MICROSATELLITE (SSR) MARKERS REVEAL GENETIC IDENTITIES, GENETIC DIVERSITY AND RELATIONSHIPS IN A MALUS X DOMESTICA BORKH. CORE SUBSET COLLECTION

A collection of 66 Malus x domestica Borkh. accessions from the USDA-A RS Plant Genetic Resources Unit's core collection was screened with a set of eight SSR (simple sequence repeat) primers developed at the PGR U in order to determine genetic identities, estimate genetic diversity , and to identify genetic relationships among these accessions. All ei ght primer pairs generated multiple fragments when used in amplificati on reactions with DNA from these accessions. High levels of variation were detected with a mean of 12.1 alleles per locus and a mean heteroz ygosity across all eight loci of 0.693, The eight primer pairs utilize d in this study unambiguously differentiated all but seven pairs of ac cessions in this collection of 66 M. x domestica Borkh. genotypes, The probability of matching any two genotypes at all eight loci in this s tudy was approximately 1 in 1 billion. The markers detected two misnam ed accessions in the collection. Genetic-identity data produced a gene tic-relatedness phenogram which was concordant with geographic origins and/or known pedigree information. These SSR markers show great promi se as tools for managing Malus ex situ germplasm collections as well a s for collection and preservation strategies concerning wild Malus pop ulations in situ.