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-ARS Plant Genetic Resources Unit's core collection was screened with a set of eight SSR (simple sequence repeat) primers developed at the PGRU in order to determine genetic identities, estimate genetic diversity, and to identify genetic relationships among these accessions. All eight primer pairs generated multiple fragments when used in amplification reactions with DNA from these accessions. High levels of variation were detected with a mean of 12.1 alleles per locus and a mean heterozygosity across all eight loci of 0.693. The eight primer pairs utilized in this study unambiguously differentiated all but seven pairs of accessions in this collection of 66 M. x domestica Borkh. genotypes. The probability of matching any two genotypes at all eight loci in this study was approximately 1 in 1 billion. The markers detected two misnamed accessions in the collection. Genetic-identity data produced a genetic-relatedness phenogram which was concordant with geographic origins and/or known pedigree information. These SSR markers show great promise as tools for managing Malus ex situ germplasm collections as well as for collection and preservation strategies concerning wild Malus populations in situ.