What They Did
The researchers carried out a genetic comparison of fungus
species in or closely related to the genus Fusarium in the family
Nectriaceae. In addition to the 236 genomes already available, they sequenced
another 40 from a variety of genera for a more representative sample of the
family. A fungus in a related family was used as the outgroup, expected to be
similar to the ancestral state of Nectriaceae.
By comparing 263 genes that were present in all the genomes,
they determined which genomes were most similar and therefore more likely to
represent closely related species. They found that the species within the Fusarium
genus were in fact more genetically similar to each other than to members
of other genera and that accepted taxonomic groups within the genus also
largely matched the genetic relationships.
The fungi in the family Nectriaceae have a variety of
survival strategies: many primarily live on or in plants; a handful are insect
symbiotes; several are saprotrophs that digest decaying organic matter; and a
few live primarily on other fungi or on animals. The researchers concluded that
the common ancestor of all Fusarium species was likely a plant pathogen.
Although some members of the genus do grow inside plants without causing
disease, they may become harmful if the environment changes. The common
ancestor of Fusarium and closely related genera was probably either a
plant pathogen or a saprotroph, but since the earliest diverging groups are
saprotrophs, the researchers believe that to be the more likely ancestral
niche.
Further Exploration
The authors mentioned that the species Fusarium
xyrophilum produces pseudoflowers on plants in the genus Xyris. It
grows within the plant and causes sterility, then forms fruiting bodies that
look like the flower petals (see https://www.ars.usda.gov/news-events/news/research-news/2020/fungus-commits-floral-fraud-to-fool-insects-into-spreading-it/.)
Not only does it look like a flower to human eyes, but it also reflects
ultraviolet light for insects and produces an attractant chemical. The insects
that are normally pollinators of Xyris land on the fungus and carry
spores to new hosts.
There’s also a Fusarium that’s an animal pathogen,
aptly named F. veterinarium. I couldn’t find much information about it;
apparently it was only described in 2018 (see https://wi.knaw.nl/details/89/567135.) Several other Fusarium species,
however, can cause animal diseases (see https://www.midogtest.com/blog/impacts-of-the-pathogenic-fungus-fusarium-in-animals/.)
Of the animal pathogens on the linked site, F. oxysporum is closely
related to F. veterinarium, so it’s not surprising that it can affect
animals, even though it’s primarily a plant pathogen. Fusarium
verticillioides, F. graminearium, and F. solani are also
primarily plant pathogens, though F. solani is now in the genus Neocosmospora.
Fusarium culmorum is primarily a saprotroph.
Fungi used to have different names for the sexual and
asexual forms, which made sense because they can look different and even
produce different types of spores. It’s not quite like the alternation of
generations in plants, with a regular switch between sexual and asexual forms.
Instead, the type of reproduction is determined by environmental conditions.
There are a lot of details about how sexual reproduction works in fungi, but
that’s a rabbit hole for another day!
https://commons.wikimedia.org/wiki/File:Culture_soil_fungus_Fusarium_sp._with_purple_color.jpg
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