Surely many of us associate the Mediterranean region with a picturesque landscape dotted with numerous olive groves. No wonder, the cultivation of the olive tree (Olea europaea L. subsp. europaea) in this area has a tradition of almost 6000 years. However, the origin of the Mediterranean olive trees remains a matter of speculation. The prevailing theory is that their high genetic variability is the result of the last Quaternary glaciation and the isolation of smaller populations in, for example, the Middle East, Cyprus and Gibraltar. To this day experts did not fully uncover the relationships between domesticated olive species, wild forms and their related subspecies. Thousands of years of cultivation have played a role. It resulted in the same varieties having different names in different regions or, conversely, different varieties carrying the same name.
Morphological features always have been a traditional tool for the identification of varieties. They are still being used today, especially in the initial rough identification. However, this identification method can be often unreliable, as morphological features can be highly variable depending on the environment, age of the tree, or level of human care applied. The real revolution in this regard occurred with the discovery of molecular methods and genetic markers, which are able to very reliably reveal the identity and variability of species according to unique sections in their DNA. One of the most used markers are the so-called microsatellites. These are short sections of DNA composed of repeating motifs that are scattered throughout the genome of eukaryotic organisms. In practice, they have been used for over 20 years, for example to verify parenthood.
In the case of the olive tree, microsatellite markers are an established method for determining parenthood or in studies of population genetics. Their use to identify a specific variety from olive oil samples is also very interesting. The main advantage of olive trees, which is far from being the case for all species, is that the same markers are transferable between subspecies. However, despite their great importance, less than 100 such markers have been developed for the olive tree to date. The main goal of this study, in which a researcher from the Faculty of Forestry and Wood Sciences participated, was to design and develop a set of microsatellite markers and verify their ability to identify 36 olive varieties, which represent the core group from the main Mediterranean centres of its cultivation.
The results of the study carried out 8 microsatellite markers, which were able to reliably distinguish individual varieties. Together with two other markers that have proved successful in previous studies, they were tested on 36 core group varieties and the result was very favourable. It has been shown that 17 of the 36 varieties can be unambiguously identified using only a single marker that is able to distinguish a specific region in their genotype. With a combination of three different markers, it was possible to identify 34 varieties and the combination of four different markers clearly distinguished all 36 varieties of the core group. This confirmed the determination ability of the developed set of markers and the next step is to apply it to hundreds of other varieties that are waiting for their correct taxonomic classification and naming. The results of the study thus provided a very valuable tool that could shed light on the complex taxonomy of this symbol of the Mediterranean.
Gómez-Rodríguez M. V., Beuzon C., González-Plaza J. J., Fernández-Ocana A. M. (2020): Identification of an olive (Olea europaea L.) core collection with a new set of SSR markers. Genetic Resources and Crop Evolution 1-17.
Juan José González-Plaza, Ph.D.
Juan J. González-Plaza is a researcher with main focus on transcriptomics as a tool to understand different aspects of the symbiosis between termites and their allied microbiome. Additional interest and research lines in metagenomics and functional metagenomics, for mining key prokaryotic genes used for lignocellulose catabolism, and microbial warfare/defence including resistance to antimicrobials.
Author: Dagmar Zádrapová