Self pollinators: Back-cross breeding
The idea of backcrossing is to correct a fault in an otherwise good variety. An example: if a popular variety becomes susceptible to a new race of a pathogen, the aim is to move a gene from a donor into the variety (the recipient) to produce a resistant version of the variety.
Lines fixed for AA are selected by testing for segregation in BC4F3 families.
Backcrossing is essential when wide crosses are used, to return the material to an adapted type.