Xylella fastidiosa: New threats from an old bacteria

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Xylella fastidiosa is a bacteria which has been known to cause wilting and vine death in the form of Anaheim disease in the grape vineyards of southern California since the end of the 19th century. However, in the past few decades it has spread beyond its former range to four continents and has been found to be the cause for a plethora of diseases in a variety of plants.

Xylella fastidiosa infects the xylem of woody plants and trees, from there it is able to exploit the flow of water and nutrients effectively starving the infected plant. As the infection progresses, leaves brown and fruit develop to be smaller than normal before progressing to dieback and eventual death of the plant. While the disease is most virulent in plants like grapevines and fruit bearing trees, more than three hundred different species can act as reservoirs for the bacteria. Furthermore the bacteria may use a wide variety of xylem-fluid feeding insects from the Leafhopper and Froghopper insect families as vectors from the infection. As there is no cure due to the systematic nature of the infection, treatment and control is limited to the destruction of affected plants and the creation of exclusion zones, however such efforts are limited in effectiveness as the range of the vector insects can exceed six miles and symptoms can be similar to other diseases.

Despite previously being present only in southern California, in the 1990s illegal transport of infected cuttings spread the disease into the fruit trees of Brazil and Taiwan. Also, beginning in 2013 a number of strains have appeared in Europe, infecting olive trees in southern Italy where it managed to affect over a million trees in the space of just two years. From Italy, it has spread into France and Germany as well as the islands of Corsica, Majorca, and Ibiza spreading across boarders on ornamental plants.

Now on a global scale, Xylella Fastidiosa presents a major economic and ecological threat. Already, it has caused a major economic impact upon the agricultural industry costing hundreds of millions of damages to both trees and fruit. Furthermore, the disease threatens many of the plant species native to South America and Europe which are already under stress due to habitat loss from human activity. 

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