Ganoderma in South Africa
Article prepared by Dr Martin Coetzee
Ganoderma is a genus of wood-degrading fungi that grow on coniferous and hardwood trees. They are
frequently observed on trees in natural forests, plantation forests and gardens as large, perennial, woody brackets, also called "conks" (Fig. 1). The genus includes more than 80
species, many of them occurring in the tropical regions of the world.
Several Ganoderma species are important to a number of diverse industries. Some species occur as saprophytes, utilising dead wood as nutrient
source; these species are important to biopulping by virtue of their ability to produce enzymes that degrade lignin
and cellulose. Some species are also valued for their
medicinal properties and have been used in traditional Asian medicine for thousands of years. They are believed to have therapeutic effects on cancer, cholesterol, hypoglycaemia,
fungal infections and many other diseases or disorders. A number of Ganoderma species survive as phytopathogens, causing wood rot and eventually the death of infected
trees. Pathogenic species may cause extensive infection centres, leading to great financial losses to forestry industries due to the death of commercially grown trees. For
example, in Malaysia mortality of Acacia mangium due to G. phillippii has been estimated at up to 40% in severely infected plots.
On account of their importance to different industries, the taxonomy, distribution and host range of Ganoderma species have received much attention
by mycologists and plant pathologists world-wide. In South Africa, a number of Ganoderma species have been reported from various indigenous and introduced tree species, where
they give rise to Ganoderma root rot disease. The Ganoderma species most frequently linked with this disease in South Africa are G. lucidum and G. applinatum. It
is known, however, that these two species actually represent species complexes and may include several species not previously identified. Another gap in scientific knowledge of
Ganoderma relates to the fact that very little attention has been afforded to elucidating the species occurring in the rest of Africa. As a result, the taxonomic status and
the distribution of Ganoderma species on this continent are currently uncertain.
Because of the uncertainties described above, we have embarked on a research project to investigate the taxonomy of Ganoderma in South
Africa. This has led to a number of interesting discoveries to date. For example, the results of an investigation undertaken by Ms Vuledzani Muthelo showed that a Ganoderma
species similar to G. lucidum is causing root rot on Jacaranda trees in the Brooklyn suburb of Pretoria (Fig. 2). A number of these trees have died as a result of this
disease, and many more have been infected by the fungus since this research project commenced. A large number of Ganoderma samples were also collected from various hosts and
localities in South Africa by researchers in the DST/NRF Centre of Excellence in Tree Health Biotechnologgy (CTHB). Preliminary DNA sequence comparisons have revealed the presence of
Ganoderma species not previously reported from South Africa.
Future work on Ganoderma will focus on the species diversity of this genus in selected indigenous forests. Earlier this year, Prof. Jolanda Roux
was awarded a research grant from the South African Biodiversity Initiative (SABI) to investigate the systematics of a number of fungal genera, including Ganoderma, from natural
forests in South Africa. While the flora and fauna in these forests are well documented, little is known about their fungal diversity. We believe that information gleaned from
research projects funded by this grant will make a significant contribution to our understanding of the taxonomy and distribution of Ganoderma species in these forests.
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Fig 1 Typical fruit body (bracket) of a Ganoderma species growing on an infected tree. |
Fig 2 Jacaranda tree in Brooklyn, Pretoria, showing symptoms of Ganoderma root rot. |
