Study suggests climate change opens the door to a vine disease that Europe dodged 150 years ago

• A collaboration between IFISC and the company Tragsa analyzes the global expansion of Pierce's disease, which has been spreading in the Mediterranean for a decade.

Until the 21st century, the bacterium Xylella fastidiosa, responsible for causing Pierce's disease in vineyards, was considered a pathogen exclusive to North America. This situation changed radically with the detection of the first case on the island of Mallorca in 2017, in Taiwan, and recently in Portugal and Italy. The vines infected by this epidemic transmitted by insect vectors produce few fruits and of poor quality, their branches necrotize and fall, eventually perishing within a few years. A scenario that which climate change worsens and for which the wine sector is concerned due to the millions of dollars in losses caused to entire crops of olive and almond trees since the affected plants have to be uprooted immediately.

Among the European outbreaks of Pierce's disease analyzed, with samples from Italy, France, Germany, and Spain, the origin of the X. fastidiosa bacterium has been traced to California (USA). Now, in a new scientific work that applies epidemiological models to historical research, scientists from the Institute of Cross-disciplinary Physics and Complex Systems (IFISC-CSIC-UIB) wanted to know how Europe got rid of the disease 150 years ago.

The study of this joint center of the Consejo Superior de Investigaciones Científicas (CSIC) and the Universitat de les Illes Balears (UIB), originally published in the specialized scientific journal Proceedings of the Royal Society B, was named “the most outstanding in research in the scientific literature” of other journals by Science that week.

The new research sheds light on a curious key historical event. In the mid-19th century, the export of new grapevine lineages from North America to southern France introduced multiple organisms previously unheard of in European fields. This caused a massive decline in the wine industry at the time, mainly due to the phylloxera plague in the Iberian Peninsula, caused by an aphid that annihilated the plant by devouring it at the root. However, X. fastidiosa did not spread in the Mediterranean in 1875 and there was no trace of Pierce's disease until two centuries later.

Biogeography determines the virulence of epidemics

The first author of this new paper, Eduardo Moralejo of Grupo Tragsa, points to how it was probably the European climate of the time, of “cooler temperatures,” that prevented X. fastidiosa from spreading across the continent. “The climate was a natural barrier to the disease”, the scientist explains. As well as the fact that the areas of the United States from which the new grafts were exported to the French vineyards had not yet contracted Pierce's disease.

Among the multiple historical coincidences of the work, Manuel Matías, co-author of the study and leader of the team, points out that the massive importation of North American vines resistant to phylloxera was carried out during the 1870s to fight against this vine pest that was devastating the vineyards of southern Europe at that time.

“The massive importation of vines was due to their resistance to phylloxera, precisely because historically they had coexisted, so, surprisingly, Xylella did not become established in Europe, since they were potentially infected vines,” reflects the IFISC-UIB-CSIC scientist. He warns that the conclusions of the research also serve as a warning for future epidemics: “The increase in temperatures caused by climate change, especially pronounced since 1990, makes the spread of Pierce's disease more likely in areas that were previously unaffected”. His scientific team closely documents this olive-devouring bacterium in the Mediterranean.

Analysis of the phylogeny of the X. fastidiosa bacteria has allowed scientists to “trace the last common ancestor” and date its origin to 1884, in Anaheim, California (USA). From where, in less than a decade, it spread from Napa Valley, an area still renowned today for its vineyards, to the north of the state.

IFISC-UIB-CSIC researcher and co-author of the analysis, Àlex Giménez-Romero, argues that few documented examples specify the processes by which “a disease is paralyzed or spreads geographically”. Hence the need to apply mathematical models that combine history, statistics, and plant genetics to explain why, at a time when Pierce's disease was already a problem in the U.S. towards the end of the 19th century, Europe remained on the sidelines.

European vineyards avoided the pandemic thanks to their “climatic conditions, most of which were below the threshold necessary to develop the disease”, summarizes the expert. A conclusion they reach thanks to their approach from epidemiology and ecology that analyzes “the development of the pathogen X. fastidiosa over 150 years”.

For this reason, Giménez-Romero, from IFISC (UIB-CSIC), insists that the wine industry and the authorities must “know the phenomenon” of Pierce's disease and be aware that “Europe is facing an imminent risk of epidemics, especially in the southern regions”.

Moralejo E, Giménez-Romero À, Matías MA. 2024 Linking intercontinental biogeographic events to decipher how European vineyards escaped Pierce’s disease. Proc. R. Soc. B 291: 20241130. https://doi.org/10.1098/rspb.2024.1130

Jon Gurutz Arranz/IFISC/CSIC Comunicación

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