Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 1997
Publication Date: N/A
Interpretive Summary: The narrow genetic base of U.S. soybean production is very likely to reduce the rate of yield improvement in future varieties as the level of genetic diversity in the commercially used gene pool decreases. This research was designed to identify exotic germplasm lines that are genetically distinct from the ancestors of U.S. varieties and have the potential to increase the yield of modern U.S. varieties. We were able to find 281 places on the DNA that differed among the ancestral lines and exotic germplasm tested. By analyzing the pattern of these differences we were able to put the lines into groups that are more closely related to each other than to the other lines tested. The major ancestors of the U.S. varieties were placed into four groups. Two groups contained mostly ancestors of northern varieties and two groups contained mostly ancestors of southern varieties. The exotic germplasm was separated in three groups. Only two minor ancestors were included with the groups of exotic germplasm and only two exotic lines were included with the groups of ancestral lines. These results show that there are significant genetic differences between the ancestors of the southern soybean varieties as compared with the northern soybean varieties. Crossing northern by southern varieties could be a very useful strategy to exploit the genetic diversity already available in the commercially used gene pool. The exotic germplasm that we tested was genetically very different from ancestral lines of our modern varieties. Since these germplasm lines were selected because they had already produced high yielding progeny, the genetic differences that we found may be useful for expanding the genetic base and increasing the yield of future soybean varieties.
Technical Abstract: The genetic base of soybean [Glycine max (L.) Merr.] breeding in North America is very limited. The focus of this research was to assess the diversity of 18 soybean ancestors and 17 selected plant introductions (PIs) maintained in the USDA Soybean Germplasm Collection. Estimates of genetic relationships among the 35 genotypes were calculated from 281 random amplified polymorphic DNA (RAPD) markers using the simple matching coefficient and expressed as Euclidean distances. Two forms of hierarchical and non-hierarchical cluster analysis as well as multidimensional scaling (MDS) were employed to reveal associations among the genotypes. Genetic diversity within the species was generally low and the average genetic distance among all genotypes was 0.5581. All methods of cluster analysis identified distinct groups of ancestors and PIs. Grouping of the ancestors generally agreed with known pedigree, origin, and maturity data. The genotypes within the distinct PI clusters may possess useful genetic diversity that could be exploited by soybean breeders. Results from the five methods of clustering generally agreed and genotypes were assigned to the same cluster 87% of the time. The MDS plots displayed relationships among the genotypes and may be a useful method of selecting genetically distinct individuals.