Cultivated peanut (Arachis hypogaea L), an important agronomic crop, exhibits a considerable amount of variability for morphological traits and for resistance'to diseases and pests. In contrast, molecular marker assays have detected little variation at the nucleic acid level. Identification of molecular markers would be of great help to peanut breeders, geneticists, and taxonomists. The objectives of this work were to identify simple sequence repeat (SSR) markers in cultivated peanut and to test these markers for their ability to discriminate among accessions. Peanut total genomic DNA libraries were constructed and screened with 3~p-labeled dinucleotide repeats, (GT)I0 and (CTh0. DiNA sequences were obtained from the SSR-containing clones and, when possible, primer pairs were designed on the basis of DNA sequences flanking the repeat motif. Primer pairs were tested in polymerase chain reaction (PCR) assays using a collection of 22 peanut DNAs, representing both cultivated peanut and wild species. In all, six SSR markers, five from the library screening procedure and one additional marker obtained from a search of publicly available DNA sequences, detected polymorphisms among the peanut DNAs. Discrimination power was high among the cultivated peanuts, with 17 unique genotypes represented among the 19 accessions tested. From two to 14 DNA fragments were amplified per SSR marker, and as a group, the six markers may amplify up to 10 putive SSR loci. The SSR markers identified in this study were more effective in detecting molecular variation in cultivated peanut than all other DNA-based markers evaluated to date. C ULTIVATED PEANUT is an important crop internationally for both direct human consumption and as an oilseed crop. Peanuts were domesticated in South America, probably in Southern Bolivia or Northern Argentina (Gregory et al., 1980; Kochert et al., 1996). Peanut culture was subsequently dispersed to many areas of South America, Mexico, and the Caribbean islands. The crop was unknown to the Europeans when they arrived in the New World early in the 16th century. The value of peanuts was quickly recognized, however, and the crop was later distributed to Africa and Asia by the Portuguese and Spanish. Peanuts are now widely grown in both the New and the Old World. China and India are the largest producers. The genus Arachis contains about 70 taxa, all of which are native to South America (Krapovickas and Gregory, 1994). Nearly all Arachis species are diploid, but cultivated peanut is an allotetraploid. Evidence from molecular marker studies of genetic variation suggests that

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