Xanthomonas Threats project - Angular leaf spot of Strawberry

Xanthomonas fragariae is a pathogen of strawberry first identified in the US in the 1960s and present in some regions of Europe and other continents. This pathogen causes angular leaf spots which can spread across the leaf, leading to vascular collapse and yield reduction. X. fragariae is an EPPO A2 listed pathogen and a regulated non-quarantine pest in the EU and in the UK. The disease is considered absent in the UK, although there have been infrequent findings. It is thought the disease has the potential to establish in many of the European countries which produce strawberries, and the changing climate may alter the distribution of this disease. Through this project we are aiming to improve our understanding of X. fragariae in a UK context by assessing risk to UK strawberry production and improving existing diagnostic methods.

We have tested 12 X. fragariae and X. arboricola pv. fragariae isolates for pathogenicity on wild strawberry plants, with five isolates giving typical angular leaf spot symptoms. This was followed by successful re-isolations onto a range of media, improving our isolation method and our knowledge of symptom development. Twenty-nine popular UK strawberry varieties have been screened with two strains of X. fragariae and a strain of X. arboricola pv. fragariae and scored for disease severity up to 8 weeks after inoculation. No symptoms were observed with X. arboricola pv. fragariae and some popular varieties were found to be very susceptible to X. fragariae. Varieties of strawberry which may be more resistant or tolerant to X. fragariae have been identified; these varieties could contribute to successful disease management.