OVERVIEW OF Hymenoscyphus fraxineus IN BRITAIN THROUGH POnTE PROJECT

European ash (Fraxinus excelsior) is a common tree species in the UK. This has been the main Fraxinus species affected by ash dieback (Hymenoscyphus fraxineus) since the first detection of this fungus in England in 2012. Since 2015 the disease has been monitored in England, Scotland and Wales. Hosts, symptoms and airborne inoculum have been recorded. Pathogenicity test to assess the susceptibility of different hosts have been carried out. The role of ash fruits as a potential source for the spread of the disease has been studied trying to determine if the infection was present on ash pericarps, seeds or embryos. A new protocol for the detection of the pathogen in seeds has been developed using a real-time PCR that is H. fraxineus-specific. Furthermore, a hot-water treatment (HWT) to reduce biosecurity risks and facilitate the movement of seeds between diseased and non-diseased areas has been investigated. Because of the monitoring, the disease has been confirmed on different non-native ash species and it has been recorded for the first time worldwide on the non-ash hosts Phillyrea spp. and Chionanthus. The highest abundance of airborne inoculum was detected in July/August. A pre-DNA extraction homogenisation step enabled a larger number of ash fruits to be tested at the same time; this enabled efficient high-throughput diagnostics of ash fruit lots. H. fraxineus DNA was detected in seed lots from uninfected, lightly and highly infected sites collected in all years between 2015 and 2018. The pathogen was detected on ash fruit pericarps. After HWT, H. fraxineus was only detected on the surface of the fruits. Seedlings from infected seeds that had the HWT are currently growing under controlled conditions and are tested for the presence of the pathogen periodically. The latest results and future research will be discussed.