Invasive pathogens - from Dutch elm disease to sudden oak death

摘要

Fungal pathogens can cause long-term damage to trees, and changes in forestry management may even increase the susceptibility of trees to some diseases. However, a consequence of growing global trade and travel is the increased opportunity for introduction of previously unknown pests and pathogens into new geographical regions. One of the best known examples is Dutch elm disease, caused by two closely related fungal species, Ophiostoma ulmi and O. novo-ulmi. Both pathogens have killed millions of elms throughout the Northern Hemisphere in two pandemics spanning the 20th century. Much more recently, populations of riparian and shelterbelt alders across Europe have come under threat from another new pathogen: Phytophthora alni. This pathogen has arisen as a result of a recent hybridization event between two well-known species of Phytophthora. Over the past decade, P. aim has established along river systems in 12 European countries, killing many trees in the process. Yet another new Phytophthora species now threatens a wide range of tree genera and also many ornamental and understorey plants. Identified as the cause of sudden oak death in USA in 2001, this previously unknown species P. ramorum, has now been found in 14 European countries, including the UK, but is currently most damaging in the USA, notably California. Based on its behaviour, P. ramorum has the potential to be another highly invasive pathogen, although many factors will play a role in the process.