Genetic diversity in the Olive tree (Olea europaea L. subsp europaea) cultivated in Portugal revealed by RAPD and ISSR markers

To assess the genetic diversity of the most important olive cultivars used in Portugal, a base collection was established with two hundred and one accessions of eleven cultivars from the different agro-ecological- regions (AER) of olive oil production. Inter-cultivar diversity was evaluated using seven RAPD primers producing fifty-nine polymorphic markers that enable cultivar distinction. Discriminant analysis according to fruit use and AER revealed a genetic structure associated with local selection both for fruit exploitation and agro-ecological adaptation. Intra-cultivar diversity of the ancient cultivar 'Galega' was also investigated. Three RAPD and five ISSR primers produced ninety-three polymorphic markers upon seventy-seven accessions from five AERs. Total accession discrimination was achieved. UPGMA clustering and discriminant analysis revealed that the genetic diversity was predominantly structured according to accessions origin. The within and among AER variation revealed by AMOVA supported this genetic structure and showed a high proportion of intra-AER variability. These evidences suggest that 'Galega' is composed by a mixture of different genotypes adapted to local conditions, indicating that this cultivar is in an early stage of domestication and should be treated as a landrace instead of a uniform cultivar. The assessment of 'Galega' genetic diversity within each of the five AERs indicated the highest significant level (H-g = 6.23 at p < 0.001) in "Ribatejo-Santarem". This finding associated with the distinctiveness of 'Galega' in relation to other Portuguese cultivars and with the recent insights of olive tree domestication allowed us to hypothesize that 'Ribatejo-Santarem' was the ecological region of origin and dispersion of this ancient cultivar.