Molecular studies for disclosing the genetic identity of local cultivars in olive and understanding the stilbene synthase pathway in grapevine

This study has been focused on two main fruit trees, olive and grapevine, from the genetic and genomic point of view. Olive (Olea europaea L.) is one of the oldest tree crops of the Mediterranean regions. In spite of the increasing economic importance and wider diffusion of monovarietal virgin olive oils, very few studies have focused on the genetic characterization of olive cultivars locally grown in the Veneto region, North-Eastern Italy. Since the genotype mainly affects the composition and sensory properties of extra virgin olive oils, the characterization of autochthonous olive cultivars is a key step for the production, marketing and traceability of high quality olive oils. Here we have performed a survey of mapped SSR marker loci for the analysis of nuclear DNA polymorphisms to distinguish olive cultivars and cultivar groups within the entire olive cultivation area in Veneto, from the Garda Lake to the Euganean and Trevisan hills, in order to obtain a systematic examination of the Veneto regional olive germplasm patrimony. The final aim of the study was to resolve cases of homonymy and synonymy, and to warrant the genetic authenticity of olive cultivars and of their clones in case of mislabelling. A total of 204 unknown olive tree accessions along with 25 olive reference cultivars were subjected to molecular analyses using ten highly polymorphic nuclear SSR markers. The overall molecular data were used for the computation of genetic similarity and diversity statistics, for the construction of ordination dendrograms and the determination of centroids of local accessions, along with reference cultivars. A genetic structure analysis of the olive population as a whole was also performed for the definition of cultivar groups. Based on multi-locus SSR genotypes and pair-wise SM coefficients, we found that on one hand most of the olive samples displayed genetic identity with the reference cultivars “Casaliva” (60 samples) while several others showed identity with different national and local varieties: “Miniol” (21 samples), “Grignano” (20 samples), “Tonda di Villa” (19 samples), “Leccino” and “Capolga” (17 samples each), “Gargnà”, “Compostaro” and “Oblica” (9 samples each), “Rossanel” (8 samples), “Fort” and “Baia” (5 samples each), “Grappolo” and “Favarol” (3 samples each) having bootstrap values greater than 85%. As few as 2 samples were attributable to “Moraiolo”, “Carnica” and “Maurino” each. The uppermost hierarchical level of population structure suggested a clear maximum of cultivar groups for K=15. It is worth noting that more than 98% of individual trees revealed a pure ancestry and only 13 accessions were admixed showing a membership to the associated cultivar group