Genetic Base for North American Public Soybean Cultivars Released between 1947 and 1988

A negative consequence of four decades of modern soybean breeding is the evolution of cultivars with complex pedigrees that tend to obscure the genetic base of applied breeding. A result is that the genetic base of North American soybean Glycine max (L.) Merr. has never been described fully. We attempt here to define the genetic base as sets of genotypes that contain 99% of the genes found in modern cultivars. For clarity, the base is defined both in terms of the original plant introductions (ancestors) used for hybridization and in terms of the progeny derived from them. In a first analysis of pedigree data, 80 ancestors were identified and their fractional genetic contributions to 258 cultivars were computed using coefficient of parentage (r) estimates. In a second analysis, six breeding lines and 133 cultivars were identified as first progeny of the 80 ancestors, and their contributions as parents to modern cultivars were computed using r. This analysis revealed that 91 first progeny constituted 99% of the genes found in modern cultivars. Lincoln and Harosoy in the North and Lee and its full sib (D49‐2491) in the South contributed nearly 40% of the genes to North American cultivars. Nearly 75% of the genes in modern cultivars trace to 17 first progeny released before 1960, indicating that breeders have remained dependent upon this early genetic core of breeding material. For practical study of the genetic base of North American soybean, we propose using a combination of the results from the two analyses described here. Twenty‐eight ancestors and seven first progeny were identified which contribute 95% of the genes found in modern soybean cultivars. This group of 35 genotypes would be a useful core collection for evaluating the presence, absence, or distribution of a trait in North American soybean cultivars.