The American bug ravaging Italy's olive oil industry: Bacteria causes trees to wither and die - and there's no cure

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A bacterial pathogen is destroying olive trees in southern Italy, and local Italian authorities are doing little to contain the disease.

The pathogen - for which there is no cure - most likely arrived from the Americas and requires the uprooting of infected trees to prevent it from spreading. 

But protestors and a local public prosecutor in the southern Italian town of Puglia are trying to block the felling of ancient olive trees, and have even opened a criminal investigation into whether researchers caused the infection themselves.

Olive trees infected by the bacteria 'Xylella fastidiosa' in Gallipoli in the Puglia region of Italy. The pathogen causes Olive Quick Decline Syndrome (OQDS), a disease which causes withering and desiccation (extreme dryness) of terminal shoots, which then expand to the rest of the canopy, causing the tree to collapse and die

According to Nature News, last year Italian authorities failed to track the olive tree infection, caused by a bacterium called Xylella fastidiosa. 

It hadn't been seen in Europe until 2013, when it was found in Puglia, Italy. 

Researchers found that the pathogen causes Olive Quick Decline Syndrome (OQDS), a disease which causes withering and desiccation (extreme dryness) of terminal shoots, which then expand to the rest of the canopy, causing the tree to collapse and die.

WHAT IS OLIVE QUICK DECLINE SYNDROME? 

Olive Quick Decline Syndrome is a disease caused by a bacterium called Xylella fastidiosa. 

The bacterium invades and multiplies within the plants xylem vessels, which transport water and nutrients from roots to shoots and leaves.

The bacteria block these vessels, impairing water uptake in the plants.

The disease causes withering and desiccation (extreme dryness) of terminal shoots, which then expand to the rest of canopy, causing the tree to collapse and die.

Plants contain vessels called Xylem, which transport water and nutrients from roots to shoots and leaves. Xylella fastidiosa bacteria block these vessels, impairing water uptake in the plants, causing withering and desiccation (extreme dryness) of leaves 

Source: Italy's National Research Council 

Italian authorities didn't follow the disease containment plan agreed to with the European Commission, and an audit published by the Commission includes the failures of the local governments, who began monitoring the infection too late and delayed removing infected trees.

Two years ago in the town of Oria in southern Italy, task forces in charge of uprooting infected olive trees encountered difficulties when protestors chained themselves to ancient trees

In most of 2016, laboratories in Italy analyzed almost no Xylella samples. 

The European Commission is concerned that the pathogen X.fastidiosa pauca - the subspecies that causes OQDS - will spread throughout Europe, threatening its olive industry as whole. 

Monitoring programmes coordinated by the Commission have identified other subspecies of Xylella in other EU countries, and in May, a devastating subspecies of the pathogen, X.fastidiosa fastidiosa, which causes Pierce's disease and regularly wipes out vineyards in California, was found in Mallorca, Spain. 

While the spread of the infection was contained there, researchers worry that other undiscovered subspecies could infect other crops. 

Two years ago in the town of Oria in southern Italy, task forces in charge of uprooting infected olive trees encountered difficulties when protestors chained themselves to ancient trees. 

Map of Xyllella fastidiosa bacteria worldwide. Countries in orange show where the bacterium is present, and countries in purple where the bacterium is transient. It shows the spread of the bacterium species, but not specific subspecies

The challenges in Oria began in 2015 when military-police general Giuseppe Silletti began containment measures which included cutting down healthy trees around infected ones. 

Following EU regulations, he drew a map of infected areas, including a 20-kilometers 'buffer zone' around the area where trees were mostly healthy, but needed to be monitored. 

A scanning electron micrograph of Xylella fastidiosa bacteria in the xylem vessel of an infected sweet orange leaf. The bacteria block these vessels, impairing water uptake in plants, causing withering and desiccation (extreme dryness) of leaves

However, protestors and Puglia's publig prosecutor hampered his team's efforts by suspending the felling of trees, and Silletti resigned in December of 2015 because his plans were being blocked.  

The prosecutor finally lifted the felling ban when the European Commission threatened to report the Italian government to the European Court of Justice. 

While Puglia's regional governor has since appointed a new task force to tackle the problem, its goals and composition haven't been made public. 

The disease causes withering and desiccation (extreme dryness) of terminal shoots, which then expand to the rest of canopy, causing the tree to collapse and die. Pictured is a dried branch of olive tree, partly infected by Xyella fastidiosa, in Caprarica in Italy's Puglia region

Some protestors don't believe that the pathogen is causing the infection, and some sent a new complaint to the prosecutor in May saying that researchers ignored other potential causes of infection such as a fungus, even though this has already been ruled out by the European Commission.

Despite these setbacks, researchers in Puglia have identified two types of olive tree that are mostly resistant to the disease, and the Commission suggested that they could be planted in infected areas to replace dead trees. 

However, developing full resistant trees could take time - a decade or more.  

The Xylella fastidiosa pathogen - for which there is no cure - most likely arrived from the Americas and requires the uprooting of infected trees to prevent it from spreading

Different subspecies of the pathogen have been seen in countries across the EU, and more may be found. 

Genes flow 'relatively easily' between the different species, says Dr Rodrigo Almeida, who studies Xylella at the University of California, Berkeley.

This gene flow could result in even more pathogenic version of the infection. 

Some protestors don't believe that the pathogen is causing the infection, and some sent a new complaint to a Puglia prosecutor in May saying that researchers ignored other potential causes of infection such as a fungus, even though this has already been ruled out by the European Commission