Abstract
During May 2010, sporocarps of what appeared to be an Armillaria sp. were found in large clumps in historic Kirstenbosch Botanical Gardens on the foot of Table Mountain, Cape Town, South Africa. These sporocarps could be physically linked to the roots of unidentified dead trees and Protea spp. The aim of this study was to identify the Armillaria sp. found fruiting in Kirstenbosch. To achieve this goal isolates were made from the mycelium under the bark of dead roots linked to sporocarps. The ITS and IGS-1 regions were sequenced and compared to sequences of Armillaria spp. available on GenBank. Cladograms were generated using ITS sequences to determine the phylogenetic relationship of the isolates with other Armillaria spp. Sequence comparisons and phylogenetic analyses showed that the isolates represented A. mellea. They were also identical to isolates of this species previously discovered in the Company Gardens in South Africa and introduced from Europe apparently by the early Dutch Settlers. Armillaria mellea is alien and apparently invasive in Cape Town, fruits profusely and has the potential to spread to sensitive native forests on the foothills of the City.
Highlights
Species of Armillaria are some of the most important pathogens of woody plants in the world
While the taxonomy of these Armillaria spp. has been controversial and widely debated over an extended period of time, application of the biological species concept (Korhonen 1978, Anderson & Ullrich 1979, Ota et al 1998, Qin et al 2007) and more recently DNA sequence comparisons (Coetzee et al 2000a, 2003a, 2005, Gezahgne et al 2004, Keča et al 2006, Mwenje et al 2006, Hasegawa et al 2010) have resolved many problems relating to the delineation of species
Sporocarps linked to infected roots from which cultures were made in this study were morphologically similar to those of A. mellea previously found in the Cape Town city centre
Summary
Species of Armillaria are some of the most important pathogens of woody plants in the world. These fungi have been known as tree pathogens since their first discovery by Danish botanist Martin Vahl. In native forests, Armillaria spp. cause disease but this is most typically a natural process (Kile et al 1991). Species of these fungi exist as clones covering huge areas of land and in these situations they are considered to be amongst the largest and oldest living organisms (Gould 1992, Smith et al 1992)
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