Fusarium: more than a node or a foot-shaped basal cell

Authors: CROUS, PEDRO - Fungal Biodiversity; LOMBARD, LORENZO - Fungal Biodiversity; SANDOVAL-DENIS, MARCELO - Fungal Biodiversity; SEIFERT, KEITH - Agriculture And Agri-Food Canada; SCHROERS, HANS-JOSEF - Agricultural Institute Of Slovenia; CHAVERRI, PRISCILA - University Of Maryland; GENE, JOSEPA - University Rovira I Virgili; Salgado-Salazar, Catalina

Submitted to: Studies in Mycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2021
Publication Date: 8/17/2021
Citation: Crous, P.W., Lombard, L., Sandoval-Denis, M., Seifert, K.A., Schroers, H., Chaverri, P., Gene, J., Salgado-Salazar, C. 2021. Fusarium: more than a node or a foot-shaped basal cell. Studies in Mycology. 98:100116. https://doi.org/10.1016/j.simyco.2021.100116.
DOI: https://doi.org/10.1016/j.simyco.2021.100116

Interpretive Summary: The fungal genus Fusarium (Ascomycota, Hypocreales, Nectriaceae) includes many important animal, human, and plant pathogens. However, there has been much controversy over how many species belong in this genus and whether it should be split into multiple genera. After an initial period of discovery and cataloging by 19th century naturalists, different schools of thought emerged that promoted different taxonomic solutions for fusarium-like organisms. With the arrival of an objective and reproducible framework from molecular phylogenetics, controversies regarding the accepted taxonomy of Fusarium and its species have continued. This manuscript proposes solutions with the aim of promoting stability for the names of this important group of fungi. This will enable plant pathologists and others to communicate accurately about pathogens among this group of fungi, enhancing the ability to manage diseases caused by these fungi.

Technical Abstract: Publications by O’Donnell et al. (2020; MSphere 5:e00810-20) and Geiser et al. (2021; Phytopathology: doi.org/10.1094/PHYTO-08-20-0330-LE) argue that there are potentially serious consequences for researchers in recognising distinct genera in the terminal clade of Nectriaceae, for which they prefer to retain a paraphyletic concept of the genus Fusarium. In doing so, however, they disregard a significant body of data that support distinct genera in Nectriaceae based on morphology, biology, and phylogeny. To argue a case for a very broad concept of Fusarium , they presented a DNA phylogeny based on 19 orthologous protein-coding genes in support of the F1 node in Nectriaceae, which is where they prefer to pin their concept of Fusarium. Reanalyses of their dataset show that all 19 genes support the F3 node representing Fusarium sensu stricto as defined by F. sambucinum (sexual morph synonym Gibberella pulicaris). However, only six of the 19 genes fully support the F1 node, representing Fusarium sensu lato. Species of Fusarium s. str. are characterised by Gibberella sexual morphs, asexual morphs with thin- or thick-walled macroconidia showing variously shaped apical and basal cells, and trichothecene mycotoxin production, separating it from other fusarioid genera. In this study we show that the Wollenweber concept of Fusarium presently accounts for 20 segregate genera, and that fusarioid macroconidia represent a character that has evolved multiple times throughout Nectriaceae . In this study four new genera are introduced, along with 18 new species and 16 new combinations. These names convey information about relationships and behaviour that are lost in a broader definition of Fusarium with much greater diversity of ecological and biochemical behaviours. To assist users to correctly identify the genera and species, we introduce a new online identification database, Fusarioid-ID (www.fusarium.org). The database comprises partial sequences from multiple genes commonly used to identify fusarioid taxa (act1, CaM , his3 , rpb1 , rpb2 , tef1 , tub2 , ITS and LSU). In this paper we also present a nomenclator of names that have been introduced in Fusarium up to January 2021 and, their current status, types and diagnostic DNA barcode data. Researchers from 46 countries, representing plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students and researchers, strongly support the application and use of a more narrowly defined Fusarium (= Gibberella) concept for accommodating taxa from the robust monophyletic node F3 on the basis of a well-defined and unique combination of morphological and biochemical features. This F3 node includes, among others, species of the F. fujikuroi, F. incarnatum-equiseti, F. oxysporum, and F. sambucinum species complexes, but not species of Bisifusarium (F. dimerum species complex (SC)), Cyanonectria (F. buxicola SC), Geejayessia (F. staphyleae SC), Neocosmospora (F. solani SC) and Rectifusarium (F. ventricosum SC). The present study represents the first step in generating a new online monograph of Fusarium and allied fusarioid genera (www.fusarium.org).