Urban Pathways of Oomycete Dissemination: A Case Study from Warsaw Parks

Urban green spaces are essential components of city ecosystems, providing environmental and social benefits while simultaneously serving as potential entry points for invasive plant pathogens. In recent years, increasing attention has been directed toward the role of urban environments as reservoirs and transmission corridors for oomycetes, a group of highly destructive microorganisms affecting trees and shrubs. This study aimed to investigate the diversity and potential introduction pathways of oomycetes in three Warsaw parks representing distinct ecological settings: a historical city park, a large landscape park with aquatic features, and a newly constructed linear park. Samples of soil, and surface water were collected and analysed using standard isolation and molecular identification methods. Four species were identified: Phytophthora cactorum, P. cambivora, Phytopythium vexans, and Ph. montanum—the latter two representing first records for urban parks in Poland. The results indicate that nursery plant material, surface water systems, and wildlife activity, particularly birds, are likely contributors to the introduction and spread of these pathogens in city landscapes. The findings underscore the growing phytosanitary risk associated with urban greenery, where the interplay of anthropogenic disturbance, high plant turnover, and complex hydrological networks facilitates pathogen establishment. This research highlights the urgent need to integrate urban biosecurity strategies with routine molecular monitoring, nursery inspections, and wildlife surveillance to limit further dissemination of invasive oomycetes and enhance the resilience of urban tree populations.