SSR-based fingerprints reveal the great genetic diversity of Sicilian olive (Olea europaea L.) germplasm

Twelve published simple sequence repeat (SSR; microsatellite) markers, belonging to the ssrOeUA-DCA, GAPU and UDO series, were tested in a panel of 46 accessions of olive germplasm belonging to 30 unique cultivars collected in seven Provinces of Sicily. Four well-known reference olive cultivars were also added. The analysis was carried out on an automatic capillary sequencer using fluorescent dyes, and fragment sizes were determined using internal standards. The results allowed us to rank the SSRs assayed according to their information content and reproducibility. Up to 115 alleles were identified (119, if those unique to sport mutations were included), the frequency of which allowed genetic relationships among accessions to be investigated. The probability that two unrelated genotypes displayed the same SSR pattern at all loci examined was calculated to be as low as 1.18 X 10(-11). Sixteen accessions were identified as synonyms. Of these, eight matched perfectly with another accession at all SSR loci examined. The others showed one or two allelic differences from the reference accession. These were interpreted as mutations. Otherwise, all accessions were clearly separated from each other. Two likely parentages were also identified ('Giarfara' = 'Nocellara del Belice' X 'Cacaridduni'; and 'Pizzo di Corvo' = 'Nocellara Etnea' X 'Tonda Iblea'). The genetic diversity of the pool represented by the unique accessions was very high, reflecting the richness of the olive germplasm accumulated in Sicily. A database of the accessions is available to the scientific community (http://www.unipa.it/germolive/ssr.html) to facilitate comparisons of data.