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Xylella fastidiosa has a wide plant host range and spectrum of insect species capable of serving as vectors which should increase the bacterium's invasiveness and make it difficult to prevent introduction via live plants from the tropical or subtropical Americas. The spread of phony disease of peach within the south-eastern USA from the 1890s until about 1930 and of citrus variegated chlorosis disease of orange throughout Brazil in the 1990s indicates that new strains of X. fastidiosa have the potential to spread over a few years to cause increasing damage. Intersubspecific homologous recombination of strains is implicated in the potential for invasion of new host plants (Nunney et al., 2014). X. fastidiosa represents a very serious threat for the EPPO region. In 2013 the bacterium was reported causing serious damage to olive trees in Puglia, Italy. It was also detected in numerous other host plants (mainly ornamentals). Colonisation of a host with X. fastidiosa does not always equate to disease development and an endophytic life stage has been suggested (Chatterjee et al., 2008). These non-symptomatic hosts and hosts which are slow to develop symptoms can limit the effectiveness of quarantine procedures and may provide a reservoir for maintenance of the pathogen in the wider environment. According to the EFSA Panel on Plant Health (European Food Safety Authority, 2015), establishment and spread of X. fastidiosa in the EU is very likely. The consequences are considered to be major because yield losses and other damage would be high and require costly control measures. X. fastidiosa is included in the EPPO A1 list of pests recommended for regulation as quarantine pests. Among potential insect vectors, only Homalodisca vitripennis, Xyphon fulgida, Draeculacephala minerva and Graphocephala atropunctata are also listed in the EPPO A1 list. The European Food Safety Authority suggests that all xylem sap feeder insects should be regarded as potential vectors of X. fastidiosa. Elbeaino et al. (2014b) detected X. fastidiosa in the phloem feeder Euscelis lineolatus in Italy, suggesting that potential vectors may include phloem feeding insects. Further studies are needed to confirm transmission in E. lineolatus. Newly introduced isolates of X. fastidiosa are likely to be transmitted by endemic vector species even without the introduction of non-native vectors (Almeida et al., 2005).In summary, X. fastidiosa may have the potential to invade agro-ecosystems in Mediterranean regions wherever suitable vectors (overwintering in the adult stage and thus able to inoculate vines during spring) are endemic or become established. The same may be true for tropical-subtropical Asia and Africa. |
