Xylella fastidiosa
A scientific and community Internet resource on plant diseases caused by the bacterium Xylella fastidiosa

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Welcome to the Xylella fastidiosa website. In this site you will find information on diseases caused by this bacterium, its insect vectors and control guidelines for Pierce's disease in California. In addition, a list of references is available, although it has not been recently updated. However, we have a link to Pubmed so you can find out search the most recent literature.

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Q&A Xylella fastidiosa in Italy

April 20, 2015

We are scientists that have worked with the bacterium Xylella fastidiosa and the diseases it cause for several years, both in the USA and Brazil. Interest in the current olive disease epidemic in Italy associated with X. fastidiosa has recently led to a large volume of information requests. In addition, we have found that there is a substantial amount of scientifically incorrect information on the internet/media. This is a brief Question & Answer document with some facts about this emerging problem in the southern region of Apulia in Italy. To the best of our knowledge all statements here are well supported by robust science.

Sincerely,

Alexander Purcell, PhD; Professor Emeritus; University of California, Berkeley

Rodrigo Krugner, PhD; Research Entomologist; Agricultural Research Service, United States Department of Agriculture

Rodrigo Almeida, PhD; Associate Professor; University of California, Berkeley

When was Xylella fastidiosa first detected in Apulia, Italy?

The first report of X. fastidiosa occurred in October 2013 by CNR researchers in Bari. Several independent research groups have now detected this bacterium in the region. Because it is found so consistently from olive trees with a severe newly recognized disease and not in healthy olive trees, it is considered the main suspect as causing the olive disease. It is not known in what year the new olive disease first appeared or when X. fastidiosa was introduced, but given the size of the area affected we speculate that the introduction occurred as many as ten or more years ago.

What plant species is this bacterium associated with in Italy?

The main plant species currently associated with X. fastidiosa is olive. In addition the following plants have been reported as hosts harboring X. fastidiosa: almond, oleander, cherry, and several other perennial ornamentals. Previously, researchers in Florida, California, and Brazil have found that most plant species tested as hosts support some multiplication of the bacterium without showing symptoms.

Where did this strain of X. fastidiosa, dubbed CoDiRO, come from?

There has been only one genotype of X. fastidiosa detected in Apulia, the strain was named CoDiRO (Complesso del Disseccamento Rapido dell'Olivo) due to its association with an olive disease emerging in the region. Molecular testing by different Italian research groups has yielded identical results, demonstrating that the CoDiRO strain matches a strain previously found in Costa Rica.

How did the CoDiRO strain arrive in Apulia?

There have been several recent interceptions of X. fastidiosa in infected ornamental coffee plants in Italy, France, Holland, and Germany. In all but one case these plants originated from Costa Rica. Together with the genetic data, the most logical interpretation of available information to date is that the CoDiRO strain arrived from Central America via the introduction of infected plant material.

Is X. fastidiosa causing disease in olive trees in Italy?

Xylella fastidiosa has been detected and isolated from symptomatic olive trees. In plant pathology, conclusive evidence that a pathogen causes a specific disease requires fulfillment of Koch's postulates, a series of experiments that lead to proof of pathogenicity. Researchers in Italy are currently working on fulfilling Koch's postulates for strain CoDiRO and olive, among other plant species. However, there is very good correlation between disease and the presence of X. fastidiosa.

How is the bacterium spreading in the region?

Movement of X. fastidiosa from one plant to another occurs exclusively via insect vectors and use of infected grafting material. Researchers in Apulia have already identified one vector species.

A USDA-led study in California indicated that X. fastidiosa does not cause disease in olive, correct?

Yes, that is correct. The study was led by one of us (R. Krugner) and it failed to demonstrate that X. fastidiosa causes disease in olive in California. However, the strains of X. fastidiosa used in that study belonged to two subspecies: fastidiosa and multiplex. The CoDiRO strain belongs to a different subspecies, named pauca, which is not known to occur in the USA. Because of differences in plant host range among X. fastidiosa subspecies and genotypes within subspecies, the results obtained in California are not directly transferable to the case in Apulia. The role of the CoDiRO strain on the etiology of the olive disease in Apulia remains to be proven by scientists.

But all these subspecies are considered to be within the species X. fastidiosa. Are there any meaningful differences?

Yes. By definition bacterial species group large amounts of genetic and phenotypic diversity. As an analogy, this might be the equivalent of calling all primates one species. In the case of X. fastidiosa, specifically, it is known that two genotypes within the same subspecies that occur at the same site and share insect vectors can have different plant host ranges. Subspecies of X. fastidiosa are categories used to classify genetic groupings of strains that have similar plant host ranges.

Are efforts to manage the problem going to work?

Unfortunately this is an emerging disease and a new introduction of a pathogen in the region. We suggest that first control attempts must rely on past experiences that show what works best in other diseases caused by X. fastidiosa, such as in grape (Pierce’s disease in North America) or citrus (citrus variegated chlorosis in Brazil). Management methods evolve from a combination of basic and applied field research and the results from testing the most promising control methods. Because property lines do nothing to stop flying vector insects from spreading X. fastidiosa, most effective control measures require regional education and coordination. Effective disease management may also need to vary from region to region because of regional differences in insect vectors, climate, and other factors. Unfortunately, we cannot speed up nature to answer these questions.


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