Concept of Combining Ability | Vegetable Breeding

The concept of combining ability was developed by G.F. Sprague and L.A. Tatum in 1942. The average or overall performance of a line in a series of crosses is known as general combining ability (gca) and the deviation in the performance of a particular cross than what would be expected based on the gca effects of the lines involved is called as specific combining ability (sea). For illustration, Table 8.6 may be referred.

Well known procedures of combining ability analysis using diallel cross analysis and line x tester analysis are available. Mean squares due to gca and sca are converted into gca and sca variances (σ²_g or S²_gCa and σ²_s or S²_sca) respectively.

They have following relationship with additive genetic and dominance variance:

Thus, additive genetic variance is equal to twice the estimated gca variance component, whereas non-additive variance is directly equal to sea variance.

The proportions of the total genetic variance accounted for by additive and non-additive variances are computed as follows:

General combining ability effect of parental lines and specific combining ability effect of crosses is determined, using appropriate formulae.