Sunburn-induced bark damage facilitates Eutypella decipiens infection of Carpinus betulus in Serbian urban landscapes.

European hornbeam (Carpinus betulus) is a significant component of urban green spaces in Serbia. Recently, a decline characterized by crown dieback and distinct spindle-shaped bark cankers has been observed in planted alley trees. This study aimed to identify the causal agent of these symptoms and investigate the role of environmental stressors in disease development. Field surveys were conducted in central Serbia, assessing the orientation and morphology of cankers. Following isolation and molecular identification, Eutypella decipiens (previously known as Anthostoma decipiens) was identified as the causal agent of bark cankers and the decline. Pathogenicity was tested using two-year-old C. betulus saplings inoculated with E. decipiens and, for comparison, Cryphonectria carpinicola, another bark pathogen on this host. Inoculation sites were monitored weekly for six weeks in a controlled glasshouse environment. Field observations revealed that cankers were exclusively located on the south and southwest sides of trunks, suggesting a correlation with sunburn damage. In pathogenicity trials, E. decipiens successfully colonized host tissues, with over 50% of plants exhibiting dieback symptoms within six weeks. The recorded necroses were on average 10.2 times longer and 22.9 times larger in area than the control. Necroses in the C. carpinicola treatment were smaller being 2.9 times longer and 6.1 times larger in area compared to the control. Our findings demonstrate that sunburn-induced bark damage may facilitate E. decipiens infection highlighting the enhanced vulnerability of urban C. betulus populations to synergistic climate-driven stressors. This study provides the first evidence of an abiotic-mediated infection pathway for this pathogen and represents its initial record within urban landscapes, extending its known range beyond the natural forests of Serbia. Implications of these findings and general recommendations to reduce the damage are discussed.