Woodrot fungi in the Garden Route National Park and surrounds of South Africa : identification and taxonomy

Abstract

Addressing the concerns of microbial diseases affecting natural forests, particularly those caused by wood-rotting Basidiomycetes, is of paramount importance for the protection of these woody ecosystems. This is of particular importance in Africa, where the threat of these fungi to the health of trees and woody plants have received less attention compared to human-induced threats such as deforestation, mining and agriculture. Basidiomycete wood-rotting fungi are essential components of forest ecosystems, which, as primary decomposers of dead plant materials, play an important role in nutrient recycling. However, some are a threat to the well-being and sustainability of natural forest ecosystems and the leading causes of wood-rot diseases of living trees. They can, depending on the fungus involved and other factors, induce a complete and permanent change in the structure and composition of forests. Although their ecological importance and epidemiology has been extensively documented, particularly in the northern hemisphere, aspects such as their diversity and taxonomy in natural ecosystems are still under-explored in the southern hemisphere regions. This thesis contributes to the knowledge of the diversity, ecology and taxonomy of wood-rotting macro-fungi in natural ecosystems in Africa, focusing on indigenous forests in the Garden Route National Park (GRNP) (South Africa). In these forests, native trees are selectively harvested for timber based on signs and symptoms resembling those induced by wood-rotting Basidiomycetes. Material collected from infected trees from surrounding areas was also included in the studies presented in this thesis. The research conducted for this thesis have led to the recognition of several previously unknown fungal species as well as first reports of previousely described fungi for South Africa. The results that emerged from these studies are documented in five chapters in this thesis. The first chapter of the thesis is a synthesis of the scientific literature, which provides a general context for the studies presented in the research chapters. It includes a review of the importance of wood-rotting Basidiomycetes in forest ecosystems, with an emphasis on their ecological role and epidemiology. It also provides information regarding the various categories of wood-rotting macro-fungi, and discusses the principal methods used for their characterisation. The chapter concludes by presenting some of the management strategies applied to control their dissemination and impact. The four research chapters focused on the identification, ecology and taxonomy of wood-rotting macro-fungi associated with declining trees in the GRNP and surroundings. Chapter Two, provides base-line information pertaining to the identity and species richness of wood-rotting Basidiomycetes occurring on trees showing wood-rot symptoms in timber-harvesting compartments of the GRNP indigenous forests. It also discusses the effects of timber harvesting on the spread of these macro-fungi and their distribution across the investigated forest compartments. Chapter Three focuses on the characterisation of Ganoderma species associated with Acacia cyclops trees, which are dying in the areas adjacent to the GRNP. This was done based on morphology and phylogenetic analyses. Results from these analyses led to the discovery of two new species and a previously described species. In Chapters Four and Five, the taxonomy and phylogeny of members residing in the two main groups of macro-fungi associated with wood-rot symptoms reported in Chapter Two and Three, namely Ganoderma and Hymenochaetaceae, are considered. Hence, Chapter Four deals with the taxonomy and phylogeny of Ganoderma species recovered from the GRNP, supplemented with material from other localities in the country as well as those of non-native A. cyclops identified in Chapter Three. Chapter Five addresses the same two aspects, but with a focus on species in the Hymenochaetaceae. Morphological and phylogenetic studies presented in both chapters revealed eight species of Ganoderma, of which two are new to science. Ten Hymenochaetaceae species were identified, of which four were described as new species in the study. This thesis makes a significant contribution to the knowledge of the diversity, ecology and taxonomy of wood-rotting macro-fungi in natural forests in general, and more particularly in those in southern Africa. Although studies in the different research chapters focused mainly on the GRNP of South Africa, it laid the foundation for future studies on other indigenous forests. This is particularly important in southern Africa, where very little information is available on the presence of these macro-fungi in natural ecosystems.