Fungi, best known as the group of organisms that include mushrooms, are
known for their beautiful and colourful fruiting bodies that we see in our
gardens and our forest floors. Many fungi are, however,
inconspicuous and much less obvious, although equally beautiful.
While most are friends, some of these fungi are destructive plant killers and
these seriously threaten South Africa's agricultural and forestry crops.
An example of one of these fungi is the one that causes the stem disease
known as Cryphonectria canker. This is one of the most important
pathogens of plantation-grown Eucalyptus
trees (Gum trees) in tropical
and sub-tropical regions of the world. For many years, the disease
was reported to be caused by the fungal pathogen known as Cryphonectria
. Recent studies, genetic information and comparisons
of this fungus from various parts of the world, have shown
differently. We now know that the fungus in South Africa is
actually not the well known Cryphonectria cubensis
that occurs in
countries such as Brazil and Indonesia, but is rather a novel South African
fungus, which we have named Chrysoporthe austroafricana
1). In South Africa, this fungus causes severe cankers on
trees and on ornamental Glory Bush trees (Figure 2A) that are
commonly planted in gardens. These Eucalyptus
native to Australasia and the Glory Bush is native to relatively high elevation
areas of South America. A fascinating discovery emerging from our
research is that Chrysoporthe austroafricana
occurs on native
Waterberry trees (Syzygium cordatum
) (Figure 1 B, C, D) in South
Africa. This tree is related to Eucalyptus
more distantly to the Glory Bush. Our recent research has provided
strong genetic evidence to show that the fungus is almost certainly native to
South Africa. It has made the uncanny jump, what we call in
scientific terms a host jump, to non-native plants that we grow for timber
production or for the beautification of our gardens.
Figure 2. (A) Glory Bush tree (B) Waterberry tree (C) Waterberry seeds (D)
on Eucalyptus trees in South Africa can cause serious economic losses to
the forestry industry and our research team at FABI has many studies to reduce
its impact. However, perhaps more perplexing is the fact that an
entirely new disease of Eucalyptus has emerged in the world. The fungus
that causes the disease can very easily be moved accidentally to Australia where
Eucalyptus are native an the result could be disastrous for the
biodiversity of that country. Every effort must be made to prevent
it from moving to other parts of the world. At the same time,
substantial efforts are needed to protect Eucalyptus in South Africa from
being damaged and reducing the profitability of forestry in this
Myburg H, Gryzenhout M, Heath R, Roux J, Wingfield BD, Wingfield MJ (2002).
Cryphonectria canker on Tibouchina in South Africa. Mycological
Research 106, 1299-1306.
Heath, R.N., J. Roux, M. Gryzenhout, A.J. Carnegie,
I.W. Smith and M.J. Wingfield. 2007.
Holocryphia eucalypti on Tibouchina urvilleana in Australia.
Australasian Plant Pathology 36: 560-564.