Evidence from mortality dating of Fraxinus excelsior indicates ash dieback (Hymenoscyphus fraxineus) was active in England in 2004-2005

摘要

Ash (Fraxinus excelsior L.) planted at six sites over the past 20 years was investigated. Three geographically isolated sites (Northumberland, Leicestershire and Devon) were compared with three sites in established areas of ash dieback in East Anglia, and the causal pathogen, Hymenoscyphus fraxineus, confirmed at all. Dieback severity, the frequency of stem basal lesions and pathogen apothecia, were quantified at all sites but despite high disease levels, tree mortality was low. Some trees had typical H. fraxineus stem cankers but had apparently died between 2001 and 2011, before the earliest UK records of H. fraxineus. Ring counts established beyond doubt the year of death and canker initiation in 27 dead trees. Cankers on the same trees were then tested for H. fraxineus using PCR-based detection, with pathogen presence confirmed as early as 2004/05 in some. This places H. fraxineus in England much earlier than previously thought, even pre-dating its documented arrival in neighbouring European countries. The advanced disease levels at some sites plus confirmation of H. fraxineus in old stem cankers, suggests that planting of infected H. fraxineus tree stock in England could date back to the early 1990s, with affected trees dying in the mid-2000s. Additionally, it raises questions about the origins of the infected plants and uncertainties about plant trade pathways.