Abu Dhabi, UAESunday 18 August 2019

Fears rise that Europe’s silent olive tree killer will spread to the Middle East

Xylella fastidiosa has been detected in France, Spain and Portugal but June marked its arrival to the region

Dead olive trees in the countryside of Ugento, in Salento. Entire swathes of the region now look like an eerie cemetery of desiccated trees, some of which had stood for centuries if not thousands of years. János Chialá / The National
Dead olive trees in the countryside of Ugento, in Salento. Entire swathes of the region now look like an eerie cemetery of desiccated trees, some of which had stood for centuries if not thousands of years. János Chialá / The National

For more than 5,000 years, olive trees have been a central element of agriculture from Morocco to Iran. This enduring relationship between people and trees has shaped landscapes, cultures and even religions, yet today it is threatened by a newcomer to the region: Xylella fastidiosa, a plant bacteria from Central America.

In recent years, hundreds of thousands of olive trees have died in Puglia, southern Italy, an area at the heart of the Mediterranean sea known for its beautiful, centuries-old olive groves, many of which are now turning into vast cemeteries of desiccated trees.

“For us, the death of an olive tree was a taboo,” Pantaleo Piccinno, the president of one of the region's unions of farmers, told The National. “We couldn't accept, psychologically, that a tree that for us is a symbol of longevity could die. I lost more than 80 per cent of my olive oil production, and I don't expect to harvest any olives in the coming years.”

After much controversy about the causes of this disaster, scientists have established its connection to Xylella fastidiosa, a dangerous plant pathogen whose presence was detected in the olive trees of Puglia in 2013.

This bacteria has been the scourge of wine, coffee and citrus growers in the Americas since the late 19th century, and takes its name from the “xylem vessels” of the plants that it colonises, sometimes growing until these vessels become clogged, causing the branches to wither and die.

Beside the movement of infected plants, its only mean of transmission is through small insects that feed on sap, as for example the many species of spittle bugs and leafhoppers that can be found almost everywhere on this planet.

The search for ways to coexist with Xylella fastidiosa has led to grassroots researchers such as Roberto Polo (left) investigating the importance of soil health in order to strengthen the olive trees and allow them to withstand the bacteria. János Chialá / The National
The search for ways to coexist with Xylella fastidiosa has led to grassroots researchers such as Roberto Polo (left) investigating the importance of soil health in order to strengthen the olive trees and allow them to withstand the bacteria. János Chialá / The National

Because of its capacity to mutate and colonise a wide range of cultivated plants, Xylella fastidiosa is universally regarded as a “quarantine organism,” a pest that has to be contained and possibly eradicated because of the danger it poses to the world's agriculture. And this danger seems to have materialised.

Since 2013, Xylella fastidiosa has been detected in France, Spain and Portugal. But, in June 2019, it was also discovered in Israel, marking its arrival to the Middle East. Most of these new outbreaks did not affect olive trees, yet they indicate that infected plants are still being imported to the region, and that Xylella fastidiosa is capable of spreading much beyond Puglia.

This danger was predicted long ago by one of the world's greatest experts on this bacteria, Alexander Purcell, who wrote in 1997 that “tropical and subtropical climates, including Mediterranean climates, are probably most at risk to X. fastidiosa”.

Aware of the risk, the various plant protection organisations of the region, such as the Near East Plant Protection Organisation (Neppo), began cooperating and carrying out Pest Risk Analyses, whose results were collected in a publication.

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Throughout the reports, the scientists stressed “their concern and the need to get information and training for setting up efficient measures for preventing the introduction and spread of this pathogen”, with the delegates from the FAO (Food and Agriculture Organisation) Regional Office for the Near East and North Africa noting that the strain of Xylella fastidiosa found in Puglia “poses an enormous threat to olive production in all the Mediterranean countries”.

But the climate is not the only element in the region that is favourable to Xylella fastidiosa: this pathogen is capable of infecting more than 350 different plants, with at least 20 affected by the specific strain found in Puglia. This list of host plants includes grapes, almonds, peaches, plums and citrus, making this bacteria a threat to the entire agriculture of the region.

Since there is no known cure to the diseases caused by Xylella fastidiosa, there are only three pest management strategies available at the moment: exclusion, preventing it from reaching new areas; eradication, through the destruction of any newly infected plants; and containment, aimed at preventing its spread out of the affected areas.

All of these strategies are based on monitoring all host plants in order to detect any new outbreak as soon as possible.

Yet, with many countries in the Middle East gripped by much more pressing concerns than checking their plants for the presence of a bacteria, the danger that Xylella fastidiosa could spread through the region is high, casting a shadow on the economies of entire countries, and also on our ancient relationship with olive trees.

Updated: August 8, 2019 02:49 PM

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