Physiological and biochemical responses of olive fruit to Colletotrichum spp. infection: a metabolomic insight

Olive anthracnose, primarily caused by species of the genus Colletotrichum, represents a serious threat to olive production, with variable impacts depending on both host cultivar and pathogen virulence. This study aimed to investigate the physiological and biochemical responses of three olive cultivars, ‘Ottobratica’, ‘Dolce Agogia’, and ‘Leccino’,to infection by four Colletotrichum species: C. acutatum, C. gloeosporioides, C. godetiae, and C. karsti. Pathogenicity assays on detached drupes were conducted under controlled conditions to evaluate differences in susceptibility among the cultivars. Physiological traits, including chlorophyll a, chlorophyll b, and total carotenoid concentrations, were measured at different time points after inoculation. To monitor oxidative stress and metabolic adjustments, biochemical responses were assessed through quantification of malondialdehyde (MDA), via the reaction of thiobarbituric acid (TBA), hydrogen peroxide (H2O2), determined with a UV–VIS spectrophotometer method, and soluble sugars, determined with the phenol-sulfuric acid method. Results revealed significant variability in disease severity and physiological responses among cultivar–pathogen combinations. ‘Ottobratica’ was the most susceptible, with a Disease Severity Index of 100 % at 168 h post-inoculation with C. acutatum, the most aggressive species while C. karsti the least virulent one. ‘Leccino’ showed the highest tolerance. ‘Dolce Agogia’ exhibited elevated constitutive levels of photosynthetic pigments and the most pronounced increase following infection, whereas ‘Leccino’ showed the lowest, suggesting cultivar specificity in response to infection. Oxidative stress markers indicated strong early responses, particularly in infections by C. acutatum and C. gloeosporioides. Sugar levels also showed noticeable variations depending on olive cultivar/fungal species binomial. These findings highlight the cultivar-dependent nature of olive responses to Colletotrichum infection and provide metabolomic insights that may support the development of targeted, eco-friendly disease management strategies.