Evaluation of genetic diversity of soybean introductions and North American ancestors using RAPD and SSR markers

The genetic base of soybean [Glycine max (L.) Merr.] cultivars developed fo r North America is very narrow. This may threaten the ability of breeders t o sustain improvement and increase vulnerability of the crop to pests. The objective of this research was to assess the relationship of 18 major ances tors of North American soybean germplasm with 87 plant introductions (PIs) that are potential new sources of genetic variation for soybean breeding pr ograms. Genetic distances (GD) among the 105 genotypes analyzed were calcul ated from 109 polymorphic DNA fragments amplified with random oligonucleoti de primers and simple sequence repeat (SSR) primer pairs. Two hierarchical clustering algorithms were combined with data resampling and multidimension al scaling (MDS) to evaluate relationships among the genotypes. Genetic dis tances ranged from 0.08 to 0.76, with a mean of 0.52. Genotypes were placed in 11 clusters on the basis of a consensus of the different methods utiliz ed. Co-occurrence values calculated from the resampling iterations showed t hat the stability of clusters varied. The most stable grouping was among an cestors that corresponded with known relationships based on pedigree and ma turity. Several groups of PIs are distinct from the majority of the ancesto rs. These genotypes may be useful to breeders wanting to utilize geneticall y diverse introductions in soybean improvement.