The olive tree is a hardy plant. Some trees are hundreds of years old and revered for their longevity, part of the cultural and historical landscape of Mediterranean countries. But the olive tree is also a hugely valuable crop in many of the poorer regions of Europe, such as Puglia in southern Italy. Major pest and disease outbreaks are therefore big news, as the unfolding story of olive quick decline syndrome (OQDS) illustrates.

Plant pathologists first reported OQDS from the Salento peninsula, the southern-most part of Puglia, in 2013. The foliage becomes scorched, branches dry up and eventually the whole tree dies in a matter of months, alarming farmers and local authorities and highlighting the urgency to confirm the cause. Up to 30,000 ha are now reported to be affected by OQDS. There is huge concern that the disease will spread further, possibly on to other valuable crops.

OQDS is a new problem, closely linked to a bacterium called Xylella fastidiosa. Although Xylella has been intercepted on imported plants, the Italian discovery was the first confirmation it had become established in Europe. Xylella causes major diseases of grapevine, citrus and peach in the Americas, but not on olive, which often grows alongside these susceptible hosts.

Xylella is a diverse organism, found in many plant species that fail to show symptoms. The major diseases in the Americas are caused by strains different to the one associated with OQDS. Olive trees were dying in Puglia since at least 2010, though sporadically by all accounts. At first there was doubt that Xylella was the cause of OQDS, and it is only in the last week that its pathogenicity on olive has been confirmed.

It takes a lot to kill trees and it is more than likely that Xylella has been associated with olive trees in Puglia for some years before losses due to OQDS became of public concern. Pathogens can lurk in plants for many years, causing few noticeable symptoms or losses. So what happened around 2013? Olive trees need care and attention, and prolonged droughts in southern Italy may have weakened them. Xylella is transmitted by insects and increases in populations could have hastened the spread.

It is difficult to say what happened in 2013, or to know exactly when Xylella was introduced to Italy. Uncertainty surrounds all major diseases outbreaks and it takes a long time to fill gaps in knowledge. Farmers and local, national and international authorities cannot afford to wait for answers, and this is where things start to get messy. In 2015 the European Union gave official notice that “eradication measures� should be applied with a “buffer zone … 10 km wide�. Angered by the decision from Brussels to create a cordon sanitaire across the neck of the Salento peninsula (40 km wide), farmers and environmentalists took radical action.

First, the protagonists claimed that Xylella was not the cause of OQDS, which they said was due primarily to fungi isolated from decaying wood. A panel of experts appointed by the European Food and Safety Agency (EFSA) roundly rejected these claims, even before the recent pathogenicity trials confirmed Xylella as the cause of the disease. The farmers took their case to local courts in Lecce, claiming negligence in handling of Xylella fastidiosa strains brought from the US for diagnostics training in 2010. Although the strains were different to those found on olive, local prosecutors indicted nine scientists, who were accused of “fraudulent misrepresentation and destruction … of natural beauty� and “spreading of a plant disease�.

Legal disputes about causes of medical conditions are not uncommon – vaccines linked to autism, for example – and gaps in knowledge create false hope in unproven remedies. I have never heard of plant scientists being prosecuted for honest endeavour. It points to a lack of trust and poor relationships between officials and farmers in Italy, and a more general failure to understand how science works. When scientists say ‘on the basis of the available evidence’ they are being honest about what they do and don’t know. Yet waiting for new knowledge is not an option for plant health authorities in Italy and Europe, who have to make difficult decisions that farmers in Puglia find acceptable while addressing the concerns of olive farmers elsewhere.

Mutual respect is in short supply in Puglia, weakened by the legal action, but also perhaps because the authorities showed a lack of empathy in imposing radical control measures. OQDS is a serious threat that needs serious, urgent action. Hopefully the science can move fast enough to restore public trust and come up with solutions that protect a valuable and much loved tree.

For regular updates on OQDS (CoDiRo in Italian) see:

http://xylellacodiro.blogspot.co.uk/

www.infoxylella.it/

See a previous blog story on the loss of the American chestnut. Of chestnuts and cherries.