Fungal endophyte communities in olive fruits: effect of maturation index and anthracnose incidence

Olive anthracnose, caused by different species of Colletotrichum genus, is considered as one of the most economically harmful fruit disease of olive crop worldwide. In Trás-os-Montes region (Northeast of Portugal), although the presence of the pathogen has been reported on olive orchards in almost all areas, lower levels of incidence were observed in specific areas. This work evaluated the diversity of endophytic fungi inhabiting fruits of the susceptible-anthracnose cultivar Madural, in olive groves from areas of high and low anthracnose incidence, in order to evaluate differences in the endophytic community composition. For this, fungi were isolated from symptomless olive fruits at three different maturation index (MI). The isolates were identified by rDNA sequencing. Overall, the frequency of colonization and abundance of endophytes was higher in areas with high anthracnose incidence (12.4%; 78) when compared to areas with low incidence (7.3%; 46). Despite this, the composition of fungal communities in both areas was very similar, being the genera with the greatest abundance Trametes (33%), Alternaria (43%) and Neofabraea (26%). Over fruit maturation, the frequency of colonization, abundance and diversity of endophytes increased significantly and progressively up to 16.0-, 6.0- and 8.0-fold, respectively. Although endophytic community of the three MI was found to overlapped, several fungal genera preferred either olives from MI2 (e.g. Apodospora, Hyalodendriella, Pyrenochaeta), or from MI3 (e.g. Mollisia, Ulocladium) or MI4 (Colletotrichum, Epicoccum). In addition to providing insights into fungal endophyte community structure, our survey provides candidates for further evaluation as potential management tools against olive anthracnose disease.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013). The first author also thanks the award of a PhD Scholarship (ref. SFRH/BD/112234/2015) by FCT