Selection for heterosis from crossbred populations: estimation of the F1 heterosis and its mode of inheritance.

Abstract

The heterosis inheritance backcross evaluation technique (HI-BET) is proposed as a selection strategy for developing a pair of complementary strains from a crossbred population descended from a F1 population possessing considerable heterosis. These complementary strains are expected to produce a strain cross superior to the F1 population from which they were derived. In the first stage of an experimental evaluation of HI-BET, Australorp and White Leghorn hens were compared with their F1, F2 and F1 by parental breed backcross populations for a range of egg production traits. The substantial heterosis for survivors' egg production and total egg mass was largely lost in the F2 and backcross populations indicating that this heterosis was mainly due to parental epistasis. The uneven distribution of residual heterosis in the backcross populations suggests that about two-thirds of this parental epistasis was inherited from the White Leghorn line. As the Australorp line was substantially superior to the White Leghorn line for survivors' egg production and total egg mass, it most likely contained additive genes for both these traits that were not present in the White Leghorn line. It is suggested that HI-BET should be an effective strategy for incorporating these additive genes into the White Leghorn line, together with some brown egg shell genes if also desired, as a means of further improving the performance of the F1 cross.