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Climate Change Is Boosting the Bacteria That Devour Olive Trees

Olives on a tree.
Credit: Nazar Hrabovyi/ Unsplash
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Xylella fastidiosa , the deadly disease-causing bacteria that has already wiped out millions of plants by clogging their ducts and plant tissues, benefits from climate change. Research staff from the Institute of Interdisciplinary Physics and Complex Systems ( IFISC ), a joint center of the Higher Council for Scientific Research (CSIC) and the University of the Balearic Islands ( UIB ), have studied its propagation over the last 20 years using a  new technique to know what their future will be like in the different scenarios posed by global warming. Researchers from the Cantabria Institute of Physics (IFCA), a joint center of the CSIC and the University of Cantabria, have collaborated in the work.  These findings , recently published in a study in the scientific journal Scientific Reports , describe how an increase of more than 3 degrees in the average temperature of the planet would be a “turning point in the risk” that the bacteria, which affects olive trees, almond trees and vineyards of the Mediterranean countries, expand further north in Europe.

The climate determines the area in which these diseases can occur, hence a favorable temperature enhances the development of epidemic outbreaks. Scientist  Manuel Matías , from the  IFISC-CSIC-UIB and author of this research, considers climate change key in the “drive and distribution of diseases in plants around the world.” The team led by Matías has defined the contagious effect of preindustrial levels. In all scenarios, the pattern of increased risk of infection due to increased temperature is repeated.

A global epidemic with millions of losses

A decade has just passed since  the first detection of the bacteria X. fastidiosa  in Europe, which until the 21st century was officially considered a pathogen restricted only to the American continent. In  California (United States) , this bacteria causes lethal Pierce's disease in the vine, generating million-dollar losses in the wine sector annually. Infected plants produce few and poor quality fruits, their leaves discolor, necrotize and fall, and the vines can die in a few years. Regarding the European outbreaks analyzed, insects from the cycad group - also known as cicadas or cicadas - are considered, specifically the insect Philaenus spumarius, as the main and only transmitting vector. The rapid spread of the disease has already caused the destruction of crops in Italy, and is also to blame for thousands of almond trees having to be uprooted in the Balearic Islands and Alicante.

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The research, which  can be consulted here , shows how the prolonged increase in temperatures expands the distribution of X. fastidiosa throughout southern Europe and especially the Mediterranean region, with France, Italy and Portugal being the most affected countries. The work also indicates a decrease in the insect P. spumarius , although marginal in some areas, such as a good part of Spain, which would slightly increase its ecological niche in the more continental or mountainous European areas.

The designation of origin does not escape the 'annoying'

Researchers consider climate change as one of the biggest challenges for the European Union's agricultural policy. Hence, they argue that knowing what is going to happen in certain regions will help make better decisions in the future and prevent the possible impact of the disease on crops. For this reason, scientists have quantified the risk of X. fastidiosa  infection at different spatial scales; at the country level, designations of origin and known wine plantations.

Based on an analysis of the area at risk by country, scientists have compared how, in an initial scenario that projects a temperature increase of 1.5 degrees, Portugal and Greece face the highest risk of contagion, with 12% and 2%. more, respectively. A scenario that, with 4 more degrees, would rise to a “surprising” risk, they admit, of 47% and 63%. The authors describe how in this scenario France and Italy would also experience a “relevant” risk, although smaller. In the case of Spain, the second largest wine producer, they clarify that the risk would remain similar to current levels.

A situation that contrasts with the areas with designation of origin, where an increase of more than 2 degrees would put wine crops, such as those in the southeast of France, at serious risk; Penedés, in Spain; the Portuguese Bairrada or Tuscany, in Italy, among others. These data can be consulted  online on the IFISC website , accompanied by a detailed analysis by designation of origin, types of risk, scenario according to the increase in temperature, and which is also organized by country and geographical area.

The authors admit the limitations of their model that works with climate projections when faced with the intricacy of the microclimates that occur in some wine-growing areas. Despite this, they consider it important to try to understand the way in which the disease spreads, hence the interdisciplinary origin of the study, which combines epidemiological and climatic models. The research concludes by arguing that the new information will serve to better manage resources destined for prevention, thus giving priority to areas according to their percentage of risk of infection. A way in which Europe can, despite uncertainty,  make better decisions and effective strategies to mitigate the risks posed by Pierce's disease. A way, scientists say, to safeguard the future of viticulture against climate change.

Reference: Giménez-Romero À, Iturbide M, Moralejo E, Gutiérrez JM, Matías MA. Global warming significantly increases the risk of Pierce’s disease epidemics in European vineyards. Sci Rep. 2024;14(1):9648. doi: 10.1038/s41598-024-59947-y

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