Isolation and Characterization of Globisporangium glomeratum (syn. Pythium glomeratum) from Declining Holm Oak in a Historical Garden

<i>Pythium</i>-like organism species are widespread soilborne oomycetes known to cause root diseases in a wide range of plant hosts. However, their involvement in the decline of woody species in historical and urban gardens has received limited attention. This study reports the isolation and identification of a <i>Pythium</i>-like organism from declining <i>Quercus ilex</i> specimens in a historical garden, where affected trees showed symptoms of root rot and sucker dieback. Integration of morphological observations and molecular analyses of ITS, LSU, and Cox II sequences confirmed the identity of the isolates as <i>Globisporangium glomeratum</i> (formerly <i>Pythium glomeratum</i>). Pathogenicity tests confirmed the aggressiveness of these isolates on <i>Q. ilex</i> seedlings, resulting in significant reductions in plant height and shoot and root biomass. The detection of <i>G. glomeratum</i> in the soil of a historical garden underscores the risk of its unintentional dissemination through nursery stock or soil movement, particularly in urban settings where plant replacement is frequent. This is the first report of <i>G. glomeratum</i> as a pathogen of <i>Q. ilex</i>, emphasizing the importance of phytosanitary monitoring in culturally and ecologically valuable green spaces.