Efficiency of SSR markers for exploring olive germplasm diversity through a genetic comparison between the USDA-NCGR and the CRA-OLI olive collections

The national olive collection at the United States Department of Agriculture-Agricultural Research Service National Clonal Germplasm Repository, Davis, CA (NCGR-Davis) contains a number of accessions with uncertain origin. In order to determine their genetic identification, a genotypic comparison was made with the Mediterranean cultivars of the Italian national collection at the Agricultural Research Council - Research Centre for Olive Growing and Olive Oil Industry (CRA-OLI) and with data available at CNR - Institute of Plant Genetics (CNRIGV). This study was conducted using seven SSR (Simple Sequence Repeat) markers. At present, SSR markers represent the most useful molecular tools to characterize olive cultivars, because of their high polymorphism, uniform distribution across the genome, co-dominant inheritance and the availability of a common set of loci with reference alleles. However, most SSR markers isolated from olive, with a di-nucleotide repeated motif, can still easily lead to misinterpretations in allele assignment. SSR data produced from both collections were compared and standardized using previous reference data. Highly comparable molecular profiles were obtained. A preliminary identification of the NCGR olive collection is described herein.