Comparative host range and aggressiveness of Phytophthora ramorum and Phytophthora kernoviae sp. nov. on North American and European trees

Phytophthora ramorum and P. kernoviae are recently introduced, invasive pathogens in woodlands in southern Britain. P. kernoviae, previously known as Phytophthora taxon C, is a newly discovered taxon, (Brasier and others 2005), found during surveys for P. ramorum in Cornwall, southwest England in November 2003. Both species are aggressive pathogens on foliage and shoots of understory rhododendron, especially R. ponticum. From this infection base they can spread aerially to attack the inner bark of tree stems, especially European beech (Fagus sylvatica) and some Quercus species, causing bleeding lesions. (Brasier and others 2004). To date P. kernoviae has been found causing bleeding lesions on about 50 mature F. sylvatica trees, two common European oaks, Quercus robur, and a Liriodendron at several adjacent woodland sites. The wider international risk to trees that P. kernoviae poses is unknown. The comparative host range and aggressiveness of P. kernoviae and P. ramorum to bark and foliage of North American and European tree species is therefore being investigated. The potential host range of P. ramorum on bark of native and plantation trees in the U.K. has been assessed previously (Brasier and others 2003;