Genetic Diversity and Agronomic Improvement of North American Soybean Germplasm

From 1970 to 2008 there were 2242 soybean [Glycine max (L.) Merr.] cultivars registered in North America through U.S. Plant Variety Protection (PVP), U.S. utility patent, and journal registration. Of these, 80% were developed through proprietary and 20% through public programs. Our objective was to characterize the development and genetic diversity of North American soybean cultivars. The most frequently used germplasm for cultivar development were the cultivars Williams (parent used in last cross before inbreeding in 70 cultivars), A3127 (63), Essex (45), Amsoy (38), Corsoy (33), Wayne (30), Forrest (27), Hutcheson (25), MO13404 (23), and Bedford (23) Genetic diversity (1 - coefficient of parentage), estimated from pedigree lineage, was 0.89 overall. Genetic diversity was the same within public (0.89) and proprietary (0.89) cultivars. The cultivar A3127 is a major progenitor of recently developed proprietary cultivars registered from 1999 to 2008. Of these 494 cultivars, 23% have a genetic contribution of at least 25% from A3127. New cultivars were predominantly developed from the following crosses: two-parent (70% of cultivars developed), complex (12%), three-parent (5%), one backcross (5%), multiple (two, three, or four) backcrosses (3%), and five or greater backcrosses (2%). In comparisons where both parent and progeny were evaluated together, seed yield increased 3.2% per breeding cycle. In these comparisons, seed yield had a correlation of 0.29 with parental diversity.