FABI Articles : A fungus from Africa threatens our Eucalyptus plantations

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.

Figure 2 Bar = 0.1mm

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 cubensis. 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 (Figure 1). In South Africa, this fungus causes severe cankers on Eucalyptus trees and on ornamental Glory Bush trees (Figure 2A) that are commonly planted in gardens. These Eucalyptus trees are 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 and slightly 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.

A fungus from Africa - Image 2
Figure 2. (A) Glory Bush tree (B) Waterberry tree (C) Waterberry seeds (D) Waterberry flower.

Chrysoporthe canker 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 country.

1. 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.