Genetic diversity patterns in Chinese soybean cultivars based on coefficient of parentage

China released 651 soybean [Glycine mar (L.) Merr.] cultivars from 1923 to 1995. However, their diversity is not well characterized, The objective of this study was to quantify genetic diversity in Chinese cultivars via coeff icient of parentage (CP), and the relative importance of geographical growi ng region, province of origin, intended cropping system, era of release, an d breeder preferences in determining that diversity, A very low mean CP of 0.02 was found in Chinese soybean cultivars, suggesting the presence of a p otentially high level of genetic diversity in Chinese soybean breeding, Cul tivar pools from each of the three growing regions of China were almost com pletely unrelated to each other and exhibited low within-region mean CP val ues (<0.06). Similarly, mean CP values within- and between-provinces were l ow (0-0.2). Cropping systems and release eras also exhibited tow within- an d between-CP relationships (all <0.07). The low CP values detected here for Chinese soybean breeding resulted from Chinese breeder initiatives to intr oduce new germplasm into applied Chinese-breeding since the 1970s and from a strong tendency to avoid the mating of related parents. Half- and full-si b matings and backcrossing are almost absent from Chinese pedigrees, Althou gh mean CP for cultivars was low, cluster analysis proved to be a surprisin gly effective discriminator of diversity patterns, This analysis assigned 2 70 cultivars to 20 clusters explaining 41% of the total variability in CP. Clusters were almost completely unrelated to each other and could be used a s a basis for selection of parents for breeding. Pedigree analysis revealed that more than 30 cultivars grown currently in China trace to U.S. stocks. This successful use of U.S. germplasm in China may provide an important ex ample for future U.S. breeding strategy.