Araucaria (Araucaria araucana) canker disease in Chile : etiology and fungal diversity

Thesis (PhD (Plant Pathology))--University of Pretoria, 2022.The thesis titled ‘Araucaria (Araucaria araucana) canker disease in Chile: etiology and fungal diversity’ considered a serious disease that has recently emerged on Araucaria araucana, an iconic conifer species endemic to the mountain ranges of Chile and Argentina. The main objective of the study was to describe the main symptoms of the disease and to determine its causal agent, as well as to consider associated organisms. The first chapter of the thesis provides an extensive literature review on diseases of the Araucariaceae. This review highlighted the scarcity of studies and information available regarding the health of this mostly endangered family of trees, and the threats posed by invasive alien organisms and climate change. The first experimental research chapter in this study described the symptomatology associated with the cankers found on A. araucana. Through systematic sampling, isolations and pathogenicity tests, it was shown that the causal agent of the disease was a fungus in the Coryneliaceae. Morphological and phylogenetic analyses demonstrated that the fungus resides in a novel genus and species, described in the study as Pewenomyces kutranfy. In the second experimental chapter, additional Pewenomyces species present on the diseased A. araucana samples were characterised. Phylogenetic and morphological analyses, including an examination of relevant herbarium specimens for two Caliciopsis species (C. brevipes and C. cochlearis) previously described from the same host, revealed the presence of three new distinct species of Pewenomyces. These were described as Pewenomyces lalenivora, P. tapulicola and P. kalosus, none of which appeared to be pathogenic. The last experimental chapter of the thesis described two fungal species in the genus Resinogalea (R. araucana and R. tapulicola) found growing on the resin released from cankers on branches of A. araucana. This rare fungal species has only one close relative species, found on resin patches on branches of Araucaria humboldtensis in New Caledonia, and it resides in a recently described subclass of fungi, the Cryptocaliciomycetidae. All the fungi discovered during this thesis are rare species and seem to have a close relationship with A. araucana and the environmental conditions where they occur. This supports the hypothesis that these trees have a large biodiversity associated with them that and they will have coevolved after the continental drift.Plant Production and Soil SciencePhD (Plant Pathology)Unrestricte