Blanca Landa still remembers with horror the day she came face to face with the plague for the first time. It was in 2014, she walking through the olive groves of Apulia, on the heel of the boot that makes up Italy. “It’s like a disaster movie in which a bomb has fallen and everything has dried up. You go by car and you see miles and miles of dry trees. Thousands and thousands of hectares. It is an ecological disaster”, warns this agronomist. She speaks in the present because since then the plague, caused by the bacteria Xylella fastidiosa, has not stopped spreading and is already in Spain, France and Portugal. It is one of the greatest threats to world agriculture, but also to the immemorial landscape in which grandchildren and grandparents have grown up in each town. Landa, born in Córdoba 52 years ago, has just taken over the reins of an international project to try to stop the microbe, capable of reaching a region and turning it into a kind of plant Chernobyl.
The Xylellanative to America, measures just over one thousandth of a millimeter. The bacterium multiplies in the vessels that carry the sap in a tree and can clog them, suffocating the branches. Some insects, known as cigarettes, are responsible for transporting the microbe from one plant to another. The main hypothesis is that the microorganism entered without making noise in the south of Italy in 2008, aboard ornamental coffee plants from Costa Rica. When it was detected, in 2013, it was already too late. In a few years the bacterium signed the death warrant of more than six million of trees. Landa remembers scenes of elderly farmers crying hugging the centuries-old olive trees sick from her. The main strategy against the bacteria is to uproot the infected tree and all those within 50 meters of it.
Landa opens a small cold room in one of his laboratories, in the Institute of Sustainable Agriculture (CSIC), in Cordoba. There are samples of almost a hundred different strains of the bacteria, at 80 degrees below zero. “This is the largest collection of Xylella that there is in Europe”, he explains. The list of microbes present in the freezer makes your hair stand on end: they come from vines from California, cherry trees from Mallorca, broom from Corsica, coffee plants from Mexico, elms from Washington, almond trees from Alicante, olive trees from the Balearic Islands and Apulia. . The Xylella it is capable of infecting about 600 plant species, often without causing symptoms. He travels the world without arousing suspicion and is merciless with the great protagonists of the Mediterranean agricultural landscape: olive trees, vines, almond trees, citrus and stone fruit trees.
In Spain, the microbe was detected for the first time in October 2016, in three cherry trees in a garden center in Manacor (Mallorca), but Landa believes that the pathogen had entered the Balearic Islands much earlier, around 1994, in almond trees. introduced from California. The regional government ordered the uprooting of thousands of trees in 2016, before surrendering to the evidence that it was already impossible to eradicate the bacteria in the archipelago. The other major focus is in Alicante, with an out-of-control epidemic, despite the fact that almost 190,000 almond trees since 2017. The olive growers of the peninsula are alarmed. In Spain there are more than 300 million olive treesthat produce almost half of olive oil from around the world.
The microbe is winning the battle. “You have to learn to live with the bacteria and minimize the damage. What the farmer would like —to add a product and the problem to end— will never happen”, recognizes Landa, the new president of the Spanish Society of Phytopathology. The international project that he directs, with almost seven million euros of European funding, is largely focused on developing methods to detect the microbe. “The best way to fight the bacteria is to keep it out,” he warns.
Landa coordinates the work of around thirty institutions from 14 countries. Three Italian organizations are training dogs so that they are able to sniff out the bacteria at border ports, even on infected plants without symptoms. The Spanish researcher’s team Pablo Zarcofrom the University of Melbourne (Australia), perfects a system to identify affected trees using special cameras placed in airplanes.
The engineer and her group work in the largest high-security greenhouse in Spain, recently opened in Córdoba. To get to its 400 olive seedlings, you have to go through three doors with three different codes, including the scientists’ fingerprints. A negative pressure system prevents air from escaping to the outside. And all waste is treated with soda and hydrochloric acid before being sent to the sewer. It is a bunker to investigate plant pests.
In the coming days, Landa’s team is going to start inoculating the bacteria in eight of the most economically important olive varieties. agricultural engineer Miguel Roman walk among the seedlings and recite the types of memory: picual, arbequina, hojiblanca, gordal, arbosana, cornicabra, frantoio and a kind of wild olive. The objective is to check which varieties of olive trees best resist the attack and find out why, explains Landa. “We are going to inoculate the Ibiza strain, because we consider that it is the one with the highest risk for Spain, and also that of Mallorca”, details the engineer. This subtype that devastates the hundred-year-old olive trees of Ibiza is similar to the variant that has destroyed millions of trees in Apulia.
In southern Italy, “the perfect storm” has occurred, according to Landa: there is a variety of very susceptible olive trees, a very virulent strain of the bacterium, a favorable climate and an abundance of cigarettes thanks to the habit of letting the grass grow in the olive groves “There the populations of carrier insects are beastly, you have to be removing them from your head. In Spain, studies have been carried out on olive trees and their number is very low”, underlines Landa. However, the microbe spreads throughout the Iberian Peninsula. Portugal announced in december the first detection of Xylella fastidiosa in citrus within the European Union.
the biologist Pilar Velasco shows his experiments with different strains of the bacteria, in silicone conduits that mimic the blood vessels of the trees. “They clog up in a week,” he says. In the tree, Landa points out, the process is slower and more capricious. “It is not yet known how long it takes. We have inoculated the bacterium in olive plants and it has colonized the entire tree, but in three years it has not killed it nor have we observed symptoms. It is still not very well understood what triggers the plant to start to get sick”, affirms the engineer.
Another biologist on the team, Manuel Anguita, investigates the “more than 2,000 species of bacteria” that live inside an olive tree. He is happy because he has just extracted 13 milliliters of sap from a branch, a considerable volume. The goal of the group is to design a cocktail of beneficial bacteria that can be injected into young seedlings in nurseries, so that the presence of these healthy microbes makes it difficult for the pathogen to enter.
The disease caused by Xylella It has been known since 2014 as “the Ebola of the olive trees”, but Landa does not like the nickname. The engineer explains that this nickname arose in 2014 in a conversation with a journalist, when she was trying to explain to him what a “quarantine organism” is. Ella Landa clarified that they are pathogens that must be isolated from healthy plants and she gave the example of the Spanish priest with Ebola who had just been repatriated from Liberia at the time and was in isolation in Madrid. From that interview it emerged that the Xylella It is the Ebola of the olive trees.
Blanca Landa sadly recounts that, on her expeditions to southern Italy and the Balearic Islands, she has felt “centuries of history collapsing” on her shoulders. One of the oldest olive trees in the world, called the Farga del Arion, is located in the municipality of Ulldecona, in Tarragona. It was planted by Roman farmers in the year 314, in the time of Emperor Constantine, according to scientific dating. It is over 1,700 years old. What is at stake, Landa insists, is not only the economy, but the collective memory of the people. The poet Miguel Hernández proclaimed it in a verse: “The orange tree tastes of life and the olive tree tastes of time.”
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