Browsing by Author "Gryzenhout, Marieka"

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    Celoporthe Dispersa gen. et sp. nov. from Native Myrtales in South Africa
    (Studies in Mycology, 2006) Nakabonge, Grace; Gryzenhout, Marieka; Roux, Jolanda; Wingfield, Brenda D.; Wingfield, Michael J.
    In a survey for Cryphonectria and Chrysoporthe species on Myrtales in South Africa, a fungus resembling the stem canker pathogen Chrysoporthe austroafricana was collected from native Syzygium cordatum near Tzaneen (Limpopo Province), Heteropyxis canescens near Lydenburg (Mpumalanga Province) and exotic Tibouchina granulosa in Durban (KwaZulu-Natal Province). The fungus was associated with dying branches and stems on S. cordatum, H. canescens and T. granulosa. However, morphological differences were detected between the unknown fungus from these three hosts and known species of Chrysoporthe. The aim of this study was to characterise the fungus using DNA sequence comparisons and morphological features. Pathogenicity tests were also conducted to assess its virulence on Eucalyptus (ZG 14 clones), H. natalensis and T. granulosa. Plants of H. canescens were not available for inoculation. Results showed distinct morphological differences between the unknown fungus and Chrysoporthe spp. Phylogenetic analysis showed that isolates reside in a clade separate from Chrysoporthe and other related genera. Celoporthe dispersa gen. et sp. nov. is, therefore, described to accommodate this fungus. Pathogenicity tests showed that C. dispersa is not pathogenic to H. natalensis, but that it is a potential pathogen of Eucalyptus and Tibouchina spp
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    Population Structure of the Fungal Pathogen Holocryphia Eucalypti in Australia and South Africa
    (Australasian Plant Pathology, 2008) Nakabonge, Grace; Burgess, Treena; Gryzenhout, Marieka; Wingfield, Brenda; Wingfield, Michael J.; Roux, Jolanda
    Holocryphia eucalypti is a fungal pathogen that causes stem cankers on Eucalyptus species in South Africa and Australia. In South Africa it is considered opportunistic but in Australia it has been associated with occasional but serious disease problems. The aim of this study was to determine the genetic structure of a South African population of H. eucalypti and compare it with three Australian populations of the fungus. Seventy-two isolates from Eucalyptus spp. and clones in South Africa were compared with 30 isolates from E. globulus and 24 isolates from Corymbia calophylla in the south of Western Australia and 23 isolates from E. dunnii in eastern Australia.DNA of these isolates was amplified using eight pairs of microsatellite markers previously developed for H. eucalypti. Nei’s gene diversity (H) showed that the eastern Australian population is the most genetically diverse and the Western Australian populations from Corymbia and Eucalyptus are somewhat less diverse. The South African population displayed the lowest genetic diversity. The high genetic diversity in the Australian populations supports the view that H. eucalypti is native to that region and was introduced into South Africa.