A novel species of Microsphaeropsis causing cankers on Rafnia amplexicaulis in South Africa

Cankers leading to branch, stem and plant death were observed on the South African endemic Rafnia amplexicaulis ( Fabaceae ) in the Cederberg Wilderness Area, South Africa, during September 2021. Conidiomatal pycnidia were found developing on the cankers, and isolations consistently yielded a Microsphaeropsis species. Phylogenetic analysis based on partial nucleotide sequences of the internal transcribed spacers (ITS), the nuclear large subunit (LSU) and RNA polymerase II second largest subunit ( RPB2 ) regions showed that the fungus represented an undescribed species. Based on the multigene phylogeny and morphological characteristics, we describe the species here as M. rafniae sp. nov . Pathogenicity tests and the fulfilment of Koch's postulates confirmed that M. rafniae sp. nov . is the cause of the cankers of R. amplexicaulis . Presently, this disease is known from a single location in South Africa, and further surveys are required to determine its distribution and relative importance.