Where are the basal fungi? Current status on diversity, ecology, evolution, and taxonomy

Abstract

To date, the majority of mycological studies are focused on Ascomycota and Basidiomycota. Research on basal fungi is rather limited with an obvious scarcity of data. Classification of basal fungi has witnessed ongoing changes in the last few decades. There have been numerous taxonomic revisions, establishment of new phyla and debates on the possibility to exclude some basal lineages from the currently circumscribed fungal groups. Zoosporic phyla such as Rozellomycota, Aphelidiomycota and Chytridiomycota are characterized by zoospores, which are motile spores with a flagellum. The position of the first two within the fungal kingdom is currently being debated. Non zoosporic phyla are collectively called zygomycetous fungi and include Mucoromycota and Zoopagomycota. Basal fungi perform important ecological roles. Some groups of basal fungi control the population density of plankton, Oomycetes, aphids, and small invertebrates, while taking part in recycling of energy and matter in food webs. A few basal fungi are known for uptaking toxic heavy metals from the environment. The earliest basal fungi emerged just after the divergence of the nucleariid line of phagotrophs. Various taxonomic studies question the monophyly of some basal phyla, such as Chytridiomycota. Depending on the life mode of the fungi and whether motile or non-motile spores are produced, the isolation methods differ. For the culture of parasitic zoosporic fungi, co-culturing the fungi with their host is recommended while for saprobes ones, baits can be used. For zygomycetous fungi, common methods include dilution plating and direct inoculation. In this review, we pinpoint research gaps and discuss the current classification schemes along with information on evolution, diversity, current methods and challenges to isolate and culture basal fungi.