Preliminary red-list assessment: EN B2ab(i,ii,iii,iv) (Endangered)
This species is described as Sphacelotheca suddiana (Spooner 1984). Considering that the members of Sphacelotheca are restricted to host plants in the Polygonaceae, it was transferred to Ustilago (Vánky 2002).
Ustilago suddiana is a host specific smut fungus in the ovaries of Suddia sagittifolia (Poaceae), a remarkable aquatic plant with restricted distribution (Northeast & East Tropical Africa). Suddia sagittifolia is known only from South Sudan (the Sudd Swamps) and Uganda (three localities). This plant in itself is included in the IUCN Red List of Threatened Species, evaluated as VU D2 (Ali 2010).
Suddia sagittifolia is a well visible, perennial rhizomatous grass, with a stem 1.4–3 m high. In the Sudd Swamps, it was found for the first time in 1978. The known localities are situated in the northern, eastern, southern, and southeastern part of the Sudd. It is noteworthy that almost all collected and/or observed plants are sterile (consisting of vegetative organs only). Flowering inflorescences are collected only from the southern part of the swamps, near Jonglei village. In that location, all of the observed plants and collected individuals of S. sagittifolia (including these of the holotype and four of total five paratypes), were found to be infected with Ustilago suddiana (Renvoize et al. 1984; Spooner 1984). Thus the only location of U. suddiana in the Sudd Swamps is situated near Jonglei village.
In Uganda, Suddia sagittifolia is assessed as a regionally vulnerable plant, with three known localities: Victoria-Nile before joining Lake Albert, Lake Nakuwa (in the Kyoga Lake basin), and Lake Namabare (Lye et al. 2000). In the Kyoga Lake basin, S. sagittifolia is seen in a vegetative state at several sites while fertile plants are collected only from Lake Nakuwa (K. Lye, pers. comm.). The only Ugandan locality of Ustilago suddiana is situated in the easternmost part of the Lake Nakuwa where the smut fungus was collected for the first time in 1999 (Vánky et al. 2011).
In both locations, the host plant and its parasitic fungus are threatened by drought. In the Sudd Swamps location, the Jonglei Canal project is a threat (as an action that convert or degrade habitat in service of “managing” natural systems to improve human welfare) because it is expected that once completed and operated, it will reduce the Sudd wetland and associated floodplains. In the Lake Nakuwa area, aquatic macrophytes have been destroyed as a result of harvesting of papyrus and reclamation for agriculture. In the area of the Kyoga plains, it was found a strong reduction of the wetlands. These changes are attributable to the gradual substitution of traditional cropping systems with paddy rice and vegetable growing, both of which need wetlands. Most of the farmers there have resorted to use wetlands for crop farming due to declined fertility of the upland agricultural areas.
Preliminary red-list assessment: EN B2ab(i,ii,iii,iv) (Endangered)
This is an endangered parasitic fungus on a threatened plant species. Ustilago suddiana fulfills B-criterion using AOO (area of occupancy estimated not to exceed 500 km2) and meets EN B2, regarding subcriteria a (number of locations) and b (i, ii, iii & iv) (continuing decline – observed, inferred or projected – in the extent of occurrence, area of occupancy, area and quality of the habitat, and number of locations).
Ustilago suddiana is known to date only from two locations in the Nile Basin: the first is situated near Jonglei village (South Sudan, the Sudd Swamps), and the second, in the easternmost part of the Lake Nakuwa (Uganda, Kyoga Lake basin, near Busulumba, alt. ca. 1000 m) (Spooner 1984; Vánky 2011; Vánky et al. 2011).
There is no specific information on population size or trends. However, the host plant has limited distribution and is restricted to an area subjected to ongoing threats: drought, the Jonglei Canal project, agriculture, reclamation of wetlands for agriculture, and harvesting of papyrus.
Population Trend: Deteriorating
The sori of Ustilago suddiana are developed within the ovaries of Suddia sagittifolia. The fungus is host-specific and depends on its host plant.
Suddia sagittifolia is a very high (up to 3 m), perennial aquatic plant, with rhizomes, forming large patches among papyrus sedge. In the Sudd Swamps, larger and more widespread patches of infected Suddia sagittifolia are observed on the landward side of permanent swamps, usually in areas which bear a mosaic of patches of Vossia cuspidata, Cyperus papyrus, and Typha domingensis. Such areas are usually inaccessible but can be reached on foot at the end of the dry season in years of low river flood. Most of the sites occupied by S. sagittifolia are thus permanently wet, with a highly organic soil, underlain by sandy clay in the swamp margin sites (Renvoize et al. 1984).
The host plant and its parasitic fungus are threatened by drought (International Resources Group 2007: 47; Turyahabwe et al. 2013). Regarding the Sudd Swamps location, although the Jonglei Canal project is currently stopped, the Jonglei Canal continues to be a potential threat because it is expected that once completed and operated, it will reduce the Sudd wetland and associated floodplains (International Resources Group 2007: 45; Ali 2009: 491). The South Sudanese locality of Ustilago suddiana is situated in the southern part of the swamps, from the side of the channel. The political factor may be added, as a contributing factor. In the Lake Nakuwa area aquatic macrophytes have been destroyed, as a result of harvesting of papyrus and reclamation for agriculture (Byarunhanga & Kigoolo 2005). In Uganda, for the period 1994–2009 a loss of 30% of the country’s wetlands was reported by WMD (2009). Specifically in the area of the Kyoga plains, reduced wetland cover changes are attributable to the gradual substitution of traditional cropping systems with paddy rice and vegetable growing, both of which need wetlands. There the most farmers have resorted to use of wetlands for crop farming due to declined fertility of the upland agricultural areas (Turyahabwe et al. 2013).
The locality of this smut fungus near Jonglei village is not included in a protected area. The second locality is situated in the Lake Nakuwa Wetland System which is listed as a wetland of international importance under the Ramsar Convention (Ramsar Site).
Conservation of the host plant is needed. Ex situ conservation of the plant will not necessarily protect the fungus: in situ conservation is needed.
Further information is needed about population levels of the fungus.
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WMD. 2009. Mapping a Better Future: How Spatial Analysis Can Benefit Wetlands and Reduce Poverty in Uganda. Wetlands Management Department, Ministry of Water and Environment.
Denchev, C.M. & Denchev, T.T. 2015. Ustilago suddiana (Spooner) Vánky. In: The Global Fungal Red List Initiative. http://iucn.ekoo.se/iucn/species_view/484829/.