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The taxonomic status of Colletotrichum gloeosporioides sensu lato (s.l.) associated with olive anthracnose is still undetermined and the pathogenic ability of this species complex is controversial. In the present study, isolates obtained from olive and provisionally identified as C. gloeosporioides s.l. on the basis of morphological and cultural features were reclassified using ITS and TUB2 as DNA barcode markers and referred to seven distinct species, recently separated within C. gloeosporioides (C. aenigma, C. gloeosporioides sensu stricto (s.s.), C. kahawae, C. queenslandicum, C. siamense and C. theobromicola) and C. boninense (C. karstii) species complexes. Furthermore, isolates of C. kahawae were ascribed to the subspecies ciggaro by analysing the GS gene. A single isolate, not in either of these two species complexes, was not identified at the species level. In pathogenicity tests on detached olive drupes some of these species, including C. aenigma, C. kahawae subsp. ciggaro, C. queenslandicum, C. siamense and C. karstii, were shown to be weakly pathogenic. Moreover, they were found very sporadically on olive. In contrast, some isolates of C. gloeosporioides s.s. and isolates of C. theobromicola proved to be virulent on both green and ripening olives. This study gives a better insight into both the aetiology and the epidemiology of olive anthracnose and might have implications for biosecurity and quarantine because C. theobromicola has never been reported in major European olive-producing countries.

Summary The filamentous fungus Alternaria alternata is a potent producer of many toxic secondary metabolites, which contaminate food and feed. The most prominent one is the polyketide‐derived alternariol (AOH) and its derivative alternariol monomethyl ether (AME). Here, we identified the gene cluster for the biosynthesis of AOH and AME by CRISPR/Cas9‐mediated gene inactivation of several biosynthesis genes in A. alternata and heterologous expression of the gene cluster in Aspergillus oryzae. The 15 kb‐spanning gene cluster consists of a polyketide synthase gene, pksI, an O‐methyltransferase, omtI, a FAD‐dependent monooxygenase, moxI, a short chain dehydrogenase, sdrI, a putative extradiol dioxygenase, doxI and a transcription factor gene, aohR. Heterologous expression of PksI in A. oryzae was sufficient for AOH biosynthesis. Co‐expression of PksI with different tailoring enzymes resulted in AME, 4‐hydroxy‐alternariol monomethyl ether (4‐OH‐AME), altenusin (ALN) and altenuene (ALT). Hence, the AOH cluster is responsible for the production of at least five different compounds. Deletion of the transcription factor gene aohR led to reduced expression of pksI and delayed AOH production, while overexpression led to increased expression of pksI and production of AOH. The pksI‐deletion strain displayed reduced virulence on tomato, citrus and apple suggesting AOH and the derivatives as virulence and colonization factors.

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