Characterisation of New Zealand Fusarium populations using a polyphasic approach differentiates the F. avenaceum/F. acuminatum/F. tricinctum species complex in cereal and grassland systems

The purpose of this study was to determine the diversity and prevalence of Fusarium species in a survey of cereal and grassland systems from the South Island of New Zealand by applying morphological and molecular techniques. Isolates were collected from soil, roots, and stems from 21 cereal and grassland sites. Ten Fusarium species were identified using morphological characters, including F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. oxysporum, F. poae, F. pseudograminearum, F. sambucinum, and F. tricinctum. In general, their distribution was found to be unrelated to biogeographical location, although agricultural practice increased the overall diversity of Fusarium. Phylogenetic analyses were successfully used to identify morphologically similar isolates belonging to the F. avenaceum/F. acuminatum/F. tricinctum species complex and to resolve previously undetermined relationships amongst these species. Fifty-eight isolates classified as either F. avenaceum, F. acuminatum, or other closely related species as well as several well-characterised isolates from international culture collections were examined using DNA sequence data for β-tubulin (βTUB), translation elongation factor 1α (EF1α), and mitochondrial small subunit ribosomal RNA (mtSSU). Analyses of DNA sequence data from both βTUB and EF1α discriminated among isolates of F. avenaceum, F. acuminatum, and F. tricinctum and determined that these three distinct sequence groups formed a single clade. By contrast, mtSSU was unable to differentiate F. avenaceum from F. acuminatum and other closely related species believed to be F. tricinctum. Comparison of the EF1α sequences with the international FUSARIUM-ID database supported the identification of isolates in this study. As in other studies, F. avenaceum was found to be widespread in agricultural and native ecosystems. However, F. acuminatum in New Zealand was found only on non-wheat hosts. The reason for the absence of this wheat pathogen in cereal-based ecosystems in New Zealand remains unknown.