Macruropyxis fulva sp. nov., a new rust (Pucciniales) infecting sugarcane in southern Africa

Abstract

An unknown species of rust was observed on sugarcane in Swaziland and South Africa in 2008. Infected leaves showed rust-like symptoms on the abaxial and adaxial leaf surfaces. Uredinia appeared bright orange when fresh, releasing profuse, bright orange urediniospores, which distinguished it from Puccinia melanocephala, the only rust species known to infect sugarcane in southern Africa at that time. No identical matches were obtained from the NCBI database for the combined ITS and 28S nuclear large subunit (nLSU) regions for the unknown rust. Phylogenetic analyses based on the same gene region showed that this rust was closely related to Macruropyxis fraxini and Puccinia sparganioides, which infect Fraxinus spp. (Oleaceae). Also closely related were Aecidium klugkistianum, P. mysuruensis, and P. physalidis which infect host species in the Oleaceae, Rubiaceae, and Solanaceae, respectively. This group of rusts is phylogenetically distinct from both Puccinia melanocephala and Puccinia kuehnii, which cause brown and orange rust of sugarcane, respectively. Phylogenetic reconstruction showed that the unknown rust falls outside the Puccinia I and II clades and groups with the Macruropyxis clade with strong bootstrap support. Hence the name proposed for this newly discovered rust species is Macruropyxis fulva sp. nov., causal agent of tawny rust of sugarcane. A rust observed to be infecting Miscanthus ecklonii in 2016 matched the accessioned M. fulva sp. nov. sequences and was morphologically and genetically distinct from the Miscanthus rust Puccinia miscanthidii, providing evidence of an alternate host for M. fulva sp. nov.