Pathogenicity of nineteen Phytophthora species to a range of common urban trees

Diseases caused by pathogens, alone or in combination with other stress factors, are a major threat to the future health of urban forests. Root diseases caused by Phytophthora species are frequently evident in urban environments due to conducive environments for these pathogens, and to conditions predisposing trees to attack. Urban environments are also an important pathway for the introduction of Phytophthora species into novel ecosystems. We have detected many different Phytophthora species from dying and declining trees in the urban and peri-urban environment, and for many of these species, little is known about their host range. Therefore, the aim of this study was to examine the host range of 19 Phytophthora species, including many recently described species, against fifteen tree species commonly used in urban plantings in Perth, Western Australia. Excised branches of each tree species were under-bark inoculated with each Phytophthora species, incubated and lesions were measured after 8 days. Six Phytophthora species were pathogenic to all fifteen-tree species, with ~75% of the species each causing disease in ≥85% of plant hosts. All Phytophthora species formed lesions in Eucalyptus marginata and Corymbia calophylla. Phytophthora cinnamomi, P. pseudocryptogea, and P. citrophthora were the most pathogenic species causing the largest lesions in most of these trees species. It is likely many of these Phytophthora species have a negative impact on the health of urban forests where they are present.