Genetic diversity and clonal variation within the main Sicilian olive cultivars based on morphological traits and microsatellite markers

• Identification of the most discriminant morphological traits in olive which should be prioritized.
• Successful combination of UPGMA cluster analysis and CDA analysis for olive intra-cultivar diversity study.
• Intra-cultivar variation analysis among the olive Sicilian germplasm and discovery of clonal variants.
• Identification of new and superior olive genotypes through clonal selections.

The richness of Olea europaea (L.) genetic resources in Sicily is well documented. In the last 30 years, most of the local cultivars, landraces and ecotypes have been gathered together in a large ex-situ collection, containing more than 300 genotypes. In this study, 45 putative clones of the main Sicilian olive cultivars were characterized morphologically using microsatellite markers to unambiguously identify possible superior genotypes. The microsatellites employed were polymorphic (observed heterozygosity = 0.71; polymorphic information content = 0.59), discriminated 52% of the genotypes and enabled the detection of intra-cultivar polymorphism, derived from both somatic mutations, indicating the presence of polyclonal cultivars, or from gametic origin, thus suggesting the presence of cultivar-populations. A high level of genetic variability was detected within the ‘Biancolilla’, ‘Giarraffa’ and ‘Moresca’ genotypes, whereas low variation was found within the ‘Cerasuola’ and ‘Tonda Iblea’ genotypes. The combination of UPGMA cluster analysis of data obtained from microsatellite analysis, with canonical discriminant analysis (CDA), based on 18 morphological variables, measured under the same conditions, enabled intra-cultivar diversity, attributable to genetic factors rather than to environmental ones to be identified. The goodness of fit between microsatellite profiles and the CDA analysis was significantly supported by the Mantel test (r = 0.3; p < 0.001). Genotypes and clonal variants with superior traits (larger fruit size; compact tree habit, apt for high density planting; higher oleic acid content) were identified, suitable for enlarging their area of cultivation.