Secondary metabolites produced by Colletotrichum spp. on different olive cultivars
This study was aimed to characterize the secondary metabolites produced by four Colletotrichum species, C. acutatum, C. gloeosporioides, C. godetiae and C. karsti, both in vitro, on potato dextrose agar (PDA) and oatmeal agar (OA), and during the infection process of fruits of four olive cultivars differing in susceptibility to anthracnose, Coratina and Ottobratica, both susceptible, Frantoio and Leccino, both resistant. The metabolites were extracted from axenic cultures after seven days incubation and from olives at three different times, 1, 3 and 7 days post inoculation (dpi). They were identified using the HPLC-QTOF analysis method. In total, as many as 45 diverse metabolites were identified; of these 29 were detected on infected olives and 26 in axenic cultures on agar media (OA and PDA). Only 10 metabolites were present in both fruits and axenic cultures while 19 were found exclusively on olives and 16 exclusively in axenic cultures. The 45 identified metabolites comprised fatty acid, phenolics, pyrones, sterols, terpenes and miscellaneous compounds. Each Colletotrichum species produced a different spectrum of metabolites depending of the type of matrices. On artificially inoculated olives the severity of symptoms, the amount of fungal secondary metabolites and their number peaked 7 dpi irrespective of the cultivar susceptibility and the virulence of the Colletotrichum species. The metabolite profiles as represented by heat maps were the result of the interaction olive cultivar x Colletotrichum species.