THE USE OF MICROSATELLITE DNA MARKERS FOR SOYBEAN GENOTYPE IDENTIFICATION

Conventional morphological and pigementation traits, as well as disease resistance, have been used to distinguish the uniqueness of new soybean cultivars for purposes of plant variety protection. With increasing numbers of cultivars and a finite number of conventional characters, it has become apparent that such traits will not suffice to establish uniqueness. The objective of this work was to provide an initial evaluation of microsatellite or simple-sequence-repeat (SSR) DNA markers to develop unique DNA profiles of soybean genotypes. Microsatellites are DNA sequences such as (AT)(n)/(TA)(n) and (ATT)(n)/(TAA)(n) that are composed of tandemly repeated 2-5-basepair DNA core sequences. The DNA sequences flanking microsatellites are generally conserved allowing the selection of polymerase chain reaction (PCR) primers that will amplify the intervening SSR. Variation in the number of tandem repeats, ''n'', results in PCR product length differences. The SSR alleles present at three (AT)(n)/(TA)(n) and four (ATT)(n)/(TAA)(n) loci were determined in each of 96 diverse soybean genotypes. Between 11 and 26 alleles were found at each of the seven loci. Only two genotypes had identical SSR allelic profiles and these had very similar pedigrees. The gene diversity for the seven markers averaged 0.87 for all 96 genotypes and 0.74 for a subset of 26 North American cultivars. These are much higher than soybean gene diversity values obtained using RELP markers, and are similar to the average values obtained for human microsatellite markers, SSR markers provide an excellent complement to the conventional markers that are currently used to characterize soybean genotypes.