Xylella: new studies assessed
There is currently no scientific evidence to support the suggestion that fungi rather than the bacterium Xylella fastidiosa are the primary cause of the olive quick decline syndrome observed in Apulia, southern Italy. That is the main finding of an analysis carried out by EFSA of new studies and other information submitted to the Authority.
In addition, there is no published evidence that treatment of fungal disease will reduce the establishment, spread and impact of Xylella, although good orchard management is generally beneficial for plant health.
The papers examined by EFSA observe that tracheomycotic fungi are often associated with olive wilt and could also be involved with olive quick decline syndrome. However, the research neither states nor demonstrates that these fungi are the primary cause of olive decline.
EFSA stated in its risk assessment of X. fastidiosa, published in January 2015, that diseased olive trees “were generally affected by a combination of pests, including X. fastidiosa, several fungal species belonging to the genera Phaeoacremonium and Phaemoniella and Zeuzera pyrina (leopard moth)”. The new studies, together with other available evidence, support this statement.
The European Commission asked EFSA to examine the scientific papers after they were cited in support of a hypothesis that tracheomycotic fungi rather than X. fastidiosa are the primary cause of olive decline in Apulia. As well as looking at the new evidence and revisiting studies used in its January risk assessment, EFSA’s plant health experts held a technical hearing with one of the authors of the papers to ensure that they fully understood the findings.
In January 2015 EFSA’s Panel on Plant Health published a Scientific Opinion which assessed the risk to plants posed by X. fastidiosa in the EU territory and evaluated risk reduction options.
EFSA’s Panel concluded that X. fastidiosa presents a major risk to the EU territory. This is because potential host plants – including citrus, olive, grapevine, almond, peach, oak, sycamore and oleander – and insect carriers of the disease (known as “vectors”) are present throughout the EU, and environmental conditions are favourable in some regions. Outbreaks of X. fastidiosa have led to severe losses of citrus in South America and grapes in North America.
EFSA concluded that eradication of X. fastidiosa – i.e. its total elimination from an outbreak area – is unlikely to succeed in areas where the pest is widely established, because of the broad range of host plant and insect vector species. X. fastidiosa is established across tens of thousands of hectares in the Lecce province of Apulia.
However, using a combination of containment measures – such as preventing the movement of infected plants or infectious insect vectors, removing infected plants, controlling insect vectors and managing surrounding vegetation – could help to prevent or slow down the spread of the pest from Lecce province to neighbouring areas or other territories of the EU.
EFSA recommended in January that further research be carried out on the host range, epidemiology and control of the Apulian outbreak of X. fastidiosa. This could help to substantially reduce uncertainties and enable a more thorough assessment of the risks posed by the Apulian strain of X. fastidiosa to be carried out. EFSA is currently contributing to such research in Apulia.