Abstract
The area of the Garda Lake within the Trentino province (north of Italy) is the northernmost part of Europe where the Mediterranean species Olea europaea L. is traditionally cultivated. ‘Casaliva’ is claimed as the main variety traditionally grown in the Garda Trentino area (GT) from which a world renowned niche extra virgin olive oil is produced. Since a dominant presence of ‘Casaliva’ would link the fruit set success and yield to a self-pollination compatibility system, a deep genetic survey of the olive tree population in the GT has been performed with the aim of establishing the actual varietal composition and of understanding from which pollen donor the ‘Casaliva’ olives originate. Forty-four different genetic profiles were observed among the 205 leaf samples collected from 106 ancient trees through the analysis of 20 nuclear microsatellite markers. The varietal composition in modern orchards was also explored and the vast majority of the additional 151 trees analyzed showed the same genotype as the ancient accessions of ‘Casaliva’. The results support the long historical link of ‘Casaliva’ with the GT and, besides a high varietal homogeneity, they also revealed the presence of olive genetic resources essential to fruit production. In fact, the parentage analysis of 550 embryos from drupes of ‘Casaliva’ evidenced that a cross-fertilization system is favored and a list of candidate cultivars most suitable as local pollinizers of ‘Casaliva’ was identified.
Highlights
The area of the Garda Lake within the Trentino province, due to its particular insubric mesoclimate [1,2], is the northernmost part of Europe where the Mediterranean species Olea europaea L. is traditionally cultivated
The 21 sequence repeats repeats (SSR) markers used for genotyping the reference material from the WOGBC, the CREA-OFA, and the 108 olive accessions from the Garda Lake germplasm collections were selected as those showing the most robust results among an initial set of 24 tested markers, which comprises the standard set of 11 SSRs [30], together with 13 additional markers used for characterization of the CREA-OFA
Samples of the 13 true-to-type olive cultivars from the WOGBC analyzed presented similar genetic profiles to those reported by the database of origin for the 17 SSRs analyzed in common; a high percentage of homozygous genotypes, instead of heterozygous as reported by the WOGBC [31], was observed for locus DCA11, which could be due to the presence of null alleles (r) in our analysis (r = 0.4454 for DCA11, Tables S5 and S3)
Summary
The area of the Garda Lake within the Trentino province (north of Italy), due to its particular insubric mesoclimate [1,2], is the northernmost part of Europe (beyond the 45th parallel) where the Mediterranean species Olea europaea L. is traditionally cultivated. Despite the climatic events in time, the ancient presence of olive-trees in the Garda Trentino area (GT) has been reported by a number of historical documents (reviewed and collected in [3,4]), where references to the nomenclature of cultivars and their identity were described. Recent studies based on genetic fingerprinting through molecular markers have evidenced that these two cultivars are synonyms of ‘Frantoio’ [5,6,7,8]
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