The Fusarium incarnatum-equiseti, F. tricinctum , and F. nisikadoi Species Complexes in Korea: Taxonomy, Species Diversity, and Host/Substrate Records

The Fusarium incarnatum-equiseti species complex (FIESC), F. tricinctum species complex (FTSC), and F. nisikadoi species complex (FNSC) comprise diverse and taxonomically challenging groups associated with a wide range of plant hosts and environmental substrates. However, their diversity and host/substrate associations in Korea remain insufficiently documented. In this study, we re-identified 60 Korean isolates belonging to these three species complexes based on multilocus sequence data, using the translation elongation factor 1-α (tef1), RNA polymerase II second-largest subunit (rpb2), and calmodulin (CaM) genes for the FIESC and tef1, RNA polymerase II largest subunit (rpb1), and rpb2 for the FTSC and FNSC. As a result, 19 species were recognized among the re-identified isolates, comprising 11 FIESC, six FTSC, and two FNSC species. Among these, Fusarium diversum sp. nov., a new species in the FIESC, is described, and 10 species are newly recorded from Korea. Together with previously published records, a total of 28 species are documented in Korea, including 15 FIESC, 10 FTSC, and three FNSC species. In total, 154 fungus-host/substrate associations were documented, involving plant hosts, a brown alga, air, and various environmental substrates, with the FTSC accounting for the highest numbers of documented associations and host taxa, followed by the FIESC and FNSC. Of these, 53 associations are newly documented for Korea, expanding the known ecological associations of these species. Our results improve the understanding of the species diversity and host/substrate associations of the three Fusarium species complexes in Korea and provide an updated taxonomic framework for future studies of their distribution and ecology.