Submitted to: Australasian Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2016
Publication Date: 1/25/2017
Citation: Martin, L.A., Lloyd Evans, D., Castlebury, L.A., Sifundza, J.T., Comstock, J.C., Rutherford, R.S., McFarlane, S.A. 2017. Macruropyxis fulva sp. nov., a new rust (Pucciniales) infecting sugarcane in southern Africa. Australasian Plant Pathology. 46(1):63–74. doi: 10.1007/s13313-016-0460-1. Interpretive Summary: Fungi can cause billions of dollars of plant damage and yield losses on many different crop plants. This research describes a new fungus causing a disease of sugarcane called tawny rust. This rust fungus was first observed in Swaziland, South Africa, and Mozambique in 2008 and can cause economic losses on susceptible varieties. Symptoms include bright orange pustules on both the lower and upper leaf surfaces. Using DNA sequences and spore characteristics, it was determined that this fungus had not been described previously and that it needed a new name. Tawny rust is currently a very serious economic threat to sugarcane in southern Africa and is a potential threat worldwide if it spreads to other sugarcane production areas in Africa, Asia, Australia and the Western Hemisphere. This report of tawny rust is significant because it is a new disease of sugarcane and its potential for spread and economic losses has not yet been fully determined.
Technical Abstract: An unknown species of rust was observed on sugarcane in Swaziland, South Africa and Mozambique in 2008. Infected sugarcane leaves showed typical rust symptoms on the lower and upper leaf surfaces. Uredinia appeared bright orange when fresh, releasing profuse, bright orange urediniospores easily distinguishable from Puccinia melanocephala, previously the only rust species known to infect sugarcane in southern Africa. Over time and with the dispersal of the urediniospores, the uredinia appeared dark reddish-brown, making diagnosis in the field more difficult. No identical matches were obtained from the NCBI database using sequences combining the ITS and 28S nuclear large subunit (nLSU) regions. 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 related were Aecidium klugkistianum, P. mysuruensis, and P. physalidis which infect species in the Oleaceae, Rubiaceae, and Solanaceae, respectively. This group of rusts is phylogenetically distinct from both Puccinia melanocephala and Puccinia kuehnii, the pathogens causing 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 infecting sugarcane is Macruropyxis fulva sp. nov., causal agent of tawny rust.