The researchers said that Xylella came to Italy from a Costa Rican coffee factory

An international team of researchers has studied the constant question of how Xylella fastidiosa reached Europe and adapted to its new environment.

The study, published in Microbial Genomics, sheds new light on the origin of the bacterium Xylella fastidiosa and on how the pathogen developed and killed millions of olive trees in Puglia.

Our analysis indicates that the pathogen arrived in Italy with a single introduction from Costa Rica, confirming that 2008 was the most likely year when Xylella was introduced in Italy.– Maria Sabonari, National Research Council

Although the presence of the bacterium was confirmed in Europe in 2013, there is still very little information on the biological relationship between the genotypes of the bacterium and the host plant species, which is of particular relevance as Xylella fastidiosa continues to spread throughout Europe.

By analyzing a combination of Italian olive tree trunks and closely related genomes from other plant species and loci, the researchers concluded that the outbreak in Italy was caused by a single coffee plant imported from Central America in 2008.

See also: Researchers have discovered another disease affecting olive groves in Puglia

The study spanned a five-year period – from 2013 to 2017 – during which researchers collected samples from more than 70 trees affected by the rapid olive degeneration syndrome, the disease caused by the bacterium Xylella fastidiosa, using a new protocol to extract the trees’ DNA. .

Genomic sequences of the Xylella fastidiosa isolate affecting olive trees were compared with three Costa Rican coffee and oleander isolates, which had been previously sequenced and were widely available.

Previous studies and several reports of Xylella fastidiosa-infected coffee plants imported into Europe from Central America have identified the same bacteria in some Central American plants. However, there was no scientific evidence for a genetic link between the coffee isolates from Costa Rica and the olive isolates from Puglia.

Comparison of the genetic sequence data presented in the study showed that the bacterium Xylella fastidiosa from olive trees is directly related to the Mesoamerican variants.

The data also indicate that infection occurred with the introduction of Infected “asymptomatic” coffee plant, which may have been brought to Italy as an ornamental plant.

The study was conducted by an international team that includes researchers from the United States, France and Italy.

Among the authors, the Italian biologist Maria Sabonari from the National Research Council in Puglia was the first to discover Xyella fastidiosa in the nearby Salento region in 2013.

Felling olive trees in Puglia, Italy (Getty Images)

It was previously thought that the discovery of Xylella fastidiosa in Europe was limited to America, he said, and has raised new concerns around the world because of its extremely harmful potential. The first confirmed report in Europe in 2013 was soon followed by its gradual discovery in several other EU countries ”.

The pathogen has gradually expanded its geographical area around the world, as well as its ability to form new associations with host plants ”. In this framework, we used a genomic tool to study the processes that drive an emerging bacterium against an epidemic of plant diseases. “

With particular attention to the spread of bacteria in southern Puglia, genomic data have enabled us to reconstruct the emergence of the syndrome of the rapid decline of olives, which led to the death of several million olive trees, with significant environmental, social, political and economic consequences . , Sabonari continues.

Our analyzes indicate that the pathogen arrived in Italy with a single introduction from Costa Rica, which confirms that 2008 was the most likely year when Xylella was introduced in Italy ”. This is in line with the first reports from Apulian farmers about infected trees in 2010 where the incubation period for the disease can be more than two years ”.

Coffee plants are often used in gardens, villas and resorts: their dense green leaves make them ideal for decorating outdoor spaces.

In cold areas, the plant is always kept indoors; In Salento, it is likely that it was held outdoors, which led to the spread of the infection “.

To show that Xylella fastidiosa can be transmitted from one species to another, the researchers also conducted experiments in which they grafted the bacteria into coffee plants and spread the infection to olive trees in a controlled way using spit lice, the vector nature of Xylella fastidiosa.

The researchers concluded that the results show that coffee plants can represent a latent vector for the bacteria.

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