PROGRESS TOWARDS CHARACTERIZING THE FACIAL ECZEMA CAUSING FUNGUS

Goal 1: Clarify the taxonomy of Pseudopithomyces chartarum (now P. toxicarius) and analyze the genetic composition of its mating type loci.

It was confirmed that the fungus responsible for facial eczema (Sporidesmin Induced Liver Disease) in South African livestock is Pseudopithomyces toxicarius, which produces the liver toxin sporidesmin A. Until recently, this fungus had been misidentified, but through analysis of 152 fungal strains from international collections and the generation of over 900 DNA sequences at FABI, the correct identity and presence of P. toxicarius in the Eastern Cape was confirmed.

In order to develop a targeted screening method for P. toxicarius, a PCR assay was used which can amplify regions of the NRPS gene which are connected with sporidesmin production. This method is now being used to screen Eastern Cape isolates to confirm toxin gene presence, supporting the toxin production findings. Isolates lacking the gene cluster may be selected for whole genome sequencing to better understand potential non-toxigenic variants.

Goal 2: Investigate whether Pseudopithomyces chartarum (now P. toxicarius) is seed-borne.

The concerns that the fungus might have been introduced through imported ryegrass seed was addressed by screening both local and imported seed samples from New Zealand and the Netherlands. The comprehensive testing using culture methods and DNA-based assays showed no evidence of P. toxicarius, confirming that the fungus is not seed-borne and unlikely to have arrived through international seed trade. This shifts the focus of disease control from import regulation to local environmental factors that promote fungal growth and toxin production.

Goal 3: Identify the predominant species and strains of Pseudopithomyces in the outbreak region.

Extensive fieldwork across five dairy farms in the Humansdorp region, although also substantially influenced by the outbreak of FMD, confirmed the year-round presence of P. toxicarius, with spore concentrations peaking in summer. The fungus was most prevalent in perennial ryegrass pastures, especially in areas exposed to western and northern winds. Phylogenetic analysis further confirmed that the isolates belonged to P. toxicarius.

Goal 4: Improve toxic pasture prediction through detection of Sporidesmin A and genetic insights.

The genetic studies revealed that both heterothallic and homothallic mating types are present among South African strains, indicating potential for sexual reproduction, although sexual structures have not yet been observed under laboratory conditions. Heterothallic implies more genetic diversity and faster adaptation, whereas homothallic implies limited genetic diversity and slower adaptation, but through this method a single introduction is sufficient to start a new outbreak. Understanding this reproductive potential is important for predicting how the fungus might persist or evolve in the field.