Genetic Variation and Relationships among Cultivated, Wild, and Semiwild Soybean

Some annual Glycine accessions are intermediate between the standard phenotypes of Glycine max (L.) Merr. and Glycine soja Sieb. & Zucc. and have been labeled semiwild. Few studies have examined both the genetic and phenotypic relationships among G. soja, G. max, and semiwild-types by combining morphological traits and DNA markers. The objectives of this research were to quantify genetic variation within G. soja, G. max, and semiwild accessions; to investigate the relationships among the G. soja, G. max, and semiwild accessions; and to examine the relationships among phenotypes on the basis of morphological traits and genotypes on the basis of DNA markers. Ninety-two semiwild, G. soja, and G. max accessions from the USDA Soybean Germplasm Collection were evaluated for 20 phenotypic traits and with 137 RAPD markers. Mahalanobis distances and a Jaccard genetic similarity matrix were calculated for phenotypic traits and DNA data, respectively. Nonhierarchical and hierarchical clustering as well as multidimensional scaling (MDS) were used to evaluate relationships among semiwild, G. soja, and G. max accessions. Principal component analysis was applied to identify the morphological traits that were most significant in separating the three groups. For the accessions examined, unique RAPD markers were found for each taxonomic type. Three clusters defined by either phenotypic or DNA data are highly consistent and strongly corresponded to G. soja, G. max, and semiwild classifications. On the basis of the analysis of RAPD data, G. soja accessions have the greatest genetic diversity and semiwild accessions the least. Glycine max and semiwild accessions are more closely related to each other than to G. soja accessions. These data will be useful in helping to define a core collection of annual Glycine.