# Molecular investigation on hazelnut-associated Fusarium isolates belonging to the Fusarium citricola species complex

## TL;DR

This study investigates fungi associated with hazelnuts and finds they belong to a specific fungal complex, suggesting a need to reevaluate species boundaries.

## Contribution

The study provides a phylogenetic analysis and suggests reevaluating species boundaries in the Fusarium citricola complex using statistical methods.

## Key findings

- All hazelnut isolates belong to the Fusarium citricola species complex.
- Species boundaries within the complex may need reconsideration.
- Statistical methods help assess species reliability in related fungal complexes.

## Abstract

Recent studies on Fusaria associated with hazelnut have pointed out a role of these fungi as both disease agents and endophytic symbionts, raising concern for the possible mycotoxin contamination of kernels and derived products. Molecular evidence has shown that previous classifications of these isolates as Fusarium lateritium were incorrect, indicating that most of them instead belong to the Fusarium citricola species complex (FCCSC). Based on a set of isolates collected in Italy and Poland, the present work provides a phylogenetic analysis supported by three species delimitation algorithms. The results confirm that all the available hazelnut isolates belong to the FCCSC, and that the discrimination between three currently accepted taxa in this species complex, namely F. aconidiale, F. celtidicola and F. juglandicola, should be reconsidered. The inclusion in our analysis of 25 species identified in the closely related Fusarium tricinctum species complex provides an indication that the statistical methods for species delimitation represent a useful tool for checking the reliability of the species boundaries currently defined in these fungi.