Pedigree analysis for composing a core collection of modern cultivars, with examples from barley (Hordeum vulgare s. lat.).

A method for analyzing the pedigrees of cultivars is developed that allows for the calculation of the 'effective number of origin lines' (n OL ). The n OL is defined as the average number of alleles, not identical by descent, per locus in a set of lines. Its relationship with the commonly used 'coefficient of parentage' is clarified. A related quantity, the 'effective overlap of origin lines' (r OL ) is defined as the average number of alleles, not identical by descent, per locus common in two sets of individuals. A set of 85 modern barley cultivars is used to illustrate the application of n OL and r OL . This set originated from 153 mutually unrelated ancestors. The degree to which each ancestor contributed was quantified, and the result was a n OL of only 43.1. In the set were 51 spring and 34 winter cultivars, with a n OL of 25.0 and 21.0, respectively. Consequently, the r OL of these two groups was 2.9, indicating that the two groups can be considered to be nearly distinct genetically since they have only 2.9 origin lines in common. How the effective number of origin lines can be used to create a core collection of cultivars with known pedigrees by maximizing the n OL in a set of cultivars of given size is also discussed.