Why Did the Cause of Pierce’s Disease in Grapevines Spread to Europe Only in 2013?

Greenhouse gases have, according to measurements, increased the Earth's average temperature by nearly 1.5 degrees Celsius per year. As a result of this change, harmful pathogens may spread to regions where they have not previously been found. This applies to both alien invasive species and so-called newcomer species, which are spreading to new areas without human intervention.

Eduardo Moralejo and his colleagues have published a study examining the phylogenetics, epidemiology, and history of Xylella fastidiosa, a North American bacterium spread by insect vectors that causes Pierce’s disease in grapevine. Their research provided insight into why European vineyards have, until now, avoided this pathogen.

Before this study, it was a mystery why the export of American grapevines to France in the late 19th century to combat phylloxera did not lead to the spread of X. fastidiosa at that time. Phylogenetic analysis revealed that the most recent common ancestors of the bacterial populations lived around 1875. This timing aligns with the first epidemic caused by the bacterium in the U.S. and its subsequent spread to the southeastern United States.

Moralejo and his team also showed that continental Europe's climatic conditions were too cool from the 19th century until the early 1990s for Pierce’s disease to develop into an epidemic. Consequently, the pathogen could not establish itself or spread from the plants imported into Europe at that time, even if they had been infected.

However, the situation has changed due to global warming. As a result, the risk of epidemics has been increasing for over three decades. It remains to be seen when this bacterium will be found beyond the limited areas of Europe’s southernmost regions, where it was first detected in 2013.

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