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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, sz, and sM, 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 sz or sM, 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.

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Wild relatives are valuable genetic resources for crop improvement . Evaluating genetic variation in these species is not only important for their use in breeding programs, but will also provide information about evolution of crops . Seeds representing six natural populations were used to study the level of variation in the South Korean wild soybean . Electrophoretic assays of the seeds on horizontal slab gels were conducted to determine the genotypes of each natural plant at 35 loci in 17 isozymes and one protein . The results indicated a surprisingly high variation. The number of alleles at each locus was as high as four . Seventy two of the 94 reported alleles for the 35 loci were present in these populations . The average number of alleles per locus, 99% polymorphism and the expected heterozygosity in the total population were 2 .1,77 .1% and 0 .215, respectively. This amount of variation was not only higher than that reported for 857 soybean cultivars and wild soybean populations from other geographic regions, but also higher than the average for 123 self-fertilized plant species and 473 plant species of all mating systems . The high variation in the South Korean wild soybean as well as cultivated soybean indicated in this and other population genetic studies prompts us to propose that South Korea is one of the major soybean gene centers .