Assessment of the Tuscan olive germplasm by microsatellite markers reveals genetic identities and different discrimination capacity among and within cultivars

Microsatellite markers were used to characterize the accessions in the Tuscan olive (Olea europaea L.) germplasm collection. One hundred fifty-four genotypes were considered for genetic fingerprinting using 12 pairs of microsatellite primers. Investigation was focused on genotypes with similar morphologies and clones of the same cultivar from different agroecological areas within Tuscany. All 12 primer pairs produced microsatellite fragments for all the accessions amplifying from three to 10 alleles with a mean of 5.7 alleles/locus. The discovery of 30 synonyms and several misnames set the final number of genotypes representing the whole germplasm collection at 79. For Frantoio, Leccino, and Pendolino, no intracultivar diversity was found, although Leccino was known to have morphological distinction. Heterozygosity levels for the loci ranged from 0.287 to 0.722 with a mean value of 0.524. Some accessions presenting small differences in fingerprinting with similarity index greater than 0.87 were morphologically indistinguishable. The study demonstrates that for the management of the olive germplasm collection, it is necessary to use the morphological information in addition to the fingerprint when dealing with accessions presenting a microsatellite profile with high similarity index; otherwise, the risk is to overestimate the diversity among cultivars or presumed cultivars and to underestimate the one diversity already present within the cultivars.