Centuries-Old Italian Olive Trees Die as Scientists Track Killer

A plant germ found in Europe for the first time is killing off centuries-old olive trees in southern Italy’s Apulia region, and researchers haven’t yet figured out how far the pathogen has spread.

Scientists found xylella fastidiosa, a bacterium native to the Americas, in plants across Lecce province in Apulia’s south and are now widening their search to all the region, Anna Maria D’Onghia, head of integrated pest management at the Mediterranean Agronomic Institute of Bari, said by phone today.

The pathogen, detected last month, is linked to die-back of olive trees over 8,000 hectares (19,768 acres) near the city of Lecce, the European Food Safety Agency reported two days ago. Apulia is Italy’s largest olive growing region with production of about 11 million metric tons last year, or 36 percent of the national crop, government statistics show.

“It is a very important olive production area, of course it means a big impact on producers,” D’Onglia said. “The problem is evident because the biggest trees are declining. We are speaking about really ancient olive trees.”

The pathogen is wasting 500-year-old olive trees, the researcher said. The Bari institute is testing plants without signs of infection to determine a protective buffer zone. The germ may have been introduced via the import of ornamental plants, according to D’Onghia.

“Xylella goes everywhere, the host range is so wide,” D’Onghia said. “We are researching how far the pathogen has moved from this area, or is still moving. Usually when you see the diseased trees it’s too late.”

Task Force

Italy’s Agriculture Ministry said Oct. 27 it was setting up a task force to determine the boundaries of the infected areas and develop a plan to prevent further spread.

The strain of the germ in Lecce’s olive trees is xylella fastidiosa multiplex, not known to infect grape vines and citrus trees, D’Onghia said. The multiplex strain does infect almonds and stone-fruit trees such as peach and apricot, according to the Parma, Italy-based EFSA.

“This strain should not be the strain that affects grapes and citrus,” D’Onglia said. “I say ‘should.’ Research is in progress.”

A xylella fastidiosa variety can cause Pierce’s disease, which kills infected grapevines, according to the University of California. The disease costs the state’s grape growers an estimated $105 million a year, including $47 million in lost production and replanting costs for wine makers, a 2012 study by the university found.

The bacterium infects the woody water-transporting tissue of plants, known as xylem, and all insects in Europe feeding on sap in woody parts should be considered potential carriers, according to EFSA. D’Onghia said it could be spread by various species of insects known as leaf hoppers.

Uprooting, Destruction

The only recommended course of action is uprooting and destruction of the diseased trees, Raffaele Baldassarre, an Italian member of the European Parliament, wrote in Oct. 24 questions to the European Commission, asking the EU’s executive arm what financial aid could be given to affected growers.

The number of host plants in Europe is uncertain because many species would encounter the bacterium for the first time, EFSA wrote.

The germ is a “very serious threat” to Europe, the European and Mediterranean Plant Protection Organization, or EPPO, wrote in an online alert. The bacterium blocks plants’ transport of water and mineral nutrients, though “numerous” wild plants such as grasses can carry xylella fastidiosa without symptoms, the Paris-based group said.

Dying Trees

The dying olive trees in Apulia also contained various fungi, according to EPPO.

“There is no record of successful eradication of x. fastidiosa once established outdoors due to the broad host range of the pathogen,” EFSA wrote. The agency said controls should focus on living plants and insects shipped in plants.

The disease “could be a major problem” with “a huge scope,” Francesco Serafini, head of the environmental department at the Madrid-based International Olive Oil Council, said in e-mailed comments yesterday.

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