Biocontrol Agents for Disease Management in Mediterranean Agroforestry Species Within the Genus Quercus: Holm, Cork, Lusitanian and Pyrenean Oaks

Mediterranean agroforestry systems (AFSs), typified by the Iberian Dehesas and Portuguese Montados, are multifunctional landscapes where Quercus species act as ecological keystones sustaining biodiversity, soil fertility, and rural livelihoods. These systems are increasingly affected by complex oak decline syndromes driven by drought, soil degradation, and climate-induced pathogen outbreaks. Conventional chemical controls are often ineffective and environmentally detrimental, underscoring the need for ecologically sound management alternatives. This review synthesizes recent advances in the application of microbial biological control agents (MBCAs) to manage diseases in Mediterranean Quercus species, including Q. ilex, Q. suber, Q. faginea, and Q. pyrenaica. We conducted a structured literature review using predefined keyword searches in Web of Science and Scopus, followed by the screening of records to identify 22 relevant peer-reviewed studies on microbial disease control in Mediterranean Quercus species. We identified 20 peer-reviewed studies that reported that MBCAs—primarily from Bacillus, Serratia, Streptomyces, Trichoderma, Simplicillium and Alternaria—exert biocontrol effects through antibiosis, mycoparasitism, competition for ecological niches, and the induction of host defense responses. Although most experiments were conducted in vitro, some demonstrated significant disease suppression in seedlings infected by Phytophthora cinnamomi, Diplodia corticola, and Biscogniauxia mediterranea. Future research should integrate field-based validation and microbiome-oriented forest management approaches to enable the operational use of microbial-based disease control strategies in AFS landscapes.