Backcross breeding is one of the most commonly used
methods to insert single disease or insect resistant genes into a susceptible high yielding cultivar. The high yielding
cultivar is the recipient and the resistant cultivar is the
donor in this case. The high yielding cultivar (suppose A)
is crossed with the resistant cultivar (suppose B) during
the first year. The resultant progeny is called backcross 1
(BC1) and has 50% genetic content of both cultivars. To
recover high yielding genes of recipient cultivars, the
recipient cultivar (A) is backcrossed with BC generations
in subsequent years until almost 99% genes of A cultivar
are recovered in the BC6 generation. This strategy has
been used by plant breeders to develop disease resistant
cultivars in most cases. Zhang et al. (2000) reported the
transfer of the cryIA gene of transgenic cotton through
backcross breeding. They concluded that a balanced
durable transfer of the Bt gene cryIA gene was observed
through backcross breeding, which conferred resistance
against chewing insects.