When cork oak no longer persists: Susceptibility and ecophysiological responses of alternative Mediterranean species to Phytophthora cinnamomi in montado ecosystems

Mediterranean montado and dehesa ecosystems face escalating decline driven by the soilborne oomycete Phytophthora cinnamomi Rands, for which effective management strategies remain largely unavailable. Identifying woody species with reduced susceptibility is therefore critical for the management of affected areas. This study evaluated the susceptibility and ecophysiological responses of four Mediterranean species, Quercus suber L., the keystone species of montado systems; Pinus pinea L., an economically and silviculturally important Mediterranean pine; Ceratonia siliqua L., a deep-rooted xerophytic species; and Ficus carica L., traditionally present across the Mediterranean basin, to P. cinnamomi, under controlled greenhouse conditions. Mortality, pathogen reisolation, biometric parameters, spectral vegetation indices, stomatal conductance (gsw) and chlorophyll fluorescence (ΦPSII) measurements were integrated into a Composite Impact Index (CII). Pathogen reisolation confirmed root colonization across all inoculated species, including F. carica (86.7%) and P. pinea (100%), indicating host tolerance rather than true resistance. Quercus suber showed the most severe physiological decline; C. siliqua displayed pronounced spectral and biomass reductions despite relatively preserved gas exchange; F. carica maintained growth and physiological function across treatments, although this controlled-condition tolerance may not persist under sustained field pressure; P. pinea showed intermediate responses. Species ranked by CII as: F. carica (CII = 3.5, Minimal) < P. pinea (CII = 56.1, Moderate) < C. siliqua (CII = 76.7, High) < Q. suber (CII = 94.7, Severe). These findings provide comparative evidence on species-level pathogen tolerance relevant to areas where P. cinnamomi has already compromised Q. suber viability, identifying F. carica and P. pinea as the species best suited to sustain ground cover and partial ecological function under such conditions.