Relationship Between Coefficient of Parentage and Genetic Similarity Indices in the Soybean¹

Abstract

Estimates of genetic similarity or distance between populations or strains of plants are useful in planning crosses for hybrid or pureline cultivar development. We compared coefficients of parentage ( r ) and similarity indices ( s , s z , and s M , based on 20, 13, and 7 genetic loci, respectively) for combinations of 115 soybean [ Glycine max (L.) Merr.] cultivars and ancestral introductions. Correlations between r and s were higher than those between r and s z or s M , primarily because s includes information from more loci. The correlation between r and s was higher for the group of soybean cultivars released in the 1970s than for earlier cultivar groups, primarily because of the greater importance of identity by descent relative to identity in phenotype in determining s . The most useful estimate of genetic relationship is a composite index that includes both r and s .