Phylogenetic and evolutionary applications of analyzing endocarp morphological characters by classification binary tree and leaves by SSR markers for the characterization of olive germplasm

Abstract

Seed (endocarp) morphology is useful for genotype discrimination and cultivar classification. Over a 20-year period, 504 olive trees (Olea europaea subsp. europaea) previously assigned to different cultivars originating from Greece (n = 37), Spain (n = 2), and Italy (n = 2) as well as one accession of Olea europaea subsp. cuspidata were evaluated employing 11 endocarp morphological markers and 9 SSR markers. A matrix of 42 morphotypes in total was subjected to classification binary tree (CBT) analysis. In addition, cultivars were fingerprinted employing 9 microsatellite (SSR) markers and placed on a similarity dendrogram. All 41 olive cultivars and one accession of Olea europaea subsp. cuspidata employed in the present study yielded different morphological profiles produced by the 11 endocarp traits. In the resulting CBT, the total reduction in error, that is, the total information in the set of all 42 morphotypes, was 100%. This meant that the set of 11 morphological characters—having 28 different states in all—was sufficient to remove all data noise and to correctly classify all examined olive cultivars. In addition, all olive cultivars were successfully discriminated by the 9 SSR markers employed. It is suggested that cultivars with large seeds—and concomitantly large fruits—are more distant from the wild forms and probably more evolved compared to cultivars with small seeds. In corroboration to the above, based on seed shape, some of the olive cultivars showed high resemblance to wild olives leading thus to the hypothesis that they were produced or selected during the early ages of olive domestication.