Phytophthora nicotianae and Ph. mediterranea: A biosecurity threat to Platanus orientalis and P. x acerifolia in urban green areas in Greece

Abstract

Field surveys conducted in two urban green spaces in Athens (Greece) revealed the presence of Phytophthora-related diseases on Platanus orientalis and P. x acerifolia trees. Declining trees showed a range of disease symptoms including root rot, stem bleeding cankers and extensive canopy dieback. Since there is little information about the etiology of these diseases, a study was conducted from 2016 to 2021 to define the main pathogens involved. A total of 71 Phytophthora isolates were obtained from bark tissues and rhizosphere samples collected from symptomatic plane trees. Based on morphological traits and DNA sequence data, Phytophthora isolates were identified as Ph. mediterranea (11 isolates) and Ph. nicotianae (60). Over a five-year period 41% of P. orientalis trees associated with Phytophthora infections died and were removed from the park. Pathogenicity tests confirmed that all Phytophthora species including Ph. cinnamomi used for comparison, are pathogenic on both P. orientalis and P. x acerifolia trees. Phytophthora cinnamomi was shown to be the most aggressive species on both P. orientalis and P. x acerifolia. Phytophthora nicotianae was the dominant species, whereas Ph. mediterranea was associated with a few trees. Our finding has contributed to expanding knowledge on the host and geographic range of Ph. mediterranea, an invasive pathogen with a high potential for diffusion in Mediterranean regions and highlights the importance of enhancing biosecurity measures to prevent and limit the spread of invasive pathogens in urban and natural ecosystems.