MARB has also been used in generating genetic materials for genetic studies of complex traits.

Introgression lines (ILs) have many advantages for QTL mapping compared to other population types such as recombinant

inbred lines (RILs) and double haploids (DH). Near isogenic lines (NILs) are commonly used in further study of identified

quantitative trait loci (QTL). MARB also offers the possibility of fine mapping QTL by breaking down the QTL-containing

segment into smaller pieces.

Key Words: Background selection, Breeding, Foreground selection, Linkage drag, Marker assisted selection,

Recurrent backcrossing