Abstract
Recent publications have argued that there are potentially serious consequences for researchers in recognising distinct genera in the terminal fusarioid clade of the family Nectriaceae. Thus, an alternate hypothesis, namely a very broad concept of the genus Fusarium was proposed. In doing so, however, a significant body of data that supports distinct genera in Nectriaceae based on morphology, biology, and phylogeny is disregarded. A DNA phylogeny based on 19 orthologous protein-coding genes was presented to support a very broad concept of Fusarium at the F1 node in Nectriaceae. Here, we demonstrate that re-analyses of this dataset show that all 19 genes support the F3 node that represents Fusarium sensu stricto as defined by F. sambucinum (sexual morph synonym Gibberella pulicaris). The backbone of the phylogeny is resolved by the concatenated alignment, but only six of the 19 genes fully support the F1 node, representing the broad circumscription of Fusarium. Furthermore, a re-analysis of the concatenated dataset revealed alternate topologies in different phylogenetic algorithms, highlighting the deep divergence and unresolved placement of various Nectriaceae lineages proposed as members of Fusarium. Species of Fusarium s. str. are characterised by Gibberella sexual morphs, asexual morphs with thin- or thick-walled macroconidia that have variously shaped apical and basal cells, and trichothecene mycotoxin production, which separates them from other fusarioid genera. Here we show that the Wollenweber concept of Fusarium presently accounts for 20 segregate genera with clear-cut synapomorphic traits, and that fusarioid macroconidia represent a character that has been gained or lost multiple times throughout Nectriaceae. Thus, the very broad circumscription of Fusarium is blurry and without apparent synapomorphies, and does not include all genera with fusarium-like macroconidia, which are spread throughout Nectriaceae (e.g., Cosmosporella, Macroconia, Microcera). In this study four new genera are introduced, along with 18 new species and 16 new combinations. These names convey information about relationships, morphology, and ecological preference that would otherwise be lost in a broader definition of Fusarium. To assist users to correctly identify fusarioid genera and species, we introduce a new online identification database, Fusarioid-ID, accessible at 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 as well as their current status, types, and diagnostic DNA barcode data. In this study, researchers from 46 countries, representing taxonomists, plant pathologists, medical mycologists, quarantine officials, regulatory agencies, and students, strongly support the application and use of a more precisely delimited Fusarium (= Gibberella) concept to accommodate 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) or Rectifusarium (F. ventricosum SC). The present study represents the first step to generating a new online monograph of Fusarium and allied fusarioid genera (www.fusarium.org).
Highlights
The relevance and impact of Fusarium (Ascomycota, Hypocreales, Nectriaceae) to humankind is substantial
In Minimum evolution (ME) analysis (Supplementary Fig. S3), we found that the backbone architecture is less solid than previously thought and a large monophyletic clade containing Neocosmospora, Albonectria, and several other genera formed as sister group to Fusarium s. str. with strong support
Generic delimitation of fusarioid taxa in Nectriaceae: The analyses included nectriaceous taxa historically ascribed to Fusarium s. lat., including several recently segregated fusarioid genera (Gr€afenhan et al 2011, Schroers et al 2011, Lombard et al 2015), cylindrocarpon-like taxa (Chaverri et al 2011), and the closely related – morphologically distinct – phylogenetic relatives Cosmospora and Mariannaea
Summary
The relevance and impact of Fusarium (Ascomycota, Hypocreales, Nectriaceae) to humankind is substantial. After an initial period of discovery and cataloguing by 19th century naturalists, its taxonomy became the target of research from a broad range of scientists, that resulted in the emergence of distinct “schools” that promoted different taxonomic approaches to fusarium-like organisms. With the advent of an objective and reproducible framework for phylogenetic relationships inferred from molecular phylogenetics, it might have been expected that controversies would melt away, and a stable, universally accepted taxonomy of Fusarium and its species would emerge, but this does not yet appear to be the case (Fig. 1). The generic treatment of Fusarium by Geiser et al (2013, 2021), produced an ill-delimited genus without clear synapomorphies, as fusarium-like macroconidia are strongly polyphyletic within Nectriaceae and occur outside their very broadly circumscribed Fusarium concept. We argue that a narrower concept of genera with a clear, unique combination of features is needed for the majority of fusarioid species
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