A TAXONOMIC RE-EVALUATION OF PHIALOCEPHALA PHYCOMYCES
R JACOBS1, MJ WINGFIELD1, K JACOBS1 and AJ KRUGER2
1Tree Pathology Co-operative Programme, Forestry and Agricultural Biotechnology Institute (FABI), Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, Republic of South Africa; 2Anatomical Pathology, Faculty of Science, University of the Orange Free State, Bloemfontein, 9301, South Africa
Background and objectives
The Leptographium complex, including Phialocephala, includes many species of fungi that cause sapstain of lumber. The genus Phialocephala was established in 1961 to accommodate species that produce their conidia in phialides . This is in contrast to the annelidic conidium development in species of Leptographium. Although some species of Ophiostoma have been suggested to have Phialocephala anamorphs, most of these fungi would best reside in Leptographium. The teleomorph connections of Phialocephala remain unclear. Species of Phialocephala are distinguished from those in Leptographium based on their host specificity. In contrast to the predominantly coniferous hosts of Leptographium species, those in Phialocephala are associated with decaying organic matter and soil. Species in Phialocephala can also be distinguished from Leptographium based on the fact that they are sensitive to cycloheximide .
The taxonomic placement of Phialocephala phycomyces has been a matter of considerable debate. Auerswald described this species in the genus Hantzschia, and it was later transferred to Leptographium. Kendrick then transferred it to Phialocephala. Conidia in this species are produced on what seem to be phialides with inconspicuous collarettes which can easily be confused with annelidic conidium development. The aim of this paper was to re-consider the taxonomic placement of P. phycomyces based on its morphology, sensitivity to cycloheximide and its ecological occurrence.
Materials and methods
Living cultures, as well as herbarium collections, of P. phycomyces were studied using light, scanning (SEM) and transmission (TEM) electron microscopy. Cycloheximide tolerance in the species was determined by growing it on 2% MEA, amended with a range of cycloheximide concentrations.
Results and conclusions
Light, as well as scanning electron microscopy showed that the conidiogenous cells are phialides with inconspicuous collarettes, which makes P. phycomyces typical of Phialocephala. Ultrastructural examination of the conidiogenous cells, confirmed that annelations are absent and that conidium development is phialidic. This is unlike Leptographium francke-grosmanniae which, at the light microscope level appears to have phialides and thus to represent a Phialocephala sp. In that fungus, however, TEM showed that conidium development was annelidic, typical of Leptographium. The presence of phialides in P. phycomyces justifies its retention in Phialocephala. It is, however, very different to the type species of the genus i.e. P. dimorphospora. Its tolerance to cycloheximide also suggests an affinity outside Phialocephala. Further studies based on DNA sequence data are under way to finally resolve this question.
1. Kendrick WB, 1961. Canadian Journal of Botany 42, 1291-1295.
2. Mouton, M, Wingfield, MJ & Van Wyk, PS 1992. Mycologia 84, 857-862.