Structure of genetic diversity in Olea europaea L. cultivars from central Italy
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The olive is considered one of the most important fruit crops of the Mediterranean basin where it shows a wide range of variability, with about 2,000 cultivars. Italy, with about 500 cultivars, plays a fundamental role. The ability to discriminate olive cultivars and estimate genetic variability are important factors in better management of genetic resources and in helping to understand how genetic diversity is partitioned among cultivars. The two main objectives of the present investigation were to evaluate the identity of cultivars grown in Abruzzo region, central Italy, and to study their genetic structure. We applied amplified fragment length polymorphism (AFLP) methodology on 84 genotypes belonging to the most relevant and oldest varieties cultivated in Abruzzo and on six unknown genotypes. The information content of data was evaluated using the Marker Ratio index and the Polymorphic Index Content. Moreover, STRUCTURE software was used to investigate the genetic population structure. The analysis enabled us to clearly distinguish eight cultivars within seven clusters. Additionally, one cluster was found to have various minor cultivars and showed a relatively high level of diversity. The partitioning of genetic diversity showed that the largest amount of molecular variance was within groups. Our data suggest that both sexual and clonal propagation have played an important role in the evolution of olive cultivars. In our hypothesis, some ancestral population spread in central Italy with a relevant role of seed propagation, followed by a selection of superior clones from which more traditional varieties originated. In a few cases, hybridization should be taken into consideration to explain the diffusion of recently developed cultivars.