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Corresponding author: Alistair R. McTaggart ( alistair.mctaggart@gmail.com ) Academic editor: Dominik Begerow
© 2017 Alistair R. McTaggart, Dean R. Beasley, Michael J. Wingfield, Alan R. Wood, Zakkie A. Pretorius, Andre Drenth, Roger G. Shivas, Jolanda Roux.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
McTaggart A, Beasley D, Wingfield M, Wood A, Pretorius Z, Drenth A, Shivas R, Roux J (2017) A dynamic, web-based resource to identify rust fungi (Pucciniales) in southern Africa. MycoKeys 26: 77-83. https://doi.org/10.3897/mycokeys.26.14602
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Rust fungi (Pucciniales) are some of the most important plant pathogens that cause diseases of agricultural and tree crops. There are approximately 8,000 described species worldwide. The rust fungi of South Africa were extensively studied by Ethel M. Doidge (1887 – 1965), who listed 468 species. Many nomenclatural and taxonomic changes, together with the discovery of new species and incursions of exotic species, have subsequently outdated Doidge’s monograph. To address this problem, we have developed an interactive Lucid key for the identification of 50 species of rust fungi in 17 genera from countries in southern Africa. The key is dynamic and may be updated in real-time. The Lucid key provides a platform to progressively provide descriptions and images for all rust fungi in southern Africa. Plant pathologists and mycologists are invited to participate in the development of this resource.
cybertaxonomy, key, Lucid, morphology, Puccinia porri , rust fungi, taxonomy, Uredinales
Rust fungi (Pucciniomycotina, Pucciniales) are highly specialized obligate plant pathogens. They cause some of the most important diseases of plants used for agriculture and forestry, as well as for natural ecosystems globally. There are approximately 550 species of rust recorded from southern Africa (
Subsequent to
Lists of species have two weaknesses for identification of taxa. Firstly, a list is outdated after any taxonomic change or new discovery. For example, since
Accurate identification of plant pathogenic fungi and the discovery of cryptic species has been advanced by molecular data (
A web-based resource to identify rust fungi by host and morphology in southern Africa is introduced in the present study. The resource is based around a Lucid key, freely available to all users. The key is dynamic, and can be updated according to taxonomic changes or the discovery of new taxa. The scientific community is invited to contribute specimens and images to the development of this key.
The first 50 species of rust that accompany the release of this key were collected from the Gauteng, KwaZulu-Natal, Limpopo and Mpumalanga provinces in South Africa, and from Botswana and Swaziland. Specimens were usually collected during field surveys of forestry plantations as well as in adjacent native or farmed vegetation. These 50 species are commonly encountered or important pathogens of trees in natural and planted forests, including Austropuccinia psidii, Phakopsora myrtacearum, Ravenelia macowaniana, Uromyces aloës and Uromycladium acaciae. Specimens were identified on the basis of their host and morphology of spores. In some cases molecular barcodes were used for identification. This is described below for the identification of Puccinia porri, and was published for identifications made in prior studies (
Spore stages, such as aeciospores, urediniospores and teliospores, were removed from host material with a scalpel, then mounted in clear lactic acid (100% v/v) on a microscope slide and gently heated. Slides were examined with a Leica DM 2500 compound microscope using differential interference microscopy and images were taken with a Leica DFC550 camera. Measurements of each examined spore stage were made from a minimum of 20 spores per specimen.
The approach to stacking multiple images follows that of
Host symptoms were photographed with hand-held digital cameras, for example a Coolpix Nikon S9300. Host symptoms of fresh leaf material were scanned on an Epson Perfection V700 flatbed scanner with a minimum resolution of 300 dpi. Images that were finally used for the website were selected based on their quality and diagnostic potential.
An interactive key, the Rust Fungi of Southern Africa, was built using Lucid 3.5.32 (http://www.lucidcentral.org). The dataset used for rust fungi had 93 features and 320 character states, which included the morphological features of all spore stages present on the examined specimens.
The key has been made publicly available at the following URL: http://collections.daf.qld.gov.au/web/key/africarust.
There are 50 taxa uploaded to the website. Two of these are species of Ravenelia that may represent new taxa. There are 18 genera on the website, of which Aecidium and Uredo are anamorphic genera used for species with unknown telial stages that have uncertain phylogenetic positions. The website contains 190 images, of which 38 are field shots, 48 are scanned host symptoms and 104 are spore stages taken from a light microscope.
A comprehensive list of rust fungi reported in southern Africa since
One taxon included in the Rust Fungi of Southern Africa is a new addition for the region. Puccinia porri, which was taxonomically resolved by
Identification of rust fungi is challenging for a number of reasons, including their complex lifecycles, multiple species on one host, multiple hosts and the fact that there are few contemporary resources with information about their biology and morphology. Furthermore, identification based on a molecular barcode is not always possible, as many species have not been sequenced. The Rust Fungi of Southern Africa is a web-based, interactive resource that allows users to identify taxa based on host range and morphology. The identification is supported by comparison to images of symptoms and spore stages made from reference specimens. It further acts as a real-time list of rust fungi in southern Africa.
Further diversity may be expected from cryptic species, which have been found in multiple genera of rust fungi on hosts in the Annonaceae (
Two rust fungi were recently described in southern Africa from agricultural and forestry hosts, namely Macruropyxis fulva on Saccharum and Phakopsora myrtacearum on Eucalyptus (
The Rust Fungi of Southern Africa is the second publicly released Lucid key to identify rust fungi. The Rust Fungi of Australia (available at: http://collections.daff.qld.gov.au/web/key/rustfungi) currently contains 122 species (
We thank the members of the Tree Protection Co-operative Programme (TPCP), the THRIP initiative of the Department of Trade and Industry, and the Department of Science and Technology (DST) / National Research Foundation (NRF) Centre of Excellence in Tree Health Biotechnology (CTHB) for financial assistance that made this study possible. The authors have no conflict of interest to declare.