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

Abstract

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.