The Maltese olive: more unique than we thought

utting-edge DNA profiling has enabled a researcher to identify the extent of indigenous olive cultivars in Malta, and highlighted both their uniqueness, and the need to preserve them from the commercial temptation to import the bulk of our olive supply.

Oriana Mazzitelli, supervised by Dr Marion Zammit Mangion at the University of Malta, employed genetic methods to investigate the DNA diversity of the Maltese olive cultivars and the Maltese wild olive, and compared them to those of two Italian and Tunisian cultivars, Carolea and Chemlali respectively. Mazzitelli compared the genetic patterns generated by the DNA markers to investigate genetic relationships much the same way as DNA profiling is used in paternal testing.

Mazzitelli identifies four cultivars indigenous to the Maltese islands: the Bidni, Malti, White Olive or bajda and the Maltese wild oleaster.

Though concrete evidence is lacking, the Bidni cultivar appears to be the oldest on the island, dating back from the Roman occupation. Its name comes from a few ancient trees pertaining to this variety located in an olive grove in Bidnija, which are believed to be the offspring or survivors of very old plantations, and produce oil of excellent quality with low acidity and rich in chemicals that have many health benefits. Its long-standing pedigree has allowed it to evolve and thrive on the Maltese islands better than any newly introduced commercial variety.

The Malti cultivar is the most common and widespread cultivar in the islands, and is traditionally believed to be the tree that constituted the bulk of the olive groves in past times.

Less renowned, but boasting an extra curiosity factor is the White Olive or Bajda cultivar, first discovered in 2010. Conspicuous in that it produces attractive white olives that turn slightly pink as they mature, the white olive may have survived on Malta from old times as the Perlina olive and the ‘Pearls of Malta’ referenced in Renaissance literature might be referring to this white olive.

The Maltese wild oleaster, with smaller shrubs and having shorter leaves than cultivated olive trees and a small, bitter-tasting fruit with low oil content, is found usually in Maquis (shrubland) habitats. Our true wild olive is thought to have originated within the islands, however due to human impact its presence is no longer very common and thus requires urgent conservation.

“Unfortunately, the potential of the aforementioned Maltese varieties may be overlooked and the numbers of commercial imported varieties could outweigh the native varieties,” Mazzitelli told MaltaToday.

As a way to counter this assault, Mazzitelli suggested that efforts should focus on artificial propagation and re-plantation of Maltese varieties, along the lines of The Project for the Revival of the Maltese Olive (PRMO). Launched in 2001 and coordinated by Sam Cremona in collaboration with the Bank of Valletta and the Ministry of Rural Affairs and the Environment, PRMO distributes cuttings of the Bidni variety among farmers which they then plant in various sites both in Malta and Gozo.

“The other way is to preserve our current native trees. The native wild olive is protected by national law whereas the grove in Bidnija, where the ancient Bidni trees are located, is a Tree Protected Area,” Mazzitelli added.

As to how she proposed to identify the local varieties in the interests of perseveration, Mazzitelli explained how the ‘genetic’ approach, which focuses on locating the varieties through DNA structures as opposed to the conventional method of relying on outward appearance alone, proved to be an accurate and effective system.

While locating varieties through appearance – using features such as tree size and shape as well as fruit and oil characteristics – may have been the tried-and-tested method, factors like the surrounding environment, growing practice and development stage may obfuscate this analysis and render it unreliable.

“A more accurate identification method would be to use markers made of DNA codes found in the genome of all organisms,” Mazzitelli said, explaining that the process works much in the same way as DNA testing in humans.

“A few of these markers are selected and, as with human individuals, these can be present, absent or have a different DNA code in different olive varieties. Each variety would therefore produce a characteristic DNA marker profile to allow identification of the native ones which can then be selected and successfully propagated.”

The starting point of Mazzitelli’s research clearly illustrates the effectiveness of this method to dismantle face-value assumptions. Initially setting out to compare the Maltese olive varieties to its Italian (Carolea) and Tunisian (Chemlali) counterparts – by dint of geographic proximity – Mazzitelli in fact discovered that the Maltese olive was far more unique than she had previously imagined.

She compared the genetic patterns generated by the DNA markers to investigate genetic relationships much the same way as DNA profiling is used in paternal testing. Interestingly, Bidni and Malti produced completely distinctive profiles from each other as well as the foreign cultivars.

This means that these cultivars are unique and can be easily identified using this DNA marker profiling technique.

To further highlight the distinction from the foreign cultivars, a number of DNA marker regions found in the Carolea, Chemlali and in the Maltese wild olive were undetected in Bidni, Malti and the white olive.

This research is part of a Master of Science in Biochemistry at the Faculty of Medicine and Surgery, University of Malta, funded by the STEPS (Strategic Educational Pathways) scholarship which is part-financed by the EU’s European Social Fund (ESF). Article written in collaboration with Think, the University of Malta’s magazine http://www.um.edu.mt/think/