AN UNBIASED ESTIMATOR FOR IDENTIFYING LINES USEFUL FOR THE IMPROVEMENT OF ELITE SINGLE CROSSES, BASED ON A COMBINING ABILITY MODEL

Elite single crosses are frequently identified through combining abili ty analysis of the results obtained from a diallel cross of selected i nbred lines. The parents of these elite single crosses can be improved further by identifying a source of favourable alleles that are not pr esent in the single cross. An unbiased estimator of the potential of a n inbred line to donate favourable alleles, mu a(B + G), that is easy to compute and free from the assumption of complete dominance, is prop osed. The theory for the identification of donor inbred lines is based on a combining ability model. Five methods of identifying donor lines are compared theoretically with the proposed unbiased estimator. A wo rked example, based on a 12 x 12 diallel cross across two environments , illustrates the relationships between the various statistics used to identify donors. The unbiased estimator, mu a(B + G), is shown to pro vide an appropriate means of identifying donor inbred lines.