Update of Oak Decline in Apulia Region (Southern Italy).

Quercus ilex plays a pivotal role in Mediterranean agroecosystems due to its ecological, ornamental, and landscape value, both in urban settings and natural environments. However, over the past decade, a slow and progressive decline of numerous trees has been observed across various forest, urban and periurban ecosystems in the Apulia region (southern Italy). In response to these observations, systematic sampling campaigns were conducted to investigate the potential biotic causes of this phenomenon. Morphological and molecular analyses revealed the presence of several xyleminhabiting fungi, notably Diplodia corticola, a well-known pathogen associated with branch cankers and decline in Quercus spp. In addition, bacterial isolates belonging to Brenneria and Gibbsiella genera, were also recovered from symptomatic tissues. Concurrently, the presence of phytophagous insects, particularly Kermes vermilio and Nidularia pulvinata (Hemiptera: Kermesidae) and xylophagous pests belonging to Cerambycidae and Buprestidae (Coleoptera) families, were frequently recorded from holm oak trees in urban and forest areas, suggesting a potential synergistic role in weakening host trees. Given the complex aetiology of the observed decline, ongoing studies are examining climatic data to assess the correlation between seasonal meteorological patterns, such as drought stress during dry summers and symptom fluctuation in natural Mediterranean scrub during winter. These preliminary findings support the hypothesis that holm oak decline in Apulia results from a multifactorial disease complex involving pathogenic fungi, phytophagous and xylophagous insects, and abiotic stressors, rather than a single causal agent.