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

Area of Science:

• Mycology and Plant Pathology
• Molecular Systematics
• Taxonomy and Phylogenetics

Background:

• Recent proposals advocate for a broad genus concept of Fusarium within Nectriaceae, potentially overlooking significant data.
• This broad concept disregards substantial evidence from morphology, biology, and phylogeny supporting distinct genera.
• A previous DNA phylogeny was presented to support a wide Fusarium circumscription (F1 node).

Purpose of the Study:

• To re-analyze existing DNA data and challenge the broad Fusarium genus concept.
• To establish a precisely delimited Fusarium (sensu stricto) based on robust phylogenetic and trait evidence.
• To introduce new genera and species, and provide tools for accurate identification of fusarioid taxa.

Main Methods:

• Re-analysis of a 19-gene orthologous protein-coding DNA dataset using various phylogenetic algorithms.
• Comparative analysis of morphological, biological, and biochemical traits distinguishing Fusarium from allied genera.
• Development of the Fusarioid-ID online database for identification, incorporating multiple gene sequences.

Main Results:

• Re-analysis confirms all 19 genes support the F3 node, representing Fusarium sensu stricto (based on F. sambucinum).
• Only six of 19 genes support the broad F1 node; alternative topologies were found, indicating deep divergence.
• Fusarium sensu stricto is characterized by Gibberella sexual morphs, specific macroconidia, and mycotoxin production, differentiating it from other genera.
• The broad Fusarium concept lacks clear synapomorphies and incorrectly includes genera with fusarium-like macroconidia.
• Four new genera, 18 new species, and 16 new combinations are introduced.
• The Fusarioid-ID database and a nomenclator of Fusarium names up to January 2021 are presented.

Conclusions:

• A precisely delimited Fusarium (sensu stricto) concept, supported by robust phylogenetic and trait data (F3 node), is strongly endorsed.
• The broad circumscription of Fusarium is scientifically untenable due to lack of synapomorphies and unresolved phylogenetic placements.
• This study provides a foundation for a new online monograph of Fusarium and related genera, enhancing taxonomic clarity and identification.