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Overview The insect-transmitted Gram-negative bacterial plant pathogen Xylella fastidiosa infects >500 plant species, including crops, ornamentals and trees. Symptomatic plants show leaf scorching, premature abscission of leaves and fruit and eventual plant collapse and death. The bacterium was primarily limited to the Americas (Purcell and Hopkins, 1996). In 2013 X. fastidiosa subsppauca was found in the Salento area of southern Italy where it caused olive quick decline syndrome (OQDS) (Saponari, 2013). By 2015, the bacterium had spread to other zones of Italy and was detected in more than 30 other plant species in southern Italy. It has appeared to have migrated to the Provence-Alpes-C?te d’Azur (PACA) region and Corsica, France (EFSA Panel on Plant Health, 2018). There were at least three more independent introductions of X. fastidiosa into Europe, including X. fastidiosa subsp. multiplex, introduced in the 1980s (Yuan et al., 2010), and now found in Corsica and PACA regions of France and in Majorca, Menorca, Ibiza and Alicante provinces of Spain (EFSA Panel on Plant Health, 2018).

X. fastidiosa is exclusively transmitted by xylem-feeding insect species, predominantly sharpshooter leafhoppers in the Americas and spittlebugs/froghoppers in Europe (Sicard et al., 2018; EFSA Panel on Plant Health, 2018). The common and polyphagous froghopper Philaenus spumarius is responsible for the spread of X. fastidiosa in Europe, though it is anticipated that other froghopper species also play a role in epidemics of the bacterium (Saponari et al., 2014; Cornana et al., 2017; Cornara et al., 2018). P. spumarius is one of the most polyphagous insects known and is common throughout the Palearctic region, including northern European countries such as UK and Finland (Halkka and Halkka, 1990). The insect has been introduced into the USA and Canada (Halkka and Halkka, 1990).

The introduction of X. fastidiosa into the UK is highly probable given that (ornamental) plants from nurseries in X. fastidiosa-endemic countries, including for example, Costa Rica, are regularly imported. Also, UK Plant Health Services have already intercepted shipments with X. fastidiosainfected plants. Currently we know almost nothing about how the bacterium may spread in northern European climates, as most of the research on X. fastidiosa and its insect vectors has been undertaken in the warmer climates of southern Europe, California and Central and South America. The transdisciplinary BRIGIT consortium aims to rapidly develop methods to detect the bacterium and acquire a high level of understanding of the parameters that will contribute to X. fastidiosa spread in the UK. It will interact with stakeholders and policymakers to reduce the risk of X. fastidiosa introduction and mitigate the impact of the pathogen.