Xylella fastidiosa is one of the most dangerous plant-pathogenic bacteria worldwide.
This pest of worldwide significance poses a threat to agricultural and food production industries globally.
Xylella fastidiosa can infect cherry, almond and plum trees as well as olives.
It has, however, become closely associated with olives after a strain was discovered in trees in Puglia in Italy in 2013 and since then has completely wiped out entire olive groves wherever it has passed.
Spread by insects Philaenus spumarius (better known as the Meadow Spittlebug) that fly from tree to tree, the bacterium causes the Olive Quick Decline Syndrome OQDS (or CoDiRO) and poses a potential major threat to olive plantations in Greece, Italy, and Spain, as these countries account for around 95% of European olive oil production.
The bacterium has also now been found in France and Portugal.
Researchers say the economic costs of the deadly pathogen affecting olive trees in Europe could exceed €20 billion.
In Italy, the consequences of the spread of the disease have been devastating, with an estimated 60% decline in crop yields since the first discovery in 2013.
"The damage to the olives also causes a depreciation of the value of the land, and to the touristic attractiveness of this region," said Dr Maria Saponari, from the CNR Institute for Sustainable Plant Protection in Italy.
"It's had a severe impact on the local economy and jobs connected with agriculture."
In a new study, researchers modelled different economic scenarios, making projections for Italy, Spain and Greece, which in effect together comprise almost the entire source of European olive oil production.
In Spain, if the infection expanded and the majority of trees became infected and died, the costs could run to €17 billion over the next 50 years.
A similar scenario in Italy would amount to over five billion, while in Greece, the losses are calculate to total almost €2 billion.
If the rate of infection is slowed down, or resistant varieties are planted instead, then these costs would be significantly reduced.
Since it was first found in Puglia, Italy in 2013, Xylella fastiosa has since completely wiped out entire olive groves wherever it has passed.
It is thought that the disease came to Italy via an ornamental coffee plant that travelled from South America into Rotterdam, Netherlands, where it seemingly passed through customs without the required quarantine before being transported to Italy.
“So this plant entered Italy, Salento where the bacterium found an ideal environment which allowed it to spread,” says Adriano Abate, Director of Confagricoltura, the General Confederation of Italian Agriculture, whose entire 15 hectare olive grove was sadly and completely destroyed by Xylella.
The epidemic quickly spread from 8,000 hectares in 2013 to the 775,000 hectare area - three entire provinces of Italy - estimated to be infected by the bacterium today.
Currently there is no cure or antidote to stop the disease, hence initial measure to contain the bacterium were crucial.
However, authorities failed to establish proper measures required to contain the bacterium, and to therefore prevent the spread and expansion of the disease.
“The infected plants should have been removed, along with the plants around them to make a sanitary zone around the infected plants,” says Abate.
“This type of operation was not carried out in Salento. Who knows why,” he says simply.
The bacterium spread from olive grove to olive grove, completely annihilating entire properties.
Whilst most research studies relating to the spread of Xylella fastidiosa look at economics, there are also potentially large touristic and cultural losses caused by the bacterium that can't be ignored.
"You really hear devastating stories of infected orchards that were inherited over generations," said lead researcher Dr. Kevin Schneider from Wageningen University in the Netherlands.
"It's the same orchard that their grandparents were once working on. So how do you put an economic number on the loss of something like this. The cultural heritage value would be far larger than we could compute."
Paola Ghislieri is an award winning Italian filmmaker and director who has made a short documentary titled Xylella Fastidiosa - The Apocalypse of Salento about the effects of the deadly Xylella disease on the historic olive trees in Puglia, Italy.
Paola’s father has a farm that produces olives in Apulia, Italy, which was left to him by her grandmother.
He had been running the farm for several years when disaster stuck last year and his olive trees were infected by Xylella.
He was devastated, as his trees will all die in the next few years.
Paola decided to make a documentary about the impact of the arrival of Xylella in Apulia, giving a voice to local farmers, agronomists, olive mill owners and farm workers, and their timid sign of hope for a new form of olive cultivation.
Nonetheless, Apulia's landscape, Salento’s in particular, won’t have the same charm without its century-old olive trees.
Paola filmed the documentary by herself in three weeks.
She drove around Puglia and captured various images of the landscape to convey how it was, how it is, and how it will be after Xylella.
Paola studied Media Arts at Royal Holloway, University of London, and specialised in Cinematography. During her studies she directed several short films.
Later Paola worked at a production company in London and at The Walt Disney Company for several years.
Paola decided to pursue her passion for filmmaking and Xylella Fastidiosa - The Apocalypse of Salento is her first independent documentary, which she produced, directed and edited.
The film won the award for Best Ecological Film at the Silk Road Awards in Cannes.
It’s also been selected for the Golden Short Film Festival, New York International Film Awards, Docs Without Borders Film Festival and Prisma Rome Independent Film Awards.
Measures to combat Xylella fastidiosa presently revolve around the removal infected trees, trying to limit the movement of plant material and also the eradication of the insects that spread the disease.
The growing number of scientific initiatives include the use of insect repelling clays, vegetative barriers and genetic analysis to determine why some plants are more susceptible to the infection than others.
Ultimately, researchers believe that beating the pathogen will require trees that are resistant to the disease.
"Seeking resistant cultivars or immune species is one of the most promising, and environmentally sustainable, long-term control strategies to which the European scientific community is devoting relevant research efforts," said Dr Saponari.
A study conducted at the University of Bari Aldo Moro recently produced supporting evidence that the employment of a North American ‘assassin bug’, Zelus renardii in the control of the Meadow Spittlebug, the known vector of Xylella fastidiosa pauca causing the Olive Quick Decline Syndrome OQDS (or CoDiRO).
Researchers should be able to breed the insect on a mass scale, in order to use it as living insecticide.
Ultimately, the European scientific community is calling for research in this area to be significantly boosted.
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