Brenneria goodwinii and Gibbsiella quercinecans as a Threat to Quercus coccifera L.

Acute Oak Decline (AOD) is a complex and rapidly progressing disease affecting several Quercus species across Europe. While previously reported in Quercus ilex in Italy, this study provides the first evidence of AOD symptoms and associated bacterial infection in Quercus coccifera (kermes oak). Symptomatic trees were identified in a Mediterranean forest in southern Italy, and bacterial isolation, qPCR detection, and 16S rRNA sequencing confirmed the presence of Brenneria goodwinii and Gibbsiella quercinecans. Phylogenetic analyses clustered the isolates closely with known AOD-related strains. Pathogenicity tests on excised Q. coccifera branches demonstrated that both bacteria induced wood necrosis and external exudates consistent with natural symptoms, confirming their virulence. These findings expand the known host range of AOD-related bacteria and highlight the potential threat to Mediterranean oak ecosystems. Early detection and monitoring of Q. coccifera decline are essential to inform conservation strategies and forest management practices aimed at mitigating AOD spread.