KIAAT (Pterocarpus angolensis) HEALTH

Prepared by: James Mehl

Research projects in the DST/ NRF Centre of Excellence in Tree Health Biotechnology (CTHB) focus on the health of native South African trees. One such project involves the investigation of the fungal diversity on kiaat (Pterocarpus angolensis) trees. Kiaat is well-known amongst carpenters as a source of beautiful timber for furniture production. Rural South Africans also use different parts of the tree for medicinal and therapeutic purposes. This can result in bark being stripped off of trees, thus establishing wounds which are susceptible to infection by fungi. It is illegal to fell kiaat in South Africa and so most of the wood in South Africa is imported from neighbouring countries such as Mozambique.

Kiaat trees have been reported dying in several nature reserves in the Mpumalanga Province of South Africa. A review of the literature has indicated that trees were also dying in the Livingstone district close to the Victoria Falls in Zambia in the late 1950s and early 1960s. The cause of the latter problem was thought to be a combination of drought and infection by Fusarium oxysporum, a well-known soil-borne pathogen that causes wilt diseases. The described symptoms, however, suggest to us that the fungus was probably not the primary pathogen.

In South Africa, a complex of factors, mostly centering around fire and fire management, seem to be associated with the death of kiaat trees. Samples taken from these trees have indicated that wood rotting fungi are also involved in the decline. These organisms probably gain access when the trees are wounded by fire, thus enabling them to penetrate the bark and infect the tree.

The kiaat health project is considering several groups of potential pathogens of kiaat. These include species of the Botryosphaeriaceae that are endophytic and cause disease when the trees are stressed.

Eight species of the Botryosphaeriaceae have been isolated from the trees. Four of these are new to science and are being characterized and described. The other four represent known species. Representative isolates of all eight species are being used in pathogenicity trials to assess their effect on trees.

Species of Ceratocystis that are carried by beetles to wounds on trees are amongst the potential pathogens of Kiaat that also being considered. One species belonging to this group of potential pathogens has been isolated from trees. This is a species that is known to members of the CTHB from other studies and it is currently being described as part of another project. Pathogenicity trials are being conducted on the fungus to determine its relative importance in the decline of kiaat.

Results from this study will provide a valuable contribution to our knowledge of the fungi associated with the death and decline of kiaat. This will increase our understanding of the role of both the biotic and abiotic factors that affect and influence kiaat health. It is hoped that the knowledge gained from this project will provide guidelines for better management of the trees and the areas in which they occur.

 

Left: A seemingly healthy tree develops branch die-back. Right: A tree wounded at the base by elephants. Branch die-back is evident.

 

 

Two students busy inoculating branches of a tree with representative isolates of fungi from the tree for the pathogenicity trials. Results from these will indicate what effect the fungi have on the tree.