backbreeding

Backbreeding is a plant and animal breeding technique used to reintroduce or recover a specific trait from an ancestral or unusual donor into a modern recurrent parent while preserving most of the recurrent parent's genome. The donor carries the desirable trait or character, while the recurrent parent is a well-established line with desirable agronomic properties but lacking the trait. The process involves crossing the donor with the recurrent parent, then repeatedly backcrossing the progeny to the recurrent parent while selecting for the target trait and for resemblance to the recurrent parent.

After n backcross generations, the offspring is expected to contain most of the recurrent parent's genome, with only a small proportion from the donor (approximately (1/2)^n of the genome from the donor). Final steps often include selfing or sib-mating to fix the trait and regain homozygosity. Backbreeding is used to reintroduce traits such as disease resistance, drought tolerance, quality attributes, or specific morphological features that were present in older varieties or species but were lost during modern cultivar development.

It is a form of introgression and is sometimes complemented by marker-assisted backcrossing to track donor segments and minimize linkage drag, i.e., unwanted donor DNA linked to the target gene. Limitations include the time and resources required, the possibility of undesirable donor genome segments, and the challenge of recovering complex traits. Backbreeding is commonly employed in crop improvement (e.g., cereals, vegetables) and, less frequently, in animal breeding.