Faculty of Natural and Agricultural Sciences
School of Biological Sciences
Department of Microbiology and Plant Pathology
Selected Highlights from Research Findings
Diseases of trees may result in their extinction, especially in the case of introducted pathogens. Alternatively, they lead to thousands of rands of losses to industry and private farmers. Fungal and bacterial pathogens, causing these diseases, are easily spread between countries. It is, therefore, of crucial importance to South Africa to know the exact situation regarding tree health in our neighboring countries so that we can more effectively manage new incursions and learn from our neighbours about managing these exotic pests and pathogens.
Prof Jolanda Roux of the Tree Protection Co-operative Programme (TPCP) at the Forestry and Agricultural Biotechnology Institute (FABI) undertook two research and survey visits to Eastern and Southern African countries in 2004. These two trips was a follow-up from two similar trips in 2003. Visits were made to Forestry Research Organizations and private companies in Mozambique, Zimbabwe, Malawi, Tanzania, Kenya and Zambia. The visits were done by road, using a vehicle sponsored by THRIP, to facilitate travel and survey work in the countries visited and enable participation by post-graduate students. A number of articles co-authored by researchers from the respective organizations will appear in the international press in 2005.
Contact person: Prof J Roux.
Prof Teresa Coutinho and Dr Fanus Venter from the Department of Microbiology and Plant Pathology and FABI have a collaborative project with the Laboratorium voor Microbiologie at the University of Ghent, jointly funded by a Flemish/South African Government agreement. The project has focused on an economically important phytopathogenic bacterium, Pantoea ananatis, in South Africa with the primary objective to develop a rapid, reliable diagnostic method for distinguishing P. ananatis from the other six species and two sub-species in the genus. The results were presented at a one-day workshop in Ghent in late 2004 and the funding has now been extended for a further two years.
Contact person: Prof TA Coutinho.
Cryphonectria canker is one of the most serious diseases of Eucalyptus in South Africa. The disease has been known in the country for approximately 15 years and it is reasonably clear that it was not a problem prior to this time. Cryphonectria canker also occurs almost predominantly in warmer, sub-tropical regions of South Africa. Recent research conducted in this programme has focused on the distribution of the disease. Predictions have also been made concerning global warming and the likely extension of the range of this disease if temperatures in the country were to rise.
Intriguing and important results have continued to emerge concerning the origin of the Cryphonectria canker pathogen. This disease agent has been known in South Africa as Cryphonectria cubensis and the assumption has been that it was introduced into the country, either from Latin America or from South East Asia. During the last few years research in this programme has accumulated increasing evidence that the pathogen is native to South Africa. This has led to a change of name for the pathogen that is now known as Chrysoporthe austroafricana. The implications of this work are very significant. Certainly there is evidence to show that the fungus is more pathogenic than the fungus now known as Chrysoporthe cubensis. This fungus threatens Eucalyptus forestry in other parts of the world, including native Eucalyptus, potentially other Myrtaceae, in countries such as Australia. There is also a great danger of Chr. Cubensis being introduced into South Africa, and clearly all breeding and selection work done up until now is against a pathogen native to the country and will probably not apply to Chr. Cubensis.
Discovering that Chr. Cubensis (formerly C. cubensis) does not occur in South Africa has raised the question of the origin of this fungus. This is important to South Africa because such knowledge will increase our capacity to exclude the fungus from the country. Some early evidence has suggested that the origin of the pathogen might be South America, and that the fungus of the same name in South East Asia might represent a different species. As a result of research with a student from Colombia, we have gained added information supporting the view that Chr. Cubensis is probably native in South America. This work is not complete and is being continued through additional collections and intensive DNA sequence comparisons.
Contact person: Prof MJ Wingfield.
One of the more fascinating but worrying discoveries in recent years by members of the Tree Protection Co-operative Programme (TPCP) at FABI is that many new disease and pest problems are being caused by native insects and microbes. The unexpected appearance of a serious wood-boring cossid moth on Eucalyptus during 2004 illustrates this worrying trend. Larvae of the insect were found and these were reared to the adult stage. This work led to the conclusion that the insect is the native cossid moth Coryphoderma tristis, also known as a Goat Moth due to the unpleasant odour associated with infestations. The recent damage caused by Coryphoderma tristis on E. nitens is sufficiently significant to the forestry industry to have necessitated an intensive study. Current activities include a search for the cause of the sudden host shift as well as to consider the moth's natural enemies. This will make it possible to formulate an effective pest management programme in the context of South African forestry practices.
Contact person: Prof MJ Wingfield.
Mycotoxins are the products of storage fungi growing on seeds that have been stored under humid sub-optimum conditions. Cooking the seeds does not destroy the mycotoxins. Recently Dr Quenton Kritzinger and Prof Terry Aveling reported for the first time the production of fumonisins in cowpea seed by Fusarium proliferatum. This was also the first report of this fungus producing fumonisins in legumes. Cowpea (Vigna unguiculata) is important to the livelihood of many subsistence farmers and rural communities in the tropical and subtropical countries. It is an important discovery as these mycotoxins cause adverse health effects in animals and humans. Fumonisin B1 has been known to cause leukoencephalomacia (LEM), a fatal brain disease in horses, pulmonary edema syndrome (PES) in pigs and has been statistically linked to the incidence of oesophageal cancer in humans in Transkei, South Africa and China.
Contact person: Prof TAS Aveling.
The serious losses caused by the fungal pathogen Pitium in hydroponically grown crops prompted an investigation into the Pitium species involved, their pathogenicity and possible control strategies. Eight Pitium species and five heterothallic groups were isolated from eleven hydroponica in South Africa. Pitium group F was isolated most frequently and from the greatest variety of crops, followed by P.irregulare, P. spinosum, P. aphanidermatum and Pythium group HS. Various new Pythium/host associations for South Africa emanated from the study, e.g. P. acanthicum on strawberry, P. aphanidermatum on parsley, P.coloratum on lettuce, and Pythium group HS on cucumber.
An integrated disease management protocol was thus developed for control of the disease in hydroponic systems. The strategy involves sterilization of the growth substrate and irrigation water, introduction of pathogen-free seedlings and chemical as well as biological control measures.
Contact person: Prof N Labuschagne.
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