Fungal flora from Tunisian olives carposphere: diversity and volatile organic compounds

Plant phyllosphere is an enormous environment on Earth densely colonized by microorganisms. Those microbiomes play essential roles in processes related to plant development and pathogen defense. They release different metabolites working as interspecies messages in the environment. Volatile organic compounds are among those released messages. Among the worldwide phyllosphere, oliveyards are widely spread in the Mediterranean basin. Like all foods, olives and oil quality begin in the field. Fungal microbiomes through their interactions with olives trees could have an impact on oil quality. In this work we were interested on fungal microbiomes from olives carposphere. Fifteen Tunisian fields from four climatic regions were studied. Fungi were isolated and identified to species with microscopic and molecular techniques. Their aromatic profiles were analysed by solid-phase micro-extraction (SPME) coupled to gas cromatography and mass spectrometry. Results showed that genus Penicillium (P. polonicum, P. crustosum and P. expansum) was predominant. The major volatiles identified were: Styrene, 1-octen- 3-ol, 3-octanol, 3-octanone, 1,8-cineole. Styrene is a volatile hydrocarbon reported as 80 times more toxic than the volatile phase of toluene. The following three are oxylipins. They play essential roles in fungal morphogenesis and pathogenesis and are reported as metabolites with musty and earthy characteristics able to induce mycotoxin production. The last one is a terpene with a eucalyptus herbal camphor odor note. Could those volatiles be found on olives and olive oils? Could they impact chemical and sensory olive oils qualities? Could they induce mycotoxin production in olive oils? All those questions still to be answered