AUTOMATED SIZING OF FLUORESCENT-LABELED SIMPLE SEQUENCE REPEAT (SSR) MARKERS TO ASSAY GENETIC-VARIATION IN SOYBEAN

Simple Sequence Repeat; (SSR) allele sizing provides a useful tool for genotype identification, pedigree analysis, and for estimating geneti c distance between organisms. Soybean [Glycine max (L.) Merr.] cultiva rs are identified for Plant Variety Protection (PVP) purposes by stand ard pigmentation and morphological traits. However, many commercial so ybeans arise from a limited number of elite lines and are often indist inguishable based on these traits. A system based on SSR markers would provide unique DNA profiles of cultivars. Fluorescent labeling of all eles combined with automated sizing with internal size standards in ea ch gel lane was used as an alternative to standard [P-32] labeling to assess genetic variability in soybean. Allelic frequencies at 20 SSR l oci were determined in 35 soybean genotypes that account for greater t han 95% of the alleles in North American soybean cultivars based upon pedigree analysis. An average of 10.1 alleles per locus (range: 5-17), with a mean gene diversity of 0.80 (range: 0.50 to 0.87) were observe d at the 20 SSR loci. The 20 loci successfully distinguished modern so ybean cultivars that are identical for morphological and pigmentation traits, as well as 7 soybean genotypes reported to be indistinguishabl e using 17 RFLP probes. Pedigrees of 7 cultivars were studied to estim ate stability of SSRs in soybean across generations. Of the 7 pedigree s 6 had one locus in the progeny with an allele(s) that was not presen t in either parent. These new alleles are most likely the result of mu tation. The mutation rate of SSR alleles in soybean was similar to tha t reported in humans. To avoid difficulty associated with mutation, DN A fingerprint data should be determined from the bulk of 30-50 plants of a cultivar.