Puglia, Southern Italy.
In 2013 olive trees began to show unusual symptoms of decline
The spread of this disease was and seemed very unusual
something strange was going on
The ancient olive trees were dying
Xylella fastidiosa – a bacterium previously unreported in Europe – was the likely cause.
It was very alarming to find that this pathogen because
before 2013 it was never detected
outside the American continent except some finding in Taiwan.
Following the reports from Puglia
the European Commission asked EFSA to provide scientific and technical assistance.
EFSA identified the most urgent knowledge gaps to be filled in
and fund small scientific research projects to fill in these gaps.
The European Union has since provided funding for two larger research projects
called POnTE and XF-ACTORS
and scientists in Puglia are already making significant breakthroughs.
As different strains of the pathogen appear in other parts of Europe,
the threat to a huge variety of fruits and plants across the continent is very real.
The situation is quickly evolving, each month is a month less to react.
Here apparently we are in a symptomless plant, a symptomless tree.
But if we move on the canopy we will see there are very early symptoms;
no flowering yet, there is some delay.
Bordering to this another part of the canopy where there are already evident symptoms,
with some yellowing, some leaf scorching.
When we go here where we see complete desiccation of the twigs.
Xylella is the cause of the problem. Now, we have the evidence
The xylella bacterium grows in a plant’s water carrying arteries, known as xylem.
The bacteria multiply and clog the arteries, starving the plant of water and nutrients.
Four key elements, known as the epidemiological triangle,
demonstrate how the bacterium is transmitted and causes disease.
Generally in plant pathology the disease
is defined as the interaction of the environment in which the plants grow:
the hosts – the plants; and the pathogen.
And in addition if the pathogen is transmitted by a vector there is also the interaction with the vector.
Firstly, it was essential to establish the full list of potential host plants,
as well as those plants not at risk, and which could still be traded.
An experimental field in Puglia became the primary source of this critical information.
This is the first experimental plot that was realised in 2015
with 10 olive varieties and different varieties of grape, citrus and stone fruit.
Because some interesting characters of resistance and tolerance were observed,
we expanded the evaluation of the olive grove, by planting additional 40 different cultivars or varieties.
This initial research demonstrated that while citrus and grape were so far unaffected,
olive plants were highly susceptible to the strain of xylella present in the area.
However, some olive varieties showed potential tolerance to the disease.
The fact that we already found some source of resistance is
very encouraging for us in order to continue the screening to look for this kind of things.
There are more than 1000 varieties known in the Mediterranean area so
we will complement this field research with the laboratory research,
to breed and to produce varieties that are resistant to xylella fastidiosa.
A commonly found insect emerged as the chief suspect in the transmission of the disease…
This one is one… here we have one more… we have one more here… so there is plenty of them.
Xylella spread exclusively by vectors.
The vector is philaenus spumarius; that is spittlebugs. Spittlebugs is probably the key pest for olives.
Adult spittlebugs feed on the xylem of olive plants.
After feeding on an infected plant, they can transmit the bacterium to other plants.
Field surveys have recorded up to half a million juvenile spittlebugs per hectare.
To control this vector means to arrest the spread of xylella fastidiosa
a detailed understanding of this endemic insect is therefore central to any containment strategy.
My first hope is to get good methodological approach.
We need good methods to score the number of individuals per square meter.
We need to know which part of the year is most critical for transmission.
Xylella is a genetically diverse pathogen.
Once the causal link between the bacterium and olive plant decline in the area had been established,
the researchers went on to identify the precise strain present in Italy
and to map the genome of this strain, named CoDiRo, or Olive Quick Decline Syndrome.
We’re the first group to work with infected plant from the field.
So we have developed a specific protocol to detect the bacterium in olive trees, in order to identify the positive olive trees.
In addition we developed molecular tools that can identify the type of strain that is causing the epidemic in Apulia.
So far only one strain could be identified and sequenced.
Xylella very well know in the history of plant pathology
for the epidemic of Pierce Disease that begun in Los Angeles Bay more than one century ago.
Well, if we compare the climatic conditions of the Los Angeles Bay
with those of the Salento Peninsula where this epidemic originated
we found exactly the same climatic conditions. So the optimal condition
for the spread of xylella for the surviving and multiplication of xylella.
By studying the different parts of the triangle, scientists can identify the weakest links
and help to find control solutions that will assist olive growers to preserve their livelihoods.
With a climate of warm, mild winters suited to the spread of xylella,
the best hope for tackling the problem rests on the natural resistance already detected in the olive groves.
Researchers are also exploring other possible solutions, such as:
• releasing antagonist bacteria that compete with the xylella infection in the plants;
• grafting tolerant varieties on to ancient trees;
• and using pathogen confusion to reduce the ability of the bacteria to multiply.
We can see at the moment many institutions all around Europe are exchanging information
exchanging data there is an urgence and they have all the same interest to solve it.
For this complex problem solid solution can be found only by a serious scientific programme of research.
The combination of the different factors and their interaction is very very complex.
Research is the only way to help finding solutions and find the right way to react. And the fastest one.