Soybean [Glycine max (L.) Merr.] was domesticated in China but has a long history of cultivation on the Korean peninsula and in Japan. All three areas are considered important sources of soybean germplasm. The objectives of this study were to evaluate the genetic variation in soybean within and among China, S. Korea, and Japan by means of 120 accessions from eight Chinese and three S. Korean provinces, and three Japanese districts; and to relate genetic diversity patterns to geographical regions. Genetic relationships were estimated by 115 random amplified polymorphic DNA (RAPD) markers with simple matching coefficients expressed as Euclidean distances. Hierarchical and nonhierarchical cluster analyses as well as principal component analysis were used to define relationships among the genotypes. The results indicate that the mean genetic distance within China is much larger than that within Japan or S. Korea, but smaller than that between China and Japan or S. Korea. Cluster and principal component analyses almost completely separated the accessions from China from those of Japan and S. Korea, but could not distinguish between the accessions from Japan and S. Korea. These results are consistent with previous research using enzymes and morphological data to classify soybean germplasm from Asia. The groups formed by cluster analysis were mainly based on the frequencies of RAPD fragments among accessions and generally reflected the geographical regions of origin. No clear relationship was found between latitude and genetic diversity among accessions from these countries. Although the soybean accessions from Japan and S. Korea originally came from China, these data indicate that current accessions from Japan and S. Korea are genetically very distinct from those from China and more similar to each other.
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