Global diversity analysis of plant-associated Pseudopithomyces fungi reveals a new species producing the toxin associated with facial eczema in livestock: Pseudopithomyces toxicarius sp. nov.

Facial eczema (FE) in ruminants is associated with the fungal toxin sporidesmin that can cause significant mortality in grazing livestock. Incidences are particularly severe in New Zealand but are reported worldwide. The syndrome has historically been attributed to Pithomyces chartarum, a species transferred to Pseudopithomyces in 2015, but the classification of many other Pithomyces species remains unresolved. In this study we investigated the taxonomy of Pseudopithomyces using modern species concepts and clarified which species make sporidesmin. Fungal isolates were cultured from grass samples obtained from New Zealand farms and roadside collections in 2014–2022. International isolates, including all available types, and historic isolates deposited in the International Collection of Microorganisms from Plants (ICMP) were also evaluated. Phylogenetic analyses of the ITS region plus four concatenated protein coding genes distinguished 15 species in the genus. We describe Pseudopithomyces toxicarius sp. nov. as a novel sporidesmin producing species, most formerly identified as Pse. chartarum, with 80 % of isolates in this study able to produce the toxin. Two Pithomyces species are combined into Pseudopithomyces as Pseudopithomyces cynodontis comb. nov. and Pseudopithomyces pavgii comb. nov. We also place Pseudopithomyces pandanicola in synonymy with Pseudopithomyces palmicola. Pithomyces terricola is reclassified into the family Longipedicellataceae as Pseudoxylomyces terricola comb. nov. Pseudopithomyces chartarum was the only other species where sporidesmin was detected, but this was found in only one of 14 isolates we tested. The extent of sporidesmin synthesis in this genus remains to be determined due to the limited availability of strains for testing in other species. Analysis of single nucleotide polymorphisms from whole genome Illumina sequences of isolates from Pse. toxicarius, Pse. chartarum and Pse. palmicola revealed distinct genetic subclades within each species. Four species were detected in New Zealand. Pseudopithomyces toxicarius and Pse. chartarum were recovered from grass samples collected from the North and South Islands, Pse. palmicola ICMP 12878 was recovered once from pasture at a North Island research station in 1993, and Pseudopithomyces sp. ‘gladiolus NZ’, which is currently undescribed. No species were unique to New Zealand, suggesting widespread global distribution.