Rapid Pest Risk Analysis (PRA) for: Candidatus Phytoplasma fragariae
Ca. Phytoplasma fragariae is a poorly understood plant pathogen whose full distribution and host range are unlikely to have been elucidated. It has been associated with moribund hazel (Corylus) at an outbreak in the UK, which triggered the initiation of this PRA. Without knowledge of the vector of the pathogen, risk assessment and management decisions are subject to high levels of uncertainty.
Risk of entry: The only pathway of entry assessed was plants for planting, as phytoplasmas are obligate parasites. This pathway is considered likely, due to the presence of the pathogen in Europe on widely traded material, but with low confidence as its full distribution and host range is unknown. As the vector is unknown, entry via this pathway could not be assessed.
Risk of establishment: If an insect vector is absent from the wider environment the disease may be self-limiting in the UK. However, establishment could occur in the absence of a vector by natural root grafts transmitting between trees. Though no spread has been observed at the outbreak site, establishment is rated as moderately likely due to the risk of establishment via root grafts or vegetative propagation. Confidence is low, because the vector is unknown.
Economic, environmental and social impact: The lack of reports concerning this pest suggests that impacts are small elsewhere, with medium confidence. Mortality rate in hazel in the UK has been very high, but there is no evidence of spread from the current site, thus economic, environmental and social impacts have been rated as small. Should a vector be introduced in the future, or spread from the current site become apparent, then environmental impacts could be large due to the importance of hazel as a native species.
Endangered area: If a vector is present, then the endangered area is wherever there is crossover between the vector and hazel. Clonal propagation of hazel and strawberries may also be endangered.
Risk management options: Because the pathogen is poorly understood, exclusion is very unlikely. Eradication or containment is only feasible if a vector is not present in the area where the disease is found, and can be achieved by destroying infected plants or preventing propagation. There should be a zero tolerance for the presence of the pathogen in propagating material of strawberry and hazel.
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- United Kingdom