What is Xylella fastidiosa?

What is Xylella fastidiosa? With the increased number of Xylella outbreaks in Europe, this question seems to be on everyone’s mind. Xylella was first detected in 2013 within the European Union on the leaves of olive trees in Puglia, southern Italy. Since then, Xylella infections have been reported in France, Portugal, Spain and Germany. Today, scientific communities are working closely with authorities such as the European Food Safety Authority to find a sustainable solution.

What is Xylella fastidiosa?

Xylella fastidiosa is a bacterial plant pathogen which is transmitted by pests, more specifically xylem fluid feeding insects. The bacterium colonizes the Xylem vessels, leading to blocking of essential nutrients and water for plant health.  In essence, Xylella is a bacterium which infects plants and causes serious plant diseases.

These include the grapevine Pierce’s disease, plum leaf scald, olive quick decline syndrome, citrus variegated chlorosis, oleander leaf scorch and many more. Consequently, these diseases have a devastating impact on the economy, agriculture and the environment.

According to the European Food Safety Authority, there are a total of six most frequently reported species of Xylella. They are fastidiosa, pauca, sandyi, multiplex, tashke and morus.

 Xylella host list

Approximately 600 species of plants host the dangerous bacterial plant pathogen. For instance, Xylella can be found in:

  • crop plants – grapevine, blueberry, plums, citrus trees, etc.
  • stone fruit – olives, almonds, cherries, etc.
  • ornamental plans – lavender, oleander, milkwort, rosemary, etc.
  • native trees – ash, elm, oak, etc. 

In fact, the European Food Safety Authority added 37 new plant hosts to its Xylella host list in April 2020. Click here to view the entire Xylella plant host list.

Where did Xylella fastidiosa come from?

It is argued by some scientists, that Xylella infecting European plants originated in the American continent. Specifically, the Xylella pauca subspecies is believed to be native to South America, where it appeared first in coffee crops. 

How does Xylella fastidiosa spread?

Xylella fastidiosa is spread through insects such as spittlebugs, which feed on the contents of the xylem. Xylem is the network of tubes present within plants which carry nutrients and water from the root to the leaves and flowers. These insects (which carry the bacterium) then insert a stylet (thin probe) into the xylem. The bacterium then infects the plants and lives within the xylem plant tissues.

Next, Xylella fastidiosa will be carried to other species and plants as the insects will feed elsewhere. Hence, Xylella fastidiosa is spread through the insect vector.

However, Xylella fastidiosa can also be spread unintentionally through plant trade. For this reason, certain countries impose strict regulation in trading and importing plants, as means of controlling the spread.

Xylella fastidiosa symptoms

Symptoms of the Xylella infection range variously across different plant hosts. Depending on the level of bacterial inoculum, the plants can show case any of the following symptoms:

  1. leaves scorching
  2. discolouration of the leaves (leaves often turn yellow or brown)
  3. stunting, reduced plant growth / height
  4. wilting of leaves
  5. bare petioles
  6. poor fruits (shriveled fruit)
  7. premature abscission of leaves and fruit
  8. dieback
  9. plant death

The above-mentioned symptoms worsen over the summer months to autumn, where juvenile insects become adults and feed more on the xylem contents. Moreover, during these months, the plants can experience dry periods with limited water supply worsening the conditions of the infection.

Arguably, some species which host Xylella and are infected don’t show any signs of the infection.

Impact of Xylella fastidiosa

Xylella fastidiosa is one of the most dangerous pathogens which threaten the European agriculture industry in Southern Europe and the Mediterranean region.  

Since it has been identified in Italy and Spain in 2013, it has spread rapidly across Europe, oftentimes destroying entire orchards. In some regions a point of no return has been reached, where the disease continues to spread uncontrollably.

As a direct consequence, Xylella is projected to cause yield losses of 35% – 70% in olive harvests and 13% in almond harvests in the European Union.

One of the most impacted regions in Europe is the region of Apulia (Italy), where olive production diminished by an alarming 65%-80%. Heritage 400-year-old olive trees have been destroyed and an estimated 100,000 jobs have been lost.

It has become apparent ever more, that farmers lack effective disease management measures against Xylella fastidiosa.

Xylella fastidiosa treatment

Unfortunately, there are currently no known curative treatments for plants infected with Xylella fastidiosa. In response to the increasing outbreaks of Xylella infections, the BIOVEXO project has been funded through the Bio Based Industries Joint Undertaking (BBU-JU)

The BIOVEXO project aims to eliminate the disease in the long-run with novel bio pesticides for curative and interpretative purposes. Click here to learn more about BIOVEXO’s research plan. 

Don’t forget to share your thoughts and experiences on Xylella in the comments section below. 

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