A Review on crop improvement through marker-assisted recurrent backcrossing
Guoyou YE, Kevin F Smith
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.
Hybrid seed production mechanisms in rice (Oryza sativa L.)
Commercial development of hybrid rice depends on the availability of high quality seed, which can come about only through improved hybrid seed production techniques. Improved technique has to depend on its basic tools; improved male sterility, its maintenance and fertility restoration system. Rice being strictly self pollinated crop, to achieve high outcrossing potential on cytosterile lines is a serious challenge to hybrid rice breeders. High and true to type outcrossing will depend on strict isolation of seed production areas, through roguing of off-type plants and rigid operating rules can help to achieve required seed purity. In this review of literature the factors that control hybrid seed production mechanism in rice are discussed.