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

Fukuda (1933) proposed that G. gracilis is an intermediate evolutionary type between G. soja to G. max, but Some annual Glycine accessions are intermediate between the Hymowitz (1970) suggested that G. gracilis is a hybridstandard phenotypes of Glycine max (L.) Merr. and Glycine soja Sieb. & Zucc. and have been labeled semiwild. Few studies have ization product of G. max and G. soja. The latter hypothexamined both the genetic and phenotypic relationships among G. esis was supported by Broich and Palmer (1981) on the soja, G. max, and semiwild-types by combining morphological traits basis of the results from their study of the frequency and DNA markers. The objectives of this research were to quantify and distribution of 10 alleles among G. max, G. soja, genetic variation within G. soja, G. max, and semiwild accessions; to and G. gracilis accessions. On the basis of numerical investigate the relationships among the G. soja, G. max, and semiwild taxonomic analysis, Broich and Palmer (1980, 1981) recaccessions; and to examine the relationships among phenotypes on ommended that the designations G. max and G. gracilis the basis of morphological traits and genotypes on the basis of DNA both be utilized. They reasoned that G. gracilis phenomarkers. Ninety-two semiwild, G. soja, and G. max accessions from types can be distinguished from G. max and they reprethe USDA Soybean Germplasm Collection were evaluated for 20 sent an intermediate form of domesticated soybean. In phenotypic traits and with 137 RAPD markers. Mahalanobis distances and a Jaccard genetic similarity matrix were calculated for phenotypic addition, G. max and its semiwild relative should be traits and DNA data, respectively. Nonhierarchical and hierarchical regarded as taxonomically distinct from G. soja since clustering as well as multidimensional scaling (MDS) were used to both are domesticated. evaluate relationships among semiwild, G. soja, and G. max accesHermann (1962) removed G. gracilis from the species sions. Principal component analysis was applied to identify the morrank and incorporated it into G. max on the basis of phological traits that were most significant in separating the three classical taxonomy. Several studies support the eliminagroups. For the accessions examined, unique RAPD markers were tion of G. gracilis as a separate species. Singh and Hyfound for each taxonomic type. Three clusters defined by either phenomowitz (1989) demonstrated that G. max, G. soja, and typic or DNA data are highly consistent and strongly corresponded G. gracilis all hybridized readily, and F1 seeds produced to G. soja, G. max, and semiwild classifications. On the basis of the viable, vigorous, and fertile plants with normal meiotic analysis of RAPD data, G. soja accessions have the greatest genetic diversity and semiwild accessions the least. Glycine max and semiwild pairing. Wang (1976) suggested all three classifications accessions are more closely related to each other than to G. soja in subgenus Soja could be a single species since they accessions. These data will be useful in helping to define a core collecwere not reproductively isolated, but on the basis of tion of annual Glycine. cultivated status, he recommended that G. soja be kept as a species and G. gracilis reclassified as G. max. Dae et al. (1995) applied isozyme and RAPD techT are two species usually recognized within niques to evaluate genetic variation within the subgenus the genus Glycine subgenus Soja, Glycine max and Soja and concluded on the basis of morphological apGlycine soja. On the basis of data from morphology pearances that the intermediate forms of G. max were (Palmer et al., 1987), cytogenetics (Hymowitz and Singh, also intermediate between G. max and G. soja on the 1987), phytoalexins (Keen et al., 1986), restriction endobasis of genotypic measurements. Fei and Chen (1996) nuclease fragment analysis of mitochondrial DNA analyzed genetic diversity of the Glycine genus with (Doyle, 1988), ribosomal RNA (Doyle and Beachy, RAPD markers using 21 accessions from 10 species of 1985), chloroplast DNA (Shoemaker et al., 1986), and the Glycine subgenus and the three species of the Soja sequences from the ITS region of nuclear ribosomal subgenus (G. max, G. gracilis, and G. soja) with eight DNA (Kollipara et al., 1997), G. soja is considered the primers. In this analysis, they found that the three speancestor of G. max. Besides G. max and G. soja, an incies within the Soja subgenus were clustered as one termediate form sometimes known as G. gracilis Skvortz. group with G. gracilis classified a subgroup within G. has been described. This form has numerous characterismax. This research supports the idea that there should tics intermediate between G. max and G. soja and was only be one species, and earlier Smartt (1984) had profirst proposed as a new species by Skvortzow (1927). posed that G. max, G. soja, and G. gracilis should all be classified as subspecies. Although there are many Y. Chen, Dep. of Crop Sciences, 1101 W. Peabody Dr., University arguments about the designations of species in subgenus of Illinois, Urbana, IL 61801; R.L. Nelson, USDA-ARS, Soybean/ Soja, it is well accepted that G. soja is the ancestor of Maize Germplasm, Pathology, and Genetics Research Unit, Dep. of cultivated soybean and most taxonomists have kept G. Crop Sciences, 1101 W. Peabody Dr., University of Illinois, Urbana, max and G. soja as separate species. IL 61801. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the Several traits have distinct differences between G. USDA or the University of Illinois and does not imply its approval max and G. soja accessions. In general, G. soja has to the exclusion of other products or vendors that may also be suitable. much smaller seeds ( 3.0 g 100 seeds 1) than G. max Received 16 Dec. 2002. *Corresponding author ([email protected]). Abbreviations: MDS, multidimensional scaling; MG, maturity group; Published in Crop Sci. 44:316–325 (2004).  Crop Science Society of America PCA, principal component analysis; PCR, polymerase chain reaction; PI, Plant Introduction; RAPD, random amplified polymorphic DNA. 677 S. Segoe Rd., Madison, WI 53711 USA