Colletotrichum acutatum is an economically important fruit rot pathogen in strawberry. At the molecular level, little is known about the infection. In my PhD study, I therefore set to comprehensively understand the interaction between C. acutatum and strawberry fruits by applying multiple omic/high-throughput methods. As a novel approach, I linked transcriptomic, metabolomics and proteomic data and suggest new fungal pathogenicity related pathways to be involved in plant - fungal interactions. I also found that sesquiterpenoids produced by C. acutatum are important for the interaction.However, these bioactive compounds are also of interest to industry and when cultured in vitro, various sesquiterpenoids are secreted by fungus, including unknowns. In addition, I have functionally characterized the first sesquiterpene synthase (STS) of Colletotrichum sp. using yeast expression systems and multiple sesquiterpenoid products are formed by STS.Furthermore, molecular diagnostics and molecular phylogenetic analyses of herbaria specimens with Colletotrichum sp. symptoms and of isolates collected from multiple plant species, revise the history of C. acutatum in the Nordic countries.