The first withered olive trees appeared near Gallipoli, in the Apulia region of southern Italy. Bunches of leaves turned brown and crunchy around the edges. Then, whole groves started to wane. Farmers whose families had tended olives for generations watched their trees dry up and their businesses plummet.
At first, it wasn’t clear what was causing the decline. Was it a fungus? A virus? Something else entirely? Scientists showed up in the olive groves to sample the trees, urgently trying to find the cause.
One researcher from a local agricultural institute had just come back from a conference in California, where he’d learned about the plant bacterium Xylella fastidiosa. The symptoms the olive growers were seeing, he realized, looked exactly like what seen in the talks he'd attended. Sure enough, when he and his colleagues tested the Italian trees, they found the bacterium lurking in their woody hearts.
This was not good news. The European Commission considers Xylella to be among the most dangerous plant bacteria in the world. Different strains of it have wreaked havoc on vineyards in California and citrus trees in Brazil, killing acres of valuable plants and causing billions in lost revenue.
Until the olive trees fell ill, Xylella had never been seen in Europe, and its identification in Italy set off alarm bells across the scientific and political communities of the European Union. Italian olive growers produce 15 percent of the world’s virgin olive oil, worth more than $2 billion each year. Spain produces even more. Anything that threatened the trees threatened the entire European economy.
Olives are also central to the identity of the region. Over 60 million trees stand in stately rows across Puglia, which—until recently—produced about 40 percent of all the olive oil Italy exports. Nearly half a million trees are the beloved “ulivi secolari,” centuries-old trees whose gnarled trunks have stood firm even as vast changes swept across the region.
But the arrival of Xylella upends the traditional order, threatening to wipe out groves worth billions of dollars. Rather than succumb to great loss, scientists and some growers have been throwing themselves into the fray to figure out what, exactly, is going on and whether they can mitigate the damage.
Xylella causes plants to die of thirst from the inside out. The bacteria get passed from tree to tree by tiny pests called spittlebugs, which latch onto their hosts’ xylem—the straw-like tubes inside plants that transport water from roots to leaves. If the bugs suck liquid out of an infected tree, they can carry the bacteria in their maw and inject them into the next plant they feed upon. The bugs are native to the region, and before Xylella arrived on Italian shores, they weren’t seen as a problem. Now, their presence incites fear.
Once planted in the tree, the bacteria spread slowly, colonizing the xylem tubes and thickening into a sort of biofilm—a gloppy mass that blocks water from flowing, starving the tree’s extremities of water. Sometimes, the trees die outright. Other times, they linger in a shadow-like state, too weak to grow fruit but ripe with bacterial loads.
There is no known cure. Once the bacteria infiltrate a host, the plant stays infected until it dies.
On the farms, the news was bleak. Giovanni Melcarne and his wife Daniela, olive producers from the Lecce Province, watched helplessly as their trees weakened. The Melcarne family has grown olives in the province for over 500 years, and many of Giovanni’s gnarled trees are older than he is.
“From the beginning, when I saw what was going on, I knew that the olive culture would have been destroyed by the bacteria,” he says. “It would affect our character, our way of living.” It was clear, he thought, that something had to be done. So he reached out to scientists at the nearby university who were desperately trying to understand the basic biology of the disease.
Melcarne ultimately connected with Donato Boscia, a plant biologist at an Italian National Research Council (CNR) institute in the nearby town of Bari, whose own father-in-law had recently shown him the characteristic crisped leaves on their family trees. Boscia knew that Xylella could sit latent in a plant for months or a year before it started tightening its grip. By 2013, when the disease made itself known to farmers and plant pathologists, it had probably already been percolating in the region’s trees for some time.
Boscia was worried that it was already too late to get rid of the disease completely. But he also knew that they had to try. So he and his colleagues threw themselves into research: They mapped out the affected territory. They learned how the disease spread and what other plants could serve as hosts. They developed tools to test trees for the bacterium, so farmers could figure out if their trees were infected.
The Growers Revolt
But in a 2014 bid to protect the olive market, a European Union commission specified that Italy should get rid of all the plants known to be infected or suspected of being so. In practice, that meant farmers were being told to uproot and burn their precious trees—and in some cases, to destroy even nearby trees that hadn’t yet visibly succumbed to the disease. More recently, officials instructed farmers to use pesticides to control the spittlebug population, angering farmers who prided themselves on growing organically.
Many farmers revolted against the state’s directives, mistrusting that the bacterium actually caused the tree deaths or claiming that traditional management practices could cure the problem.
Under pressure from farmers and activists, Lecce police and prosecutors even started investigating scientists at the CNR, accusing them of introducing the disease to the region. Conspiracy theories swirled: Were developers trying to crater the land’s agricultural value so they could build hotels? Were scientists at fault for the disease? The accusations were unfounded and later dropped, but the uproar highlighted the deep distrust lurking in the province.
“You are telling to farmers which have olives that are maybe a thousand years old that they have to uproot it,” says Enrico Bucci, a researcher associated with the Sbarro Health Research Organization at Temple University in Pennsylvania. “My family has an olive orchard in Tuscany, and it would be especially difficult to accept that my trees have to be uprooted. There is an emotional attachment to the trees.”
But like most of the other scientists working to understand and contain the bacterium, Bucci is sure that containment, however painful, is necessary.
While the debates raged, the bacteria spread. When Boscia and his team surveyed the scene in 2013, they found the infection across about 30 square miles of the province. In the most recent survey, which wrapped up this summer, teams found infected trees across nearly 300 square miles—about 40 percent of the region.
The bacterium is now fully entrenched in the southernmost part of the province, and its eradication is unlikely, if not impossible. Containment efforts are focused on the “buffer zone” at Lecce’s northern edge, a roughly 19-mile-wide swath of land stretching from the Adriatic to the Ionian Sea. Hundreds of agronomists stalk the olive groves in this zone, checking hundreds of thousands of trees for signs of infection.
It’s “a huge and messy monitoring activity,” says Gianluca Nardone, head of the department of agriculture for the region—but it’s absolutely necessary to understand the scope of the problem.
Meanwhile, state-sponsored monitoring efforts below the buffer zone have stopped, and many farmers deep in the heart of the infected zone, whose groves have withered and businesses cratered, feel left behind.
Maria Saponari, a Xylella researcher at the CNR Institute for Sustainable Plant Protection in Bari, comes from a family of olive growers, and she knows very well how severely growers feel their losses. She watched with dismay as the bacteria spread while also feeling a deep responsibility to help in whatever way she could.
“We’re agronomy people. Our families are growers or farmers—we all know what was the situation and the damage for the growers,” she says. “They were losing jobs and olives.”
Saponari was especially frustrated going to farms to sample or inspect the trees and having no answers when people would ask her what they could do to save their trees.
“There is no effective treatment, and the pathogen is almost endemic now. For three or four years, I couldn’t answer anything promising to growers,” she says.
The region has lost about 11 million olive trees, and farmers in the infected zone need help to survive, Nardone adds: “In the infected area, there are all these trees that are dead. We need to revitalize that area, the whole heel of Italy.”
Sliver of Hope
Recently, the slightest glimmers of hope have emerged. Boscia, Saponari, and their colleagues have started testing hundreds of cultivars of olives to find ones that might be resistant to the bacteria. So far, they’ve found at least two very promising possible options. The Melcarnes have been grafting some of those finds onto trees in their groves to see how they’ll do, and so far, they seem to be taking nicely.
But their efforts are driven in part by desperation: By this year, they’d lost more than 65 percent of their trees. Daniela estimates that by next year, they’ll have lost nearly 90 percent.
“Every year that we lost in the intervention in the fields, in delaying what should have been done, it adds 10 years in reestablishing production,” she says. It’s been five years since the disease was identified, and she estimates that it will take 50 years to restore the groves.
But she can wait. For her family, it’s important to remain clear eyed about the challenges, but any hope is better than giving up.
“The olive tree had an enormous importance for our society because it is the symbol,” says Giovanni. “We thought they cannot be touched, are immortal. Now, we are facing a truth that is a natural truth—that nothing is untouchable.”