Bacterial Necroses and Stem Exudates on Young Urban Oak Plantings: First Record of Lonsdalea quercina Subsp. Britannica in Poland

Decline symptoms, including bark necrosis and dark stem exudates, were observed in newly planted pedunculate oak ( Quercus robur ) trees in an urban roadside site in Poland. Bacteria isolated from symptomatic tissues were characterised using biochemical tests and 16S rRNA gene sequencing. Among the isolates, strains putatively assigned to Lonsdalea quercina subsp. britannica and Brenneria goodwinii were recovered, co‐occurring within the same necrotic lesions. Pathogenicity tests performed on oak seedlings confirmed that L. quercina subsp. britannica induced necrotic symptoms and fulfilled Koch's postulates. This study represents the first preliminary record supported by phenotypic traits and 16S rRNA sequencing of this subspecies in Poland and extends its known distribution to urban environments in Central Europe. The results support the view that oak decline is associated with a polymicrobial complex and highlight the need for further research on the epidemiological role of L. quercina subsp. britannica , particularly under urban conditions where environmental stress may favour disease development.