Invasive alien pathogens as a threat to global biodiversity

This is an overview paper introduces and invasive alien species (IAS) and emerging infectious diseases (EIDs) are known to interact as a threat of biodiversity loss, encompassing species extinction and ecosystem change. The paper describes the main pathways of invasive pathogens introduction demonstrating the known examples of forest damages due to the spread of the emerging infectious diseases. The global trade of ornamental plants for planting is shown as the main pathway of the invasive pathogens spread. We tried to discussed the reasons that lead to large-scale damage to tree species and significant transformation of forest ecosystems under the influence of invasive pathogens. The problems related to an insufficient level of alien species spread by forest pathologists, scientists and forestry practitioners are also overviewed. The terminology for invasions of various taxa of pathogenic organisms is still incorrectly unified or developed and it was summarized to present the basic terms concerning invasions and invasive organisms. This paper indicates the main phases that the organism goes through to acquire the status of invasiveness and the factors that contribute to the successful establishment of invasive pathogens at the local, regional and continental levels. The vast majority of introductions of forest invasive species are happened unintentionally e.g., by morphological structures of pathogens (spores, mycelium) that cannot be detected during the import of plants, or on packaging material. It is also indicated that the effects of forest disturbances due to global climate change (e.g. drought, storms, forest fires, outbreaks of pests and pathogens) will increase the vulnerability of trees and shrubs to the impact of invasive pathogens. Currently, that is one of the major problems facing forest phytopathologists. Due to the global climate change, the introduction of invasive organisms might be significantly accelerated with affecting the success of their penetration, spread, establishment and susceptibility of host plants in new areas. The overview is also provided on plant protection regulation on national and international levels. There is no legal framework in Ukraine that would regulate the introduction of invasive pathogen at the national level except the Law of Ukraine "On Plant Quarantine" which contains lists of: 1) quarantine organisms absent in Ukraine; 2) quarantine organisms limited in Ukraine; 3) regulated non-quarantine pests. The list of regulated pests and diseases with the high potential threat of introduction and risk for plants in Ukraine is designed on the information about pests and diseases included in lists A1 and A2 by the European and Mediterranean Plant Protection Organization (EPPO) and/or lists of other relevant international organizations. Some of the pathogens and pests listed in these lists are invasive, but there is no information and understanding of their invasiveness and the threat they may pose. The spread and influence of invasive pathogens after their penetration are also influenced by factors that allow their successful establishment at the local, regional and continental levels: 1) host diversity; 2) host connectivity; 3) host susceptibility. The analysis of host plant diversity and vulnerability to invaders, which depend on the three factors listed above, will improve the ability to foresee the spread of invasive pathogens on a large scale and to prevent potential negative effects on ecosystems