Race to save EU's crops and landscape from lethal bacteria
Recent outbreaks of a plant bacterium have led to losses in olive and almond orchards in southern Europe. Known as Xylella fastidiosa (XF), there is no known cure. An EU-funded project is making major strides in improving prevention, early detection and control of the disease, aiming to avoid further economic damage and to save jobs.
© Alberto Fereres, 2019
Xylella fastidiosa was first detected and reported in olive trees in southern Italy, in the region of Apulia, in 2013. This was alarming as the pathogenic bacterium had previously been restricted to the American continent, where it had caused diseases that destroyed vineyards and citrus orchards. The spread of the bacterium threatens the EUs agricultural sector, affecting regions which rely on centuries-old crops.
Several outbreaks have since occurred elsewhere in southern Europe, including France and Spain, where the suitable climate conditions favour the persistence of the bacterial infections. Other than olive trees, the main EU crops affected are almonds and several species of ornamental and landscape plants. On the Balearic Islands in Spain, XF has also been detected in grapevines, where it causes Pierces Disease.
The EU-funded XF-ACTORS project is helping to combat the spread of this bacterium and reducing the impact of Xylella-induced diseases. It has identified olive varieties genetically resistant to the bacterium, allowing authorities to lift the prohibition on planting new trees in infected areas and enabling farmers to replant olive groves and rebuild the economy.
In addition, the project has identified a plant-sucking spittlebug, or froghopper, as one of the main vector species responsible for spreading the disease in the EU outbreaks.
The project is investigating how the bacterium was introduced into the EU so that surveillance and preventative measures can be adopted to stop new invasions on the continent. Data is being collected to track the pathogens occurrence and spread to predict and control potential outbreaks. Scientific advances are informing guidelines for nurseries to ensure their plants are XF free and to update EU regulations and pest risk assessments.
Currently, there is no effective treatment to cure Xylella-infected or diseased plants, so major efforts are being put into prevention measures and controlling new outbreaks, says project coordinator Maria Saponari of the Institute for Sustainable Plant Protection in Italy. This includes removing the infected source and controlling insect vectors that are mainly responsible for spreading the bacterium from plant to plant both near and far.
Genomic research has yielded important information on how XF interacts with host plants. This has led to a better understanding of the genes responsible for susceptibility to XF, the characteristics associated with resistance against the bacteria, and an understanding of micro-organism communities in diseased plants.
Innovative and sustainable strategies to control and reduce populations of insects spreading the bacteria are being tested. The spittlebug, for example, feeds on an olive plants xylem, the tissue that transports water and nutrients from the roots to the stems and leaves. Studies are ongoing to better understand the life cycle and feeding behaviour of these insects, to stop population growth and halt the spread of XF.
New remote-sensing techniques are helping researchers identify Xylella-infected trees early, before the symptoms become visible to the naked eye. The project has also contributed to the optimisation and harmonisation of diagnostics in the field and laboratory.
The projects achievements have resulted in updated EU rules, risk assessments and guidelines related to the management of XF under the European Phytosanitary Authority. Along with another EU-funded project, PONTE, and guidance from American research groups, critical information on the biology and traits of XF has been developed.
The current XF epidemic in southern Italy has affected olive oil production. This, along with restrictions on nurseries and plant transportation, has caused job losses. To compound the damage, the landscape has been ravaged by the death of centuries-old trees.
Saponari says finding a scientific solution to fight the bacterium will have a positive socio-economic impact, too. Before 2013, there were no active research programmes on Xylella fastidiosa in the EU. We are taking advantage of the information gathered by American research centres which have worked on this topic for a long time, he adds.
XF-ACTORS is testing several biocontrol agents, such as micro-organisms that can counteract the bacterium or reduce the fitness of the insect vectors. The international research network now set up in the framework of XF-ACTORS is contributing significantly to improving EU research capacity building and to strengthening international collaborations and exchange programmes, concludes Saponari.